Motor vehicle machnic's textbook

Motor Vehicle

Mechanic's Textbook

Fifth Edition

F. K. Sully

Heinemann Professional Publishing

Heinemann Professional Publishing Ltd

Halley Court, Jordan Hill, Oxford OX2 8EJ

OXFORD LONDON MELBOURNE AUCKLAND

First published by Newnes-Butterworths 1957

Second edition 1959

Reprinted 1960, 1962, 1963, 1965

Third edition 1968

Reprinted 1970, 1975

Fourth edition 1979

Reprinted 1980, 1982

Fifth edition published by Heinemann Professional Publishing 1988

© F. K. Sully 1988

British Library Cataloguing in Publication Data

Sully, F. K.

Motor vehicle mechanic's textbook. -

5th ed.

1. Motor vehicles

I. Title

629.2 TL145

ISBN 0 434 91884 9

Typeset in Great Britain by Keyset Composition, Colchester

Printed in Great Britain by L. R. Printing Services, Crawley

Preface to the Fifth Edition

Present-day production of motor vehicles in all parts of the world

necessitates the availability of fully trained service mechanics if these

vehicles are to be maintained in a state of efficiency and ensure a viable

capital investment for the company or private owner. The development

of the natural resources of many home and overseas areas relies largely

on the satisfactory operation of commercial and public service vehicles,

and this, in turn, is entirely dependent on correct maintenance and

repair.

In recent years the replacement of complete assemblies - rather than

the repair of individual items from the unit - has become the mechanic's

standard procedure. With the increasing application of the micro￾computer to motor vehicle control systems, fault diagnosis has

necessarily become more sophisticated. However, in spite of such

changes, a simple and clear understanding of basic principles remains

fundamental to satisfactory work and to job satisfaction.

Motor Vehicle Mechanic's Textbook covers various City and Guilds

course syllabuses. Special attention has been paid to preserving the

balance between theory and practice, a sound knowledge of both being

essential to the art of diagnosis. The book will also prove useful to those

engaged in the maintenance, repair and overhaul sections of the motor

industry, as well as to motorists who wish to know more about their

vehicles.

For this Fifth Edition the text has been substantially revised and is

illustrated by over 200 line illustrations. The SI system of units is

employed throughout and, as a few non-SI units remain in motor vehicle

usage, a comprehensive conversion table is included.

F. K. Sully

Chapter 1

Calculations and science

1.1 International system of units (SI)

The Systeme Internationale d'Unites was adopted in 1960 as the title for

an MKS A system based on the metre (m), the unit of length; the

kilogram (kg), the unit of mass; the second (s), the unit of time; the

ampere (A), the unit of electric current; the kelvin (K), the degree of

temperature; and the candela (cd), the unit of light intensity.

Associated with these basic units are a variety of supplementary

derived units which are adopted worldwide.

Derived units

Physical quantity SI unit

Force newton

Work, energy, quantity of heat joule

Power watt

Electric charge coulomb

Electrical potential volt

Electric capacitance farad

Electric resistance ohm

Frequency hertz

Unit symbol

N = kg m/s2

J

W

Nm

J/s

C = As

V =

F =

W/A

As/V

Ω = V/A

Hz = s"1

Multiplying factors

Factor

106

103

102

10

10"1

10"2

10"3

10~6

Prefix

mega

kilo

hecto

deca

deci

centi

milli

micro

Symbol

M

k

h

da

d

c

m

μ

Motor Vehicle Mechanic's Textbook

1.2 Mensuration

Area

Square Z2

Rectangle lb

Parallelogram Ih

Triangle \lh

Circle irr1

where: / = length of side

b = breadth

h = perpendicular height

r = radius (smallest)

R = radius (largest)

Annulus Tr{R + r){R-r) π

circumference

diameter = 3.1416

The perimeter of a circle is 2irr or πά, where d = 2r is the diameter.

