Haynes Motorcycle Basics Techbook 2nd Edition [3515, 2 ed.] 185960515X, 9781859605158

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ium 9082 08555 0351 629.287 Coo

Motorcycle Bas TechBook by Matthew Coombs incorporating material fronttthe Haynes Motorcycle Basics Man

Coombs,

Matthew

Motorcycle

basics

techbook

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Introduction

Page

03

About this book

Page

093

Acknowledgements

Page

0°3

Page

004

Chapter 1 Engine

Page

1°1

Chapter 2 Fuel system and exhaust

Page

2°1

Chapter 3 fgnition

Page

3e1

Chapter 4 Transmission

Page

4e1

Chapter 5 Engine lubrication and cooling

Page

Chapter 6 Wheel, brakes and tyres

Page

61

Chapter 7 Front suspension and steering

Page

7e1

Chapter 8 Rear suspension

Page

8e1

Page

91

Page

10°14

Technical Terms Explained ’

Page

REFe1

Index

Page

REFe11

_ Safety first!

,

Chapter 9 Frames and handling Chapter 10 Electrics

4

4

|

5e1

3 9082 08555 0351

MAR 1 0 2003 ad

Introduction Quite a large number of motorcycles and scooters in everyday use are ridden by owners who have little understanding of how their machine works. Many are quite content to remain in this state of blissful ignorance,

having their machine serviced at regular intervals as and when the need occurs, or repairs carried out when problems necessitate. Not everyone has the ability or inclination to look after these matters themselves and it is as well that they are aware of their own limitations. Unfortunately, roadside breakdowns are likely to occur without warning, and always at a bad time. They can range from something mildly irritating, such as the refusal to start one morning, to a complete breakdown in

some remote spot on a dark wet night. It is on occasions like these that most people begin to have some regret at not having even a basic understanding of how their machines work so that they could, perhaps, have taken precautionary measures,

or, at the very least,

have an idea of where the fault lies. No book, however well written, can turn an

unskilled amateur into a skilled mechanic. What it can do is to explain in simple terms how each major component of a motorcycle or scooter functions and the role it plays in ensuring the machine remains in good running order. No previous understanding of the subject is assumed and all technical terminology used is explained in a glossary at the end of the book.

Today’s motorcycles are the end product of many years’ continual development work, becoming both complicated and sophisticated in the quest for improved performance. Although the use. of electronics is increasing, especially for the control of fuelling and ignition, many components on the motorcycle are still of mechanical operation and it will often be found that a complicated looking assembly is nothing more than a number of relatively simple basic units bolted together to make up a single, compact unit. This book is also aimed at students on Further Education courses in Motorcycle Engineering.

About this book The text in each chapter is arranged in numbered section order and will correspond

with the contents list at the beginning of the chapter.

If a section

in another chapter is

referred to, a typical instruction ‘see Chapter 4, Section 8’ will be found. All illustrations are keyed into the text with their chapter number and section number. Where several illustrations relate to a single

section, they carry an alphabetical code, e.g. 5.3b relates to Chapter 5, Section 3, 2nd illustration. It has been our objective to present the information given in this book in as simple a form as possible, using line drawings wherever possible to illustrate components and systems in their basic form. Technical terms have been kept to a minimum, and to

help further, a basic glossary of technical terminology can be found immediately before the index. Whilst every attempt is made to ensure that the information in this book is correct,

no liability can be accepted by the authors or publishers for loss, damage or injury caused by any errors in, or omissions from, the information given.

Acknowledgements Our thanks are due to the following companies who provided many of the illustra-

International Ltd, Heron Suzuki (GB) Ltd, Kawasaki Motors (UK) Ltd, Mitsui Machinery

tions used throughout this book: Cooper-Avon Tyres Ltd, Burmah Castrol Ltd, Ducati Meccanica SpA, Dwek

Sales (UK) Ltd, NGK Spark Plugs Ltd, NVT Motorcycles

Ltd,

Robin

Chan

of

Contact Developments and Vespa (Uk) Ltd.

We would also like to thank Tony Tranter who gave permission to use line drawings from his book The Motorcycle Electrical TechBook.

o4 Safety First!

accidents, and the following is not a compre-

@® Always disconnect the battery earth terminal before working on any part of the fuel or electrical system, and never risk spilling fuel on to a hot engine or exhaust. @ |tis recommended that a fire extinguisher of a type suitable for fuel and electrical fires is kept handy in the garage or workplace at all times. Never try to extinguish a fuel or electrical fire with water.

hensive list of all dangers; it is intended rather to make you aware of the risks and to

Fumes

Professional mechanics are trained in safe working procedures. However enthusiastic you may be about getting on with the job at hand, take the time to ensure that your safety is not put at risk. A moment’s lack of attention can

result in an accident,

as can failure to

observe simple precautions. There will always be new ways of having

encourage a safe approach to all work you carry out on your bike.

