Haynes Classic Motorcycle Race Engines: Expert Technical Analysis of the Worlds Great Power Units 1844259943, 9781844259946

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MOTORCYCLE RACE ENGINES EXPERT TECHNICAL ANALYSIS OF THE VVORLD’S GREAT POWER UNITS

KEVIN CAMERON

Racing motorcycle engines are the product of evolution in understanding, in design, and in materials and processes. Engineers, with and without formal degrees, have worked to draw more fuel/ air mixture into cylinders, to burn that mixture more quickly and at the highest possible pressure, and to simultaneously prevent the abnormal variety of combustion known as detonation. Careful work and measurement has gone into the process of determining and reducing friction, cutting unnecessary loss of

combustion heat to piston and cylinder head, and reducing misalignments resulting from the flexing of parts. In our own era we have seen the drive to make super-power at very high revolutions take engine rpm to 20,000. People are drawn to this work by the emotional power of machines, by their ability to multiply our own limited strength, speed, and endurance. Riders, engineers, and crew chiefs have

collaborated to civilize the rough, spikey power of highly tuned engines, making it controllable by human abilities. In years gone by, this was done directly,

by physical adjustments to cam and ignition timing, and to intake and exhaust systems. Those methods continue in use today, but are supplemented by the use of electronic sensors and controls. The engine tuner of even twenty years ago

monitored combustion by ‘reading’ spark plugs. Today, spark plugs are hardly ever

removed, and adjustments take place by laptop computer. Every racing motorcycle engine has a place in this evolution. In this book Kevin Cameron tells some of their fascinating stories and interrelationships.

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CLASSIC MOTORCYCLE RACE ENGINES

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629.227 © Kevin Cameron 2012

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission in writing from the publisher.

First published in November 2012 A catalogue record for this book is available from the British Library ISBN 978 1 84425 994 6

Library of Congress control card no 2012940363

Published by Haynes Publishing, Sparkford, Yeovil, Somerset BA22 7k Tel: 01963 442030 Fax: 01963 440001 Int. tel: +44 1963 442030 Int. fax: +44 1963 440001

E-mail: [email protected] Website: www.haynes.co.uk

Haynes North America Inc., 861 Lawrence Drive, Newbury Park, California 91320, USA

Designed and typeset by James Robertson Printed and bound in the USA by Odcombe Press LP; 1299 Bridgestone Parkway, La Vergne, TN 37086

£30.00

CLASSIC MOTORCYCLE RACE ENGINES

CONTENTS An affordable single for racing privateers

AER MACCHI

8

HONDA 250-4 The new math: rpm equals horsepower

1959-1967

1959-1964

AJS PORCUPINE

14

HONDA

250-6

Ambition unrewarded

Pinnacle of its era

1947-1954

1964-1967

AJS 350 7R Tailor-made for the working short-circuit racer

22

1947-1963

HONDA NRSO00O But we learned so much!

28

HONDA NS500 Reed-valve revolution

1948-1962

1982-1984

BULTACO 125/250 SINGLES 36 Simplicity and light weight are never out of place in racing

HONDA NSR500 SERIES Steps to complete dominance

1958-1970

1984-2001

DFV V8

44

Auto racing gives back to motorcycling

HONDA RC211V Smoothness triumphant

1967-1982

2002-2006

DKW 350 TRIPLE A forefather of two-stroke dominance

oes

1952-1956

116

58

1956-1959

66

1970 to date

HARLEY-DAVIDSON XR

KAWASAKI H2-R 750 TRIPLE It outgrew its cooling

156

KAWASAKI KR250/350 IN-LINE TWINS Quelling vibration

162

v4

KAWASAKI Z1-BASED SUPERBIKE Sit up and roar 1976-1982

170

82

KAWASAKI ZX7-BASED 750 SUPERBIKE

178

Those Ducatis were tough

2003 to date

A permanent racing engine

148

74

MotoGP’s junior partner

GILERA 500-4

138

1975-1982

DUCATI 8V Bordi’s revenge 1986 to date

Father of all fours 1948-1957

130

1972-1974

DUCATI BEVEL-DRIVE V-TWIN Hitting the big time

DUCATI D16 MOTOGP

KAWASAKI H1-R 500 TRIPLE Troubled but workable

124

1970-1971

DUCATI THREE-CAM 125 DESMO Reaching for unlimited revs

1970 to date

110

1978-1982

BSA GOLD STAR All things to all riders

COSWORTH

102

1989-2002

90

KONIG Out of the water and onto the track 1968-1976

96

MONDIAL

125 SINGLE

A proper four-stroke

1949-1957

186

190

MORINI 250 SINGLE One of the heroic designs

SUZUKI GSX-R Everyman’s race bike

1958

1986 to date

MOTO

GUZZI 120° 500 V-TWIN

196

202

298

TRIUMPH TWINS AND TRIPLES

A common-sense design

Years of versatility

1933-1951

1937-1973

306

MOTO GUZZI HORIZONTAL SINGLES A partnership of development and design 1920-1957

208

VELOCETTE KTT Doing one thing extremely well 1925-1952

314

MOTO GUZZI V8 Brilliant packaging, vaulting ambition

216

VINCENT The collaboration of two Phils

Ba.

1955-1957

1935-1955

MV-AGUSTA 125 Design leader of its time 1950-1961

224

YAMAHA EARLY AIR-COOLED ENGINES 330 Mastering the subject 1955-1965

MV-AGUSTA 500-4 Enough to do the job 1950-1965

230

YAMAHA TD TWINS Trainer of future champions 1963-1971

338

238

YAMAHA RDOS5 FOUR-CYLINDER 250

346

MV-AGUSTA

350/500 TRIPLES

Horsepower was not enough

Giant slayer

1966-1968

1965-1973

TWIN

354

MV-AGUSTA NEW 350/500 FOURS Four-stroke ‘Last Hurrah’ 1971-1976

246

YAMAHA 250 & 350 A modular racing system 1972-1980

MZ TWO-STROKES A powerful new synthesis 1954-1973

254

YAMAHA TZ-750 A-F Yamaha’s great equalizer 1974-1980

362

NORTON 30M 500 SINGLE As good as it gets 1927-1962

262

YAMAHA IN-LINE FOURS They improvised with what they had at hand 1973-1981

368

NSU 125 AND 250 Lessons in systematic engineering

270

YAMAHA YZR 500 Hard ups and downs

SUZUKI 125 Dogged determination 1955-1967

276

YAMAHA TZ250S POST-1980 Rising technology, rising price 1980-2006

382

SUZUKI RG-500 SQUARE-FOUR Interrupted champion 1974-1983

284

YAMAHA YZR M1 SERIES Improving the classic four 2002 to date

390

SUZUKI TR750 Undisputed horsepower king 1972-1976

292

INDEX

400

TWIN-CRANK V4

374

1983-2001

1951-1954

INTRODUCTION

ertain things have power to summon Caan complete reality. For me, the lost smell of mimeograph ink puts me back in elementary school. For many people, a motorcycle has this same iconic power. The front wheel of an idling Triumph twin shakes rapidly fore-and-aft, driven by the crankshaft counterweights. The cam-drive case of a Guzzi V8 suggests the moving mysteries within. This emotional potency makes it dangerous to write about classic motorcycle racing engines. Vincent enthusiasts take offense easily, but the post-war twins have to be in this book. A wide population of four-stroke adherents regard the entire period of two-stroke dominance as an error of history that ought never to have happened — a ‘lost era’. Another but smaller population of two-stroke loyalists yearn for their return. Still others, not finding their favorite within these pages, will be disappointed. Those risks are cheerfully taken, for I regard the motorcycle as a story, a long development resulting from problems and their solutions. There is no right or wrong, cool or un-cool, but just a fascinating unfolding of ideas, materials, and processes. This likewise implies that there are no ultimates — design is an undertaking that moves toward solution without ever reaching it. Honda’s RC-30 V4 Superbike was updated and modified until its capacity for further improvement was exhausted. At the peak of its abilities, it had become obsolete, and had to be replaced by a fresh design, the RC-45. As a more general example, we see that engines produce heat as well as power. If this

heat is not removed as rapidly as it is made, it will accumulate, driving up the temperatures of critical parts — pistons, valves, big-end bearings — until there is a failure. We can’t have that, so engine cylinder heads began with the ‘universal material’ handed down by the rail industry — cast iron — and then moved on. When power growth made iron heads too hot, they were replaced by more heat-conductive aluminum bronze, then by

aluminum, and finally by aluminum backed by cooled, circulating water. Each such change was forced by steady engine power increases. They were partial solutions, each able to move performance in the desired direction. The beauty of cooling fins is real. When I was seven, my dad took me on a birthday trip by air. The mysterious swirl of cooling fins on that airplane’s 2000hp piston engines imprinted my imagination for life. The sounds of engines are equally powerful — the extraordinary warm-up yelps of the Honda-6, the deep doodlebug bass of a Norton, the thin, high music of distant upshifting out on the circuit. Smells are potent. Soichiro Honda ran after the first car to pass through his village in Japan ~ a pursuit that continued throughout his life. English speedmen-turned-soldiers in North Africa during the war heated bits of armor scalding hot, then dripped aid-station castor oil on them and were transported to Brooklands Speedway by that rich and buttery aroma. Aviation gasoline, rich in alkylate, smells sweet. That smell tells us we have a powerful weapon against detonation. CLASSIC MOTORCYCLE RACE ENGINES

For me, and for many people I’ve known,

all this emotional power calls for some further explanation, some way of comprehending these feelings. Owning and riding motorcycles is one way to start, and many successful engineers have passed this way. Racing them is a natural next step, requiring the practitioner to get to grips with combustion by confronting the messages encoded in spark plug and piston

appearance. Think of the long list of successful engineers who once raced at Brooklands. When big-end bearings fail, something better must be found. How? I put on a tweed jacket and went to a university’s engineering library and read about failures of gas turbine bearings, about roller skidding and surface damage. With a little magnifier, I could see the same damage on my H1-R Kawasaki’s big-end rollers. The telephone eventually found me a supplier of German-made rollers in the same dimensions. The new rollers finished races, and I was hooked on the process of entering the mysteries suggested by sights and sounds and smells. That brings us to this book, which attempts to enter the mysteries of each of the engines described, to show how each came into being, encountered problems, and evolved around them. In some cases, new metal alloys would unlock higher performance, as they did for Yamaha’s air-cooled racing engines of the early 1960s. In others, new processes were necessary, as in the milling-from-solid of the crankcases of Yamaha’s M1 MotoGP engine, or in the superior durability of valve springs and twostroke big-end rollers made from the higherpurity vacuum-remelted steels that became INTRODUCTION

‘aa

available in the 1957-65 period. New ways of looking at existing processes were just as transformative. Adolph Schnuerle in 1929 saw a way to eliminate the heat-gathering deflector from two-stroke pistons, enabling them to survive at higher duty. Leo Kuzmicki at Norton saw a way to apply ‘squish’ to the problem of accelerating four-stroke combustion. Keith Duckworth let simple logic lead him to the revolutionary combustion scheme found in most four-stroke engines — production and racing, auto and motorcycle — made today. Engineering can appear cold and mechanical to outsiders. But at Ducati, the conflict between Dr Taglioni’s two-valve, air-cooled group and the new four-valve water-cooled group around Massimo Bordi was hot. So hot that much of Bordi’s work (which was to become Ducati’s stillevolving ‘Ottovalvole’ of today) had to be done outside the factory. I have known several men whose passion to solve problems tempted them to mill entire alternative universes from solid billet. One of them is myself. Others are Erik Buell and Erv Kanemoto. It can’t be done, but you can begin. I attended a gathering of long-retired aircraft piston engine engineers, some of them in their 90s. Not for them the often-heard disclaimer of the elderly — ‘Oh, it was all so long ago, and I’ve forgotten the details.’ For them, every detail was sharp, and when a late-1940s design issue was raised, opinions were hot. It is the emotions that bring us to engineering, but engineering then becomes a special way of confronting reality. It has created our material civilization, and these engines are a part of that.

An affordable single for racing privateers

1959-1967

6V 12 Bh RSH)

12 OL

he Aer Macchi 250 is one of those engines that, like those of Bultaco and early Yamaha production racers, was never going to win a world championship, or even very many grands prix. Instead, it earned our interest by providing an affordable and useful tool for racing privateers. As the name suggests, this company had been in the aviation business. Just as Yamaha had found themselves after the war with tooling to produce propellers, but with no market, the question was how to stay afloat. While Grumman in the US desperately used their aircraft experience to produce aluminum canoes, Aer Macchi turned to three-wheeled trucks. Management next decided to seek a foothold in the personal transportation market, and hired engineer Lino Tonti as designer. Motorbike production began in 1951 with the usual utility two-strokes, some record attempts, and a 250 twin. In 1956 came the aptly named ‘Chimera’. This machine embodied the post-war idea that motorcycles, to regain their former success, must combine the virtues of car

and motorcycle. Chimera, like Vincent’s Black Prince, was fully enclosed and had been drawn by a car stylist. The horizontal single cylinder of its pushrod four-stroke 60 x 61mm 172.5cc engine was cooled by enclosure in a forward-facing Buck Rogers grilled tube. Chimera bombed; only 119 were sold over six years. Engineer Alfredo Bianchi had previously worked at Alfa and Parilla. He came to Aer Macchi in 1956, and made a successful line of conventional sports machines.based on the Chimera’s engine. In 1957 came the 9hp Ala Bianca (White Wing), with modern suspension by tele fork and swing arm — and the poweredup Ala Rossa with 13hp at 7,500rpm (8.9bar, 131psi). With the price held down by pushrod instead of OHC valve drive, these sold well and the company offered racing accessories for use in the vigorous 175cc Italian national

View of engine from right-hand side: wet clutch, downdraft carburetor, hefty backbone frame. (Mortons Archive) AER MACCHI

i

road racing series, pushing power to 15.Shp at 8,000rpm (10bar, 146psi). In 1959 this was reshaped into a 250, the 66 x 72mm 246.3cc Ala Verde of 16hp at 6,500rpm (8.7bar, 128psi). By 1959 this had

become the Ala d’Oro (Golden Wing) of 20hp and a road racing version making 24hp at 8,200rpm (10.4bar, 153psi) had been built which was ridden into fifth place in the 1960 Belgian GP. The rider was Alberto Pagani and he finished just one place down from Mike Hailwood — on the 42hp Ducati parallel twin. Factory MVs finished 1-2-3. MV dominance was no more once Honda’s fleet of 250-4s arrived a year later. These Aer Macchi engines were built in a two-piece, vertically split crankcase containing crankshaft, direct-type drum-shifted four- or five-speed gearbox, an integral oil sump and oil pump. A single camshaft with two lobes operated a pair of ‘nail-head’ tappets whose shanks were 10mm in diameter, each with a round, flat cam rubbing surface of about 24mm diameter. These were piloted directly in the right side of the crankcase. Two pushrods were located inside a slightly oval tunnel in the axially finned cylinder, operating Z-form rockers in the cylinder head. Each of the two valves was held closed by dual nested helical coil valve springs. Ignition was by a single angled spark plug on the left side of the head. Valve sizes in the Pagani bike were intake 37mm, exhaust 29mm, operated on the long timings required by the extra mass of pushrods and rockers. This engine made 29 rear-wheel horsepower at 9,000rpm (11.4bar, 168psi), with usable torque from 6,700rpm, but operable from 4,000. In the Italian style of the time, ignition timing was quite early, variable by lever between 50 and 55° BIDC. This resulted from a fairly deep combustion chamber, intrusive non-squish piston dome, and single ignition. This engine had a cast piston and a 30mm Dell’Orto carburetor. Exhaust was through a straight-back header pipe and compromise megaphone — not as short and large at the exit as that of a Manx Norton, but not the long, slow taper pioneered by NSU either. These were classic racing engines, loud and elemental.

The crank was pressed together from two mainshaft-and-flywheel forgings and a crankpin, with a one-piece steel rod running on a caged roller big-end bearing and a bronzebushed small-end. Main bearings were ball. A small 135mm external flywheel was carried on the left crank end. A gear primary on the right drove a multi-plate clutch that was initially enclosed and wet, but later changed to a dry design to facilitate push-starting. Oil from the gear-driven two-gear pump enters the right-hand crank end through the cam support plate, and oil is also sent to the head through a line attaching to the front of the right-hand case half. This runs to the head, then splits in two to lubricate the two rocker pivots from the left. Oil drains back to the case by a flexible line attaching to a fitting made integral with the exhaust (lower) rocker cover. The oil sump was part of the crankcase, but separated from the crankshaft cavity. The cylinder head was a spherical segment, 23mm deep, with two valves symmetrically disposed at a 68° included angle. This chamber was a considerable advance on the full hemispheres used by Gilera and MV fours because it had only 75% of a full hemisphere’s surface area through which to lose combustion heat. Since the end of the war British designers and engineers at Ferrari had been reducing valve included angle as a means of cutting heat loss (and, surely, of reducing piston distress). They had regained the area necessary for valves of adequate size by incremental increases in bore and reductions in stroke. Such changes required the development of pistons and piston alloys capable of reliably supporting combustion and inertia loads in larger bores. Meanwhile Harley-Davidson in the US bought 50% of Aer Macchi’s stock. Although Harley had made a few dreadful DKW-copy two-strokes of their own for a time, they now had no light- or middle-weight bikes to offer to ‘the nicest people’, who were beginning to buy little Hondas. It was now decided to produce a ‘selling-bike’ racer for 1961. Intake was via a 30mm Dell’Orto pointing straight up from the engine’s inlet port. Compression was 10.2:1 from a cast, three-ring piston and peak safe revs 9,000.

10

A year later the engine had been given a higher-performance cam and a red line extended to 9,200rpm. Racing requires premium components so the 1963 engine was upgraded with less crack-prone forged piston and a con-rod made for racing. We have seen this same step-by-step march to higher-quality components in modern Supersport bikes, which now have forged pistons, shot-peened con-rods, and titanium valves. When the parts you have won't reliably operate at the revs you need, you upgrade. Harley began importing a sporty 250 — the ‘Sprint’ — in 1961 and there was a racer version

as well — the Ala d’Oro, or Golden Wing, called ‘Sprint CR’ in the US. At 66 x 72 = 246.3cc this made 28.5hp on a red line of 8,500rpm (12.6bar, 183psi). Compression was 9.5:1, ignition was by coil and battery, carburetor size was 27mm, and transmission was four-speed. With this gearbox, if the engine was revved to 9,000rpm in first, revs would drop to 6,200

in second, limiting the engine to ‘soft’ tune that could pull across 31% of its rev range. When the five-speed was adopted, the first-tosecond upshift pulled the engine down only to 7,000rpm — a big improvement as this: allowed more power-narrowing dependence on the ‘one-note samba’ of intake and exhaust tuning. Note above that ‘usable torque’ was available from 6,700rpm. How did the rider make the bike pull if revs fell back to 6,200 at the firstto-second upshift? He over-revved the engine, that’s how. Other sources list the DS at 30hp at 9,600-9,800rpm (1 1bar, 161psi) on 10.2:1 compression. A sportier DS5 cam came in 1962, raising revs to 9,200, and the following year a five-speed gearbox was provided, still with a wet clutch. The DS was produced until 1964, when in mid-year bore and stroke became 72 x 61 = 248.4cc. Alb flywheel mass was now in the crankshaft itself. The wet clutch and five speeds continued. Tappets with 10mm shank continued to be used and carburetion remained 30mm. Maximum revs were 9,400. It appears that the DS combustion chamber was retained, but now surrounded by a 3mm-wide flat area that was used as squish. As this part of the CLASSIC MOTORCYCLE RACE ENGINES

piston closely approached the head at TDC on compression, the gas trapped in this band was vigorously accelerated inward, stirring the burning mixture. This allowed ignition timing to be reduced from the 50-55° of the DS to more like 41° BTDC in the short-stroke engine. Such changes made further evolution possible, for reduced time exposure of the piston to combustion heat cut piston temperature. The cooler the piston, the higher the compression ratio that could safely be used. Valves became 39mm inlet/31mm exhaust, and there were occasional failures until the US connection brought highly fatigue-resistant S&W valve springs (high purity vacuumremelted wire, shot-peened to place the wire surface in compression) and an improvement in exhaust valve material beyond Nimonic-80A.

These were said to last two to three seasons of use. In 1966 the 250 acquired a dry clutch. The outer flywheel was dropped, replaced by crankshaft mass. Carburetion was 30 or 35mm, depending upon the course. Maximum revs rose

to 9,800. The exhaust valve now increased to 33mm — probably a consequence of reliability at

31mm with the improved material. Even today it remains fashionable to say that ‘The exhaust has 100psi to push it out, but the intake has only atmospheric pressure to push it in,’ as an excuse to concentrate flow work on the intake side. But again and again, improvements in

AER MACCHI

7

View of right-hand side of a bike with two personalities — it has both headlight and numberplate, muffler and open carburetor. (Mortons Archive)

exhaust flow in air-cooled engines have led to useful reductions in cylinder head temperature. If the engine has to pump the exhaust out against significant resistance, it’s hot work. Successful engines are masses of details, each the result of a problem solved. This year’s model had a new head with improved ports and a better combustion chamber allowing use of 12:1 compression. Power was 35hp at 10,000rpm (12.4bar, 183psi). The following year the full-circle flywheels were replaced by a traditional Italian combination of ‘porkchop-style’ flywheels and a small external flywheel. It may be that the greater weight of the full-circle wheels caused vibrations that slowly worked the wheels off the pressed-in crankpin, or broke it. Lighter flywheels push the natural frequency up, perhaps beyond excitation by the firing or rotation frequencies. Improved support of the left mainshaft was provided by stacking an additional main ball bearing on an extended shaft. In cases of flywheels working their way off a press-fit crankpin, it is always the side carrying any extra mass, such as an ignition rotor or, in this case, the external flywheel. il

There had been some tappet breakage with faster-lifting cams and this was dealt with by increasing tappet shank diameter to 12mm (this reduced the ‘overhang’ as the cam lobe applied lift force near the edge of the tappet’s face). Peak revs were now 10,200.