Solids

Solid

Cube

Square prism

Cylinder

Cone (slant height /)

Sphere

Volume

I

3

Ibh

irfh

Total surface area

6P

2(lb + bh + hl)

2nr(r+h)

7rr(r + /)

Figure 1.1 shows a circle, a cylinder and a cone.

Figure 1.1 Circle, cylinder, cone

Calculations and science

1.3 Geometry

In any triangle the sum of the three angles is two right angles, 180°. The

longest side is opposite the largest angle and the shortest side opposite

the smallest angle.

In a right-angled triangle, the sum of the other two-complementary￾angles is 90°. The longest side, opposite the right angle, is called the

hypotenuse.

In any right-angled triangle the square on the hypotenuse is equal to

the sum of the squares on the other two sides. This - Pythagoras' -

theorem is useful when checking or setting out 90°. A triangle can be

formed whose sides are in the proportion 3:4:5 or 5:12:13; either will

ensure a right angle opposite the longest side (Figure 1.2).

32 + 42

= 52

9 + 16 = 25

52

+ 122

= 132

25+ 144= 169

l

2+(v /

3 ) 2

= 22

1 + 3 = 4

V 3 = 1.732

12

+ 12

=(V2) 2

1+1 = 2

V 2 = 1.414

Figure 1.2 Pythagoras' theorem

3

Motor Vehicle Mechanic's Textbook

1.4 Trigonometry

In a right-angled triangle, given one of the complementary angles, the

side opposite the given angle is called the opposite side and the side

nearest the given angle is called the adjacent side; the remaining side is

the hypotenuse (Figure 1.3).

Adjacent Adjacent

Figure 1.3 Trigonometric ratios

All right-angled triangles having one complementary angle of a given

size are similar in shape, regardless of size. The lengths of their sides bear

the same ratios to one another, and these are called the trigonometrical

ratios. Thus:

length of opposite side

length of hypotenuse

length of adjacent side

length of hypotenuse

is called the sine (sin) of the angle

is called the cosine (cos) of the angle

length of opposite side .

length of adjacent side

is called the tangent (tan) of the angle

For a given angle, each trigonometrical ratio has only one value, since

whatever the size of the triangle the lengths of the sides will bear the

same ratio to each other. The trigonometrical values are available from

tables and calculators, and facilitate the solution of some workshop

problems.

4

Calculations and science

1.5 Mass and weight

A 'body' contains a certain amount of 'stuff' or matter called its mass.

The unit of mass is the kilogram (kg).

The pull of the earth - the force of gravity - acting on this mass is the

weight ot the body.

Owing to its mass a body has inertia - that is, it resists being

accelerated or decelerated and will remain at rest or continue moving at

a uniform speed in a straight line unless acted upon by an external force.

1.6 Density

Density is the mass of a substance per unit volume (kg/m3

). The density

of water is, for practical purposes, 1000 kg/m3

or 1 kg/1. (The litre (1) is

KT3

m3

.)

1.7 Relative density or specific gravity

The ratio

mass of a substance

mass of an equal volume of water

Table 1.1

Substance Relative density

Oxygen 0.0014

Cork 0.22

Paraffin/petrol 0.7/0.8

Water 1.0

Magnesium 1.7

Carbon 2.0

Glass 2.6

Aluminium 2.7

Chromium 6.6

Tin 7.3

Iron/steel 7.2/8.0

Copper 8.3

Nickel 8.9

Molybdenum 10.0

Lead 11.4

Mercury 13.6

Platinum 21.5

In many cases only approximate figures can be given

Motor Vehicle Mechanic's Textbook

is called the relative density of the substance, and represents how many

times it is heavier or lighter than the same volume of water (Table 1.1).

Note that relative density has no units.

1.8 Speed and acceleration

Speed is measured as metres per second (m/s), or sometimes more

conveniently as kilometres per hour (km/h). Useful conversions are 5

m/s = 18 km/h and 0.278 m/s = 1 km/h.