Asbestos @

Certain

friction,

insulating,

sealing and

other products - such as brake pads, clutch linings, gaskets, etc. - contain asbestos. Extreme care must be taken to avoid inhalation of dust from such products since it is hazardous to health. If in doubt, assume that they do contain asbestos.

Fire @® Remember at all times that petrol is highly flammable. Never smoke or have any kind of naked flame around, when working on the vehicle. But the risk does not end there - a spark caused by an electrical short-circuit, by two metal surfaces contacting each other, by careless

use

of tools,

or

even

by static

electricity built up in your body under certain conditions, can ignite petrol vapour, which in

a confined space is highly explosive. Never use petrol as a cleaning solvent. Use an approved safety solvent.

Remember... * Don’t start the engine without first ascertaining that the transmission is in neutral. * Don’t suddenly remove the pressure cap from a hot cooling system- cover it with a cloth and release the pressure gradually first, or you may get scalded by escaping coolant. * Don’t attempt to drain oil until you are sure it has cooled sufficiently to avoid

scalding you. ¥ Don’t grasp any part of the engine or exhaust system without first ascertaining that it is cool enough not to burn you. ¥ Don’t allow brake fluid or antifreeze to contact the machine’s paintwork or plastic components.

evenwhen

@ Certain fumes are highly toxic and can quickly cause unconsciousness and even death if inhaled to any extent. Petrol vapour comes into this category, as do the vapours from certain solvents such as _ trichloroethylene. Any draining or pouring of such volatile fluids should be done in a well ventilated area. @ When using cleaning fluids and solvents, read the instructions carefully. Never use materials from unmarked containers - they may give off poisonous vapours. @® Never run the engine of a motor vehicle in an enclosed space such as a garage. Exhaust fumes contain carbon monoxide which is extremely poisonous; if you need to run the engine, always do so in the open air or at least have the rear of the vehicle outside the workplace.

The battery @ Never cause a spark, or allow a naked light near the vehicle’s battery. It will normally be giving off a certain amount of hydrogen gas, which is highly explosive. ¥ Don’t

@ Always disconnect the battery ground (earth) terminal before working on the fuel or electrical systems (except where noted). ® lf possible, loosen the filler plugs or cover when charging the battery from an external source. Do not charge at an excessive rate or the battery may burst. @ Take care when topping up, cleaning or carrying the battery. The acid electrolyte,

rush

to finish

a job

or

take

unverified short cuts. xX Don’t allow children or animals in or around an unattended vehicle. ¥ Don’t inflate a tyre above the recommended pressure. Apart from overstressing the carcass, in extreme cases the

tyre may blow off forcibly. v¥ Do ensure that the machine is supported securely at all times. This is especially important when the machine is blocked up

to aid wheel or fork removal. hae V Do take care when attempting to loosen a stubborn nut or bolt. It is generally better to pull on a spanner, rather than push, so that if you slip, you fall away from the machine rather than onto it. v Do wear eye protection when using

% Don’t siphon toxic liquids such as fuel, hydraulic fluid or antifreeze by mouth, or allow them to remain on your skin. * Don’t inhale dust - it may be injurious to

power tools such as drill, sander, bench grinder etc. v Do use a barrier cream on your hands

health (see Asbestos heading). *¥ Don’t allow any spilled oil or grease to

protect your skin from infection as well as

remain on the floor - wipe it up en away, before someone slips on it.

but make sure your hands aren’t left slippery. Note that long-term contact with

* Don’t use ill-fitting spanners or other tools which may slip and cause injury.

_ used engine oil can be a health hazard. vDo keep loose clothing. (cuffs, ties etc.