In the US of the early-to-mid 1960s these machines — with Harley backing — became dominant in a new national 250 class. Their obvious competitor, Ducati, with its potentially

superior valve drive, did not have a US importer or large dealer interested in racing. In Canada, Ducatis found more success. In the early 1960s the long-stroke DS Aer Macchi had little trouble outlasting the occasionally fast but always unreliable early Yamaha TD1-A two-strokes, with their tender anodized aluminum cylinder walls. In 1965 came the improved Yamaha TD1-B, a great step forward with chrome-on-aluminum bores, and in 1967 came the C-Model, more powerful yet and

A nameless privateer hastens — note horn,

headlight, muffler. (Mortons Archive)

12

now highly reliable. In that year Harley pulled out their 250 team as a flood of importer and private Yamahas swept top positions. The last

CLASSIC MOTORCYCLE RACE ENGINES

They made a lot of power between 10,000 and 10,500, and ifyou could keep it there, you could go pretty fast. notable success was a win in the 1968 Daytona Novice 250 event. More development was done but it

essentially lifted a prototype DOHC two-valve Aer Macchi to the power level reached by Morini in 1963 — 38hp at 11,000rpm (13.5bar, 198psi). With such outstanding breathing and combustion, revs were the only realistic path to more power, and that meant a twin, a triple,

a four. Those were concepts far from Harley’s original intent to import attractive, inexpensive

lightweights. A person with experience with the last of the Aer Macchis said, ‘They made a lot of power between 10,000 and 10,500, and if you

could keep it there, you could go pretty fast.’ This describes a classic case of powerband narrowing as a design reaches maturity — which means the same in this case as obsolescence. The engine needed a six-speed, it needed an extra cylinder or three, it needed to be built as a pure racer. It needed so much that it wasn’t practical. Other interesting things were done with the basic Aer Macchi layout — a 350 single, a 500 twin, a 408 single. Two-stroke marketing had concentrated on the US and was slower in reaching Europe, with its more grueling race venues and distances. Engineer Lino Tonti, after leaving Aer Macchi, designed a twin employing two DS top ends on a common crankcase with a built-up twin crankshaft driving through a jackshaft to a dry clutch and six-speed gearbox. This work was financed by ex-racer Umberto Premoli with assistance from engineer Alcide Biotti. The initially chosen 180° crank was replaced by a 360 because of heavy vibration. About 15 were built at a price of £1,300. Initial power was 61hp at 9,800rpm (11bar, 162psi), rising to 64 at 10,000rpm (11.3bar, 166psi). A Linto first appears in GPs in 1968, after its debut at Rimini in April, going on to share AER MACCHI

x

fourth in the 500 championship. It was ridden by Alberto Pagani, who had come second to Agostini in that year’s East German GP. The following year Gyula Marsovszky rode one to second in the championship, while at the Nations GP at Imola, Pagani gave the make its single GP win. Pagani brought home his fifth in 1970, eighth in 1971, after which the Linto name Is seen no more. The 350 Aer Macchis were fairly successful because they filled a gap between the waning singles of Norton and AJS, and the coming tide of affordable two-stroke production racers. The first version was 74 x 80 = 344.1cc, making 38 rear-wheel horsepower at 7,800-8,200rpm, or 45 at the flywheel, on 11:1 compression. These were reckoned to be more than a match for a traditional 500 single, reaching that level by a thousand more revs, lighter weight, and greater handiness. Said to handle well in the wet, they offered low running costs and were ‘simple and reliable’. By 1970, when Alan Barnett on a 350 Aer Macchi beat Paul Smart on a Yamaha TR2 in the Junior TT won by Agostini’s MY, it had become 77 x 75 = 349.2cc. Also in that year ‘Angelo Bergamonti earned two seconds and a fourth in 500 GP on a 408cc Aer Macchi prototype, before being given an MV ride late in the season. Not bad for a pushrod single derived from a futuristic 1956 show bike. Aer Macchi would make the transition to two-stroke, building Yamaha-like water-cooled piston-valve twins that would, ridden by Walter Villa, take the 250 GP title in 1974, *75, and °76, and the 350 title as well in 1976 — against long lists of privateer Yamahas. One of these Aer Macchi RR250s would be bought by young American privateer Erik Buell, beginning his long and turbulent relationship with Harley-Davidson Motor Co. Harley-Davidson sold its Aer Macchi holding to the Castiglioni brothers in 1978. 13

cs)

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| 1

Ambiti on unrewarded

1947- 1954

he famed AJS E90 ‘Porcupine’ was so stuffed with innovation that had it succeeded it would be remembered as the ‘new synthesis’ of telescopic fork, swing arm rear suspension, hydraulic damping, and twin-loop chassis. Lack of money, conflicted management, and weak R&D capability stopped that, so it is Norton we remember for that synthesis. AJS get the consolation prize for glorious failure. The AJS E90 parallel twin was designed with the assumption that the pre-war supercharged racing formula would continue post-war, as in grand prix auto racing. However, the FICM had more sense than the FIA, reasoning that nations exhausted by war could ill afford supercharging’s complexities. Many features of the E90 — notably its nearly horizontal cylinders, deep combustion chambers with wide valve-included angle, and over-large exhaust ports — were either

unnecessary to an unsupercharged engine or actively sapped its performance. A single world championship was won in 1949, but rapid development from Norton and Gilera proved impossible for a small company to match. A comprehensive top-end redesign was essential but did not happen. Had E90 been designed from the start as an atmospheric engine, there was potential for 60hp at 8,500rpm (7.4bar, 108psi), which could have put it out of reach of the Nortons and in with a chance against the early Gileras (which wouldn’t reach 60hp until the winter of 1953-54). In the immediate post-war years new British designs were given shallower, faster-burning, and more efficient combustion chambers with 60° valve angle — but E90’s design pre-dated that period. Stacking the deck even more heavily against E90 was Britain’s bankruptcy, achieved through two disastrous world wars and Indian independence. British teams withdrew from GP racing after the 1954 season. Even unsupercharged, it was too rich

Three-quarter rear-left view of the E9S engine: air cooling, dry clutch, wide valve angle. (Mortons Archive)

AJS PORCUPINE

for their sales base. It was also irrelevant to the biggest motorcycle market — the US. In the late 1930s English motorcycle manufacturers seethed as continental machines gained supremacy in 500 racing and even won the TT. Germany’s BMW and Italy’s Gilera received direct help from their national governments. Their excellent multi-cylinder supercharged machines were advertisements for what admirers termed ‘virile young dictatorships’. British teams strove to adapt supercharging, with modest success in the AJS water-cooled V4. This complex and heavy machine managed in 1939 to run with Dorino Serafini’s Gilera-4 in Ireland — until it broke a girder fork link. Power was estimated at SShp. War put an end to racing but not to imagination. The tale is told of Harry Collier’s designing in early 1939 a liquidcooled laydown supercharged triple. There is important background leading to this design. English companies built mainly singles because they were affordable. In 1935 AJS broke with tradition by presenting a 50 x 63mm DOHC air-cooled 500cc 50° V4 at the Olympia show, hinting at production. This was the leading edge of a view, rather desperately revived after the war, that motorcycling must regain its 1920s popularity by making bikes cleaner, smoother, and more car-like. A racing version of this Bert Collier V4 was tried in the 1936 TT but was dreadfully slow. Matt Wright (just arrived after the 1937 closure of his previous employers, New Imperial) now suggested supercharging, which was beginning to bring the Germans and Italians results. A supercharger was added in 1938 but the bike remained uncompetitive. Heat from the front cylinders overheated the rears, forcing the team to adopt ‘fuel-cooling’ — use of a power-cutting rich mixture. The complication of four cylinders and mild supercharging added more weight and bulk than they did power. At a time when rigid frames were still admired, handling was terrible. Now Matt Wright redrew the V4 with water-cooling. It still handled poorly but was now fast — as fast as Gilera’s Rondine. Claims as high as 15

80hp were made for these fours, but actual numbers were mid-50s. Machine tools at AMC (AJS’s parent company) were ‘extremely worn-out’ but new equipment was arriving under government war production funding and supervision. Such supervision excluded non-essential manufacture of racing prototypes (Hitler would invade Poland in September 1939). Collier then scrapped the supercharged triple mentioned above after a few castings had been made. AMC director Donald Heather hired Joe Craig as chief designer. Craig had left Norton when the race team was disbanded in 1938. One informant quotes Collier as saying, ‘Craig will not learn anything from me here’ and then angrily destroying the triple’s drawings. In 1942 the war looked bleak but there was a select group of talent at AMC engaged in war work. Aside from Collier and Craig there were Vic Webb, Matt Wright, and Vincent engineer Phil Irving. Over tea and in spare moments, they refreshed their minds by creating a ‘paper racer’. If a V4 was too complex, how about a vertical, liquid-cooled supercharged parallel twin? Webb suggested aircraft-style high-temperature glycol cooling, as it made the necessary radiator smaller, potentially reducing drag (Ducati now use elevated coolant temperature in just this way). At that moment the obvious example of such a high-performance liquid-cooled supercharged engine was the Rolls-Royce Merlin V12, defending the nation overhead every day in Hurricanes and Spitfires. Substituting its bmep in a calculation for a $00cc twin turning 7,500rpm suggests an initial 6Shp. This first design had intakes straight down between the two overhead camshafts as a means of avoiding charge short-circuiting to the exhaust during overlap. To actually fit into a motorcycle chassis the between-the-cams intakes had to go. To achieve the desired weight, major castings had to be magnesium, but its corrosion sensitivity made water-cooling impossible. Air-cooling was adopted, but to deal with supercharged heat flow the engine would have to go head-first — with its cylinders 16

horizontal as in Harry Collier’s original triple. Logic marched on. Horizontal cylinders add engine length (look at any Ducati). The

length-reducing response was to abandon the established English practice of a separate gearbox with chain primary drive, and put in its place a gear-driven unit gearbox whose two shafts were stacked vertically in Guzzi style. Primary drive was by gears 5/in (16mm) wide and a direct four-speed, cam-

plate-shifted gearbox (in and out on the same axis) required the crank to spin ‘backward’ — opposite to the wheels. Today this is hailed as reducing roll stiffness in MotoGP, and Yamaha’s agile M1 has this feature. Because the engine was to be supercharged it would, like the aircraft engines that had fought the Battle of Britain, have a low compression ratio of around 7:1 (the rest of the compression would occur in the supercharger). With a flat-topped piston and the ultra-modern ‘square’ dimensions of 68 x 68.5mm = 497.5cc this would give an open hemispheric combustion chamber. With so much room, in-rushing mixture would continue to circulate vigorously, becoming combustion-accelerating turbulence as the piston neared TDC. The hemi chamber in turn implied a wide valve angle of 100 degrees. This was an important point, for a wide valve angle moves the cam boxes apart, allowing placement of generous cooling fin area between them, directly over the heat source — the combustion chambers. When the engine was converted to operate unsupercharged, the deep combustion chambers became a real liability, requiring high-domed pistons to recover compression no longer taking place in a blower. The direct result was increased piston crown and combustion chamber surface area, sapping heat from combustion, requiring intensive attention to cooling, and cutting power. Remote spark plugs fired the mixture through central spark ports, as in the Gilera-4s. Combustion was so slowed by these features that best ignition timing was a long SJ = BIDE. Causing cooling air to flow through deep cooling fins is a serious concern. With the CLASSIC MOTORCYCLE RACE ENGI NES

cylinder head pointing almost straight ahead (cylinder angle was 15° above horizontal),

air would hit the fins between the cam boxes and go... where? A similar problem existed in the deeply re-entrant heads of the sleeve-valve Bristol Hercules air-cooled radial aircraft engine. Its head fins were down at the bottom of a deep ‘cup’ just as the E90’s head fins were fenced-in by its cam boxes. Bristol’s solution was to guide the air down one side of the cup with a shaped baffle, into the fin spaces, across the finned head, and then up and out of the far side of the cup. Cooling-air baffles on a bike? Eek! Therefore the fins were

AJS PORCUPINE

é

designed so that air could flow through them in any direction — side-to-side or bottom-to-top. The between-the-valves cooling surface was therefore made as a forest of spikes rather than as continuous fins. These cooling spikes gave the bike its name — the ‘Porcupine’. The casting of deep fins (they were over Sin long!) was a high art, calling for thin cores supported by individually positioned

Left side of E95 complete bike on a workstand — note wheeling machine in background! (Mortons Archive)

iW,

lengths of wire. AJS employed a new vacuumcasting method (didn’t Ducati just adopt Ritter Vacural vacuum casting?) which enabled the most complex shapes to be cast with complete mold filling and relative freedom from oxide inclusions and porosity. Heads and iron-linered cylinders were separate and cast in aluminum. Crankcases, sump, timing case, and cam covers were

magnesium. The 360° fully counterweighted crankshaft ran in three main bearings — the center one a plain journal carried in a split housing assembled on to the crank before endwise insertion into the case (a similar split housing was used to give a third crank bearing to AJS/Matchless post-war twins). The outer mains were rollers carried in bolted-on covers. Two forged RR56 aluminum split-and-bolted connecting rods also turned on plain bearings. Why three main bearings rather than the two chosen by Edward Turner for his 1937 Triumph Speed Twin? Turner’s goal was costcutting. A racing crank needed protection against high rpm flexure. Full-skirted pistons with 74in (22.2mm) wristpins carried a pair of “ioin (1.6mm) gas rings and a one-piece oil scraper each. Intake valves seated on austenitic-iron seat rings, sodium-filled KE965 stainless exhausts had fat “Asin (11.1mm) stems and seated on bronze rings. Valve seat pressure was 100Ib (45kg), provided by paired hairpin springs. Valve tappets were rectangular to prevent rotation of the radiused surfaces facing the cam lobes. Cams were carried on rolling bearings (balls at the ends, split race rollers between) in split cam boxes fixed to each head by studs and nuts. The left end of the upper cam provided the tachometer drive. Oiling was originally dry sump. Two pressure oil pumps were located on the ‘accessory section’ atop the one-piece crankcase, one supplying the crank, the other the valve train. An oil drain pipe joined the upper (intake) cam box to the lower, whence a small scavenge pump returned it. Oil for the crank was piped to a fitting between the cylinders and then into the center (plain) main bearing. From a center groove in that bearing oil entered drillings in the crankshaft supplying 18

the crankpins. A two-gear scavenge pump in the sump, driven from the accessory shaft

above the crankcase by a quillshaft, returned oil to the remote tank. Later, in the interest of

being able to preheat the engine in the Italian style by draining and refilling a wet sump with heated oil, the remote tank was deleted. The original E90 was very cold-blooded — Matt Wright’s son recalled the dry sump bikes having to be towed to start them. The two overhead cams were driven by a Y-shaped train of nine spur gears on the right side. Vic Webb said that this gear train was lapped for 24 hours in a special jig, suggesting some difficulty in controlling dimensions or surface finish. Was this one result of ‘extremely worn-out’ tooling? It is modern racing practice to carry out exhaustive rig, dynamometer, and track testing prior to a design’s use in racing. This mimics the thorough testing required since the 1920s for certification of aircraft engines. The goal is reliability — no user wants a bad surprise on the track or in the air. Because programs like Honda’s 2,000-hour product test cycle are expensive they did not become widespread until the industrial scale of Japanese motorcycle production made them affordable — and then essential. When the results entered Western markets in the 1960s people were struck by the difference. Previously, motorcycling had been participatory. A Saturday afternoon ramble on a bike required the owner to spend half an hour beforehand topping-up liquids, tightening fasteners, and adjusting chain tensions. Japan turned the motorcycle into an appliance. When you put bread into a toaster, you expect toast, not a course in electrical engineering. Makers with serious TT ambitions — notably Norton — carried out entire test-house race simulations. Yet the many avoidable failures of the E90/95 are today regarded indulgently, as if the failures of insignificant parts somehow magnified the glory of the ambitions that created it. Reliability is

expensive. Norton bore the cost of making their Manx singles reliable — at considerable cost to their business. AJS hoped somehow to win races without this expense.

CLASSIC MOTORCYCLE RACE ENGINES

Be that as it may, the E90/95 showed that English design could step off the well-trodden path of single cylinder, separate gearbox, and all-rolling bearings. While it may be argued that Edward Turner was the pioneer who ran forged aluminum connecting rods directly against crankpins as plain bearings, the AJS Porcupine took the advanced step of applying the new three-layer insert plain bearings to both the con-rods and the center main bearing. The Porcupine also adopted the Italian practice of unit construction and efficient sealed gear primary drive. Airflow development pioneer Harry Weslake heard about the project from friends in the race shop and offered his help with head and ports. AMC director Donald Heather, ever the finance man, said no. The E90’s ports remained plumbing. In 1947 fabric clutch plates had to be replaced at the TT with Ferodo-inserted metal plates made in haste. Spark plug insulation gave trouble that was only gradually overcome. A torsional shock absorber was provided in time for the primary gear — a feature nearly all modern engines have today. At the 1948 TT no Porcupine finished. Donald Heather asked Matt Wright to take over the race shop. He narrowed the valve angle and made other detail changes. In 1949 the three best grand prix results counted toward the title, and Les Graham’s two wins and a second topped Nello Pagani’s two wins and a third (Gilera), 30 points to 29. It could have been a decisive win — Graham had led the TT (it was a GP until 1976) at the end by two minutes but the engine stopped. According to the received account, the magneto was shaken into intermittency by the engine’s torsional pulsing. The drive was later softened by conversion to chain instead of gear. The next year the Norton abandoned its obsolete ‘garden-gate’ chassis to show new speed with its twin-loop McCandless chassis, forward-mounted engine, and supple hydraulic damping. Geoff Duke was headed for the title had he not suffered tire chunking, but ended up second by a single point to Umberto Masetti (Gilera). Graham won AJS PORCUPINE

Good ideas, sadly,

are never enough. only Switzerland and was second to Duke’s Norton in the Ulster. Duke also took the all-important TT, while Graham was fourth there, and third in the championship. AJS were slipping backward. In 1951 the Norton came to full strength and Duke was champion. Graham had gone to MV. Bill Doran on the Pore was second to Duke at the TT and second in France, but the final championship order was Norton, Gilera, Gilera, AJS. For 1952 the engine was at last redesigned, raising the cylinders to a 45° angle and changing from spikes to conventional angled cooling fins between the cam boxes. This made it possible to adopt a slight downdraft intake system like those on contemporary singles. In 1954 12th place was all AJS’s rider Rod Coleman could manage. AJS and parent company AMC couldn’t afford GP racing, and even having made the decision to race anyway, could not countenance spending what it cost. The project died by degrees, slipping first behind the Gileras and then behind even the single-cylinder Nortons. The team was forbidden to employ streamlining. They were required to use the company’s own door-closer-quality suspension dampers. No outside advice. As so often, the corporate cry was, ‘Fix it, but don’t change anything! And don’t spend any MONEY!’ Let’s not romance failure. AJS were not a racing company with a strong R&D tradition

like that imposed upon Norton by Joe Craig. The time taken by Gilera to become dominant — with important help from English riders — shows that sustained R&D was necessary to get to the front. AJS lacked the R&D tradition, the income, and the will. Good ideas, sadly, are never enough.

OVERLEAE Puddingbowl-and-goggles rider on E95 with short reverse-cone megs and streamlined wet sump. (Mortons Archive) no

Woe

Tailor-made for the working short-circuit racer

1947-1963

n company with the great Norton and Velocette racing singles, the 350cc AJS 7R and its larger derivative the G50 Matchless made up the largest part of GP starting grids in the big classes for many years. These engines are of great interest because each of them received thoughtful step-by-step development over a period of years. The record of this development remains of value to this day. The 7R was drawn by Phil Walker at the instance of former racer Jock West who had taken over AMC racing in 1947 on the accidental death of Freddie Clarke. The 7R had

to subsist on whatever R&D resources were left after AJS’s ‘Big Program’ — the troubled E90 ‘Porcupine’ twin — took what it needed. After a single 500 title in 1949, E90 steadily

lost ground — at first to the newly agile Norton and then to Gilera. Walker had been chief designer at AJS since 1945. Today we expect an engineer to be a graduate of an engineering school. Walker, like so many in his time, came to AJS as a junior draftsman, rising to chief draftsman in 1925. This was a practical path trodden by many, quite unlike today’s all-academic pathway of mathematics and computer modeling. Walker’s creation was 74 x 81mm = 348.4cc, an air-cooled vertical 2-valve single with a wide valve included angle and paired hairpin valve springs. This was a new design, but informed by the line of OHC AJS racing singles dating back to 1920 — all of which had employed simple, forgiving chain cam drive from a half-time shaft geared to the crank. When you think of a chain, think of the great number of oil films — acting as tiny ‘cushions’ — through which it transmits its load. The engine was conventionally joined to a separate gearbox by engine plates and a primary chain drive. With a direct-type gearbox, engine rotation was forward. A chain-driven single overhead cam carried in ball bearings operated the valves by enclosed rockers, each of which contacted the cam

Left-hand view of 7R engine in chassis: dry ons five-spring clutch, round float bowl. (Mort Archive)

AJS 350 7R

via a radiused, hard-faced pad. Initial power was 30hp at 7,000rpm (10.9bar, 160psi). Compression ratio was set at 8.45:1 for

running on poor-quality post-war fuel, and ignition timing was 39-40° BTDC. The large ‘trumpet’ megaphone, fashionable at that time, limited range, with power beginning at 5,500rpm. In the design of the 7R ease of service was clearly an important goal for, unlike the Norton, a 7R engine can be installed or removed from the frame without head removal, and its simple construction saved time for its operators. A connecting rod of KE805 steel (like EN24, or US 4340) was 6%4in long, for a rod ratio of 2.0. The crankpin was tapered and threaded at each end to be drawn into the flywheels by special nuts whose heads were sawn off after installation. Mainshafts were separate, keyed and nutted in place. Oil from the pressure pump entered the timing end of the crank, flowed through drillings into the hollow pin, then into the big-end bearing through two holes spaced at 90°. Oil was also pumped through passages in the timing cover to the cam box where it emerged from holes in the cam lobes. To keep this oil away from the crank it drained through passages in the aluminum cylinder casting. A separate scavenge pump picked up oil from the crankcase ‘foot’ (a rearward extension of the bottom of the case) for return to the external oil tank. Circulation rate was 12 gallons per hour at 6,000rpm. The rod’s big-end bearing consisted of */in long x “in diameter rollers in an aluminum alloy cage. Aluminum cages survived in four-strokes because their circulating oil systems kept the light metal cool enough to retain its strength. In twostrokes, steel cages were necessary to preserve strength at bearing temperatures as high as 400°R. Part of the striking appearance of these engines comes from the distinctive gold finish on their magnesium crankcases, cam box, and cam chain (timing) cover. No attempt was

made to ‘style’ the 7R by making it resemble an egg — a practice Jock West called ‘... the expensive enclosure of air in cast aluminium’. Its external surfaces either revealed purpose (the complex cam box, the cooling fins) or suggested the parts within. Notice the oval 23

hole through the cam chain enclosure, which

allowed air to pass from side-to-side across the cooling fins between the valve spring cavities atop the head. One of these new 350s came fourth in the 1948 Senior TT, but desperation ruled because all three Porcupines failed to finish. On the spot, AMC director Donald Heather asked Matt Wright to take over development, ‘to knock some sense into the Porcupine program’. He would also be responsible for the 7R.

View of cam drive chain with cover removed: bottom sprocket turns at half of crank rpm. (Mortons Archive)

Wright, lately at Vincent, had been involved with the AJS 500 V4 before the war. When a shallower combustion chamber benefited the Porc (reduction of valve angle from a distinctly pre-war 100°), Wright did the same for the 7R a year later — to 80°.

By 1949 power was up to 32hp. For 1950 flywheel diameter was reduced slightly, not to achieve reduced mass but to reduce ‘oilage’ loss between crankshaft and crankcase. If unscavenged oil is swept around inside a tightfitting crankcase, several horsepower can be lost and oil temperature rises dramatically. A larger 1.75in (44.5mm) intake valve was adopted, with reduced “cin (7.92mm) stem. Exhaust valve material was the standard stainless KE965, whose tolerance for leaded fuel had in the 1920s made earlier tungsten steels obsolete. Intake downdraft became 12°,

a new supply oil pump (there were two in the timing case on the right — pressure and scavenge) was made, and a sump plate added under the crankcase ‘foot’ with a metal gauze filter to protect the scavenge pump from foreign matter. From June onward, a new magnesium-cased Burman ‘50’ gearbox was used. Compression was increased to almost 9:1. Why all the changes? Can’t design be ‘right’ straight off the board? Were designers incompetent? No computers? It is the nature of the things we make and use that they need adjustment as we discover their flaws and as their conditions of use change. This is evolution at work — and it never ceases. Initially the 7R’s competition were the Jr Norton and the KTT Velocette, but after 1950 the Norton grew stronger and the Velo relatively weaker. Norton for 1950 abandoned the aluminum-bronze combustion chamber ‘skull that had by its insulating effect limited compression ratio. Velocette management had decided to bet major resources on the ‘LE’ commuter bike, and so stopped KTT development. For 1951 the 7R’s intake cam was revised. Carburetion was by 1'in (28.6mm) 10TT Amal. There was a new cam oil feed and to keep that oil out of the combustion chamber, an O-ring seal was incorporated into the intake valve guide. Racing engines smoked as it was 24

CLASSIC MOTORCYCLE RACE ENGINES

— the high-surface-pressure oil scraper rings used in modern cars did not exist —- and would not have been appropriate. If too much oil is scraped off the cylinder, what will lubricate the hot, hard-working top ring? Ignition was still by not-too-reliable wound-rotor magnetos (race teams carried several spare armatures)

that required plugs be gapped no larger than 0.014in (0.35mm). Too much oil in the wrong place could foul a plug. Probably based upon frettage seen between main bearings and cases, it was decided to stiffen the crank against flexure by narrowing it. Narrower crankcases without ribbing were adopted. Stiffening ribs look good, but their abrupt changes of section are often a cause of cracking. Rod, big end, and crankpin were narrowed as well. Power was now 34hp at 7,200rpm (12bar, 176psi). Much of this gain traces to improved fuel, making it possible to increase compression, now at 9.4:1. In 1952 roller rockers were introduced on factory bikes. Everything is interrelated. If there’s trouble with rockers scuffing (they tried plating the cams), you make a new oil feed, but more oil returning from the head means more oil for the crank to whip into a power-eating storm. So let’s keep the oil away from the crank (the bypass was implemented in 1953). To keep step with the post-war improvement in fuels, compression ratio rose to 10:1. Anything that heats the mixture — as compression does — makes detonation more likely. But compression is a prime determinant of peak combustion pressure, and of torque. The rule of thumb is, peak pressure equals one hundred times the compression ratio. Tuners therefore always walk on the very edge of detonation. First practice at GPs was in part an experiment to ‘measure’ the quality of the local fuel. Adjustments were made with compression plates placed under the cylinder. The Porcupine’s troubles created unbearable conflict between Matt Wright and the AMC directors. Management wanted results but without changing anything, without spending any money. When the team sought airflow help from Harry Weslake, Donald Heather forbade it. Wright joined Jock West in the sales department.