Acceleration or deceleration is the rate of change of speed. It is

measured as metres per second per second or m/s2

.

An increase in speed from 36 km/h to 72 km/h during 4 s (that is from

10 m/s to 20 m/s) is an average acceleration of 2.5 m/s every second or

2.5 m/s2

.

If the speed increases from u m/s to v m/s during t seconds, then the

average acceleration a m/s2

is given by

v-u 2

a = m/s

t

1.9 Acceleration due to gravity

In a vacuum all freely falling bodies, whatever their size, shape or mass,

have the same acceleration at a given place (Figure 1.4). This acceler￾ation, given the symbol g since it is due to the force of gravity, has the

value of about 9.81 m/s2

at sea level near London, 9.78 m/s2

at the

equator and 9.83 m/s2

at the poles.

The acceleration of objects falling in the atmosphere depends on their

wind resistance. For example, depending on the conditions, the human

body reaches a terminal velocity of some 200 km/h, when the wind

resistance equals the force of gravity and no further acceleration can

occur. A motor vehicle is also subject to wind resistance; a typical

speed-time graph for a vehicle is shown in Figure 1.4.

1.10 Force

A force may be simply described as a push or a pull on a body - an action

which tends to move a body from rest or alter its speed or direction of

movement.

Force is measured in newtons (N); 1 newton is the force needed to

give a mass of 1 kg an acceleration of 1 m/s2

. The acceleration of 1 kg due

to gravity is about 9.81 m/s2

; hence the weight of 1 kg is about 9.81 N.

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Motor Vehicle Mechanic's Textbook

1.11 Work

Work is done when a force overcomes resistance and causes movement.

Work is measured by the product of the force and the distance moved in

the direction of the force, the unit being the joule (J):

W = Fs

where W = work done in joules (J), F = force in newtons (N), and

5 = distance in metres (m) moved in the direction of the force.

If the force causes no movement, then no work is done.

1.12 Power

Power is the rate of doing work. The unit, the watt, is a rate of working

of 1 joule per second (1 J/s):

power = work done per second

= newton x metre per second

= joule per second

= watt

1.13 Torque

When a force acts on a body pivoted on a fixed axis, the product of the

force perpendicular to the radius, and the radius at which it acts, is

termed the turning moment of the force or torque. Torque is measured in

newton metres (Nm) (to distinguish it from work). From Figure 1.5:

T= Fr

Figure 7.5 Torque

8

Calculations and science

where F = force in newtons (N), r — radius in metres (m), and

T = torque in newton metres (Nm).

1.14 Work done by torque

The work done by the torque per revolution is the product of the force

and the distance moved in the direction of the force - that is, the

circumference:

W= FX2T7 T

= 2nFr

where W = work done in joules (J), F = force in newtons (N), and

r = radius in metres (m) at which the force acts.

The work done in n revolutions will be:

W = lirFrn joules

If n revolutions are made per second, then the work done per second is

lirFrn joules. This is the power produced:

P = lirFm

or

P = 2πΤη

where P = power in watts (W), Fr or T = torque in joules (J), and

n = rotational speed (rev/s).

Using these formulae, the power can be calculated from the torque

and speed of a shaft.

1.15 Principle of moments

When a body is at rest or in equilibrium (a state of balance), the sum of

the clockwise turning moments about any axis, real or imaginary, is

equal to the sum of the anticlockwise moments about the same axis.

Were this not the case, the unbalanced moment would cause the body to

rotate about the chosen axis.

As an example, a beam of negligible weight has loads as shown in

Figure 1.6 and is pivoted at P so as to be in equilibrium. Taking moments

about P:

sum of anticlockwise moments = sum of clockwise moments

10 x (0.08 + 0.06) 4-12 x 0.06 = 4 x 0.53

1.40 + 0.72 = 2.12

|2.12Nm = 2.12 Nm

9

Motor Vehicle Mechanic's Textbook

The pivot P must exert an upward force on the beam equal to the sum of

the downward forces of 10 N + 12 N + 4 N. This upward force of 26 N

has no turning moment in this case since it is acting through the axis.

If we take moments about an imaginary axis at B, then:

sum of anticlockwise moments = sum of clockwise moments

10 x 0.08 + 26 x 0.06 = 4 x (0.53 + 0.06)

0.8+1.56 = 4x0.59

2.36 Nm = 2.36 Nm

The force of 12 N exerts no turning moment in this case as it is acting

through the chosen axis.

o oo £] vo 4 N

J .

ό ,[. d , | 0.53m -—-■ ~|

26 N

Figure 1.6

1.16 Centre of gravity

The centre of gravity (c. of g.) of a body can be regarded as the point

where, if the whole weight of the body were concentrated, it would

produce a moment of force about any axis equal to the sum of the

moments of force of each part of the body about the same axis. When

inertia force is involved the centre of gravity becomes the centre of

mass.

As an example, consider a body consisting of weights of 10 N, 12 N

and 4 N located on a beam of negligible weight, as shown in Figure 1.7.

Let L be the distance of the c. of g. of the body from an axis, say 0.01 m

from the right-hand end of the beam. Taking moments about that axis:

total weight of body (concentrated at c. of g.)

x distance of c. of g. from any axis = sum of the moments of each part

of the body about the same axis

(10+12 + 4)xL = 4x0.01 + 12x0.60+10x0.68

26 xL = 0.04 + 7.20 + 6.80

L =

14.04

26

= 0.54 m

10

Calculations and science

E

10Ngl2 N

|«o 4* 0.59 m

1* £ H . Centre of gravity Axis °f

reference

Figure 1.7

The c. of g. is 0.06 m from the 12 N weight and 0.53 m from the 4 N

weight, and this is the pivot point about which the body would balance.

1.17 Couple

When two equal forces act on a body so that their lines of action are

parallel but opposite in direction, they form a couple tending to rotate

the body.

The torque produced by a force acting on a pivoted body can be

regarded as the result of a couple formed by the original force and an

equal and opposite reaction at the pivot (Figure 1.8).

Figure 1.8 Couple

A couple can only be balanced by another couple of equal value

acting in the opposite direction of rotation and not by a single force.

1.18 Inertia force

All bodies have inertia - the tendency to remain at rest or in uniform

motion. For example, when a piston is decelerated from maximum

speed to a dead centre position and accelerated in the opposite

direction, it exerts an inertia force on the connecting rod.

The value of the inertia force depends upon the mass of the body and

the acceleration or deceleration:

F = ma

0.01 m

4N

I

11

Motor Vehicle Mechanic's Textbook

where F = force in newtons (N), m = mass in kilograms (kg), and

a = acceleration or deceleration in metres/second/second (m/s2

).

Thus to reduce the inertia forces produced by the reciprocating parts,

their mass must be kept as small as possible.

1.19 Centrifugal force

A moving body travels in a straight line at uniform speed unless acted

upon by an external force. If made to travel in a circle, the body

exerts centrifugal force acting outwards from the centre upon the

constraining member. The equal and opposite constraining force is

termed centripetal.

r

= ma?r

where CF = centrifugal force in newtons (N), m = mass in kilograms

(kg), r = radius in metres (m), v = linear velocity in metres/second

(m/s), and ω = angular velocity in radians/second (rad/s), where 1

revolution = 2π radians.

1.20 Mean piston speed

The product of twice the stroke, measured in metres, and the rotational

speed (rev/s) of the engine gives the mean or average piston speed in

m/s.

The higher the mean piston speed, the greater are the inertia forces of

the reciprocating parts. The maximum mean piston speed usually

employed with current production engines is about 16 m/s.

1.21 Friction force

It is found that the horizontal force required to drag a body over a

smooth, level, dry surface is approximately a constant fraction of the

perpendicular force between the surfaces. In Figure 1.9, W is the load or

W N

1

FN

Figure 1.9 Friction

12