* Don’t lift a heavy component which may be beyond your capability - get assistance.

and long hair) well out of the way of moving mechanical parts. eZ aed

prior to undertaking. dirty jobs - it will making the dirt easier to remove afterwards; _

diluted,

is very

corrosive

and

should not be allowed to contact the eyes or skin. Always wear rubber gloves and goggles or a face shield. If you ever need to prepare electrolyte yourself, always add the acid slowly to the water; never add the water to the acid. '

Electricity @ When using an electric power tool, inspection light etc., always ensure that the appliance is correctly connected to its plug and that, where necessary, it is properly grounded (earthed). Do not use such appliances in damp conditions and, again, beware of creating a spark or applying excessive heat in the vicinity of fuel or fuel vapour. Also ensure that the appliances meet national safety standards. @ A severe electric shock can result from touching certain parts of the electrical system, such as the spark plug wires (HT leads), when the engine is running or being cranked, particularly if components are damp or the insulation is defective. Where an electronic ignition system is used, the secondary (HT) voltage is much higher and could prove fatal.

v Do remove rings, wristwatch etc., before working on the vehicle - especie the electrical system. V Do keep your work area tidy -‘itis.only

too easy to fall over articles: left around. Vv Do exercise caution when com springs for removal or installation

that the tension is applied and rele controlled

manner,

using suital

which preclude the possibility of escaping violently.

—

V Do ensure that any lifting tackle t a safe working load rating adequ job.

¥ Do get someone to check p that all is well, when working ; vehicle.

V Do carry out work in a logical si and check that everything i: ' assembled and tightened afterwal v Do remember that your veh

affects thatof yourself and doubt on any point, get profess

@lfiin spite of following these you are unfortunate enot yourself, seek medical attentio possible. :

lying

Chapter 1 Engine Contents 1 cra tee: Ache 2 BaIEMONIMNCIOIGS fas cs cee ke eck see on 3 4 ine two-stroke engine .........2. 6.056 bees Improved two-stroke engine designs — influencing gas flow ...... 5 Improved two-stroke engine designs — reed valves ............. 6 Improved two-stroke engine designs — disc valves.............. 7 Improved two-stroke engine designs — exhaust port position ..... 8 Improved two-stroke engine designs — fuel injection ............ 9 HMOMOM-SUOKEXCNOING eiys Sire ciace neents ale weds elie bone a eiv ele dodo 10 Four-stroke engine designs - valve train arrangements .......... Je Improved four-stroke engine designs — multi-valve heads ........ 12 Introduction

MMR HECINGHIVGite eee cic soa atesaincr aie Te mae ousfyBSP

All powered two-wheelers share a number of similarities, even though at first glance a 50 cc scooter seems far removed from a largeCapacity sports motorcycle. Each has two wheels, an engine and a transmission system,

which afe all held together by a framework, usually with some form of suspension

Improved four-stroke engine designs - desmodromic valves...... Four-stroke engine designs — alternatives to the poppet valve..... Four-stroke engines — valve timing Engine design — engine vibration and the importance of balance .. . Engine arrangements — single-cylinder engines ...........5..... Engine arrangements — twin-cylinder engines .................. Engine arrangements — three-cylinder engines (‘triples’).......... Engine arrangements — four-cylinder engines .................. Engine arrangements — more than four ............0 eee eeees The search for more power —bore and stroke ................. «The rOtanyeenGIne Rens Rceieyactie sie we. oem he « Gm aslo ae eee a

between that and the wheels. !n this chapter we will be looking at the various types of engine to try to establish how they work and why they come in so many diverse shapes and sizes. The engine produces the power necessary for the motorcycle to move. The principle components and assemblies we_ are concerned with in this chapter are the cylinder head, the cylinder(s) and piston(s), the connecting rod(s) and the crankshaft. With the exception of the rotary engine design, all

13 14 16 17 18 19 20 21 22 23

engines have these components, the main difference between them being in the number of cylinders and pistons, and_ their arrangement.

On almost every modern design, the engine components are housed in or bolted onto cast alloy cases. These cases are almost universally called crankcases, even though they contain rather more than just the crankshaft. On many early British designs, and until recently certain American motorcycles, the engine was entirely separate

1e¢2 Engine

Gearbox

chain case 1.1a The ‘pre-unit’ engine

A_ The right-hand side view shows the separate engine and gearbox units B_ The left-hand side view shows the primary chaincase which links the engine and gearbox and also houses the clutch

from the transmission,

and they were linked

by a chain or belt (see illustration 1.14). Modern designs almost universally house all the transmission components within the crankcases,

All internal combustion engines must arrange for four events to occur to complete one engine cycle. These are the induction, the

and are normally referred to as

compression, the ignition, and the exhaust of the fuel/air mixture.

being of ‘unit construction’ (see illustration 1.1b). This has led to the earlier arrangement being called ‘pre-unit’, for obvious reasons.