AJS 350 7R

A

Larger changes came in 1953. A new head was made, with an altered intake valve position, bringing valve-included angle to 74°. The exhaust valve was now internally cooled by partially filling its 11mm stem with sodium metal. At operating temperature the motion of the liquefied sodium carried heat rapidly out

of the valve head and ‘breakage point’ (where the stem joins the head). This heat went up the valve stem and into the guide, whence it was carried away by oil circulation. Significantly, exhaust valve guide tolerances had to be adjusted the following year. With intense heat coming up the guide, compromise had to be found between tight enough to stick the valve with heat-gummed oil, and loose enough to interfere with good valve-to-guide heat transfer. Cam oil feed was adjusted again, and the connecting rod design was slightly changed to increase strength. Crank main bearings received steel sleeves to protect the soft metal of the cases from their constant motion. Quite

often designers of singles provided double main bearings on one or both sides, in an attempt to restrain vibratory ‘tuning-fork’ motions of the crank. The designer begins with lightweight, but progressively puts it back in the form of steel main bearing sleeves — often with wide flanges to distribute the load over the inner faces of the case. The apparent simplicity of the single-cylinder engine is not simple in detail! Late in 1954 ex-rider and engineer Jack Williams arrived. Power was 37hp at 7,500rpm (12.5bar, 184psi). He was told that (1) steady improvement was desired, (2) that there was no money, and (3) that use of equipment or services sourced outside AMC was forbidden. British teams withdrew from GP racing at the end of this year. To make progress Williams employed the classic small-team stratagem of putting ideas in the place of equipment. The story of his excellent work is well told in Chapter 1 of Vic Willoughby’s book Winning Motorcycle Engines. Williams’s approach was subtle and wide-ranging, not concentrating in any one area such as higher rpm or increased airflow. He wiggled many variables and followed any trend of improvement he discovered. In 1955 came a modified ‘turn-down’ inlet port, a double ball bearing on the timing side, 25

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smaller flywheels, and an enlarged crankcase breather valve. A reverse-cone megaphone was used for the first time. A more reliable rotating-magnet magneto was made possible by improved magnetic materials. Breather valves are timed breathers, intended to use the piston’s descent to evacuate the crankcase. In some engines the rapid cyclic change in under-piston volume pushes air into and out of the head, or interferes with oil return. In either case, power may be wasted, either forcing air at high speed through orifices or by oil drag on the crankshaft. These require remedies. Note also that main bearings received constant updates, indicating problems in that area. The narrowing of the crank and cases in 1951 was fundamental, for the greater the span between main bearings, the more leverage combustion and inertia forces have with which to bend the crank and flex its mainshafts and their bearings in the case. The crankshaft with its flexion is a species of wild animal whose struggles are barely contained. Changes just move the problems to a higher level of performance. When development raises the rpm again, new issues arise. We are told that AJS/Matchless flywheels were 35-ton steel, which means that at a tensile strength of 35 x 2,200 = 77,000psi they were only 18% stronger than mild steel (coat-hanger wire). There were chronic problems with keeping mainshafts in this relatively soft material. Many a fine doorstop was made from wallowed-out 7R or GSO flywheels. Jack Williams found through his airflow work that intake valve flow was masked by the close cylinder wall (recall that the valve size had been increased previously). In 1956 this was adjusted by making the bore 1.5mm bigger,

at 75.5, with a 78mm stroke. The intake port was adjusted again as well. Ignition timing now became 37-38°, some of which reduction surely came from the higher intake velocity Williams’s work achieved. Shorter ignition timing means less time for heat loss from combustion gas — and more pressure on the piston top. 26

Another change was the adoption of only two piston rings — a single L-section or ‘Dykes’ gas ring plus a two-rail oil scraper. The use of only two rings is general on racing engines today. Piston ring friction makes up a major part of friction loss because the shearing of oil in the very thin oil film between ring face and cylinder wall is extremely vigorous. Work with cam forms and springs had raised the engine’s red-line rpm to 7,800 now (in 1950 the KTT Velo’s maximum had

been 7,000). A simple approach to raising an engine’s red-line is to make the valve springs stiffer. That might work in a drag engine, running ten seconds at a time. But this was England, and 7R buyers expected an engine to run at least a season or two without major service. Williams calculated new cam forms in which opening valve acceleration (driven by the cam) was three times the acceleration ‘over the

top’ (driving force coming from the springs). Because his cams asked less of the springs, valve motion was kept stable to higher revs. An example of ‘wiggling the variables’ was intake port downdraft angle. Using a wooden head model with ‘pop-in’ ports of various shapes, Williams could get more air through a ‘flat’ port (port at near 90° to cylinder axis) but the engine made more power, on less airflow and less fuel, with a higher port. Part of this was that the higher port short-circuited less fresh charge to the exhaust during overlap, but Williams investigated further. He lined the cylinder with paper and then, with air flowing, sent a measured amount of dyed liquid through the carburetor’s needle jet. The flat port spattered the far cylinder wall with fuel (just as in early Suzuki TL1000s!) while the higher port distributed fuel more evenly. In 1958 a higher port, with 14.5° downdraft, was adopted in place of the previous 12°. Rotary charge swirl was provided by a 20° intake offset, assisted by 10° on the exhaust port. Power in 1958 was 38.5hp at 7,6007,800rpm (12.9bar, 189psi). Williams employed squish to ‘refresh’ CLASSIC MOTORCYCLE RACE ENGINES

combustion turbulence as the piston neared TDC. Piston-to-head clearance in the squish zone was set at 0.025-0.030in (0.63—0.76mm).

To get maximum benefit from squish, the clearance must be set just large enough that the parts never quite touch. But because mixture in the squish zone burns later in the cycle, the squish volume (area times clearance) must be

the minimum necessary to keep detonation at bay. Detonation occurs after cumulative, heat-driven charges have matured in the last outlying parts of the unburned mixture. If normal combustion can be made fast enough, it outruns this chemical process, burning up the charge before detonation can occur. A 1960 7R’s spec was 42hp at 7,800rpm (13.7bar, 201psi). Carburetor was the 134in GP that Williams had found best (35mm). With the faster combustion of the squish piston, ignition timing dropped to 33.5° BDC. The less ignition timing required for best torque, the better and more efficient the engine. Gearbox ratios for the 1960 engine, referenced to top gear as 1.00, are very close: 1.782 1:326 1.10 1.00 Upshifting at 7,800rpm from first to second would pull the revs back to 5,800rpm, barely keeping the engine in its pulling range. You can AJS 350 7R

Z

Alan Shepherd has evidently just landed — note flattening of front tire and front and rear suspensions at full compression. Top run of the chain indicates power on, as does rider’s facial expression. (Mortons Archive)

readily see why, with numbers like these, riders and teams were seeking five-speed alternatives in this period. The 7R was not a force on GP racing’s fast tracks (where Guzzi’s laydown 350 single was champion 1953-57) but with almost 800 machines made in 14 years, it carried a large number of clubmen on to greater things. It was the Yamaha TZ250 of its era. It is likely for this reason that Jack Williams worked not to raise peak power but to fatten the engine’s pulling range. Wise speedmen have always known that it is engine torque — averaged across the range actually used on the track — that wins the race to the next corner. Especially in that era, efforts to raise the peak rendered the bottom fussy and the mid-range weak. In English short-circuit racing, off-corner acceleration was everything. Williams, with the

tools he had made, was in 1955-62 doing just what Valentino Rossi and Jeremy Burgess were doing with a laptop in the spring and summer of 2004 — making a machine that could be first off the corners.

Dif

All things to all riders

1948-1962

he pushrod single BSA Gold Star models were not as fast or powerful as overhead cam pure racers such as the Manx Norton or AJS 7R, but in terms of versatility and performance vs cost they scored decisively. Gold Stars were ridden on the street, in

scrambles, on dirt tracks, and in road racing by a large population of enthusiasts. Produced at the rate of 1,000-2,000 per year in the period 1948-62 they were plentiful. Also plentiful were specialized high-performance parts from both factory and aftermarket. In England and in the US, the BSA Gold Star was a favored mount of the privateer racer and the beginning of many a professional competition career. Improved and refined year after year until 1956, it represented the best current thinking in design, and influenced many other machines. Notable among them, and active to this day, is the Harley-Davidson XR-750 dirt-tracker, whose cylinder heads are said to be patterned on that of the 350 Gold Star. The Gold Stars were air-cooled 350 and 500 vertical singles with two pushrod-operated overhead valves. In production form, the 500 gave 42hp at 7,000rpm (10.6bar, 156psi), but modified in private hands examples were developed to more than SOhp. Gold Star cranks were of the classic British ‘millwheel’ variety, with forged steel flywheels joined by a separate crankpin. A forged steel connecting rod ran on a roller big end. Design of the Gold Star was no accident. It was the work of sophisticated engineers from its earliest forebears, just after the First World War. While most motorcycles were then propelled by pedestrian side-valve engines, the successes of overhead valve (OHV) machines at Brooklands Speedway made them the choice of sporting riders. The reason is obvious — air flowing into a side-valve followed a tortuous, restrictive path compared with the direct flow of an overhead. Working in the opposite direction was the OHV’s heavier valve train,

Right-hand view of Gold Star engine in chassis: downdraft carburetor and offset intake tract, generous cooling fin area, classic eye-satisfying exhaust-pipe shape. (Mortons Archive) BSA GOLD STAR

7

burdened by the extra mass of pushrods and rocker arms, tending to limit rpm. Most early OHV designs placed both pushrods and rockers in the open air, the rockers pivoting on spidery structures bolted to the cylinder head. This allowed good access of cooling air to head finning, but brought the problem of lubrication. Many motorcycles of 1920 still relied upon once-through oil systems that were only one step forward from the earliest total-loss schemes. Without pumped, recirculating oil systems, OHV was a messy, under-lubricated curiosity. In 1920 best internal combustion engine design practice was exemplified by the aircraft engines of the recent Kaiser War. With the exception of the rotaries, these were liquidcooled four-valve OHV or OHC designs, the most recent often with that radical novelty, aluminum pistons. Determined to ride the wave of change, BSA prototyped a four-valve OHV single with an aluminum head. It is said to have overheated, leading to its abandonment. Overheating in air-cooled engines was all too common at this time. Sir William Weirof the British Air Board had in 1918 most unwisely chosen the ABC ‘Dragonfly’ nine-cylinder static radial as the RAF’s major future engine. Had the war continued into 1919, Britain’s air power would have depended upon an engine whose scantily finned cylinder heads glowed red at rated power, and whose crank was inadvertently designed to operate on a major vibration mode. The Dragonfly’s designer, Granville Bradshaw, had made an understandable

mistake. Taking as his model the cooling fin arrangement of wartime rotary engines like

the Gnome, he had concluded that most of the cooling should be applied to the cylinder, not the head. As the crankcase and cylinders of a rotary spun at 1,200rpm, the heads moved through the air at 250 feet per second — even if the airplane were sitting still. With that kind of air blast it took little fin area to deal with a rotary’s heat output. Bradshaw designed similar cylinders for his static radial (whose crankcase and cylinders do not rotate). This meant that they received cooling air at only 90

feet per second at take-off, and less than 15 Ofps in cruise. 29

It looks as though BSA sought further advice for their second design, which placed two parallel valves in a copiously finned iron head. One of the rules for successful air cooling was that “The fewer holes you make in the head, the fewer problems there will be with warpage and cracking’. Both Harry Ricardo, with his Triumph-Ricardo 500, and George Hack with his Rudge, discovered the propensity of aircooled four-valve engines to cracked heads. Use of two valves avoided this. And why the change from ‘progressive’ aluminum to a conventional iron head? No one at this time knew how to keep hard valve seat inserts in aircooled aluminum heads. Cast-in, screwed-in, or

shrunk-in, they all came loose as the soft metal relaxed at temperature. Valves seat reliably in an iron head. BSA took a big team of these new bikes to the 1921 TT but, like the Air Board, had not yet learned the centrality of testing. Many

Right-hand view of early Gold Star: straight pipe, sliding-pillar suspension, tiny brakes. (Mortons Archive)

30

problems occurred, including valve breakages and seizures from last-minute fitting of trendy aluminum pistons. No BSAs finished. Management were spooked and resolved never, ever again to enter the TT. The company still needed an OHV sports model. Harold Briggs had lately come from British Daimler and was assigned by Fred Hulse, head of the drawing office, to

work up a new design. Existing accounts say that Briggs took as his model ‘an old Hotchkiss engine’ that was ‘lying about the works’. Would it surprise you to learn that this engine had been designed in 1920 by a man who is today reckoned as ‘the father of the air-cooled engine’? That man was S.D. Heron, employed during the war by the Royal Aircraft Factory. From June to August 1920 he was working for another wartime engine man, F.M. Green, contracted

to British Hotchkiss. That company needed a product to manufacture in its Coventry factory. Heron drew them a 90 x 85mm aircooled two-valve OHV 90° V-twin with fully enclosed valve gear, lubricated by routing crankcase oil vapor through its bolted-on

CLASSIC MOTORCYCLE RACE ENGINES

rocker boxes. BSA put these engines into its TB10 three-wheeled cyclecar. Heron emigrated to the New World at the end of 1920. The series of air-cooled cylinders he developed there for the US Army led to the J-type, which made the large radial aircraft engine first practical, and then dominant. At Wright Aero, Heron oversaw the assembly of the Whirlwind engine, equipped with his cylinders, which powered Lindberg’s 1927 solo flight across the Atlantic. Briggs’s work became the 1924 flat-tank L-model BSA 350 of 72 x 85.5mm. Its Heron paternity is clear in its 45° included valve angle, straight rockers, full valve gear enclosure,

and copious head finning. The oil system was once-through by gravity feed from a tank to an external mechanical pump, supplemented by a hand pump. The idea of such oil systems (previously common in cars) was that the mechanical pump would supply oil at about the rate that it leaked past the piston rings and valve guides, and the hand pump could provide extra during high-power operation. Because of the poor quality of wire insulation, this engine and others of its time mounted their magnetos ahead of the hot engine, with an enclosed drive by chain. When more heat-tolerant magnetos became available they were tucked behind the cylinder, out of front-wheel splash in wet weather. The following year Hulse and Briggs updated this as the $27 ‘sloper’, with a detachable iron head and two valves set at the then-trendy 90 degrees to each other. Dimensions were 80 x 98mm and the engine had large-area flat mushroom tappets in place of Heron’s cylindrical ones — a feature that would serve reliably through the Gold Star line. Several makes built such ‘slopers’ in this period, making me suspect one reason was that, with fashion dictating a low fuel tank, there was no room for a tall, upright OHV cylinder and head. In 1929-30 the Light Series singles had an upright two-valve cylinder and a ‘twin-port’ head with two exhaust pipes. The head design still featured the 90° valve angle but the twin ports surely fed excessive heat into the head. Accessories were still located forward. BSA GOLD STAR

,

For 1932 Herbert Perkins and David Munro designed the Blue Star series, with vertical cylinder and all forward-mounted accessories. Meanwhile the Competitions Department sought something more modern. BSA’s J-Series V-twins had high-mounted camshafts, whose shorter pushrods were not excited into ‘bowstringing’. Both pushrods were housed in a single tube, giving the appearance of the ‘cammy engines’ (OHCs) that were then winning TT races. Development shop personnel blanked off the rear cylinder of one of these, brought the front cylinder upright, and placed the magneto behind it. It was also given a duplex two-gear oil pump, recirculating oil to a remote tank. This would become the standard oil system of BSA singles. In 1936, the versatile Valentine Page was hired at BSA to update all the singles. The result was three lines of side-valve and OHV engines, built on strong bottom ends lubricated by recirculating oil, with round tappets and two separate cams. Placement of magneto and oil tank to the rear allowed engine mass to come forward to the front wheel, and the fashion-dictated dual exhaust ports from a single valve were no more. The final step leading to the creation of the Gold Stars was a happy accident. Comps manager Bert Perrigo brought back racing great Wal Handley from retirement to ride a very special B23 Empire Star (one of Val Page’s creations). Running on methanol and 13:1 compression, this iron 500 single made 37hp. Starting with a nine-second handicap in a Brooklands Speedway three-lapper, Handley came through to win, lapping at over 100mph. This earned him a Brooklands Gold Star award. Capitalizing on this, BSA built a special model with aluminum cylinder head with integral rocker boxes and iron-lined aluminum cylinder, 201b lighter than the iron version. This M24 engine made 30hp at 5,800rpm, and was red-lined at 6,500 (9.1bar, 135psi). A 15/2in Amal TT carburetor was fitted, the head held screwed-in valve seats (new aluminum alloys had made this possible), and the pushrod housing was cast as part of the 31

head emerged, now with 15° intake downdraft, larger valves, and separate, bolt-on rocker boxes (the integral type had imposed compromises).

cylinder. The natural choice of model name was ‘Gold Star’. Only a few were built before World War II arrived in September 1939. As you might expect, there was gasket leakage at the cylinder’s cast-in pushrod tunnel (the cylinder ran hotter than it did, causing a height difference), so two extra head bolts were added. BSA would switch to war work, building 126,000 of Val Page’s rugged M20 side-valve bikes. When the war ended and civilian production resumed, some 1947 customers wanted the option of aluminum cylinder and head. The Competitions Department was asked for an alloy B32 (350) for clubman’s racing. Management agreed and the ZB32 of 71 x 88mm = 348.4cc was exhibited at the annual motorcycle show, with a range of optional compression ratios and cams. The next year a 500 was planned with an 85mm bore. Valve included angle was 75° —a

were Gold Stars. They also finished first, second, and third. The CB32 now made 30hp and the CB34 500 made 37hp. The new head was the joint work of two experienced and pragmatic designers — Bert Hopwood and Roland Pike. The more powerful engine needed more cooling, so they increased fin area. The turn down to the valve on the intake short side was too abrupt for good flow, so they raised the intake port. To permit greater overlap valve lift without valve-to-valve contact, the valve included angle was reduced to 66%4°. To gain more detonation resistance from charge swirl, the intake port offset was increased to 28°. Ports were opened up and compression raised to 8:1 (remember that the available fuel was still 72-ON pool petrol). In 1953 the 350 Gold Star received the new head and the con-rod was shortened to 674in

reduction from the classic (and excessive!)

(175mm, for a rod ratio of 1.98).

90. Screwed-in valve seats were again used and intake downdraft (shown in the 1930s to improve flow and reduce charge shortcircuiting during overlap) was 7°. Valve adjustment was by thread-and-lock on the tappets. To accelerate combustion, the intake port was offset 244° to the right, and the exhaust port 20, promoting rapid axial swirl of the mixture. A magneto’s spark has a long arc duration so, as mixture swirled past the plug electrodes, a streak of flame resulted. Flywheels were forged steel, originally 8in in diameter (203mm) and 134in thick (35mm) joined by a flanged, tapered, and nutted crankpin into a 30lb unit. A forged steel connecting rod 7¥sin long, eye-to-eye, with a pressed-in big-end outer race, ran on 24 ‘4 x “ein rollers, loaded as end-to-end pairs in a 12-slotted duralumin cage. BSA had their own experienced forging department so there was no cheese-paring when it came to highly loaded parts like rods and flywheels. In 1950 power was 25hp for the 350 and 33 for the 500, using a straight exhaust pipe. In late 1951 the Gold Star engine was redesigned in detail to keep it reliable as its power was developed. The big-fin die-cast CB 32

Of 41 finishers in the Clubman’s TT of 1952, 34

In 1954 the head and cylinder received more and squarer finning. The weight of valve clearance adjustment was removed from moving parts and the job given to eccentric rocker-arm spindles. To deal with frettage observed between crankpin and flywheels (evidence of relative scrubbing motion) the

b)

pin (1955) was upgraded to 110,000psi nickel-chrome case-hardening steel and its threaded ends enlarged. Because a clappervalve crankcase breather was unable to keep up with 6,000rpm, Pike designed a timed rotary breather that put an end to pushing out oil. The drive-side mainshaft and its bearing were increased in diameter. Strobe-light studies on the dynamometer revealed considerable cylinder motion (cylinders of large aircraft engines flexed 0.020in [0.5mm] to the side from the jacking effect of con-rod angularity on the power stroke). Now the iron cylinder liner’s thickness was more than doubled, to Yin. Structural flexure and power loss from cylinder distortion are timeless topics, and such work goes on today. Detail by detail, the Gold Star was evolving. Because of concern over exhaust valve durability issues (by sighting down the carburetor CLASSIC MOTORCYCLE RACE ENGINES

of an engine running on the dyno, part of the exhaust valve could be seen, glowing red), Pike reduced the exhaust port throat to 13/in (35mm) and reduced exhaust valve diameter. He was rewarded by improved valve life and a reduction in cylinder head temperature. In 1954 BSA sent six factory-prepared racers to Daytona in the US - three twins and three Gold Star singles. One of the twins won the event and five of the top six places were taken by these factory twins and singles. During 1955 the method of delivering oil to the crank end was changed. Previously, a tube pressed into the timing cover extended into the hollow crank end, but now an extension of the crank projected into an oil seal pressed into the case. This may have been intended one day to support a one-piece crank with a split rod running on plain bearings.

BSA GOLD STAR

In 1956 another exhaust port throat and valve reduction were made. This parallels a process frequently undertaken today, in which temperature problems may be solved or room found for larger intakes by exhaustside reductions. On the 500, the exhaust valve material was changed to Nimonic 80A, developed for gas turbine blades during the war. The 350 was given a 13/6in (30mm) GP carb and the 500 a 1%in (38mm) GP. This year’s DBD34 500 made 42hp at 7,000, on 8.75:1 compression (10.6bar, 156psi). This is a very good bmep for such a modest compression ratio

The Gold Stars came as close to being the universal motorcycle as was ever achieved. Affordable, durable, equally at home on pavement or dirt. (Mortons Archive)

However it came about, the Gold Stars were

classically beautiful. — testimony to this engine’s high volumetric and combustion efficiency. In factory testing with special fuel of 100 Octane Number, it was found that knock did not begin until a compression ratio of 10.5:1 was reached. Many other changes were made over these eight years, such as a four-step evolution of valve spring wire and increase of intake valve lift from 0.368in to 0.441in, and

from 86 degrees of valve overlap to 115. There being only two quite heavy valves, controlling their motion at higher revs took time — eventually 330 crank degrees — and cylinder filling was dependent upon late intake closure. The result was ‘camminess’ or ‘megaphonitis’ as at lower rpm, charge was lost to backpumping through the still-open valve, or to exhaust backflow during the long overlap period. Only when the intake charge was moving fast and exhaust and intake wave action came into step with the crankshaft could best cylinder filling occur. Modern four-valve engines can rely more on rpm and high valve lift for their power, and so work well with much shorter valveopen timings just over 250°. The result can be wider, more usable power. If you marvel at the difference between a tall 7,000rpm Gold Star and a compact modern 13,500rpm 450 MX engine, here are some points to

consider. First, modern engines have very short strokes. Roland Pike was on the trend, even if BSA were not. He tested five different 350 engines, from 63 x 112mm to 85 x 61.5mm, and said, ‘From these tests in 1953-1954-1955 I became convinced that short strokes were the way to go.’ The Gold Star 500 was 85 x 88mm. Today’s Honda CRF450 is 96 x 62.1mm. Second, the BSAs were pushrod engines, whose greater valve train weight limited their revs. Modern OHC engines avoid this. And third, liquid cooling today allows use of four valves without head cracking. Their smaller valves can follow cam profiles to a 34

speed 1.4 times that of a two-valve. Because modern 450 MX engines rev so high they need a lot less flywheel than the Gold Star’s 301b. Pike was on this trend as well, testing compact one-piece cranks with external flywheels. He left BSA in 1957. Some hold that beauty arises from function, and surely the two are intertwined. Was it the Gold Star’s 15° downdraft intake, its glorious 1¥2in GP carb, heavy finning, and its exhaust pipe’s diagonal path that made it so attractive? Or did the neverending wins in the Clubman’s TT and elsewhere create this beauty? Slow bikes aren’t beautiful. However it came about, the Gold Stars were classically beautiful. Just as in the great aircraft engines, this beauty could be found in every engine part, evolving over years of development toward ideal shape. Functional beauty, beautiful function. Gold Star dominance of the Clubman’s TT drew irrational criticism — as though the critics held BSA morally bound to make their bikes worse to ‘give the others a chance’. How ironic that such thinking now guides race-sanctioning bodies toward their bright future of ‘parity’. Slow the fast ones down to make a race with the slow! BSA management since the war regarded singles as obsolete and ‘counter-market’. Twins were the future! Gold Stars, carefully assembled and each then dyno-tested, were reckoned too labor-intensive. When in 1962 Lucas announced it would cease production of single-cylinder mag-dynos, it was excuse enough. Gold Star production stopped ie 2963:

Such photos of racers, piercing the gloom of the ordinary at blinding speed, whilst casually changing gear, have helped make lifelong enthusiasts of many of us. (Mortons Archive)

CLASSIC MOTORCYCLE RACE ENGINES

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Simplicity and light weight are never out of place in racing

1958-1970

panish two-strokes represent an authentic

third stream of two-stroke development, only in part inspired by German examples.

First Montesa and then its offspring, Bultaco, discovered that much more could be accomplished with port timing and resonant exhaust pipe than DKW engineers had imagined. Previously, such pipes had merely been used to assist traditional port timings, but through repetitive testing engineer F.X. Bulto discovered that Ing Wolf’s pioneering resonant exhaust pipe could be used to make much longer port timings — and much higher power — practicable. Bulto was a sophisticated and welltraveled man.

Bultaco arose from Montesa, a company with its own dramatic history. Montesa’s first prototype had originated in 1944 from the work of Pedro Permanyer and Francisco X. Bulto (who manufactured cylinder liners and piston rings). With Bulto as engineer Montesa’s two-stroke engine passed rapidly through quite different forms, possibly influenced by Villiers and Eysink as well as by the familiar DKW RT125. Racing was integral to the Montesa plan. In the 1951 125 TT Montesa singles were fifth and sixth, 18kmh (11mph) slower than the winning Mondial four-strokes. This put them in the same low-technology class with the DK Winspired Italian ‘megaphone two-strokes’ over which Mondial had so recently climbed to dominance. But by the 1956 TT the 70kg (156lb) 51.5 x 60mm Montesa had gained power and sophistication (Montesa may have been the first to make streamlining out of fiberglass). Marcello Cama on one of four entered six-speed Montesas with exposed chain primary drive was second to Carlo Ubbiali’s MV, with Montesas third and fourth as well. This squish-head version of the engine made 18 rear-wheel hp at 8,000rpm on 10.5:1 compression and a 30mm Dell’Orto §S1 or

Bultacos featured almost toy-like simplicity, as the sophistication of intake and exhaust waves and porting details was invisible inside ns the geometric styling of the exterior. (Morto Archive)

BULTACO 125/250 SINGLES

~

GP carburetor. Simplicity and light weight are never out of place in racing. In May 1958 the partners split over the issue of racing and Bulto was urged by a deputation of 12 of his technicians to carry on with his own company. This became Bultaco. Their first result was a 51.5 x 60mm four-speed 125 single called ‘Tralla 101’, making a modest 12hp from the simplest porting — an exhaust port, two DK W-style transfers, and a pistoncontrolled inlet. It had a steel connecting rod with a double-row caged-roller big end, a 6V flywheel magneto, an enclosed chain primary drive and a unit four-speed gearbox. It was capable of 7imph and many alternate final gear ratios and sports options such as clip-ons and exhaust pipe were offered. Such a machine, equipped with a ‘trench head’, won a rainy race at Zaragoza in 1959. The ‘trench’ was just the usual central combustion chamber of a squish head, but

elongated fore-and-aft. In later years such heads would on occasion help two-strokes that had the problem of unsymmetrical scavenge, simply by providing this channel to straighten up the scavenge stream as it reached the head. The Zaragoza machine gave 13hp at 8,800rpm. A great advantage of developing a simple machine is that many tests can be quickly run and the cost of experiments is low. In one account of Bultaco racing development in 1959, the ‘countercone’ racing exhaust pipe added 25%, raising compression to the detonation limit of best available fuel added 20%, then a combination of shortened inlet length, an ‘improved’ exhaust port, and raising the revs to 9,000 added 12%. Opening the carburetor from the stock 22mm Dell’Orto to a 29mm Dell’Orto SS1 added another 18%. This totaled a 75% power increase, from 9.8hp to slightly over 17hp. Such a machine was entered in a race at Madrid in October. After Marcello Cama came sixth, the company scrambled to ready a proper factory racer. This tuned-up machine — to be called TSS — ran in the 1960 125 TT and had other outings. A 60.9 x 60 175 version was taken to Montlhéry in France for record-setting in October. The first TSS racing model for public sale — a four-speed 125 — appeared in 1961, for which ai

CLASSIC MOTORCYCLE RACE ENGI NES

20hp at 10,300rpm was claimed. It is important to bear in mind that Spain then lagged behind the rest of Europe on an industrial level, making casting, welding, and machining sometimes matters of improvisation. Those who have repaired TSS chassis have been alarmed to find masses of body putty peeling away from the steering-head — apparently applied for reasons of appearance. Fork dampers made of brass had all the parts required for function but might need ‘sympathetic reassembly’ to actually work. In one official service bulletin of the 1960s, owners of machines troubled by oil seepage through the crankcase castings were advised to disassemble completely, then carefully peen all surfaces with light hammer blows to seal them. Rather than tackle the manufacturing problems of fast-spinning primary gearing, Bulto continued Montesa practice in using a chain — but now it was fully enclosed. And, as previously proven at Montesa, extra lubrication for the Bultaco TS$125 was provided by a drip feed directly into the carburetor (as used by DKW before Montesa). Port timings for this first TSS were EO 95 ATDC, TO 117 ATDG, for a blowdown of only 22°. Intake timing was 80° either side of TDC. Both intake and exhaust ports were bridged, and there were only two transfer ports, their flow hugging the piston and directed into the nonexhaust half of the piston crown. Bultaco made simplicity work. Just as at Guzzi, there was a respected metalworker, Antonio Sesperes, who made all the racing exhaust pipes. Instead of using the familiar method of angle-cutting and welding of cones, this man made each pipe in two longitudinal halves, cut out as his experience dictated, then body-worked them to shape, and finally seam-

welded them. Bultaco employed German-made Mahle at Every spring before the season-opening race shmen Engli of tion migra t modes a te, Alican iS went to Bultaco, to acquire that year's new the e becom had s or 250, as these motorcycle is mainstay of lightweight privateering. Here ton Thrux 1963 the at 250 his on n Paul Marti 500. (Mortons Archive) ~ BULTACO 125/250 SINGLES

-

pistons and the dimensions of their connecting rod big-end bearings suggest they received good design advice from INA-Germany on this critical part. The rod big end of a two-stroke is marginally lubricated because the only oil available to it is either dissolved in the fuel or supplied haphazardly as droplets. This, added to the plus-and-minus speed variation of the crankpin bearing, made skidding of the big-end rollers a likely outcome — unless they and their cage were very light. And that is just what they were in the Bultaco, as a result of use of a very small crankpin and small rollers. The crankpin was of 18mm diameter and the 118mm-long (1.97 rod ratio) rod’s big-end ID 26mm, with two rows of 4mm rollers guided by an aluminum-alloy cage. Needle rollers in a steel cage presently superseded this. While conrods from, say, Yamaha, had markedly larger big ends than smallends, a Bultaco rod looked more like a box wrench, with big end little larger than smallend. If you go through the numbers for crankpin inertia loadings you find that the bearing is not undersized for the load. INA’s catalog has long contained recommendations for the proper sizing of twostroke con-rod bearings. After initial assembly and truing of the crankshaft (the latter performed with V-blocks, dial gage, a soft hammer and a wedge), expander plugs were pressed into the ends of the hollow crankpin to enhance tightness. Former factory rider Jess Thomas said, *...

the racing components came from Germany. When the supply got thin, Ramon Torras and I would exercise our Metrallas up to the French border to meet a courier, slip the

customs officer 5,000 Pesetas, and be back in San Adrian de Besos for late lunch, each of us carrying some 10kg of big-end assemblies and

top-end needle units. Same with the crankshaft seals, which were from GACO in Birmingham.’ Thomas had some memorable rides in the US and Torras was Bultaco’s European star. When you look over grand prix results it’s clear that the Bultacos’ strong suit was short, twisty circuits like Montjuich Park where their light weight and two-stroke torque accelerated them faster than more powerful but heavier four-strokes. ay)

The cylinder had an iron liner, which only in time became a liability. Frank Sheene (‘Franko’), father of the late two-time 500 world champion

Barry, became noted as a Bultaco tuner in early days when the previously dominant 125 — the four-stroke Honda CR-93 production twin — was pulled down from its British 125 championship by the affordable Spanish lightweight. For racing four-strokes, engine service was a bench job, to be performed under good light with plenty of time. Bultacos, as simple as they were, could have a top-end change in a few minutes and a crank change in just over half an hour. Just as with combat aircraft, a racing motorcycle’s availability is a factor in success. In the past, riders had sometimes pushed off the grid with a rag tied around the smallend of a Manx because they hadn’t at the moment the price of a piston and needed the starting money. With the cheap, simple Bultaco, carrying spares and performing service were easier. That made it a good tool. For many European riders, the season began with a drive across France and down to the Bultaco factory near Barcelona to pick up new bikes, followed by racing at the non-point opening event at Alicante. Many a former Bultaco rider will remember Franko, moving through the paddock as ‘tuner at large’, trying everyone’s clutch lever for the necessary free play, saying, ‘Plenty 0’ slack there, boy, plenty 0’ slack.’ In 1963 Bultaco built a 200cc TSS and soon had it making 30-31hp at 9,500rpm on a 12:1 compression ratio (full-stroke measurement) and 29mm Dell’Orto carburetor. In 1965 the TSS models became water-cooled (pumpless, or thermosyphon circulation), and rider Tommy Robb reckoned the 250 was as fast as an AJS 7R. In 1968-69 the 125TSS made 29hp at 11,500rpm and the 250 almost 39hp at 9,500rpm, on compression of 13.5:1. An Amal

389 carb was used. Port timings for the 250TSS were EO 83

ATDC, TO 114, for blowdown of 31°. This is appropriate, for cylinder volume increases as the cube of dimension, while port area increases only as the square. Thus port area falls behind volume in larger cylinders, requiring longer timings to make up the difference. The rumored 350 that rider Tommy Robb 40

had hoped for was built for factory regular Ginger Molloy (he won the Ulster 250 on a Bultaco in 1966 and has a long list of GP placings) at 83.2 x 64mm dimensions. Molloy commented that, as light as it was and with so big a piston, this bike could not be push-started in GPs until its compression was dropped to 5.5:1 (measured from top of exhaust port, or ~11:1 full-stroke). Even with this compromise,

the machine’s lightness made it a useful racer. Molloy earned essential points on an ‘oversized 350° in two races in 1970, the year he was second to Agostini in the 500 championship. Molloy described carburetion development at Bultaco as a very basic process. Around a circuit he would go, and when the engine under development seized, the technicians back at the shop would ask him to hold the throttle at the same height as at the moment of seizure (he rolled his eyes in describing this). One would make a mark on the metering needle just above the needle jet, remove it, and chuck it in a drillpress. Then, with a bit of sandpaper between thumb and forefinger, he would pinch the fast-spinning needle just below the mark to reduce its diameter. Then the bike would be reassembled and testing would resume. Eventually a correct needle taper might result. Alberto Numen succeeded EX. Bulto as development engineer. As TSS engines were assembled, Molloy’s narrative continued, each went on the dyno. Those giving the highest power were reserved as ‘factory engines’. Those giving average power were sold to European privateers. The droners went to the US (a parallel situation prevails in the wine business). Power claims

for the 250TSS reinforce this — while the US importer listed 38hp, an English magazine gave 33hp, while another claim added spice at 42hp. Molloy was not only a good rider and canny tuner; he also did a bit of industrial espionage. If a friend on another factory team slipped him the loan of a spare factory cylinder (‘They'll not miss it for a week or two’) it would mysteriously show up in Barcelona to be measured and considered. Bultaco began with the simple two-transfer system and refined it. Exhaust and intake ports were rectangular, with center dividers. Main CLASSIC MOTORCYCLE RACE ENGI NES

transfer ports had only moderate backflow angle and flat roofs, making the flow parallel with the piston crown. Whereas a modern two-stroke’s multiple transfer ports occupy all available wall area, Bultaco’s single pair in the 125 are but 21mm wide, each. The natural result is a high transfer velocity that crosses the piston, hits the cylinder wall opposite the exhaust, then climbs that wall, crosses the head, and turns downward to the exhaust quickly. This is the

A widely held belief of that time was that exhaust gas should be expanded as quickly as possible upon leaving the cylinder. This ‘expansion cooling’, it was hoped, might prevent cylinder overheating and the detonation it invited. Bultacos had very large exhaust crosssections in the cylinder and, to match, very large exhaust header pipes (the first section of pipe from the cylinder). It would later be learned that there is value in postponing exhaust expansion,

old ‘train in the tunnel’ conundrum, in which

as the energy saved can be used to (1) increase

the train is the transfer stream and the ‘tunnel’ is the scavenge path. Maximum torque will occur when the maximum amount of ‘train’ remains in the tunnel as the exhaust port closes, but high scavenge velocity tends to waste fresh charge out the exhaust. This being so, there was no benefit to use of exhaust pipes with steep suction horns and large center sections — they would just pull mixture to the exhaust port sooner.

the pressure difference across the transfer ports and (2) strengthen the pipe’s return wave, which

So fresh, so promising, so beautiful. These are Franko Sheene’s new bikes one year,

photographed outside the factory. I can almost hear the ‘BAPP-weeoo’ as throttles are blipped during warm-up. (Maggie Smart)

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pushes back into the cylinder some part of the charge that has been lost. Bultaco’s success teaches the same lesson as that of Guzzi — that light weight and strong torque can prevail against bikes grown heavy with the mass of mechanism necessary to make greater power. In the early days of 250 production racers from Yamaha and Kawasaki, Bultaco TSS250s continued to win races. Gradually, the growing reliability and power of the twins prevailed, forcing the Bultaco’s weaknesses — limited cooling ability and a now-overstressed primary drive — into the foreground. A quick switch to chromebore cylinders might have kept Spanish machinery competitive a while longer, but in a development contest with ascendant industrial Japan there would be only one winner. In the larger scheme of things Bultaco’s influence was strongest off-road, showing what could be accomplished with a light bike and simple high-torque engine. Bultaco’s off-road example in the US led the Japanese makers to enter that field as well. Bultaco make me think of Phil Irving’s Formula 1 Repco V8 — an engine intentionally simplified so that it could be made competitive quickly, before the more complex engines of other constructors had time to mature. Once those more complex engines hit their stride, the Repco became obsolete. Bultaco made a strength of simplicity — for a time — and they provided to many riders an affordable, easily serviced machine that was fast enough to win national races — and be a stepping-stone to greater things. The company closed in 1987.

Barry Sheene without the microphone, Snetterton paddock 1968. See that skid plate? Bultaco and Spain’s mountainous terrain together created the super-light two-stroke enduro bike. (Mortons Archive) 43

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Auto racing gives back to motorcycling

1967-1982

he Cosworth DFV V8 is a grand prix car engine, but it is included here because it introduced design features now found in nearly

every modern sports or racing motorcycle engine. The company name — Cosworth - is a compound of the names of its founders, Mike Costin and Keith Duckworth (1933-2005). In 1966-67 Duckworth showed that the thermally inefficient deep combustion chamber and high-domed piston of the reigning two-valve paradigm could be replaced to advantage by a nearly flat four-valve chamber and flat-topped piston, with one central spark plug. Turbulence is essential to fast, efficient combustion in a two-valve, this was supplied by offsetting the intake port as it approached the head, creating a tangential swirling motion of the fresh charge around the cylinder axis. This carried mixture past one or two angled spark plugs, producing reliable, rapid ignition. Axial swirl cannot work in a flat-chamber four-valve with a central spark plug because mixture circulates around the plug, not past it. Thus there would be no motion tending to mix the flame kernel into the whole charge. Duckworth found a way to produce charge motion that did result in rapid, general ignition of the charge — a motion today called ‘tumble’. Charge entering the cylinder from the two markedly downdraft intake ports was aimed diagonally — down into and across the cylinder to hit the opposite cylinder wall. The charge flowed down the far wall to be deflected across the piston, and then rose up the intake wall to complete a looping path (reminds me of two-stroke scavenge flow!). Duckworth called this ‘barrel motion’. As the piston rose on compression this looping charge motion circulated charge through and across a smaller and smaller space, greatly speeding it up. As the spark occurred, barrel motion was rapidly circulating charge through and across the spark plug electrodes, generating a streak of flame that was rapidly

The Ford-Cosworth DFV was the selfpublicizing origin of a new combustion ction paradigm, now to be found in most produ (Ford) es. and racing auto and motorcycle engin COSWORTH DFV V8

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shredded and mixed into the general flow, resulting in rapid combustion. The steps that led Keith Duckworth to this concept are logical, and the reason it was he who made them rather than some other engineer is that he had always been skeptical of engineering’s ‘right answer culture’. Rather than simply accept ‘what is generally believed’, he preferred to draw his own conclusions. Received truth, for example, would note that Ferraris won a lot of races, and then conclude that this was because they had 12 cylinders and 24 valves. Arguments from

precedent are powerful in law, but did not persuade Keith Duckworth. Duckworth let the engines he was developing lead him to answers. First he learned to get air into engines by using downdraft intake ports in the two-valve pushrod head he designed for the Ford Angliabased 1,000cc Formula Junior four. Steep downdraft, by taking much of the turning loss out of the region near the valve, allowed smallish ports to deliver a lot of air. Such ports were used again on his next head, the SOHC ‘SCA’ F2 engine. He ‘tried very hard for three years to get that engine to burn’, seeking without important success to use squish to generate the necessary turbulence. He was very successful in filling its cylinders but as the engine needed a 49° spark lead for best power, Duckworth recognized a combustion problem. Later he would say that ‘other makers were mesmerized by airflow, but never considered how they might burn that air most effectively’. SCA dimensions, in carpenters’ measure, were 33/6in x 12%2in, for an extreme 1.67

bore/stroke ratio. This highly oversquare engine gave an initial taste of the problems Suzuki would hit with their 1988 GSX-R750 Superbike, Yamaha would find with the five-

would valve FZR750 in 1987, and Kawasaki

bore struggle with each time they enlarged the of their ZX7-based 750 Superbike. Duckworth noted that volumetric efficiency and combustion efficiency are inherently ling opposed. An ideally efficient cylinder-fil ty veloci e intak process would diffuse the high it as ty veloci n pisto down to the much lower most rt conve would This er. entered the cylind 4S

of the kinetic energy of the fast-moving intake charge into pressure energy in the cylinder. That would leave the charge in the cylinder ‘quiescent’, lacking the turbulence necessary for fast, efficient combustion. This was the

situation of Duckworth’s SCA engine. To correct that, some portion of the entering high air velocity must be sacrificed — retained in continuing motion to become turbulence as the piston nears TDC. Volumetric efficiency is the intake charge trapped in the cylinder, divided by the cylinder displacement. Tests have shown that VE can be pushed as high as 125% by careful application of ram effect, intake and exhaust wave action and, more recently, intake airbox tuning. Combustion efficiency is, formally, the fraction of the potential heat energy of the fuel supplied that is actually released in the engine. Duckworth’s usage of the term is broader. He was also concerned to reduce heat loss to engine parts, resulting from over-long combustion, and to limit the power lost through some fraction of the charge burning at a lower effective compression ratio (because the piston has significantly moved downward from TDC). Lotus Cars’ principal Colin Chapman in 1965 asked Duckworth to think about F1. After some back-and-forthing, Ford contracted Duckworth to design two engines — first a Formula 2 engine as a kind of audition, and later a 3-liter grand prix engine. Auto racing’s Formula 2 had just switched to a 1,600cc displacement, and now accident took a hand. Ford’s Cortina four-cylinder bottom end presented itself as the logical basis for this engine; Ford had no suitable six, which would have had the added valve area to enable its airflow to keep up with plenty of revs. Cylinder spacing made it impossible to put two valves of adequate area into the Cortina four simply by overbore, so Duckworth considered four valves. Anyone interested in engine design at this time could not overlook the success Honda were having with four valves in their

motorcycle racing engines. Total flow area wasn’t the only consideration — the new 1600 would have to reliably turn high revs. Duckworth wrote out the simple engineering relationships to derive 46

that with similarly proportioned valves and springs, and for equal levels of spring wire stress, a four-valve engine’s valve train would ‘float’ at 1.41 times (the square root of two) the valve-float rpm of the two-valve. The capability of 41% higher revs is seriously attractive, and is what mainly motivated Honda to give their racing engines four valves (recall that they built and raced some two-valve 125s and 50s in the early 1960s). Add to that the negative historic example of BRM’s P25 2.5-liter two-valve four, which too often broke its huge valves in its strenuous efforts to whack them open and survivably close them at competitive rpm. (Valve train dynamics engineers have to decide how much valve closing bounce is ‘normal’, Are three bounces OK?) Duckworth first examined the diametrically opposed intake valves of the Apfelbeck-BMW F2 engine because they could be made to produce traditional Harry Weslake-type axial swirl. Then he made two sound objections. First, the necessary compound valve mechanism was over-complex and heavy. Second, with its single central spark plug in ‘the eye of the storm’, it would have serious combustion problems. Fast light-up required rapid charge motion past the ignition source. How about placing two more spark plugs out near the cylinder wall, where charge motion would be rapid? No, he wanted simplicity, not a forest of spark plugs. There was pressure to succeed, and no certainty. Everything now depended on finding for the 1600cc F2 the fast combustion that had eluded him in the SCA. Duckworth gave the FVA four-valve a narrow valve angle of 40° for two reasons. With four valves, there was plenty of flow area even without a traditional (in the range of 60°) valve angle, and the flatter the chamber and

piston crown, the lower the engine’s heat loss. With this flat chamber it became practical to swirl the charge around a different axis — one at right angles to the cylinder axis, which would move it rapidly past the central spark plug. This became Duckworth’s ‘barrel motion’, today called ‘tumble’. The FVA (Four-Valv e A-Series, as the 1600 was named) made 200hp on the dyno in March, 1966. This perfo rmance CLASSIC MOTORCYCLE RACE ENGI NES

was given with a much-reduced ignition lead (the DFV would need only 27° BIDC=a huge improvement over the 49° of the SCA),

indicating that rapid, efficient combustion had

Theo Page’s elegant cutaway of the DEV. Such drawings make the simple appear complex, but multi-cylinder engines are just dense packaging of repeated simple elements. (Ford)

been achieved. With FVA a success, he could

now tackle F1. The F1 engine was designed from scratch was no suitable production bottom there as end. Duckworth believed that the mechanical efficiency of a V8 would be superior to that ing of a V12. To get some idea of his think area of here, compare the piston-ring swept

s, each two geometrically similar 3-liter design is result The ratio. having a 1.3 bore/stroke 1,408 for the 1,608 square cm for the 12 and

V8, giving the V8 12% less oil film to shear. and The V12 would have seven main bearings us obvio the ngs beari rod for and the V8 five, ratio was 12 to 8.

The new V8 would employ the tumble combustion system proven in the FVA. As the GP engine had to be of three liters rd displacement, it was decided to carry forwa en short the FVA’s bore of 85.67mm and 47

COSWORTH DFV V8

the stroke to 64.8. Since the FVA’s narrow 40° valve included angle had worked well, Duckworth reduced it to just 32°. Special constructional features were adopted which allowed the engine itself to function as the aft part of the chassis. Duckworth’s V8 F1 engine, designated ‘DFV’ for ‘Double Four Valve’, was ready for the GP at Zandvoort in 1967, which it won. It went on winning, to an eventual total of

over 160 GP victories. It also bested Matra’s high-revving but conventional new V12 with mysterious ease. The Matra, although also a four-valve design, had the combustion-slowing large valve included angle and tall piston domes of the past (features which Honda’s racing motorcycle engines had shared). The losses

Keith Duckworth and his creation in the dyno cell, April 1967. His preference for working from first principles kept him free of the unsupported assumptions that guide much of design. (Ford)

48

produced by this antique feature rendered it uncompetitive with the Cosworth V8, and it was redesigned with a narrowed valve angle. A major visual difference between the DFV

and previous engines was the fact that each cylinder bank had both of its cams under a single cover. A flat crank was used despite its residual secondary vibration because it simplified the exhaust system (it did not require connections between banks). The DFV began its career at just over 400hp at 9,000rpm (13.1bar, 193psi) and was progressively developed to an eventual S53S5hp at 11,300rpm 16 years later (14bar, 205psi). It won its last championship in 1982. As with any engine whose output is continually raised by development, there were problems. Early engines broke their cam drives. Valve springs and pistons failed as well. The cam drive was dealt with during 1970 by incorporating a compact assembly of multiple miniature torsion bars to provide the compliance to reduce dynamic loadings. Oil scavenging was improved by adoption of a high-volume

CLASSIC MOTORCYCLE RACE ENGINES

Although the Cosworth FVA and DFV were designed simply to win races, they defined a new combustion scheme which is now used in most of the auto and motorcycle engines produced in the world today. crankcase pump leading to a centrifugal oil separator. Crankcase air pumping loss was addressed by removing the lower half of the main bearing webs (those in the bottom half of the engine, which was integral with the lower halves of the main bearing caps). Connecting rods had to be redesigned to stop fatigue tensile failures at the top of the exhaust stroke. Header pipe length was progressively shortened to raise the rpm of peak torque, and intake ports enlarged. A turbo version of the engine — the DFX — was produced for US Championship-car racing. From 1975, this would be the engine that at last displaced the long-serving Offenhauser-4, which traced its lineage all the way back to pre-World War I Peugeots. High temperature erosion of the aluminum surrounding the exhaust valve seats led to adoption of a revolutionary fill-from-below casting process designed by English researcher John Campbell. Its reduction of ‘bifilm porosity’ kept hot gas from penetrating the cast metal — and when used throughout the engine, led to lighter weight from the thinner sections that were now strong enough for the loads. Other makers of racing engines had depended upon staffs of highly experienced machinists to make their parts, but Duckworth has been quoted as saying, ‘Unless it is reasonably easy for parts to be made, it is unlikely that they will be made properly.’ He therefore adopted CNC (computer numerical control) manufacturing, which produced no ‘Monday parts’ and did not alter designs in the interest of leaving at Spm. For the first several years of the DFV’s success, the Cosworth company kept quiet se about its ‘tumble’ combustion process becau prix grand with Ford de its job was to provi wins — not to tell the world how it was done. COSWORTH DFV V8

The general DFV layout was copied by others without understanding, resulting in four-valve designs that looked better than they ran. Over time, the need for more power rapidly pushed F1 toward higher bore/stroke ratios, leading during the 1990s to the extreme dimensions of 96 x 41.4mm for a 300cc cylinder. In such engines the familiar modern conflict between combustion speed and compression ratio was extreme. For a time, chemical combustion accelerants softened this conflict but ignition timings shot up to more than 60° BTDC, as they had in Honda’s racing engines of the 1960s. Considerable energy was lost to slow combustion as it had been in the SCA engine, but enough was gained by the ability to operate near 20,000rpm to make such extremes worthwhile. In Italy, Massimo Bordi, an engineering student, saw the value of Duckworth’s ‘new synthesis’ and proposed combining it with Ducati’s desmodromic valve drive. This would become the basis for Ducati’s 851, the first of that company’s many ‘Ottovalvole’ models. This was not a smooth process, for chief engineer Fabio Taglioni had from personal study and experience formed a poor opinion of four-valve engines. Test results from the fourvalve version of Ducati’s short-lived 500 V-twin GP engine showed him that charge motion in such engines was chaotic, and combustion inefficient. Taglioni very well understood the use of swirl and squish in accelerating combustion in two-valve engines. He surely knew as well that Honda’s four-valve racing engines had their troubles with overheating and also needed very long ignition timings for best power. He did however adopt on his last endurance racing engine the reduced flow loss of Duckworth’s steeply downdraft intake

ports. The Bordi faction eventually gained

49

leverage within the company and the four-valve revolution was established. Japanese motorcycle manufacturers adopted at least the appearance of Duckworth’s new paradigm. That some didn’t get it right — at least at first — was revealed by the troubles Suzuki, Kawasaki, and Yamaha had each

time they shortened the strokes of their 750-4 Superbike engines. Suzuki in 1989 had to go back to the longer stroke of 1987, Kawasaki’s

1991 short-stroke took two years to equal the power of the engine it replaced, and Yamaha’s FZR750 of 1987, with its long 45° of ignition lead, forced tuners to choose between top-end

and acceleration. Meanwhile Ducati increased their bore numerous times in Superbike racing — and each time mysteriously retained winning performance. Why were Ducati successful and the Japanese makers initially unsuccessful? Ducati engineer Claudio Domenicali explained that during development various intake downdraft angles are tested and the resulting tumble motion is evaluated with an in-cylinder anemometer. Running tests follow. Although the Cosworth FVA and DFV were designed simply to win races, they defined a new combustion scheme which is now used in most of the auto and motorcycle engines produced in the world today. Its low heat loss, ability to rev, and rapid combustion are advantages in both racing and emissionscontrolled engines. After the second ‘oil shock’ of 1979, US automakers responded to the need for smaller engines of good performance by conceptually sawing their traditional iron twovalve pushrod V$8s in half and giving them beltdriven SOHC. European and Asian automakers had already adopted the Duckworth paradigm, and to compete successfully Detroit had no choice but to follow suit.

Lotus designer Colin Chapman and Keith Duckworth survey the product at its press launch. Note the four bolt bosses at the forward end of each cam cover, by which the engine was joined to the chassis as primary structure. Ducati have lately done something similar. (Ford) 50

CLASSIC MOTORCYCLE RACE ENGI NES

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A forefather of two-stroke dominance

1952-1956

hen thinking about long-ago manufacturers, it’s necessary to realize their former importance — in 1928 DKW was the world’s largest motorcycle manufacturer. Their 150-person race team fielded bikes quite unlike the simple, crankcase-scavenged two-strokes of the 1975-2001 grand prix era. Instead of employing the crankcase to pump fresh charge into the cylinder, pre-war DK Ws had separate scavenge systems ~ at first by a separate charging piston and then by rotary scavenge blower. It was natural to adopt such systems because they allowed crankshaft and con-rods to be lubricated by pumped, circulating oil, as in four-strokes. To this day, large two-stroke diesel engines — both marine and locomotive — employ such separate scavenging. After World War II supercharging was banned by the FIM, ruling out separate scavenge systems. Crankcase scavenging was accepted because its displacement per revolution was equal to the engine’s displacement. This was charging, but not supercharging.

DK W’s post-war racers

pioneered many of the concepts that would 20 years later underpin two-stroke GP dominance. When Yamaha and Suzuki first chose this path, they studied DKW’s RT125 as their design example. Both the Suzuki 125 Colleda ST and Yamaha YA-1 were clearly derived from the RE125.

DKW in 1929 acquired Adolph Schnuerle’s patent for loop scavenging — a manner of introducing fresh charge to the cylinder, which greatly ameliorated a notorious two-stroke problem — its tendency to excessive piston temperatures. The simple cause of this high piston temperature is that two-strokes fire twice as often as four-strokes, leaving less time between firings for piston cooling. This was made worse by the common cross-scavenging.

We see the similarity between DKW’s triple,

seen here, and the near-identical architecture

of Honda’s NS3 triple of 1982. The really significant element is the primitive expansion chamber exhaust pipe, seen at the bottom. (Mortons Archive)

DKW 350 TRIPLE

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In this scheme, exhaust and fresh charge ports were located on opposite sides of the cylinder, exposed when the piston was near the bottom of its stroke. Entering charge was deflected upward by a fence or deflector, cast into the piston crown. Because this deflector added extra surface area to the piston’s crown, it acted as a ‘heating fin’, increasing the piston’s share of the combustion heat load in proportion. As in any spark-ignition engine, the resulting high piston temperature limited compression ratio, durability, and power. Schnuerle was a diesel engineer — no surprise, as so much two-stroke spark-ignition technology has been diesel-derived. Remove the cylinder head of a simple Schnuerlescavenged engine, look down into the cylinder with piston at bottom center, and you will see a single exhaust port, flanked by a pair of transfer, or fresh-charge ports. As the piston descends, it first exposes the top of the exhaust port, beginning the process of blowing down cylinder pressure to permit the crankcase pressure below to emerge from the two transfer ports. As the transfers open, their flows of fresh charge hug the top of the piston, converging at a point mid-way between the center of the piston crown and the non-exhaust cylinder wall. As the flows collide there, they join to form a column of charge, rising up the nonexhaust cylinder wall, then turning to flow across under the head to the exhaust cylinder wall, and then downward. This flow path is the ‘loop’ of ‘loop scavenging’, and is the subject of the Schnuerle patent which DKW bought. The prompt result (1939) was the DKW RT125, a lightweight Shp motorbike. About 100,000 provided one-man transport to the German Wehrmacht through World War II.

At the end of the war the British recovered the RT125 drawings, which were distributed as ‘captured technology’. BSA’s 125 Bantam — a straight copy — appeared in October 1948. In the US, Harley built its 3hp version, the ‘Hummer’, whose ports were so small they could be mistaken for casting flaws. After the partition of Germany, the RT125 served as the starting point for many racing projects in the east, among them Daniel Zimmermann’s racewinning ZPH and the officially produced IFA.

53

» powerful and reliable

All across Europe, the RT125 inspired local production of motorbikes, many of which — Montesa, MV, Morini, etc — became the basis for the post-war beginnings of ultra-lightweight road racing. The RT125 has been called ‘the most-copied motorcycle in history’. Meanwhile DKW in West Germany resumed business — so successfully that it was again able to muster a large racing organization. Tuned versions of the RT125 came first, and

then a parallel 250 twin — both air-cooled and equipped with megaphone exhausts. Germany would be readmitted to the FIM for the 1951 season so great preparations were made. Sadly for DKW, Alfonso Drusiani had by this time persuaded Mondial management in Italy that a ‘real’ four-stroke (by which he meant DOHC) would see off the post-war crowd of 125 two-strokes. And it did. While the DKW 125 cylinder was making 10hp, the Mondials (and MV’s copy thereof) were making 1S5hp. DKW development was initially overseen by Erich Wolf, himself an ex-racer. For 1952 he gave the 250 parallel twin a cylindrical rotary intake valve across the backs of its cylinders, and replaced the previous longtaper megs with the first ‘gegenkonus’ — a counter-cone — exhaust pipe. Up to this time it had been assumed that, like a four-stroke, what a two-stroke needed from its exhaust pipe was suction, generated as each exhaust pulse expanded through a divergent horn, or ‘megaphone’. The resulting long return wave of expansion, or negative pressure, maintained a substantial pressure drop across the cylinder, encouraging the inflow of fresh charge from the crankcase, through two Schnuerle-style transfer ports per cylinder. Wolf, either from his own thinking or from a routine survey of two-stroke diesel design literature, realized that a megaphone’s action could also be harmful to power. Because timings of cylinder wall ports are symmetrical, if the exhaust port opens before the transfers, it must also close after they do. If pipe suction a4

were continued throughout the scavenge period (scavenge ports are typically open for about one third of a crank revolution, symmetrical about bottom center) it would

pull fresh charge around the whole scavenge loop and out the still-open exhaust port to be lost! Power would drop — a classic case of ‘overscavenging’. This is what all post-war makers of racing two-strokes discovered — that substantial increase of port sizes or timings just led up a dead end. Part of this problem was that the system of megaphone and transfer ports could pull fresh mixture only from the crankcase — whose volume was fixed. Worse yet, it appeared to most builders to be desirable to make the crankcase as small as possible, fitting the crank tightly to the crankcase (clearance 0.015in or less), using the shortest possible con-rod, itself ground thin as a knife-blade to work between crank cheeks padded with screwed-on aluminum plates. Once the megaphone had pulled the crankcase pressure down as far as it could, there was no more mixture to pump,

and power had risen as far as it could. These limits were holding two-stroke engines to 8—12hp, developed at 7,000-8,000rpm. Trying to turn the engine higher required a taller exhaust port to provide more blowdown time, which also meant more back-pumping time, leading to charge loss. While other makers — Morini, MV, etc, just dropped two-strokes and built racing fourstrokes, Wolf thought more deeply about the problem. One way to stop power loss from back-pumping would be to provide mechanical exhaust valves as in large two-stroke diesels, but that would destroy the two-stroke’s attractive simplicity. A simpler answer was already at hand, in the pages of a variety of books on two-stroke diesel design. In my 1949 edition of Paul Schweitzer’s Scavenging of Two-Stroke Cycle Diesel Engines it says (page 144) ‘Thus, a plug of gas is used instead of mechanical means to CLASSIC MOTORCYCLE RACE ENGI NES

prevent escape of the cylinder charge through the exhaust ports early in the compression stroke, and the gas plug may even ram the charge to higher density...’. Schweitzer’s chapter on ‘Exhaust Pulse Supercharging’ goes on to give several examples of how this might be accomplished. Erich Wolf accomplished this by placing a ‘segenkonus’ on the end of his megaphone. As the expanding ‘auspuff’ exhaust wave hits this cone, it stops generating suction and instead reflects back a positive pressure. When this positive pressure is timed to arrive just as the

exhaust port is closing, it not only stops loss of fresh charge, it also stuffs back into the cylinder any that has been already lost. It can do this, even though the piston is by now well advanced into its compression phase, because the amplitude of the pressure wave in the exhaust pipe is greater than the pressure in the cylinder. DKW planners must have looked at the and FIM’s GP classes and seen that while 125 , trokes four-s rpm high by ated domin 250 were Three the 350 class looked more promising. into a 53 x 52.8mm cylinders were combined red rende ders cylin e 349.46cc engine, its in-lin and one center the down g narrower by layin DKW 350 TRIPLE

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DKW gave their racers the best of everything in a comprehensive development program that used specialized facilities. Note the hydraulic hose at the rear, evidence of use of large hydraulic drum brakes. (Mortons Archive)

leaving the outer pair upright (the necessary presence of transfer ducts on both sides of each cylinder renders them wider than fourstroke cylinders of equal displacement). Crankpins were positioned to give equal 120° firing intervals. When this bike first appeared at

Hockenheim in May 1952 it revealed a classic two-stroke problem — the need for lots of ignition sparks. Driven by angle gearing on the right side was a bulky magneto froma six-cylinder BMW 328 auto. This new engine, thanks in part to its unique exhaust system, could make power at high rpm. In July at

Solitude circuit Ewald Kluge challenged the refined single-cylinder Nortons, only to fall. The bike was a surprise to those who dismissed two-strokes as economy putt-putts. Yet confirming their prejudice was reliability so poor that after the 1953 season Auto Union corporate biggie Eberan von Eberhorst put a a)

All of these parts are recognizable to any modern two-stroke racer. Full-circle crank has knife-section rods with needle rollers at both ends. Transfer duct openings are visible on cylinder base gasket surfaces. (Mortons Archive)

Before simplicity: a DKW engine with large separate charging piston and two pistons on a single con rod and sharing a single combustion space; exhaust port is controlled by one piston, transfer ports by the other. (Mortons Archive)

56

regular engineer, Helmut Gorg, in charge of the triple’s development. The concept was clearly promising, but the details needed to be nailed down. Small things make large differences. Both ends of the connecting rods were given caged needle bearings from the new manufacturer INA. Georg Schaeffler had designed a caged form of needle bearing in 1949, making this bearing type convenient and reliable for industrial applications. Volkswagen had adopted INA caged needle bearings in its transmissions in 1952. How did such caged needle bearings come to be adopted as twostroke con-rod big-end bearings? In 1941, W. Hampp of the Stuttgart Technical University made a study of big-end roller bearing dynamics with assistance from the RLM, the German Air Ministry. It is likely the RLM’s interest arose from the use of this type of bearing in the con-rods of wartime German fighter engines, such as the DB601, used in the Me109. That paper showed mathematically that lighter, smaller rollers would better resist skidding as the crankpin bearing’s rpm constantly fluttered plus and minus 25 %o, twice per revolution. That made INA’s product ideal for application in new DKW two-strokes. The CLASSIC MOTORCYCLE RACE ENGI NES

Hampp paper resides in the INA technical

library to this day. The development of this type of bearing was a necessary precondition for the later success of the high power twostroke engine. Forged two-ring pistons came from Mahle (in business since 1928). The big magneto was replaced by three sets of contact-breakers on the RH crank end, with coil-and-battery. The complex finned crankcase was replaced by a smoother, easier-to-cast and stronger part. Engine rpm was reduced to 10,500 in the interest of piston reliability. DKW’s race department was large and impressive, boasting its own dynos, chassis and engine assembly areas, an ignition test rig,

a cylinder-grinding room, and a complex jig to enable quantitative torsional and bending tests on either chassis or complete motorcycles. This was research and development on a large scale — made possible by large-volume sales of production bikes (such as the 450,000 RT125s that were produced post-war). Aside from DKW’s large subsequent influence on two-stroke development, this story lacks a happy ending. DKW’s 42hp 350 two-stroke, turning 10,500rpm, was ultimately unable to defeat Guzzi’s 38hp fourstroke single. Why? Because Guzzi with a mature design knew exactly what they were doing, while DKW was having to create a new technology as they went. DKW racers were given the best of everything, including large, hydraulic-actuated drum brakes and hydraulicdamped swing arm-suspended chassis. Despite the potential of the counter-cone pipe to stop overscavenging and to use exhaust energy to slightly supercharge the cylinder, DKW did not make great progress toward modern port dimensions, aim, and timing. In the four-stroke world it was accepted practice to make only one developmental change at a time, but this method is ineffective on two-

strokes, which require suites of mutually . compatible changes to be made simultaneously water’s Yamaha of In the US, in the early days cooled TZ250, a wealthy sponsor determined to achieve race-winning power by the old method. Forty cylinders and a like number each of exhaust pipe sets were bought, and

part was modified in one respect only — one getting a millimeter more of exhaust height, another one taller transfers. Exhaustive dyno tests were run, evaluating each change. Result? Stock is best. Yet in those days any 250 tuner worth his salt knew that widening the exhaust ports a millimeter on each side, shortening the exhaust head pipes 20mm, milling 0.6mm off the cylinder head surface, and retarding the ignition timing to 1.6mm BTDC were worth about five extra horsepower. Each change by itself was harmful but, together, the set was highly effective. Two-stroke tuning booklets sold in the 1950s showed modification to port widths but not to height or timing — even though dimensions were presented for counter-cone exhaust pipes of modern appearance. A typical exhaust opening timing in that period was EO 107 ATDC, with transfer ports opening 12 degrees later, at 119 ATDC. This suggests that DKW’s concept in the 1950s was to use the counter-cone pipe to allow use of a stronger megaphone effect, terminated by the return wave, and at higher rpm. Port timings did not greatly advance. Even with the help of exhaust pipes of modern type, porting this conservative greatly limited power. In terms of its ability to retain the charge blown into it, the DKW 350 triple of 1956 was only about half as effective as a modern cylinder. A further limit on power was rpm. The ‘Deek’ peaked at about 10,500rpm while a modern 125 GP engine turns a bit over 13,000, accounting for another 20% shortfall. DKW did show that more powerful and

reliable two-strokes were possible, and adopted essential components such as high quality pistons and caged needle big-end bearings. They had pushed the power of a 125cc cylinder from Shp to 15hp, but the Mondial 125 fourstroke had moved on to 17hp. The stage was set for better things, gathering strength in East Germany.

When the German post-war motorcycle boom collapsed in 1955-56, DKW along with NSU ceased to be major producers. BMW settled in to building just a few conservative touring machines, and once-influential makers

such as Tornax, Victoria, and Horex vanished. 7

DKW 350 TRIPLE

DUCATI THREECAM 125 DESMO Reaching for unlimited revs

1956-1959

n 1954 Ducati’s board authorized director Giuseppe Montano to hire an engineer

to lead a racing program. The goal, surely, was to find an energetic younger man with progressive ideas, eager to escape a future of sharpening pencils for older engineers. The man he found — at Mondial, the top builder of 125s — was Fabio Taglioni, aged 32. He had begun his engineering education before the war and had resumed it thereafter, in 1948 writing a thesis on his concept of direct, springless valve actuation. He joined Ducati on 1 May 1954. At Ducati, Taglioni began design of the 100cc Gran Sport. Small machines had special importance in Europe, where so much effort was being expended in recovery from the war. The Gran Sport had the robustness of simplicity. It was an air-cooled SOHC single of 49.4 x 52mm (= 99.67cc) with its cam and exposed rockers driven by shaft and bevels. Two valves set at an 80° included angle were returned to their seats by hairpin springs in an aluminum head cast separately from the cam box. The iron-lined aluminum cylinder was inclined forward 10° and the crank was pressed together from a pair of full-circle flywheel/mainshaft units and a separate crankpin. The forged piston carried three rings. A steel connecting rod ran on a caged roller big-end bearing. Outboard of the cam drive bevel on the right end of the crank was a spur gear, driving an accessory shaft ahead of the crank. The inboard end of this drove the oil pump while the outer end drove a contact-breaker set for ignition by coil and battery. Oil was carried in an under-engine sump and supplied to the timing end of the crank on its way to the crankpin and big-end bearing. An exterior oil line, emerging from the top of the timing case, extended up and

n? The Who would suspect the complexity withi ont’s Tagli was — drive desmo — positive valve Italian response to the rpm war that raged in Pull‘Big the to 1949 from g racin t lightweigh Out’ of 1957. (lan Falloon)

DUCATI THREE-CAM 125 DESMO

over the head to enter the left end of the camshaft. Oil drained from the head at the right front via another external line, leading back to the front of the timing case. The vertically split crankcase housed a gear primary drive and four-speed gearbox with a wet clutch. Both primary and cam-drive gears were straight-cut. Outboard of the crank’s primary pinion was a flywheel generator. This was the basic ‘module’ on which years of Ducati singles to come would be based, eventually extended to the 450 single of 1969. The heavy vibration of the 450 would suggest the combination of two singles in a selfbalancing 90° vee. That, in turn, has become one of the two ruling architectures of sports motorcycle engines in the current era. In February 1955 this machine was tested at Modena. Power was 9hp at 9,000rpm (8.8bar, 130psi). The model was released in March and a few weeks later was entered for the nine-day Giro D’Italia and won its class. In February 1956 the 125cc DOHC ‘Bialbero’ was shown, and was raced in early GPs that year. It gave an initial 15.Shp at 10,500rpm (10.S5bar, 154psi), and with further development 16hp at 11,500rpm (9.9bar, 145psi). It was no match for the developed MVs. In this year Ubbiali would win five out of six with his MV making 20hp at 12,500rpm (11.4bar, 167psi). The Ducati

suffered the problem all had to deal with — the danger of a valve gear failure if a shift was missed. It was time to implement a solution. In the spring and summer of 1956 Taglioni realized his ambition of bringing direct valve operation to practicality. The now-famous ‘three-cam 125 desmo’ was another piece of simplicity — a new head with cam box cast as part of it — which was a direct bolt-on to the 125 grand prix. The Bialbero had five gears on the right side of its cam box — a center one driven by the cam driveshaft, one on each cam, and two intermediates. The desmo had only three larger gears — one on each of the two outer camshafts to operate intake and exhaust finger followers, and one on the center cam, which drove the two forked closing levers. At first, power was 17hp at 12,500rpm oy)

This is Dr Taglioni, the man who would give Ducati its unique character for 30 years. He and late-comer Massimo Bordi would contend with each other over the big question — two valves or four? (Mick Woollett Collection) (9.7bar, 142psi). As in the Bialbero, the desmo 125 had a 31mm intake valve and 27mm exhaust. In addition to the Bialbero’s

27mm carburetor, a 29mm was available for fast circuits and 22 or 23mm for Italian street circuits. A second (10mm) spark plug was located behind the cam tower, opposite the 14mm plug in the normal position. This allowed a reduction in ignition timing, from 42° with single ignition, to 36° with dual Compression was 10:1. Taglioni stood out in Italian cylinder head design because of his use of all means for 60

achieving fast, efficient combustion. Let the others seek faster combustion through small bores and long strokes. He would employ offset intake and exhaust ports to produce axial swirl, and piston-to-head squish to stir the burning mixture near TDC. Compare his 36° of ignition timing in a 55.3mm bore with Gilera’s 55° in the 52mm bore of their four-cylinder 500. This was real gain, because it allowed him to achieve fast combustion in a chamber large enough in diameter to accommodate big valves — without Gilera’s 1920s-inspired deep, heat-sapping 100° valve included angle. Taglioni evidently discovered squish for himself during the development of a 175cc single, much as Gioacchino Colombo would do during his development of the Maserati 250K In the course of this work a 125 head was occasionally used and, despite its smalle r CLASSIC MOTORCYCLE RACE ENGI NES

valves, testing in this configuration gave good power with remarkably short ignition timing — and it ran knock-free. As soon as Taglioni understood what was causing these effects — a natural squish band formed between the piston and 9mm-smaller chamber in the 125 head — he explored the concept further. Ducati’s SOHC Gran Sport 175 single became the first Italian motorcycle engine to have properly designed squish surfaces between piston and head. The desmo’s first accomplishment, as all students of Ducati history know so well, was to win a non-point international race in July 1956 at Hedemora in Sweden. This was fast work — designing, building, and proving the novel desmo head in only a few months, while at the same time bringing along the Bialbero. Rider Gianni Degli Antoni lapped the field. This engine made the same power as the Bialbero, but it was safe to 14,000rpm, allowing the rider to concentrate more on riding and less on

being a powerplant manager. The fact that the valve spring Bialbero and the desmo made the same power reveals that springless operation does not — as some believe ~ unlock vast extra power through friction reduction. Dr Froede at NSU had in 1953

measured the total friction contribution of his Rennfox 125 single’s valve drive (with spring closure) as about two tenths of a horsepower,

or 150 Watts. The real value of desmo valve operation is that it allows the designer to either lift valves higher within a given timing, or to reach higher revs — without valve float. Because four speeds were not enough for the narrow power of the racing engine, and because there was no room for additional ratios in the gearcase, two more ratios were implemented behind the clutch. During practice for the 1956 Italian GP at Monza in September, Degli Antoni (aged 26) was killed, and one Ducati, ridden by Sandro Artusi, finished fifth, one lap down. It was decided to take a year off for development. By 1957 the desmo was making 18hp at 12,500rpm (10.2bar, 150psi), but this was the year of Mondial’s masterful return to 125 and 250 dominance. Ducati did enter Monza

This sketch could not be clearer. The springs shown are there to close the valves completely, preserving compression for engine starting. (Mortons Archive)

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MO DUCATI THREE-CAM 125 DES

61

that year but rider Alberto Gandossi fell while leading, taking down some other riders. At the end of the 1957 season Gilera, Guzzi, and Mondial withdrew from racing, leaving MV as the major 125cc opposition. In 1958 Ducati made a major effort with multiple riders. First came a big push at the TT. Luigi Taveri led the 125s on the desmo but fell, allowing Ubbiali on the MV to take the win, ahead of three desmos ridden by Romolo Ferri, Dave Chadwick, and Sammy Miller. Now valve lift was increased, taking power to 19hp, and development continued through the 1958 season with new-design crankcases and chassis. Taveri was second to Ubbiali at the Dutch TT with other desmos fourth and fifth. Then in Belgium it was Ducati 1-2 by Gandossi and Ferri, with others fourth and sixth. In Sweden it was Gandossi and Taveri ahead of Ubbiali and Provini on MVs, then two MZs. At the Ulster Gandossi led but fell, allowing Ubbiali the win with Ducatis second, third, and fourth. The company gathered its full strength for the season-ending Monza in September, where Ducatis swept the top-five while the MV men revved their engines to destruction. Despite this, Ubbiali was 125 champion. It was hoped 1959 would bring a championship. Hailwood was third at the TT behind an MV and an MZ. Down in lowly sixth place was Naomi Taniguchi on the highest-finishing Honda twin — harbingers of Japanese power. Hailwood won the Ulster — the first GP win of his career — but the MVs were just too fast elsewhere. At season’s end the desmo racers were given Bialbero valve spring heads and sold to privateers. An era was ending — that of small producers like Mondial and Ducati. A new era opened — that of the giant mass-market manufacturers Honda, Yamaha, and Suzuki, with their much larger R&D resources. Little Ducati would look to its own survival until a better day. Meanwhile, a great deal had been learned and the company turned out a variety of sporty singles in many displacements. The desmo single’s planned successor, a twin, had come third at that 1958 Monza, making 22.5hp at 14,000rpm from 42.5 x 44mm dimensions. Its construction as a three62

cam desmo parallel 360° twin would later reverberate as a 175 twin of 49 x 46.2mm, a 250 twin of 55.2 x 52mm, and a 64 x 54mm

350 twin. These larger engines featured a thin central cam drive case containing spur gears,

from which shafts extended left and right to drive the cams of the two widely spaced cylinders. An interesting feature of the single was Taglioni’s use of its slender cam driveshaft as both a torsional shock absorber and a tuning device. At an 11mm diameter shaft flex moved the torque peak down to 8,000rpm, making it suitable for use on acceleration tracks. At 14.8mm, the resulting timing moved the torque peak up near the power peak. As so often on racing engines, the cam drive had early durability problems, caused by interaction between the ‘lumpy torque’ of the cam and the cyclic speed variation of the crank. At first, the top bevel was pressed into the closing cam’s gear, but slipped. Attempts to weld the two resulted in breakage (hardened steels make brittle welds), so Taglioni provided a compliant triangular nylon biscuit between the two. One of the attractions of cam drive by shaft is that by use of a spline or Oldham coupling there is no problem when operating temperature causes the engine to become ‘taller’. In the case of the Mondial/MV solution ~ a train of spur gears — thermal expansion crowds the gears when cold and causes backlash and noise when hot. To assure load-sharing in the four bevel gears the ratios were bottom, 1.4285714, and top, 1.4, which multiply out to 2.0. Note that these were heavy single valves with 7mm stems — great lumps to be accelerated and decelerated in brief instants of time, creating sudden high loads in the drive. Only when the practicality and durability of desmo valve drive was proven did Taglioni increase valve

Here is Alano Montanari on the three-cam during 1956. Salad days for full streamlini ng allowed high speeds on little power. Because of poor side-gust response, even teams that carried tail fairings like this one seldom used them. (Museo Ducati) CLASSIC MOTORCYCLE RACE ENGI NES

M O DUCATI THREE-CAM 125 DES

63

The trony is that the power of the Ducati desmo single and twin.would have been competitive with that of Honda’s 125 twin, 1959-1962 Sua! ©

lift beyond that of the original hairpin-spring grand prix model. The irony here is that the developed power of the Ducati desmo single and twin would have been competitive with that of Honda’s 125 twin, 1959-62. When later asked if Honda’s four-valves-percylinder-with-springs solution were not better than two-valve desmo, Taglioni replied that valve spring materials of the 1950s would not have permitted it to succeed. He also said the turbulence of a pentroof four-valve combustion chamber was ‘uncontrolled’. He would repeat this claim years later when younger Ducati engineer Massimo Bordi gave his new watercooled 851 twin four-valve heads. Taglioni said that with a two-valve chamber he would begin with a 20° intake port offset to generate axial swirl, and then add downdraft to make this a spiral motion as desired. Squish areas were formed on both sides of the piston. Combustion time and heat loss could be further reduced by dual ignition. A four-cylinder 125 Ducati engine was later built with four valves and springs, but was not developed. It was said that the 125 desmo single received a new crankshaft for each GP, and that there were only three crank failures in four years of racing. The con-rod ran on a steel-caged assembly of 20 3mm rollers on a very large 30mm crankpin. The very size of this bearing may have limited its durability, as roller-plus-cage inertia at some speed can no longer follow the rapid speed fluctuation at the crankpin, causing skidding and surface damage

to begin. Con-rod rod ratio of 2.04. The three-cam the cylinders and twin 250 built to

length was 106mm, for a 125 desmo lived on as heads of a 360° parallel the special order of Mike

Hailwood’s father, Stan. Mike Hailwood had this to say in his book The Art of Motorcycle Racing, page 161-2: ‘Singles I like. Fours I like. Twins I do

not like, with two exceptions — the 125cc Honda and the 250cc MZ. Perhaps I have been unfortunate with the other twin-cylinder machines I have ridden (the 125, 250, and 350cc Ducatis and the 250cc MV) but I could not get on with any of them. They all had very narrow powerbands which made them very hard work to ride for they felt rigid and inflexible and demanded constant gear-changing to get the best out of them. I persevered for a long time with the Ducatis because they had been specially built for me at very great expense as “one offs” and in theory should have left everything else in their capacity classes standing. But although I had a good run of success with them I had to give them up in the end and, in the 250 and 350cc classes, return to my single-cylinder Mondial and AJs.’ What lies behind this famous passage is easy enough to understand. The quick way to build a twin is by combining two of the single-cylinder top ends side-by-side on a wide common crankcase. The resulting engine was therefore bulky and overweight. Being based on a 125 its power was narrow and difficult

to use.

Failure teaches more than does success,

t At the Dutch GP in 1958 Ducatis set fastes Here fifth. and h, fourt d, secon lap, and finished mechanic Mario Recchia perhaps examines s of the spark plug. New technical regulation e intak steep Note 1958 limited streamlining.

downdraft angle. (Mick Woollett)

DUCATI THREE-CAM 125 DESMO

and the lesson would require a fresh opportunity. Taglioni would find a more compact manner of combining two proven cylinders as a single engine — the narrow 90° V-twin that became and today remains the basis of Ducati success. 65

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with Johnny Dodds as development rider, it was making 75hp — equal to the power of Kawasaki’s H1-R. Dodds would manage a tenth place at the West German. By 1972, with much redevelopment, Newcombe was able to take a third at the West German GP behind the two MVs of Agostini and Pagani. The fact that a small firm such as Konig could achieve such a result is testimony to how ready two-stroke technology was to take on the 500 class, if only substantial resources could be applied to it. Bear in mind that, like the Kawasaki H1-R, the Konig was a bare, ‘natural’ engine, with none of the aids to powerband width that would begin to appear in 1978. This meant that its power came in, or ‘hit’, hard, and that the engine’s working range was limited. In 1973 Yamaha entered the 500 class with Jarno Saarinen as rider. And there was the Konig as well, now a machine to ponder as it had become faster on top-end than the MV. A second place at Assen, the sixth GP of the year, put Newcombe at the top of the Championship points. With Saarinen’s death MV again got top placings and at the 11th GP, Finland, Read was 500 champion. Newcombe was killed at a Silverstone race but was still second in points at the end of the year, sandwiched between the MVs of Read and Agostini. The Kénig engine would go on to win two sidecar titles in 1975 and ’76, now making 85hp at 10,000rpm (7.6bar, 110psi). After that the availability of rapidly developing Japanese two-strokes made the K6nig uncompetitive. It had been a useful tool in demonstrating how narrow the margin of four-stroke superiority had become. Newcombe had lived the intense life of the focused rider-engineer, driving from race to race in a small van with his family. It was the comparative ease of two-stroke development that made this possible. Artisanbuilt special four-strokes had run in 5 00 GPs — the Paton and Linto, and the Vostok/ CKEB from the Eastern Bloc. None of these

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had anything near the success of the Konig developed and ridden by Kim Newcombe. The reason is that once two-stroke development is based upon workable mechanical technologies — piston cooling and durable big-end bearings — what remains is optimization of ports, port timing and exhaust pipe shaping through hand craftsmanship and endless experimenting. Four-stroke development requires sophisticated industrial backing. In either twostroke or four-stroke, success is contingent on how many questions the development personnel can get answered per unit time. The answers cost much more when ‘asked in fourstroke’. The Linto was two Aer Macchi 250 top ends on a common crankcase and the French Nougier was a clean-sheet transverse four — but neither maker could afford to develop them. Kim Newcombe and Dieter Konig were able to do much more on next to no budget.

A new world ofpaid riders, luxurious

motorhomes, and million-Euro factory bikes was dawning, but Kim Newcombe raced and traveled in the old way — hand-to-mouth, living like a gypsy from race to race. He accomplished a lot. (Mortons Archive)

189

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MEE 125 four-stroke single was an influential racing engine because it put an end to the post-war two-stroke dominance of the ultra-lightweight class, and showed how relatively easy it was to make horsepower from rpm in small engines. It was a model for similar but later efforts from other Italian makers, from NSU in Germany, and ultimately for Honda. When MV decided to switch from twostroke to four-stroke in 125 racing they bought a Mondial for study. When Mr Honda took European models back to Japan, one of them was a Mondial. The ‘FB’ of the name ‘FB Mondial’ was Fratelli Boselli — whose company produced three-wheeled trucks powered by a 600cc OHV single, just before the war. When the war ended, motorcycle makers in several nations received as the ‘spoils of victory’ blueprints for the two-stroke DKW RT125. Its appeal was simplicity and the speed with which its production could be tooled in war-damaged Europe. Britain’s version was the BSA Bantam, the US knock-off was Harley’s Hummer, and in Italy MV and Morini each had versions. MvV’s was 53 x 56mm and became a racer for the 1948 season, making at first 9hp, then 10.5. The Morini, at 52 x 58mm, featured a long-taper megaphone. There was no future in these engines for as they were made to rev higher, they needed taller exhaust ports to release exhaust in less time, but larger ports just allowed what had been drawn into the cylinder by megaphone suction to be pushed out the exhaust as the piston rose on compression. At about 12hp a dead end was reached. Former competition rider Alfonso Drusiani discussed racing with Giuseppe Boselli in January 1948, expressing the view that a ‘proper’ four-stroke — one with good control of its valve motion through overhead cam operation — would easily dominate 125 racing. Drusiani had experience of both engine types,

See all the goodies — the oil line to the head, the two cam-box drain-backs, a ‘mushroom’ engine breather behind the cylinder, and giant cooling fins to keep metal safely in its desired solid state. MONDIAL 125 SINGLE

having raced the BD 123cc two-strokes and having seen what that company’s SOHC 175cc four-stroke model could do. Boselli provided the resources to test Drusiani’s assertion. A 53 x 56.4 (= 124.37cc) prototype was ready in mid-1948, thanks to the availability of pattern makers, machinists, and specialist firms. It made nearly 11hp at 8,000rpm on a 9.7 compression ratio (9.7bar, 142psi). Its shaft-andbevels-driven valves were disposed at a fairly wide 80° angle. Cylinder and head were in light alloy, the cylinder liner austenitic iron (to better match the expansion of the three-ring aluminum piston), and the valves seated on hard seat inserts. Oiling was unusual for Italian singles in being wet sump. A forward bulge of the crankcase housed a gear-driven magneto. During 1949 power rose to 13hp and in the 1950 season 15hp was reached at 11,500rpm (9.3bar, 136psi). The top three finishers in the 125 world championship that year rode Mondials. Drusiani had applied the recognized best features of four-stroke design to a very small engine and let the numbers prevail. Valve control with such small valves was not difficult, so all that was required to make winning power was rather undistinguished cylinder filling and a dose of revs. Mondial were pioneers in the use of long, slow-taper megaphones of the kind later adopted by Honda for its race engines. That was enough proof for the others. In 1952 MV applied their greater resources to their own 125 four-stroke and took the title from Mondials now making 16hp at 12,000rpm. As a footnote, consider that Fabio Taglioni came to Mondial in that year, then left in 1954 in search of more design independence at Ducati. By 1956 the Mondial DOHC 125 had reached 17hp at 13,000rpm (9.3bar, 136psi), and with the help of comprehensive streamlining could reach 110mph. An all-new engine was designed for 1957 (author Mick Woollett says 18hp at 12,000rpm [10.6bar, 157psi]. More work in 1957, which included dual ignition, brought power to 19hp at 13,200rpm (10.2bar, 150psi). Mondial won the 125 and 250 TTs that year — and both world titles. The company then joined the industry-wide stand-down from racing at the end of that season. Looking at the numbers we see that this 191

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is a one-sided design, heavy on rpm, light on combustion efficiency. The 1950 Mondial’s

stroke-averaged net combustion pressure, or bmep, was 136psi. In Mondial’s defense we must note that even Norton, faced with

the poor fuel of that time, could muster only 150psi. This suggests that Drusiani’s rpmbased strategy was right for that time and that fuel. By devoting himself to boosting rpm he was able to bring the company three 125cc championships from 1949-51, taking the top three places in the latter two years. This has its parallel in NASCAR racing, in which air-restricted engines attempt to recover lost horsepower by turning higher revs. However, Drusiani continued with this

strategy even after the ‘pool’ gasoline era ended. His last 125’s bmep was still only 150psi, while Norton’s had risen back to its pre-war level of near 200psi. Some of the missing power might have been lost to non-optimal cylinder-filling — notquite-right valve timing, low valve lift because of dynamic considerations, or lack of full orchestration of exhaust and intake dynamics. Maybe — but in eight years spent on the same engine you’d expect Drusiani to get it all pretty close. I think the larger part of the shortfall came from the poor combustion that was a consequence of the ‘old school’ of cylinder head design. The ‘old school’ was the deep-chamber two-valve that dated back to the 1922 Fiat GP engine. Since then, the rapid rise in fuel octane (largely from Thomas Midgley’s discovery of the anti-knock tetraethyl lead in 1923) had allowed a steady increase in the compression ratios of unsupercharged racing engines. If we call the area of the cylinder bore unity, the surface area of a hemispheric combustion chamber (valves set at 90° included angle) is exactly twice that. A similar increase of surface area affects the piston as its dome is raised to achieve the desired compression ratio. The 192

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result is dramatically increased heat flow (loss) into head and piston. This is not the end of the matter. The deep chamber with the intruding piston dome define between them an unfavorable place for rapid flame propagation. Flame spreads most rapidly in a turbulent open combustion space, but in a deep chamber motion is broken up into a multitude of cells, each of a diameter roughly equal to the local clearance between piston and head. Think of these whirling cells of turbulence as little gears — each must rotate until its flame ignites the next cell, which must also rotate in like fashion, and so on, tediously and slowly. Increased chamber surface area is compounded by the need for longer ignition timing, increasing the time during which excessive heat loss occurs. This is why the Mondial, although ‘only’ a 125, needed to have great big finning that made it look almost the size of a Manx. The final piece of suggestive evidence is the adoption, in 1957, of twin ignition. Engineers don’t go to the trouble of such a conversion ‘because it might be better’. They do it because they are forced to try anything that might speed up combustion, thereby putting more of combustion’s heat energy to work as pressure. What happens when an engine has excessive heat loss? Its combustion chamber and piston crown temperatures are abnormally high, preventing the designer from using as high a compression ratio as he otherwise might. Hot surfaces accelerate the chemistry of preflame reactions that lead to detonation. Slow combustion provides the time in which those

processes can mature. This is so often the nature of engineering — much of a design is defined by ‘established practice’. Drusiani accepted the combustion chamber that an earlier tradition had created. In the supercharged era of car racing between the wars compression ratios were low and

CLASSIC MOTORCYCLE RACE ENGINES

suggested no better answer. The small Mondial company never produced

The great Tarquinio Provini on the 125 Mondial at the 1956 TT. Such comprehensive streamlining would be banned at the end of the following season. Thanks to low drag, tiny engines attained high speeds in this era.

more than 1,000-2,000 machines a year so

(Mortons Archive)

piston domes less intrusive. Engines actually needed the valve area provided by a large included angle because knowledge of airflow

development resources were limited. Even big companies have made the mistake of tackling projects for which they lacked the resources. Drusiani and Boselli focused on what they could actually accomplish and are remembered for championships won. Drusiani pioneered boldly in the matter of rpm, and is justly remembered as the engineer who set racing engine design on that course. NSU and later Honda would carry on what he began. At the 13,200 peak rpm of the 1957 Mondial, piston acceleration was 7,000G —a number equal to that of the highest revving of today’s 600 sportbikes. That was achieved 54 years ago. Available sources say the Mondial’s piston was forged, not cast. This, if true, was an important step. Forgings have higher fatigue resistance than castings, and more outright strength. Drusiani solved the problem of con-rod big-end durability as others had done — at least sufficiently to be sure of finishing the TT. A moment’s thought shows that the rpm of this bearing is at a maximum at TDC, when the connecting rod rotates opposite to the crank, and is at a minimum at BDC, when rod rotation is subtracted from crank rotation. As the eyeto-eye length of the con-rod is approximately four times the length of the crank arm, this MONDIAL 125 SINGLE

once-per-revolution rpm variation is about

plus-and-minus 25%. Use of a longer rod, such as the 2.65 rod ratio of the 1957 version of the Guzzi V8, would reduce this to plus-andminus 19%. The point here is that anything that reduces the tendency of the big-end roller set and its cage to slip rather than roll will improve bearing durability. The history of the sport is full of people who have machined weight from cages, used lighter, smaller-diameter rollers, or tried higher rod ratios in seeking either greater reliability or a higher rpm ceiling. When Mondial joined Guzzi and Gilera in withdrawing from GPs at the end of 1957, chief mechanic Giuseppe Pattoni and ex-Benelli designer Lino Tonti left. Tonti went to Bianchi where he designed their 350 twin. They formed Paton and built a 125 single very like Mondial’s.

OVERLEAF Cecil Sandford poses on the Mondial 125 in 1957. Compare the great engine height with the compactness of a 125 MX two-stroke; the mechanism for operation of poppet valves at high speed is bulky! (Mortons Archive) 193

MORINI 250 SINGLE One of the heroic designs

1958

he Morini 250 single of the 1960s has been called, “The fastest single-cylinder motorcycle of all time,’ because in its day it lapped the great circuits faster than had the classic 500s. It is one of the heroic designs — continuously developed, tweaked, and optimized as was the 500 Norton. But unlike the Norton,

it handed down no legacy of emulation — its excellence was achieved in spite of its antique 90° valve included angle. Its greatness was that in the hands of Tarquinio Provini, it came within two points of Redman’s new-technology Honda-4 in the 1963 championship — and this despite founder Alfonso Morint’s (b. 1898) determination to race only within Italy. This engine had 72 x 61mm bore and stroke, producing 37-38hp at 11,000rpm (12.1bar, 178psi). Its two sodium-filled valves were inclined at 90°, requiring a piston with a tall dome and deep valve cutouts to achieve a 10.5:1 compression. Valves were driven by DOHC. The head and cam box were separate, allowing cooling air to flow over fore-and-aft-orientated fins covering the head. The cam box contained a horizontal central shaft, one end of which was driven by five spur gears in a separate casing. The other end drove a gear, which drove the cams through one intermediate gear each. Unlike so many other Italian singles, the Morini’s flywheel mass was entirely within the crankcases, there being no external flywheel. A doubly ribbed connecting rod drove the crank through the usual set of alloy-caged small-diameter rollers. Preceding designs were lubricated by dry sump/remote tank, but the inevitable problems of oil scavenge and wet-sumping had been resolved by use of a D-section bolted-on oil sump beneath the engine, approximately 15in (380mm) long. This, with a large aperture to the crankcase above it, accomplished two goals. First, it added crankcase volume, reducing the amplitude of

Classic design — a train of five spur gears drive the two cams, everything is finned, each cambox has its own oil return to the timing case, bypassing the crank. A hairpin valve spring peeks out just ahead of the downdraft carburetor. (Mortons Archive) MORINI 250 SINGLE

the pressure pulsing caused by the piston, and second, it gave spent oil adequate room to escape to the sump before it could be whirled around by the crank (wet-sumping), with resulting spiking oil temperature and power loss. This engine, with its array of cooling surfaces, was physically large. Engines of large valve angle gather 40-50% more heat through extra piston and combustion chamber surface than they would through simple flat-disc areas. This heat must be got rid of, and the substantial castings and finning accomplish that. The bore and stroke of 72 x 61mm (bore/ stroke ratio = 1.18) represent progressive change from the early 1950s when ratios hovered at 0.9. This suggests that Morini were able to burn the 72mm chamber with acceptable speed through combination of dual ignition and chamber shape. This had been accomplished years before by Ferrari, who had combined a 58° valve angle with over-square bore/stroke dimensions since the early 1950s. Morini operated by continuous development under the dual direction of founder Alfonso Morini and engineer Dante Lambertini. Nerio Biavati, a cylinder head specialist who had come over from Mondial, later experimented with three- and four-valve heads, and the company had given up its traditional chain cam drive for gears when testing revealed several

advantages for gear drive. Other tests had evaluated differences between magneto-fired and coil ignition engines. Certain other makers seem instead to have leaned their racers against a wall during the off-season. Morini’s machines were constantly running up and down the autostrada, testing something. Morini’s first post-war product was one of Italy’s several two-stroke DKW knock-offs. When Mondial showed what a ‘real’ fourstroke could do in the 125 class, the others had

to follow. Morini’s four-stroke was designed by Dante Lambertini, with alloy cylinder and head, SOHC by chain, exposed hairpin springs, dry clutch (so useful for push-starts), and an external flywheel. It made 12hp. In 1949 the young, rangy Umberto Masetti (later to win two 500 championships on Gilera) was second, a minute behind Leoni’s winning Mondial at Monza. In the following two seasons Morini Oy

were limited to seconds and thirds but over the winter of 1951-52 the engine was made chain DOHC (no more rocker arms adding their extra mass to the valve-control problem) with power rising to 16hp at 9,500rpm (12bar, 176psi). In 1952 MV were ascendant but Morini’s Emilio Mendogni won Monza and Spain, the last two GPs. At Monza, 1953 — one of the years of NSU dominance — Mendogni lost out to Haas’s 125 NSU by only half a second. With its sales in Italy, the little company turned away from GPs to production racing for, despite its romance, racing is just a part of sales and promotion. In 1954 they enlarged the 125 for Mendogni’s use in Formula 3, where he became 175 Senior Italian champion. Meanwhile the company’s sporty pushrod ‘Settebello’ model sold very well and was successful in the hands of private racers. To secure its position Morini built a chain SOHC 175 ‘Rebello’ of 60 x 61mm dimensions (= 172.4cc). This dry sump engine had a 27mm carburetor, five-speed transmission, and 22hp at 9,800rpm (11.6bar, 170psi). The cylinder was inclined forward, there was an external flywheel, and a two-pad accessory drive behind the cylinder and atop the unit gearbox was provided, driving a magneto. This machine won important long-distance events such as Giro D’Italia and Milano-Taranto. On the strength of this success a 250 was built, again with chain-driven DOHC. It first appeared in 1957, making 29hp at 10,000rpm (10.3bar, 151psi) from the 69 x 66mm = 246.8cc engine. This wet-clutch design now had inside circular flywheels only, and three main bearings (two on the drive side). At the Monza GP of Nations in September, Mendogni was third in a crowd of Mondials until stopping with a technical problem. Now came 12 months of intensive development. Cam drive by gear was found to give better performance than the previously used chain, and the gear-drive engine gave 30hp at 10,000rpm (10.7bar, 157psi) on a moderate 9.5:1 compression. Alfonso Morini had worked with chain-driven OHC since before the war, so this change, based on the evidence of testing, is significant. It shows that performance was more important to these people than tradition. 198

This has been a difficult choice even for major manufacturers in our own time. At Monza in 1958 Mendogni led every lap of the 250 Grand Prix to beat Ubbiali’s MV by 32 seconds. Second was Gianpiero Zubani on another Morini, who passed Ubbiali near the end. By now the engine was making 32hp at 10,500rpm (10.8bar, 159psi). The carburetor was a 30mm Dell’Orto SS1 and oiling was

still by dry sump and remote oil tank. Like the 1957 version, this engine had dual ignition. The next year brought only a second and a couple of thirds in GPs, as little could be achieved against newly powerful MV and MZ 250 twins. More significant was that Tarquinio Provini quit MV at the end of the season and came to Morini. His presence plus further development created a great all-round machine. In 1961 and 62 Provini was 250 Senior Italian champion, and made a case to Alfonso Morini that this machine could win international races. During 1962 the engine had reached 35hp at 10,500rpm (11.8bar, 174psi).

The 1963 grand prix season was a contest between the mature Honda-4 of Redman, with its 46hp at 14,000rpm (11.6bar, 171psi) and 275\b weight, against Provini’s 37hp Morini,

with its much-admired bottom acceleration and single-cylinder handiness. Although Provini did not ride either the TT or the East German GP, scoring at this time was by the six best finishes, and each man had won four. Redman was champion by only two points. The machine demonstrated versatility by winning at fast circuits — Monza and Hockenheim — and at slow — Montjuich Park in Spain. It had been a tremendous performance by a brilliant rider and a small ambitious manufacturer. This engine was not cooled in the usual simple-minded fashion — as if it were a hot fencepost on a windy hilltop. A carefully molded engine cooling baffle made of fiberglass was fitted tightly against the fins of the cylinder head and cylinder, making sure that all air taken into the fairing had to pass through the cooling fins. Using the minimum air volume is the key to low cooling drag. Another fiberglass molding under the lower steering crown prevented air from escaping upward. Crankcase and covers were cast in magnesium. CLASSIC MOTORCYCLE RACE ENGINES

Compression was now 10.5:1. One spark plug was conventionally located on the left, while the second one, of 10mm, was tucked in behind the cam drive case on the right. In classic fashion the head was finned from front to back, while the

cam box was a separate unit, held in place against pads on the head by four recessed hexes, rather than the two being cast in one piece as on Gilera and MV four-cylinder bikes. This high-quality head cooling probably saved this design from the need of either an oil cooler or extensive sump finning. However, the fairing used did expose the smooth, radiused under-surface of the sump. An indication of concern over temperature is the use of phosphor-bronze valve guides and internally sodium-cooled valves. With the extra heat gathered by the deep chamber and tall piston dome, extra means for its dissipation had to be provided. Partial sodium-filling of hollow valves conducts heat away from the head and from the critical point of exhaust valves where the stem enlarges, up the stem to be transmitted

through the guide into the head casting. MORINI 250 SINGLE

Sleek and simple. All of this machine's parts have stories, and were almost organic,

evolutionary products of the forces acting on them. Successful designers let their creations tell them what is needed next. (Mortons Archive)

The rise in compression from the earlier single (9.5:1) to the 10.5:1 of the 1963 engine is no accident. Compression in racing engines

is raised to the threshold of detonation because that maximizes torque. The detonation limit arises from the surface temperatures of piston and combustion chamber, heating the compressed, unburned charge as the flame fronts expand from the spark plugs. If that heating is excessive, and if sluggish combustion allows time enough, chemical change in the unburned charge at the chamber’s edges alters it to a sensitive explosive state. This is a race between combustion speed, rushing out to consume those last bits of charge, and the fast pre-flame chemical changes that lead to detonation. 199

The Morini was a product of constant testing and refinement, of interchange between engineer and rider — an example to be heeded in our time. When Provini left, his replacement on the 250 was Giacomo Agostini, seen here in 1964. (Mortons Archive)

The designer therefore does everything to protect those last bits of unburned charge from becoming hot enough, long enough, to violently auto-ignite. That is why both valves were internally cooled, and why front-to-back cooling fins on the head were integrated into a forced-air cooling scheme. If the designer can lower the surface temperatures facing the 200

unburned charge, he can raise the compression ratio and increase torque.

As Joe Craig related from his experience at Norton, engines fail from even light chronic detonation. Detonation, by thinning the natural insulating boundary layer of stagnant gas adhering to piston crown and chamber surfaces, increases the flow of heat into them. On the dyno this is seen as a drop in exhaust gas temperature. Why a drop? Because, with no increase of power going to the rear wheel, and with greater heat loss through internal surfaces, conservation of energy requires that heat comes from somewhere. That ‘where’ is exhaust gas temperature. With heat flow into parts increased, the top piston ring land softens (think of it as a CLASSIC MOTORCYCLE RACE ENGINES

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‘heating fin’) and is forged down against the top ring, trapping it and destroying its seal. The second ring now receives the action of the verb and is either trapped in turn or broken. Now hot combustion gas can stream down the face of the piston and enter the crankcase through the drain-back holes provided for the oil scraper ring. The heat it carries causes the piston face and drain holes to gutter; it is a cutting torch. Oil temperature rises and oil vapor streams from the breather (which is large on this engine). One battle is fought by correct positioning of the top piston ring. Moving it lower makes the top land more robust and thermally connects the piston ring to a cooler region of the piston, slowing the process of oil gumming that can also immobilize the ring. But moving the ring too low provides a substantial crevice volume between the top land and cylinder wall, into which combustion pressure can push several percent of the total fuel-air charge. This lost volume may partially burn as it emerges later in the stroke from its protective grotto, but it will make no contribution to peak pressure, so its propulsive value is lost. In an air-cooled engine, unless there is a piston-cooling oil jet, piston cooling is cylinder cooling. Because there is more resistance to flow between the cooling fins than there is to flowing around the cylinder as if it were a solid object, an air baffle must be used to make the fin spaces into the only flow path. Another constant issue is cylinder roundness. If cooling air does not pass through the fin space, the rear of the cylinder will become much hotter than the front, and distortion will cause gas leakage and problems with oil control. The power to push air through the fins can come only from the difference in pressure between the front and back of the cylinder. If there is leakage from the stagnation zone ahead of the cylinder (around an unbaffled cylinder, or up through the front of the fairing, for example) much of the usable pressure will leak away. At MORINI 250 SINGLE

130kph (80mph) the stagnation pressure, or ‘Q’, is 0.71kPa (1/10 of a pound per square inch). This is all that exists to push air through the fins. The large air-cooled piston aircraft engines of World War II (all of which had carefully baffled cylinders and heads) had to maintain an airspeed of at least 225kph (140mph) during climb to cool themselves sufficiently to stay out of detonation. In general, air-cooled racing motorcycle engines are saved from certain thermal destruction only by their duty cycle — there’s always another corner up ahead. While the power is on, temperature of engine parts rises steadily. When the rider closes the throttle, the

continued flow of cooling air causes those parts to cool. Testing reveals whether or not cooling is sufficient to provide the necessary ‘detonation margin’ for survival. Air-cooled cylinder heads are substantially heavier than are water-cooled equivalents because extra metal acts as a heat sink, slowing the temperature rise of the head during full throttle. The detailed measures taken by Dante Lambertini and his crew to cool this hardworking engine indicate how serious a problem this was for their creation. People who saw it come in from race or practice have said that ‘it seemed to sweat oil right through its metal ‘surfaces’. This was normal for the time. Engine castings typically required a sealant treatment to assure even ordinary oil-tightness, and at 11,000rpm you can be sure that considerable relative motion took place between major parts. When an engine works this hard there must be a ‘life-list’ for every part — so many kilometers each for crank, piston, rings, cylinder, valve springs, and guides. The knowledge that allows creation of such a list comes from continuous testing on the dynamometer, track, and autostrada. In a very real sense, the great stature of distinguished engineers like those at Morini in this era came from the pile of broken parts upon which their achievements were founded. 201

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otorcyclists of a historical turn of mind will regard 1974-76 as the period when long-travel rear suspension dramatically improved tire grip on rough pavement. What about rear suspension itself? That revolution hit motorcycle road racing in 1935, when Irish great Stanley Woods won the 264-mile Isle of Man Senior TT on a Moto Guzzi 120° V-twin with rear suspension. Having made a success of its horizontalcylindered 250, Carlo Guzzi needed a way to combine two of its proven top-ends to make a winning 500. A V-twin was the best way to retain the 250’s narrow profile but heat from the front cylinder, streaming back over the rear one, could be expected to compromise its performance. Better to keep the front cylinder horizontal, as on the 250, and then

swing the second cylinder back as far as the rear tire would permit. This turned out to be 120°. The front cylinder was cooled by axial finning and the rear by conventional circumferential fins as seen on British singles. Crankpins were phased to bring both pistons to TDC together. The 68mm x 68mm engine tested for the first time at Monza in September 1933 made just over 40hp at 7,000rpm (10.4bar, 152psi) on 8.5:1 compression. The fuel was the usual mixture of gasoline and ‘benzole’ — itself a mixture of the high-octane aromatic compounds benzene, toluene, and xylene. The crankshaft was made in one piece with T-shaped counterweights, and con-rod big ends were split and bolted, each containing 20 loose (uncaged) 4mm needles. This split-rod/ loose-roller technology dated back to the Fiat 406 of 1923 and had been used by many since then. The problem posed by crowded rollers is that crank rotation flings the rollers outward, pinching the outermost of them quite hard. The system could work adequately up to some

Guzzi’s cooling scheme lives on in present-day air-cooled Ducatis. Note enclosed rockers, exposed hairpin valve springs, and Guzzt's ‘signature’ external flywheel, which allowed use of a smaller-diameter crankshaft. (Mortons Archive)

MOTO GUZZI 120° 500 V-TWIN 7

critical rpm at which this ‘pinch force’ could no longer be carried by the lubricant. The crank was supported on the timing side by a ball bearing and on the drive side by a pair of roller bearings with the primary pinion between them, and with the usual Guzzi external flywheel outboard. A center needle bearing was also split and bolted like the rods. Cylinder offset was 74mm, front cylinder to the right, rear to the left. As was common in Italian practice, all rolling bearings were carried in steel receivers pressed into the aluminum. A single ball bearing overhead cam in each head was driven by shaft-and-bevels from the crank. Each cam operated two valves by rockers —a 37mm intake and a 34mm exhaust, set at Guzzi’s usual narrow included angle of 58°. Carburetion was by two 28.5mm Dell’Ortos and exhaust was plain pipe of tuned length. As on the 250, flywheel mass was separated from the crankshaft in the interest of compactness. In a British vertical single, the large diameter of the crank required a chain primary drive, but Guzzi’s horizontal cylinder forced them to cut length wherever possible to end up with an acceptably short wheelbase. By using an external flywheel Guzzi could couple engine and gearbox by a single gear pair, and by vertically stacking the two gearbox shafts even more length could be eliminated. Crank and gearbox were carried in the same vertically split aluminum crankcase. Externally mounted gear-type scavenge and pressure pumps supplied a dry sump lubrication “system. Oil from a tank behind the fuel tank was pumped to a fitting on the right-hand end of the crank, from which it flowed through internal drillings to supply the two crankpins and center bearing. External lines supplied oil to cams and their drives. A four-speed close-ratio gearbox

was lubricated by oil thrown off the crank. Like any modern racing machine, the ratio spread between top and bottom gears was roughly 2:1. Ignition was by Bosch magneto, mounted in the middle of the cylinder V. Aluminum heads and cylinders were used for operation on gasoline, while iron parts cooled adequately when the fuel was alcohol-based. Guzzi sent no machines to the 1936 TT but in 1937 Woods again led on the Guzzi but was

203

out with engine problems, giving the win to teammate Omobono Tenni. At Monza in 1936 very long megaphones were tried, stiffened by curious-looking longitudinal flutes. In the 1930s Britain’s ruling 500 singles were unable to reach the Guzzi’s revs; having no rear suspension slowed them further. When racing resumed at the end of World War II Guzzi had lost some of its advantage; all engines lost power

from the 72-octane fuel and all other makes now had some form of rear suspension. On the other hand, Guzzi retained a potential

Veteran of veterans Stanley Woods, who has just won the 1935 Senior TT on the Guzzi. Rear suspension violated the long-held belief that ‘nothing steers like a rigid’. Moderate cam timings gave broader, more usable power.

204

advantage in their shorter 68mm stroke. Piston speed at 7,000rpm was 3,200ft per min — much less than the Nortons with their whacking great

100mm stroke. Rev it up! When they took the engine to 8,000rpm it evidently ran into trouble with the loose-roller big ends. During 1949 the engine — sometimes with megaphones, sometimes with straight pipes — was able to make 45hp at 8,000rpm (10bar, 146psi) with megaphones, but was redesigned to incorporate a new three-piece crank assembled with Hirth radial face splines. This would allow use of the more reliable one-piece, unsplit rod and a caged roller big-end bearing already proven in the 250. The cage would relieve the rollers of the pinch effect mentioned above, allowing them to be

reliable at higher revs. The three crank parts were the two outer flywheels, each with its integral main shaft,

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plus the two inner flywheels, joined into a single piece by their central main shaft. All four flywheels were now of full-circle design. Where each flywheel would normally have a crankpin there was instead a machined rosette of radial face splines. All that could be called a crankpin was a ring of hardened steel, its outside diameter ground to act as the bigend inner race, and each end provided with a matching set of radial face splines. Passing through this ring was a hefty drawbolt, threaded on its outside diameter to screw into each of the pair of flywheels. These threads were of different pitch on the two ends, so that turning the drawbolt powerfully pulled the flywheels inward against the ring of hardened steel. Gone was the end-feed oiling system, replaced by delivery of oil into the center bearing, from which collector rings machined into the inner faces of the inner flywheels caught the oil thrown off. This was then delivered into the hardened rings on which the rods’ big-end rollers ran. Rolling bearings require very little oil, so this system worked well, and was in any case already proven on the 250. The center main bearing, having no ‘pinch problem’, was made as a split outer race of hardened steel held together by screws, containing loose needle rollers running directly on the center main shaft of the crank. Guzzi also (at least sometimes) gave the ‘new look’ V-twin the steep 35° intake downdraft angle of the latest 250, which placed the open mouth of the 30 or 35mm carburetor on the front cylinder up just below the steering-head. It’s interesting to note that at this early date this engine’s carbs were being tubber-mounted as well as its float bowls — a trend that would in 12 years result in Honda’s adoption of center-float carbs carried on flexible rubber couplings. Valve timings on one of these engines are given in Sandro Colombo’s mighty source Moto Guzzi da Corsa as IO 51 BIDC/IC 63 ABDC MOTO GUZZI 120° 500 V-TWIN ¥

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for a duration of 294° and intake lobe center angle of 96°, then EO 51 BBDC/EC 35 ATDC, for an overlap timing of 51 + 35 = 86, and exhaust duration of 266°, lobe center angle 98°. These timings are long because it takes time to push large single valves open and shut. They are not extreme. Ignition timing for this engine was 37° BIDC and compression 9:1. It’s important to remember that the detonation resistance of the ‘pool’ post-war utility fuel was low. Despite making 47—-48hp at 8,000rpm (10.5bar, 154psi), this Guzzi and the 250 from which it was ‘grown’ were becoming obsolete. Norton’s new McCandless chassis with forward weight bias and hydraulic damping made even the 500ce Gilera-4 look pre-war. The Guzzi 250 would win world championships in 1949, °51, and ’52 but then the NSU twin would push its rev ceiling far out of Guzzi’s reach. The Bicylindrica’s pronounced rearward weight bias and friction-damped suspension were now as out of date as similar features on Norton’s previous ‘Garden-gate’ Manx. The last win for the wide-angle twin was Fergus Anderson’s ride in heavy rain at the Swiss in 1951. Very likely it was this engine’s ‘pre-war’ qualities of manageable power that enabled it to prevail over any fourcylinder opponents. At the end of the year the ‘Bicylindrica’ was retired. Guzzi had prototyped a great variety of interesting racers but now chose not to further pursue either the 250 or 500 class, for they saw an opportunity in 350. An interim 500 single would be built, and eventually engineer Giulio Carcano would replace it with what he hoped would be definitive — the V8 of 1955-57.

OVERLEAF As on steam locomotives, everything can be seen. Leading-link suspensions had a vogue in the 1950s, and the shiny object beneath the engine is the spring box for the rear suspension. Megaphones were used as needed. (Mortons Archive)

205

CLASSIC MOTORCYCLE RACE ENGINES

MOTO

GUZZI 120° 500 V-TWIN

207

A partnersh ip o f development and design

1920- 1957

hese machines look so different from other motorcycles and their execution is often so ‘veteran’ in character that it’s tempting to mentally dismiss them as quaint curiosities. In fact at their origination in 1920 the engine concept was extremely advanced, based upon the best aircraft engine and racing car technology. The first Guzzi — the GP — was built as a demonstration for a potential investor. It was given four parallel overhead valves driven through rockers by a shaft-and-bevels-driven overhead camshaft. The air-cooled cylinder was horizontal, presenting its hot head to air streaming around the front tire. Instead of the cobbled-up separate engine and gearbox design that would rule English thinking for decades to come, this Guzzi combined engine and gearbox in a unit. To allow close coupling of the two by a single gear pair, the functions of crankshaft and flywheel were separated. The small-diameter crank was made in one piece rather than being pressed-and-nutted together, and its small diameter allowed use of a lighter, more compact crankcase. An external flywheel — for years the hallmark of Guzzi singles — was rationally designed with most of its mass concentrated in its rim, at maximum radius so that a minimum

of material delivered maximum effect. The company’s founders, Carlo Guzzi and Giorgio Parodi, were engineering enthusiasts before they joined Italy’s air force in World War I, where they were exposed to Fiat, Ansaldo, and Isotta-Fraschini aircraft engines. They almost certainly also saw a French liquidcooled Salmson radial engine, whose diameter was reduced by use of distinctive hairpin valve springs. Such springs were used on the Guzzi GP and many subsequent Guzzis because (a) they placed most of the failure-prone springs away from the hot cylinder head, in free-stream air, and (b) they could be more durable than conventional helical springs because they were

The large downdraft angle seen on this 1957 350 was usually credited with reducing

but charge loss to the exhaust during overlap,

probably also improved intake flow. Keith Duckworth would adopt it in the 1960s. Guzzi favored huge carburetors. (Mortons Archive) LES MOTO GUZZI HORIZONTAL SING

less subject to ‘surge’, or coil vibration. Such springs would later be adopted by Norton, AJS-Matchless, Velocette, and Ferrari.

Other aircraft engine features adopted on the GP included aluminum pistons, tubular-shanked con-rod, forced-feed lubrication, and dual ignition. Aluminum pistons had been adopted on aircraft engines from the middle of World War I. Their superior heat conductivity enabled them to run much cooler than the previously universal iron, thereby permitting use of a torque-boosting higher compression ratio. British motorcycle engines of the early 1920s were still in slow transition from total-loss oiling, and Velocette’s 1924 adoption of pumped oil circulation was a turning point. Guzzi had adopted it four years previously! Dual ignition would be dropped as soon as it was found to be unnecessary. One mystery of the early Guzzi 500s was their over-square bore-stroke dimensions of 88mm x 82mm, unusual in a world where small bores and long strokes were almost universal. This was true also of the aircraft engines that Guzzi and Parodi had seen. One possibility is that Guzzi understood that the inherently cooler operation of an aluminum piston made larger bores workable (at high power, iron pistons ran dull red in the center unless the bore was made small enough to pull their temperature down). Whatever the reason, Guzzi would stay with the 88 x 82 dimensions right through to the end of the first post-war racing era in 1957. The bigger the bore, the larger the valves that could be fitted into the cylinder head. British racing engines would not adopt over-square dimensions until after World War II. In auto GP racing, Gioacchino Colombo’s 1.5 liter V12 of 1947, designed for Ferrari, was the first over-square engine on the GP grid since 1907. Guzzi were

not afraid of innovation! In the 1930s the company developed its 500 single, then a racing 250 in the same style, and then doubled that engine into the ‘Bicylindrica’ 120° V-twin. It rocked the motorcycle world by winning the Senior TT in 1935 — with rear suspension. A dedicated test engine was used to evaluate ideas. After the war they began again, taking the 1949, 1951, and 1952 250 world championships with their ‘Gambalunghino’, a

209

68mm x 68mm two-valve 250 single. These dry sump engines had unit gearboxes, overhead cam drive by means of shaft-and-bevels, iron-linered aluminum cylinder and head, and vertically split cases of ‘electron’ aluminum-magnesium alloy. Then in 1953 NSU got serious with a high-revving twin and that was that — even a developed ‘Bialbero’ (DOHC) version of the Guzzi, making 28hp at 8,000rpm (12.4bar, 183psi) was unavailing. In 1949 Guzzi tested a 350 version of the Bicylindrica 120° V-twin but as with most such downsizing, the result was overweight. That winter a 78mm x 73mm = 348.8cc fivespeed DOHC racing single was built, with four hairpin springs on each of its two valves. It made less power than the twin but fitted into the light 250 chassis. In March 1950 it went on the dyno for a lot of experimental running in which such things as an oil-cooled cylinder, a water-cooled exhaust valve, and single vs dual ignition were evaluated. By late April this was giving 31hp at 7,000rpm (11.2bar, 165psi). At the Mettet, Belgium, race that month it seized while vying for the lead with an AJS. At the TT in June Maurice Cann practiced with both this design and with a Gambalunghino that had been enlarged to 72mm x 76mm = 309.4cc, referred to as ‘the 310 engine’. The 310 broke a valve in the race and the bigger engine was pushed under a bench and not run again. Exhaust valve failure was a general problem of high-duty air-cooled engines in this period — even the air-cooled radial engines of airliners, developed with vast government funding through World War IL, were still occasionally breaking exhaust valves — even those made of the recently developed gas turbine alloys. Indeed, another famous 350 — the AJS 7R3 three-valve single — was given a head designed entirely around the problems of exhaust valve cooling. In the 1951 TT Fergus Anderson (Guzzi factory mechanics called him ‘Fairgooz’) used a 260cc overbored DOHC four-valve with two carbs to get some extra practice in the 350 class, but didn’t race it. A four-valve 250 with central ignition had been under test but in the end did not boost performance enough to justify its complexity. Anderson retained his interest in 350 GP, 210

suggesting it again at the end of 1952. Italian makers had been little interested because their national series had no 350 class, but Anderson

saw an opportunity. At his urging the ‘310 engine’ was reconsidered. I suspect that its rework prior to testing included some kind of updated exhaust valve, among numerous other changes. On the dyno it gave good power. Put into a 1953 250 chassis (the stick-slip era of friction dampers had during 1952 given way to the more supple motion of hydraulic damping at Guzzi), it was run at Hockenheim. In practice this very light bike was not only faster than all the 350s — it was also faster than all but three 500 entries. This was to be the core of Guzzi’s 350 success — moderate power, outstanding agility, and wide torque. In the race Anderson went from last to first on lap one and emerged victorious, defeating even the giant DKW team and their fastaccelerating two-stroke triples. The sensational result at Hockenheim caused a rush to enter the 350 in the Junior TT. Anderson promisingly finished third behind two factory Nortons. With a certain amount of boldness the separate crankpin was now moved outward as far as they could, making a 72mm x 78mm = 317.6cc engine — the largest that could be made using 250 crank-half forgings. With a 155mm one-piece rod (1.99 rod ratio) and a 60° valve angle between a 38.5mm inlet and 33mm exhaust, on 9.5 or 10:1 compression, this DOHC four-speed engine made 31hp at 7,700rpm (11.2bar, 165psi). This was worth yet more effort. In the week after the TT Carcano had 250 cases bored to accept a bigger cylinder and SOHC head, making a 75mm x 78mm = 345cc engine. Two of these ran in the Dutch TT, Enrico Lorenzetti winning the race on one and Anderson setting fastest lap on the other, then retiring. Anderson went on to win Belgium, France, and Switzerland, with a second at Monza — to win Guzzi’s first 350 title. With its 78mm stroke, this engine could, like that run at the TT, usea pressed-together crank with a strong one-piece rod and rpm-capable caged big-end bearing. Although Guzzi had been the leading exponents of hairpin springs, Ing Carcano abandoned their use in the early 1950s, preferring CLASSIC MOTORCYCLE RACE ENGINES

to bring the springs ‘indoors’ as helical coils, now cooled by oil and no longer by the passing air. In the process it became possible to better cool and lubricate the valves themselves — the probable ultimate goal. In the aircraft engine business it had become normal to flood the rocker boxes with oil as a means to supplemental cooling of the valves, springs, and heads themselves. Engineer Carcano now concocted even longerstroke engines by using 500-style one-piece crank forgings with the older split-and-bolted con-rod and uncaged rollers of 3mm x 15mm dimensions. Several displacements would be built with such cranks of 79 and 80mm stroke, including a 75mm x 79mm = 349cc version. This engine had the now-usual steep intake downdraft of 33° developed for the 250, with a 380mm (15in) intake length providing a torque boost at around 6,000rpm. The valve included angle was Guzzi’s narrow 58° — with a 37mm intake and 32mm exhaust valve. Usual carb bore was 37mm, later reduced to 35, compression was 9.5:1, and power was 33.5bhp at 7,500rpm (11.3bar, 167psi). Carcano’s tuning of this engine was aimed at maintaining maximum torque at moderate revs. Guzzi entered many riders on a variety of machines — 317, 326, and 349cc — but it is said the preferred mount during 1953 was the ‘345°. If so, this was probably because of the durability of its caged-roller bottom end. MOTO GUZZI HORIZONTAL SINGLES -

Here the Guzzi team are at work at the 1953 TT in the usual hotel basement or lock-up. In this era engine build stands were usually roughand-ready oil-stained wooden boxes, and here you see the head of a valuable prototype supported by — bricks! (Mortons Archive)

With such hastily improvised engines there were reliability problems. Big-end bearings seized, to be expected when crowded big-end rollers are run to high revs. Cylinder liners and pistons were subject to distortion, allowing heavy oil use and forcing use of a hotter-than‘normal spark plug to prevent fouling. These bodges were kept together sufficiently for Fergus Anderson to win the 1953 350 title. Readers from the English-speaking world, including myself, find it interesting that the great British singles could dominate cae I Le yet suffer Guzzi’s singles to win the 350 world championship from 1953-57, inclusive. Each was specialized for its purpose — British engines for the speed and rigor of the TT, and the Guzzis for the wide range acceleration needed on many European circuits. While the weight of the Guzzis wasted away under Carcano’s relentless efforts, British singles remained substantial for TT durability. Because there had been magneto troubles 211

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during 1953, 1954 engines were given a dual coil-and-battery system with two 10mm plugs. One was timed to fire retarded and was used only for the starts (push-starting in GPs ended in 1984). Once the engine fired, the rider switched to the second circuit, which was normally timed. During this season, seeing that the 75-bore pushed the limits of the 250 case (getting on the thin and weak side when bored for the bigger cylinder), a 500 case was built into a short-stroke DOHC 350 of 80mm x 69.5mm = 349.3cc. The cast-iron cylinder liner was replaced by a more thermally conductive chromium plate direct on aluminum bore. Bigger valves at 41mm inlet/36mm exhaust were fitted, and power was 35bhp at 7,800rpm (11.4bar, 167psi) with 9.4:1 compression. These new engines appeared late in the season. Unreliability initially prevented success but intensive development forced the issue and from the Belgian GP onward the 345 did the job. Guzzis finished first through fourth at the end-of-season Monza GP des Nations and Anderson was 350 champion again. In 1955 the short-stroke was the choice,

with 37mm carb and coil-and-battery dual ignition with the same timing on both plugs. There were some seizures this year, suggesting

that even with closely-fitted full-skirted pistons giving good thermal contact with the chromeon-aluminum cylinder wall, not all was well. Technical management of problems won through as Guzzi won all seven 350 GPs, with Bill Lomas taking their third championship. In 1956 there were retirements traced to low-octane fuel. While detonation causes eventual failure by progressive softening of the ring lands, immobilizing the piston rings, the prompt result is a rise in piston temperature —

possibly too much for cylinder air cooling to overcome. Lomas was champion again.

Four 350 titles now. Yet dark clouds were

Guzzi’s ‘Galleria del Vento’, with a machine supported on the balance. The strut disappearing into the tunnel floor led to external equipment that measured aero forces. Observation windows are seen at either side. (Mortons Archive)

MOTO GUZZI HORIZONTAL SINGLES -

213

and staff had strong accumulated racecraft and their shops were able to respond quickly with required improvisations. i aN

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visible — Gilera’s 350-4 had defeated Guzzi at the fast end-of-season Monza GP des Nations. At ten hp up on the Guzzi’s 35, the arithmetic wasn’t good. How had a modest single prevailed thus far? The usual story parallels the weak-kneed adulation of ‘British handling’, which was held to possess secrets (now lost) traceable to King Arthur in his seaside cave. In Guzzi’s case the 350’s agility has been attributed to ‘low center of gravity’, as the engine’s crankshaft centerline was below the plane of the axles. Let’s think about that. A motorcycle, in rolling over to enter a turn, rotates around its center of mass and not around a line connecting its two tire footprints. This is because countersteering drives the tires out from under the center of mass toward the outside of the turn, causing the top of the machine to fall into the turn. The top falls inward as the bottom steers outward. As Honda discovered with its 1984 NSRS00, locating something heavy — in their case the fuel — low in the chassis increases resistance to rapid roll. The Guzzi singles were quick in direction-changing (1) because they were very light and (2) because their large reverse-rotating external flywheels offset the gyro effects of the wheels. ‘Low center of gravity’ had nothing to do with it. Carcano now reviewed performances of the several Guzzi variants in past races, and then ordered track testing at Modena against a 1954 version. Thanks to its wider torque and perhaps to some updating, this ‘antique’ lapped more quickly on this tight course than the later, powered-up short-stroke. The 1957

engine was now built at 75mm x 79mm with compromise 39/33 valves. Thanks in part to the Smm smaller bore this engine made good power on single ignition — 38hp at 8,000rpm (12bar, 177psi) — and was mechanically safe to

8,400rpm. A weight-saving program even more

214

stringent than previously made this a very light machine at 98kg (216lb). One of the features

changed was to drop the heavy battery ignition in favor of a magneto and single 10mm plug. The automatic assumption seems to be that Carcano reduced the bore to ‘increase torque’. Simple arithmetic shows that, in an engine of constant displacement, as leverage from a longer stroke increases, the force acting on that leverage — combustion pressure on a smaller piston — is reduced in exact proportion. Hey presto — away goes this nonsense. Then why revert to a smaller bore? Italian design in the mid-1950s still suffered from the hemispherical combustion chamber’s poor knock resistance — the result of its slow combustion allowing time for detonation’s chemistry to mature. Hemi combustion was slow because Italian designers were not using British tools to accelerate it (Weslake’s swirl

from intake offset, and Kuzmicki’s piston-tohead squish), yet rising compression ratios were inviting an intrusive piston dome up into the chamber, slowing whatever intake turbulence might persist there. The usual Italian response to this was to apply dual ignition and to further reduce flame travel distance through use of smaller bores. As Norton and Velocette adopted bigger bores, both Gilera and MV stayed with their 52mm x 58mm 500-fours, while the great Italian 125 singles ran on dual ignition. The 350 Guzzi had had plenty of trouble with temperature, exhaust valve failure, and detonation. But high torque required above all a high compression ratio. Some data cited indicates that during 1956 the 80-bore 350 was operated on 11:1 or higher compression — a huge jump. How might this have been achieved? A clue comes from layout drawings of the 1957 Guzzi V8, which clearly show pistons designed to generate turbulence from squish. I

therefore suspect that some time during 1956

CLASSIC MOTORCYCLE RACE ENGINES

Carcano’s experiments showed the value of squish, and it was incorporated into his new work. This is suggested by the higher 12bar (177psi) bmep (net, stroke-averaged combustion pressure) achieved by the late 80-bore engines. The combination of a smaller bore, squish, and this higher compression added up to a more reliable engine with outstanding ability to accelerate the very light 350. It was given compromise valve sizes of 39/33mm. In general, the smaller the intake valve, the farther down the rev range moves the point of maximum torque. Although torque would slope downward above this point, smooth, high-flowing port shape would limit the slope (just as it does in Harley’s dirt-track engine), allowing high power still to be reached. The result would be a torque curve with wide separation between the points of maximum torque and maximum power — a wide usable range. The usual power quoted for the 1957 350 is 38hp at 8,000rpm (12bar, 177psi), with best examples reaching 40hp (12.7bar, 186psi). The ultra-light, wide-range 1957 350 again held off the opposition. On two wheels, agility is a worthy opponent of raw power. Keith Campbell was second to a Gilera at the TT, then won Holland, Belgium, and the Ulster to become champion. At Monza Gilera fours were first and third, but Guzzis were second and fifth. This made five 350 titles in a row for Guzzi. It’s more than a battle of numbers. Guzzi,

MOTO GUZZI HORIZONTAL SINGLES

Ing Carcano, and staff had strong accumulated racecraft and their shops were able to respond quickly with required improvisations — adapting this head to that cylinder, designing, pouring, and machining new castings quickly (easier to do when you have only one cylinder!), and getting most things right the first time. There were failures — piston seizures, detonation damage, probably head warpage leading to poor valve seating, valve over-temperaturing and failure — but the team took it in its stride and devised timely countermeasures. Riders themselves might not last long halfa-century ago. Once, during his time at Guzzi, American twins builder John Wittner described to a veteran engineer, the late Umberto Todero, a bad day he’d had at Daytona. Todero interrupted him. ‘I will tell you what is a bad day at the races,’ he said. “A bad day at the races is coming home with two smashed bikes in the truck, and two coffins.’

At the end of September 1957 the big pull-out was announced — Guzzi, Gilera, and

Mondial withdrew from GP racing. The heady rush of creativity became history.

Our world cannot accept the vibration of singles unless it is quelled by sophisticated measures as in Ducati’s ‘Supermono’. Yet the

appeal of the single’s elegant simplicity never disappears. (Mortons Archive)

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1955-1957

e can read in many places that the Moto Guzzi V8 was the most complex GP bike of its era and that, had a battery wire not broken and a rubber coolant union not split, it might have become the dominant machine of its age. The fact is that this very ambitious design was too much for the R&D capability of Guzzi’s 12-man race team — a condition shared with the BRM V16 GP car, Chrysler’s [V-2220 V16 aircraft engine, and Honda’s blue skies four-stroke GP bike, the 19,000rpm oval-piston NR500. In any new design, enough performance increase must be planned to make the project worth doing, but within the requirement that it can be realized promptly with the resources at hand. The story is told that Ing Giulio Cesare Carcano saw the four-cylinder 350s of Gilera and MV about to end his agile 350 single’s years of dominance and decided to challenge them in the 500 class. Six cylinders were too wide and four cylinders were derivative, so that left a V8, its cylinders liquid cooled because air cooling couldn’t reach the rear cylinder bank. The finished V8 would fit comfortably into a Ducati 916’s fairing. The Gilera and MV four-cylinder 500s were already turning 10,500rpm, so to better their performance Carcano’s notional V8 would have to (1) turn significantly higher revs and (2) not give that advantage back by being clumsy and overweight. If Carcano had learned anything from his years of refining Guzzi’s horizontal singles, it was that — on twisty European courses at least — the advantage was to the bike that changed direction quickly and accelerated strongly across a wide range of revs. In 1955, the time of the V8’s conception, the Gilera 500-4 weighed 140kg (310Ib). Despite its complexity the V8 at 12,000rpm moved its pistons through only 3,228ft per min, with a peak piston acceleration less than 60% of that of pistons in today’s top 600

Coils, water and oil pumps, pipes, hoses, eight carburetors interlaced like fingers, and a cam-drive case so distinctive that designers continue to invoke it today — a foretaste of today’s filled-in, ‘opaque’ motorcycles. (Mortons Archive)

sportbikes. Although its mythic status is high, the V8 never won a single GP. Guzzi had in 1953 finally replaced its pre-war 120° V-twin 500 (retired in 1951) with a strange 145kg (320lb) four-cylinder liquid-cooled unit whose crankshaft was arranged the long way in the chassis. Troubled handling had held it to one GP win. Then a ‘place-holder’ design — a 500 single — had followed, weighing 127kg (280Ib). All these numbers warned that the V8 must be as light as possible. When you look at the details, they show this close attention to weight. Wall thickness in the compact, unit-construction magnesium crankcase was just over 4mm (5A2in). Chassis tube wall thickness was 1.0mm

(0.039in), including the large backbone tube and the tubes in the front fork. Carcano was clearly willing to put in the design work, and pay for the more difficult fabrication, necessary to achieve weight savings. From the moment higher management approved the project, until the V8’s first test, only five months elapsed. Guzzi had learned this kind of accelerated prototyping in war work. Weight was 150kg (330Ib), only 10kg higher than the Gilera-4. That meant that half of any horsepower advantage won by being able to rev 14% higher than the fours would go into performance, and half would be consumed in driving the 7% greater weight. Carcano chose bore and stroke identical to what Honda would in 1959 give its long-serving 250-fours — 44mm x 41mm. This somewhat oversquare bore and stroke takes some explaining, as the Gilera and MV consensus was that the stroke should be greater than the bore in the ratio 52 x 58. Had Carcano’s V8 followed this tradition, its bore and stroke would have been very different — 41.5 x 46. Right from the first Guzzi motorcycle, bore had been chosen bigger than stroke, which was unusual in view of the general trend in the opposite direction. As the originators of the Gilera-4, Carlo Gianini and Piero Remor, graduated from university, auto GPs were being won by higher-revving long-stroke rollerbearing engines with two valves and very wide valve angles. Those very wide valve angles were deemed necessary to provide room for two valves big enough to flow as well as the DAG,

MOTO GUZZI V8

four valves deemed necessary in GP car engines

before World War I. Not surprisingly, both the Gilera and MV 500s (Remor drew the first MV 500 as well) shared these features. Did

Carcano make the V8 44 x 41 because that was Guzzi tradition? I doubt it, for he employed smaller bores when necessary to achieve faster combustion. I think he chose the shorter stroke because it made reaching his rpm goal easier. Why not an even bigger bore and shorter stroke? Italian engine designers of the 1950s were keenly aware of the problems of limited flame speed — this is the likely reason for the small 52mm bore and long 58mm stroke of

This version of the V8 has two cylindrical float bowls, one at either end of the row of carbs. It was later replaced by eight tiny individual bowls. Flat caps at cam ends cover four ignition contact-breakers each. (Mortons Archive)

218

the classic Italian 500-4s. A sensible rule of development is not to pioneer in too many areas at a time. Carcano chose rpm and water cooling. At the time, 12,000rpm from 62.5cc cylinders wasn’t so much to ask. Only the year before, NSU were running their 125 Rennfox single to 11,000rpm with a 50mm stroke, and it was said to be mechanically safe to 15,000rpm. Team managers made it their business to know these things, and their intelligence-gathering technology was simple — a pitch pipe. With moderately racy stroke-averaged net combustion pressure of 165psi, 500cc displacement, and 12,000rpm, crankshaft power should be just over 80hp, and taking 10% for drive train loss, 72hp at the rear wheel. That’s just what Carcano was able to roll to the line as the final version in 1957. There were endless troubles. Trouble began when Carcano at first tried simpler forms of crankshaft. Anyone with the equivalent of

CLASSIC MOTORCYCLE RACE ENGINES

We honor Carcano for boldly ima gining a future that would be 50 years in arriving. $80,000 in today’s money could have a Hirth built-up roller crank made for this job, but first a less-expensive one-piece crank with split rods and split-caged rollers was tried. Simple cranks like this had worked adequately in Guzzi singles — albeit at lower revs. At higher revs, connecting-rod big-end roller bearings face two potentially destructive conditions: 1) The rotational speed of big-end bearings oscillates by plus and minus roughly 25%, twice per revolution. The heavier the roller set and cage (if any) the more likely it is that at some high speed their inertia will resist this rapid speed oscillation by skidding rather than rolling. This accelerates heating, lubrication breakdown, and failure. 2) If there is no cage to hold apart the rollers, the centrifugal force of rotation causes the mass of rollers to pinch those outermost quite hard — generating unnecessary frictional heat. Mercedes had adopted Hirth crankshaft construction for their W196 GP car’s straight-8 engine of 1953-54, but Carcano attempted the less expensive solutions first. In racing, as in war, time is costlier than money. Sad to say, all the elements of full solutions were nearing maturity at this time. Durkopp in Germany had devised their unique ‘M-cage’, light and stiff, which guided each small-diameter, light needle roller by limited contact in six places. Fatigue-resistant VacuumArc Remelted (VAR) bearing steel was nearly ready for the marketplace, which would shortly extend the lives of rolling-element bearings by three to six times. Or, had Carcano chosen plain journal bearings and a one-piece forged crank, Vandervell in England were cranking out millions of trimetal insert bearings. One-piece forged cranks and trimetal plain bearings were eagerly adopted by Ferrari after 1950. It is said by some that had Guzzi continued racing in 1958, this option was next on Carcano’s list. The initial crank design was forged in one piece from Ni-Cr steel with full-circle flywheels carrying eight 90mm long con-rods (rod ratio

= 2.2, which is usual for high-performance engines) with split and bolted big ends, each turning on split-cage roller bearings (as were then fitted to some Guzzi singles). Balance was achieved by dovetailing heavy metal into the wheels. Split roller mains supported the flat crank at its three inner journals. It was said that unbalanced secondary forces generated by this original ‘flat’ 180° crank cracked or broke main bearing webs and studs, requiring construction of a 90° crank and matching re-timed camshafts. When the Germanmade multi-piece Hirth crank was adopted, the unsatisfactory two-piece split rods and bearing cages could be abandoned in favor of stronger steel I-beam one-piece rods and cages. Each con-rod big-end bearing consisted of a single row of 15 5 x 5mm rollers in an aluminum alloy cage. Possible reasons for adoption of longer 110mm connecting rods (rod ratio = 2.68) are

(1) reduction of secondary imbalance and (2) reduction of the speed variation of the crankpin, giving some protection against acceleration/

deceleration skidding of the traditional heavy big-end roller set. Both secondary imbalance and crankpin speed variation disappear when the rod is made infinitely long. Each flywheel was made with an integral hollow 29mm crankpin, the end face of which was provided with V-shaped radial serrations. Matching serrations were machined into one face of the mating flywheel and a 17mm internal bolt, engaging different thread pitches in crankpin and flywheel, drew the pair together with tremendous force. If the strength of this coupling seems implausible to you, consider that similar couplings were tested by Pratt & Whitney against other multi-piece crankshaft assembly schemes and were found to provide the greatest rigidity. Douglas DC-6s flew with these couplings during the piston airliner era. Lubricant was pumped to the main bearings, and oil leaving them was picked up by collector rings machined into the flywheels. This oil was routed to the crankpins to lubricate the MNO)

MOTO GUZZI V8

from two large cylindrical remote float chambers, one at either side of the row of interlaced carbs. This produced unsatisfactory carburetion and was in time replaced by eight tiny (28mm

rod big ends. Oil thrown from the crankshaft lubricated the gearbox. The basis of the V8 was its box-like Elektron unit crankcase/gearbox casting, open on both ends. The crank with its rods was installed

diameter) float chambers, one per carburetor.

from one side, then seated in its three middle

Carburetion never became trouble-free.

main bearing saddles, and their retainers were installed. Then the right and left case covers were prepared, both carrying end main bearings, and one having the gearbox shafts and shift drum in place. These covers were installed. There are no separate cylinder blocks. Part of the cylinder water jacket is formed by the crankcase, and the rest is cast as part of the cylinder heads. The actual iron cylinder liners screw into the heads in modern F1 style, eliminating the need for bore-distorting head gasket clamping forces. With the cast three-ring pistons on the rods, their wristpins retained aircraft-style with wristpin buttons, each bench-assembled head with its screwed-in liners in place is slipped over the pistons and down into place, sealing to the lower water-jacket by a long O-ring. The water pump is driven from the large timing gear on the right, sending water through mainly metal piping around the front of the engine to enter each cylinder block on the left. Water then flows across the cylinders, left to right, and upward to cool the heads, exiting each head on the right, between the cams. Engineers are more often tempted to send the coolest water to the exhaust side of the cylinder head, then to the intake side, and finally to the cylinders. This provides the greatest heat removal because it maximizes the temperature difference (the ‘delta-T’) between coolant and hot metal. But that’s not the only goal of cooling. Cooling the exhaust side first raises the temperature of water cooling the intake side, thereby heating and expanding the fresh charge more than necessary. This loss of charge density reduces power. The aircraft engine makers Pratt & Whitney addressed this problem in 1940 by cooling the intake side of their R-4360 engine’s cylinders first, then letting that warm air cool the much hotter exhaust side. Carburetion was by eight special 20mm

carburetors in Dell’Orto design, but manufactured at Guzzi. Initially fuel was supplied 220

The 1950s were an era in which magnetos were hard-pressed to produce enough sparks for a 10,000rpm two-stroke single (167 sparks per second). The Guzzi V8 needed 800 sparks per second. The contemporary 28-cylinder Pratt & Whitney R-4360 aircraft engine needed only 630 and carried 26kg (571b) of Bendix magnetos to supply them. Guzzi therefore adopted a coil-and-battery system. Two contact-breaker housings on the left ends of the intake cams carried eight sets of points and a large tin box of coils was carried on each frame downtube. Power came from a pair of 6V batteries located under the rider’s thighs. Only ten years later Honda’s 250 RC166 six-cylinder would get 850 sparks per second from one Kokusan Denki magneto. The two valves in each cylinder were set at the usual progressive Guzzi included angle of 58°. Intakes were 23mm diameter and exhausts 21, both seating directly on the hard Y-alloy aluminum head without valve seat inserts (this was a practice begun by Vittorio Jano in the Alfa P3, probably because leaving out the usual hard seat ring allowed a larger valve to fit into a given space). A single 10mm spark plug served each cylinder, angled to the left and firing the charge directly rather than through a ‘spark port’ as in the Gileras. Pistons were Manx-inspired, with deep valve cut-outs, squish surfaces, and 10.5:1 compression. Wristpins were retained in

aircraft fashion by radius-faced end-plugs which bore against the cylinder wall. This was before the day of fiberglass fairings, and for this Guzzi had a specialist who made the streamlining from magnesium > sheet by hammer-and-dolly methods. Because hammering made the material brittle, it had periodically to be softened by heating. The right temperature was indicated by watching for color change in a layer of soap, rubbed on to the metal. Exhaust pipes for Guzzi racers were heat-bent by another technician. Pipes

CLASSIC MOTORCYCLE RACE ENGINES

were filled with sand whose pressure was adjusted from time to time by taps on tapered pins at the ends. At the July 1955 Belgian GP the main bearing cap studs broke. Then came water pump failure, broken big-end cages, unscrewed tappets, overheating, and more big-end failure. There were crashes. There were a couple of wins in Italian national racing. There was a fourth in the 1957 German GP — behind two Gileras and 12 seconds down on a BMW flat-twin. Then a fourth and fifth at the TT. And there were more crashes, a famous 118.574mph lap record at Spa, the memorable timing at 178mph, and whitewashed controversy over tricky handling and high-speed instability (some riders wanted nothing to do with the V8). The V8 never won a single GP. Failures like the above list occur in every development program, even with full use of computer modeling, but they seldom happen in public. They happen on the dyno or on the company’s private test track. Intensive testing and development trample the problems to death to result (usually!) in airliner-like ’t reliability. Testing is the key and Guzzi couldn

Mass properties have changed a lot. Today’s engines are as far forward as they can be, and riders’ faces are right above the top steering crown. The Guzzi V8 is smack against the rear tire, with rider seated far aft. (Mortons Archive)

do enough of it. The V8’s development needs were just too big for a motorcycle industry based on a transportation market. The central problems Guzzi failed to overcome were new to them. The special problems of high rpm consumed a lot of time. Even had Guzzi’s engines been reliable, both MV and Gilera had the advantage of having already put in five years of hard work on 500 handling. We honor Carcano for boldly imagining a future that would be 50 years in arriving.

OVERLEAF Even seeing the photo makes our ears strain to hear the wonderful sound! Here is 1935 Senior TT winner Stanley Woods on his 50th birthday in 1956 riding demo laps on the V8 Guzzi at Monza. (Mortons Archive) 22)

MOTO GUZZI V8

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