There are a few exceptions to the pre-unit or unit between

engines, which fall somewhere the two, where the transmission is in its own case rather than the

housed crankcase, with the case being bolted directly onto the crankcase rather than mounted separately on the frame (see illustration 1.1c). The most notable of these engine types are the long-running and well-proven designs

The majority of motorcycles will have either The purpose of an engine is to convert fuel into work (power). All motorcycles use internal combustion engines, and these burn fuel inside a cylinder. The energy created by the burning fuel causes the piston to move, and

this turns the crankshaft. The reason it is called an internal combustion engine is that the fuel is burned inside the engine. In an external combustion engine, such as a steam

from BMW and Moto Guzzi, and it is of course

engine, the fuel is burned externally and heats

the arrangement used in the majority of car engines.

water, which creates steam pressure to move

the piston.

a two-stroke engine or a four-stroke engine,

both Known as ‘reciprocating’ engines, and having much in common. In both types, a mixture of fuel and air is compressed inside the cylinder and then ignited by a spark. The mixture burns very quickly, and in doing so it expands, pushing the piston down the cylinder bore. The piston is connected to the crankshaft by a connecting rod, and its up and down (or reciprocating) movement is converted at the crankshaft into the rotary motion required to turn the rear wheel and

3350-T3

‘Gearbox

Clutch (with gearbox behind)

ae

bs

1.1b The ‘unit’ engine

BE

SB

Be eas

a

~ mares

ag Steet

S

4

1.1c¢ Engine, clutch and gearbox positions as used by Moto Guzzi

Engine thus drive the machine (see Section 3). The difference in the engines is that a two-stroke will perform the four events within two strokes of the piston (one up, one down), while a fourstroke performs the events over four strokes

four-stroke designs is the rotary engine. This is also an internal combustion engine, but it

easy to look at a particular engine type and see clearly its good and bad points. The level of technology now applied to engine design and manufacture has led to a situation where almost any drawback can be engineered out of the design, though often at the expense of simplicity. Later in this Chapter we will examine the two-stroke and four-stroke engines in greater detail, but before looking at

works

the differences between them, let us deal with

of the piston. The exception to the established two- and

on

a rather

different

principle

to

conventional two- and four-stroke designs. Further details of the rotary engine can be found in Section 23.

their similarities.

Two-stroke or four-stroke? Having set aside the rotary engine, there remains the choice of two-stroke or fourstroke units. Each has its own advantages and disadvantages,

and this is why neither

has ever managed to oust the other. In its simplest form the two-stroke unit is by far the less complicated of the two, and is thus cheaper to manufacture. In the past this has been the main reason for its widespread use in scooters and lightweight motorcycles. The simple two-stroke does have its drawbacks, though, and at one stage its disappearance seemed possible because of the insurmountable problems of high noise and pollution levels. In fact it has actually been banned from road use in certain parts of the world for those reasons. In recent years the two-stroke engine has become an altogether more sophisticated device,

and the advances

are such

more

refined, however,

All reciprocating engines have a number of basic

parts

in

common,

and

these

are

recognisably similar even between the extreme examples of a two-stroke scooter and a four-stroke tourer. Two of these are the cylinder and the piston. To convert the fuel/air mixture into useful work it must be burnt in a carefully controlled manner and the resulting energy changed into movement. The combustion takes place in the cylinder and the energy produced causes the piston to move (see illustration 1.3a).

1) A mixture of fuel together with the necessary amount of air is introduced into the cylinder, above the piston. The piston, with piston rings that fit around it so that it is a tight fit in the cylinder bore to prevent leakage, is pushed upwards and the mixture is compressed. 2) The fuel air mixture now occupies a much smaller space than it did at atmospheric pressure. This effectively concentrates the energy contained in the fuel, allowing the maximum amount of power to be extracted when it is burnt. 3) At the appropriate moment a spark jumps across the spark plug electrodes, igniting the mixture. This burns very quickly, and can be considered almost a controlled explosion. The resulting hot gases rapidly increase the pressure in the cylinder, forcing the piston down with far more energy than was required to compress the mixture originally.

The crankshaft The controlled combustion of fuel in air can be used to produce power. This process is repeated many times every minute (up to sixteen thousand on some engines) to produce a relatively continuous source of motive power. In the present form, however, it is of little use in driving a motorcycle; we must first convert it to rotary motion.

that it

remains a popular choice for many applications. But with the exception of scooters and commuter-type motorcycles, the ‘low-cost’ aspect has largely disappeared, and the modern performance two-stroke is now used primarily in sports or racing machines because of its light weight and the power it produces when highly tuned. It is worth noting that certain major car manufacturers have been testing two-stroke engines in small cars. The four-stroke engine was traditionally chosen for larger machines because of its superior spread of power and fuel economy. Its main drawback was the _ higher manufacturing cost and relative complexity, and this made it a bad choice for smaller capacity engines. Just as the two-stroke became

The cylinder and piston

so did the

Spark plug Compressed mixture

Cylinder wall Ascending piston compresses fuel/air mixture

Fuel/air mixture at atmospheric pressure

Spark at plug electrodes ignites mixture

four-stroke, and over the years the distinction between the role of each type blurred; small four-strokes became just as good a proposition as large two-strokes. In the end, two-stroke and four-stroke engines can be viewed as two means to the

same end, namely a way of propelling a vehicle. Each has its supporters and detractors, and this is reflected in

Expanding gases apply high pressure on piston ...

.» forcing it down the cylinder bore

manufacturers’ catalogues, which for certain

categories often offer very similar models with two-

and

four-stroke

engine

1°3

alternatives,

leaving the choice in the hands of the prospective owner. Until recently it was quite

1.3a Compression and ignition of the fuel/air mixture in the combustion chamber

1¢4 Engine crankshaft, the flywheel picks up momentum and this is used to carry the piston back up the cylinder for the process to continue.

B

Similarly, if in the hand-operated version we

Piston

assume that the wheel is turned only by pushing in one direction (rather than pulling in the other as well), the momentum created will keep the flywheel turning until it is in the right

Small-end bearing

position to be pushed round again. To allow our example crankshaft to work, one or two refinements are needed. Firstly,

Connecting rod

there has to be some sort of bearing between the lower or big-end of the rod that connects the piston and the flywheel, to reduce friction. This can be a bush, or a ball or needle roller Flywheel

Big-end bearing

1.3b How the crankshaft converts linear motion into the rotary motion required to turn the rear wheel

A_ By alternately pushing and pulling on the handle, the flywheel can be made to revolve. At the two extremes of the stroke there will be no significant force applied to the flywheel, but stored energy, or momentum, will carry it through these dead points. B Compare this with (A). The pushing force applied by arm and hand through the handle has been replaced by the piston and connecting rod assembly through the big-end bearing and crankpin.

bearing, fitted into the big-end eye and engaging over the crankpin. Similarly, at the upper or small-end of the connecting rod, it will be necessary to allow the piston to rock in relation to the connecting rod. Again, a bush or bearing is used in the small-end eye, and the piston is located by a short pin, known as a gudgeon pin, piston pin or wrist pin. In a working example of an engine there is normally a flywheel on each side of the connecting rod big-end, and they are connected by the crankpin, which the connecting rod runs on (see illustration 1.3c). The flywheels are carried by a central shaft that runs in bearings on each side, these

being fitted into a light alloy casing, or crankcase. The cylinder is held in the correct position by being bolted to the crankcase, or on many modern sports bikes by being part of the crankcase, in which the crankshaft runs.

The principle of the crankshaft is well known and is employed by many people every day. When you ride a bicycle or wind down a car window, you are converting a more or less linear movement into a rotary one, and you can see the comparison between a hand-operating a flywheel and a piston

turning

a crankshaft

in an

engine

illustration 1.3b). The flywheel performs a very important role; as the piston is pushed down the cylinder bore and turns the

Note: Crankshaft flywheels are commonly known as ‘webs’, and are often not round (for

reasons that will be covered later).

Spark plug

(see

Cylinder Piston

Small-end

Transfer port

Connecting rod

Crankpin

1.3c The crankshaft, connecting rod and

piston assembly from a ‘parallel’ twin cylinder engine

Big-end

A Crankpin

1.4a The two-stroke engine in its simplest form

B Shaft

C Flywheels

Engine

Having established the mechanical requirements of a simple internal combustion engine we can now look at ways of making it run as a suitable power source for a motorcycle. The simplest of these in mechanical terms is the piston-ported twostroke (see illustration 1.4a). The drawing

———e

shows the engine in section, and you should be able to identify the engine components shown in the previous illustrations. You will notice that the cylinder bore has gained a few holes in its surface. These are known as ports and are fundamental to twostroke operation. The inlet and exhaust ports are obvious enough - the inlet port allows the

: