Automotive mechanics (volume i)(part 1, chapter2) workshop practices

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17

Chapter 2

Workshop practices

Automotive service procedures
Workshop operations
Production processes
Fasteners
Locking devices
Screw threads
V-threads
Workshop manuals
Vehicle identification
Technical terms
Review questions


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part one introduction to motor vehicles

Many different jobs are undertaken in an automotive
workshop. These range from general service and
maintenance to large repairs and complete overhauls.
They include electrical as well as mechanical items.
Body repairs are usually carried out in a separate body
repair workshop.

Automotive service procedures
All automotive service jobs have certain procedures.
Procedures are ways of doing things. A simple job
might consist of only one or perhaps two procedures,
while a major repair will involve a number of them.
Following are some procedures that an automotive
technician may have to carry out.
Measuring
Measurements may have to be taken of length,
thickness, diameter or angles. In some operations, the
pressure, vacuum, voltage or revolutions per minute
have to be measured.
Accuracy of measurement is important. Often,
measurement of the amount of wear determines the
suitability of a part for further use. In other instances,

measurement is used to determine the repair to be
carried out.
Taking some measurement or making a check may
often be the first step in an automotive service job, or
the final adjustment after completing a repair.
Figure 2.1 is an example, where a valve stem is being
measured for wear.

made up of a number of smaller parts which will have
to be removed or separated to gain access to the faulty
one. This can be a comparatively simple operation, or
it might require an involved dismantling procedure.
A person undertaking such work needs certain
skills and knowledge, in order to follow a suitable
dismantling sequence and to avoid damage and
confusion. Manufacturers’ service manuals provide
this detailed information.
Cleaning
Automotive components must be cleaned of dirt and
grease before they are dismantled, otherwise dirt will
be carried into the component during dismantling.
After dismantling, the parts are cleaned so that they
can be inspected and prepared for reassembly.
There are various methods of cleaning automotive
parts, which range from using a small brush and kerosene
on small parts, to steam cleaning the complete engine or
vehicle. High-pressure water spray is another method that
is used to clean large parts. Cleaning baths or tanks are
also used. With these, the part is completely immersed in
cleaning fluid which dissolves the grease and dirt.

Inspecting
Parts can become worn from normal use, or they can
suffer wear or damage from abnormal conditions of
operation or abuse. Parts can also be damaged from
careless dismantling or handling.
Dismantled parts are always checked, and often
measured to determine if they are suitable for further
service, or if they need to be replaced with new parts.
Workshop manuals provide specifications for the
various parts. For parts that are subject to wear, the specifications include the original size and also the wear
limits. Parts that are worn but are still within
specifications can be reused.
■ Parts that are suitable for reuse are classed as
serviceable. Parts damaged or worn beyond the
specified limit are classed as unserviceable.

figure 2.1

Measuring – a valve stem is being checked
for wear with a micrometer TOYOTA

Dismantling
When measurements or checks indicate that something
is at fault, repair work is needed, and it becomes
necessary to dismantle the part. Most components are

Replacing
New parts are referred to as replacement parts,
because the old part is replaced with a new one. Parts
that might have to be replaced are those that are

normally renewed during a service, such as oil filters
(Figure 2.2), parts that are worn or damaged, and parts
found to be unserviceable during repair or overhaul of
engines and components. Replacement parts can also


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chapter two workshop practices

figure 2.2

Replacing – parts such as oil filters are
renewed as part of a normal service

be re-manufactured to original specifications using the
old assembly. Engines and transmissions are often
exchanged in this way to specialist workshops who remanufacture them.
Reassembling
This involves putting the parts back together in the
correct sequence. It also involves attention to detail, so
that not only do the parts go back together again but
the repaired component becomes ‘as good as new’.
This is achieved by careful installation and

observation, use of correct tools in the correct way
(such as a tension wrench for correct tightness of
bolts), and generally good workmanship.

figure 2.3

19

Installing – a special tool is being used to
install an oil seal in a housing

Adjusting
Most parts of a motor vehicle require some adjustment
after a repair has been carried out. Adjustments
compensate for wear and restore the original settings
laid down by the manufacturer. This information is
listed in the manual for the particular vehicle.
Manufacturers supply specifications of clearances,
wear limits and adjustments. A technician is able to refer
to these and make any adjustments needed to restore the
original specifications. Where excessive wear has
occurred, adjustments may not be able to provide
correction and one or more parts will have to be renewed.
Tappets are an example of parts that have to be
adjusted, although many engines now have hydraulic

Installing
The term installing is used in relation to refitting or
replacing a part or component in its original location.
This is a similar operation to reassembling and the

terms are often interchanged. For example, parts can
be installed (reassembled) in a gearbox, or the gearbox
can be installed in the vehicle. Installation can also
relate to fitting new equipment or accessories.
Replace is another term and this can be used to
denote install or refit. It can also be used to mean renew,
where a worn part is replaced by a new one. The new
part is usually referred to as a replacement part. Remove
and replace (R&R) is a term used when an assembly has
to be removed to do another job. An example would be:
R&R the transmission to replace the clutch.
■ Special tools are sometimes needed to install parts
such as oil seals and bearings (Figure 2.3).

figure 2.4
feeler gauge

Adjusting – adjusting screws enable the valve
clearance to be set to the thickness of the
MITSUBISHI


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part one introduction to motor vehicles

tappets which do not require adjustment. With the type
of tappets shown in Figure 2.4, a screw adjustment is
provided. The clearance between the rocker arm and
the valve tip can be checked with a feeler gauge and
set to specifications.
Lubricating
Many moving parts in a motor vehicle require lubrication. Engine parts are provided with pressure
lubrication, but some other parts require periodic lubrication or a check of their lubricant. Wheel bearings are
lubricated with grease and must be repacked after
dismantling.
During reassembly, many parts are given a coating
of oil or grease. This provides initial lubrication and
also aids reassembly. This applies particularly to
engine and transmission parts.
Diagnosing
This is sometimes referred to as ‘troubleshooting’ or
‘fault-finding’. When trouble is apparent, not only in the
engine but in the transmission, drive line, suspension or
other parts and the fault is not an obvious one, it is
necessary to diagnose the source of the problem.
Guessing is not good enough and a systematic series
of checks needs to be made to isolate the fault. These
checks are often assisted by instruments, but a basic
requirement is a sound knowledge of the principles and
operation of the particular component being checked.
Many vehicles have a self-diagnosis system built

into their electronic control units. This automatically
identifies any faults that occur in the systems that they
control. An instrument connected into the system
enables information about the fault to be obtained.

■ Use of hand tools for this type of work is covered in
Chapter 3.
Machining
Machining is, in general terms, work that is done with
a machine tool. Automotive machining includes valve
refacing and seating, cylinder reboring, cylinder-head
refacing and flywheel refacing. Machining might also
be carried out when reclaiming a part after welding.
Specific skills are required to operate the various
machines that are used.
Grinding
Workshop grinding that is done by hand is often called
off-hand grinding. Grinding can be used to prepare
parts for welding, to finish after welding, or to shape
parts being fabricated. Grinding is also used to sharpen
and maintain small workshop tools.
Grinding is used to recondition engine parts, but this
is done in special machines. For example, a valverefacing machine is used to reface engine valves, and a
crankshaft-grinding machine is used to accurately grind
the journals of crankshafts during engine reconditioning.
Turning
Parts are turned to shape in a lathe and this is a type of
machining. The part is mounted in the lathe and
turned, or rotated, while a cutting tool is used to
remove metal to produce the shape and size required.

The lathe operator needs special skills to work the
controls of the lathe to produce the desired result.
Lathes can also be used to check whether a shaft is
straight. The shaft is mounted between the lathe
centres and rotated by hand. A dial gauge mounted
against the shaft will show any runout.

Workshop operations
Apart from straight-ahead vehicle repairs and service,
there are various other jobs that a mechanic might be
called upon to do. These could be repairing or
reconditioning parts which have been dismantled,
modifying a part in some way, making a tool or a
fitting, or maintaining workshop equipment. Some of
these operations are indicated below.
Fitting
Some repairs may need hand-fitting operations, such as
drilling, threading, cutting, filing, grinding or reaming.
Skills are needed to perform satisfactory repairs with
comparatively simple hand tools.

Drilling and boring
Portable electric drills are commonly used for drilling
holes but bench drills, which are permanently mounted
on a bench, are also used.
Holes that are too large to be drilled are bored. For
example, cylinders are rebored with a boring bar. This
has a bar with a rotating cutter which is fed down the
cylinder so that it cuts a small amount of metal from
the cylinder as it goes.

Welding
The two basic types of welding are gas welding and
arc (electric) welding.


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Gas welding is carried out with an oxy-acetylene
flame, using a handpiece which burns oxygen and
acetylene supplied from cylinders. Fusion welds are
made by melting the base metal and adding a filler rod
of the same material as that being welded. Bronze
welds are made using a bronze filler rod. With
bronze welds, the base metal is heated by the flame
but is not melted. Only the filler rod melts and it
adheres to the base metal to form a weld. Gas-welding
equipment can also be used for cutting metal and for
heating.
Arc welding is carried out using the heat from an
electric arc. Welding rods that are coated with flux are
used to provide a continuous arc between the end of
the rod and the metal being welded. The arc produces

heat, melts both the metal being welded and the rod,
and forms a weld. Some arc-welding machines use a
continuous wire instead of a rod, and a gas shield
instead of flux.
Welding safety
When gas welding, special dark welding goggles must
be worn to protect the eyes. During arc welding, the
complete body must be protected from the rays
produced, which will damage eyes and burn skin.
A welding shield is used to cover the face and eyes,
and gloves to cover the hands and arms. The rest of the
body must be covered by clothing. An assistant or
observer must also be similarly protected.
■ Special safety precautions must be taken with all
welding. Refer to Chapter 7 for other safety items.
Fabricating
This refers to the process of building up a part from
bar stock, sheet or plate. Sections of the part being
fabricated may, for example, be cut from a steel plate
and the sections welded together to form the basic part.
The part might then be finished by drilling, filing or
grinding. Small fabricating jobs can be done in the
workshop.
Soldering
Solder consists of tin and lead. The process of
soldering is sometimes referred to as soft soldering to
distinguish it from some forms of brazing. Solder
melts at a relatively low temperature when it comes
into contact with a soldering iron or low gas flame.
Soldering is used for electrical connections and for the

manufacture and repair of many radiators.

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Production processes
A motor vehicle consists of a large number of parts.
Some are large and others are very small. Smaller
parts are assembled together to form components.
The parts are made in various ways and then fastened
together by a number of different methods. Parts can
be cast, formed, pressed, machined, ground, drilled,
forged, fabricated or welded.
Figure 2.5 is a section of a rear suspension. The
various parts are labelled with the processes that would
have been used to produce them. The text that follows
will provide an appreciation of the processes and how
parts are produced.
Casting
Castings are made by pouring molten metal into
shaped moulds. These are usually sand moulds for
large parts such as an engine block, but moulds can be
made of metal. Wooden or metal patterns of the shape
required are used to prepare the moulds. Castings can
be of iron, aluminium alloy, or bronze. Cast parts
include the cylinder block, cylinder head and transmission housing.
With diecasting, molten metal is forced under
pressure into shaped metal dies. Smooth castings are
produced which require little or no finishing. The
metal is usually a copper/zinc alloy. Examples of parts
produced by diecasting are body hardware, throttle

bodies, carburettors and fuel pumps.
Moulding
Moulded plastics are made by shaping the plastic in
moulds or dies. Plastic mouldings are relatively easy
and cheap to produce. Radiator grilles, dash panels,
ashtrays and bumper bars are examples of moulded
plastics. Plastic parts are much lighter than equivalent
metal parts.
Fibreglass parts, which are made of glass fibres
impregnated with special resins, are also produced by a
type of moulding. Fibreglass is used mainly for special
body parts and in some truck cabs. It is a tough,
durable material, but fibreglass parts are not as easy to
mass-produce as other types of plastics and they are
more expensive.
Extruding
This is a process of forcing metals or other material in
a plastic state through a die. Aluminium is used to
make extrusions because it has the necessary physical


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part one introduction to motor vehicles
extruding and
forming to shape

welding

forming and welding

rubber
moulding
pressing
forging and
machining
pressing and
rubber moulding
casting and
machining
machining and
grinding
forming

pressing

welding
machining and
grinding

figure 2.5

Part of a rear suspension showing the manufacturing processes used to produce the various parts

properties. Different-shaped dies can produce
extrusions with different cross-sections. Plastic parts
can also be produced by this method.
Forming and pressing
The term forming is used to describe the process of
bending heavy metal sections to shape. Parts of the
frame for a truck are made from steel, which is cut to
size and then formed, or bent, into channels or other
suitable shapes. The parts of the frame are then joined
together by welding or riveting.
Pressing is used for body panels which are
produced from sheet steel or, in some cases, sheet
aluminium. This is done with large presses which press
the metal between dies. Pressing operations can
include shaping, folding, bending and hole punching.
Production welding
Many parts are welded during manufacture and a
number of different processes are used. Some
mechanical components, such as mountings, brackets,
suspension parts and subframes, are produced by
welding their parts together.

HOLDEN LTD

Many body panels are spot-welded together. In
manufacturing plants, most of this is done by machines
referred to as robots. In the basic process, the sheet
metal surfaces to be joined are held together between

two electrodes. A high electric current is passed
through the electrodes and through the sheet metal.
The heat from the current melts the sheet metal which
is joined together to form a spot-weld. A number of
these side by side can form a continuous weld.
Forging
Some parts are produced by forging. During this
process, the metal (usually steel) is heated until it is
white-hot and then hammered to shape. In the simple
process, a steel bar is heated in a forge and is then
hammered into shape by hand.
Front axles on trucks are an example of a large
forging. Open-ended spanners are an example of a
small forging. Both items are hammered or pressed
into shape by machines and shaped dies rather than by
hand. The term drop-forging is sometimes used to
describe a process where a mechanically operated
weight, or hammer, is dropped onto the forging to
produce the shape.


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Machining operations
Various types of machine tools are used in producing
the mechanical parts of a motor vehicle. Operations
include machining surfaces (flat, round or to some
particular shape), drilling holes, threading, boring,
grinding or cutting. Machined parts include shafts
ground to size, gears with various forms of teeth,
cylinder blocks with flat surfaces and bored cylinders,
pistons which accurately fit the cylinders, wheel hubs
and axles, pulleys, pins, bearings and many other parts.

Fasteners
Fasteners used on motor vehicles include studs, bolts,
nuts, screws and rivets as well as associated parts such
as washers, snap rings, keys and cotter (split) pins. The
method of using bolts and studs is shown in Figure 2.6.
■ The terms bolt, stud and screw sometimes overlap,
but the meanings which follow are the ones usually
given to these parts.
Bolts

Classes of bolts are identified by markings on
the head

classes and their head markings. For bolts with
numbers, the higher the number, the stronger the bolt.
Some bolts with recessed heads have embossed lines:

two lines represent class 5 and three lines represent
class 7. Bolts with a plain head are usually class 4
bolts.
Bolts should always be fitted in their original
location, and a replacement bolt should be of the same
class as the original, or of a higher class.
Studs

Most bolts have hexagonal heads and are threaded for
only part of their length. Bolts are often used with nuts,
but they are also used in threaded holes. Most exposed
bolts are zinc or cadmium plated to prevent rusting.
Some bolts have to carry a greater load than others
and so bolts are made in various diameters. As well as
this, bolts are made from different steels, so that some
are stronger than others. Metric bolts are classed
according to their strength and have their heads
marked for identification.
Figure 2.7 shows a number of bolts of different

figure 2.6

figure 2.7

Methods of using bolts and stud

Studs have no head and are threaded at both ends. One
end is often a coarse thread which is screwed into a
threaded hole in a casting, while the other end of the
stud has a finer thread fitted with a nut.

Nuts
There are various types of nuts. Most nuts are
hexagonal, but square nuts are sometimes used
(Figure 2.8). Plain nuts are used with a lock washer to
prevent them from working loose. Some nuts have
slots for a cotter pin (split pin), while others are selflocking. An acorn or dome nut is used to provide a
neat finish or to protect the threaded end of the bolt.
Slotted nuts and castle (or castellated) nuts have

figure 2.8

Various types of nuts


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part one introduction to motor vehicles

slots, and the bolt or shaft on which they fit is drilled
to allow a split pin to be inserted.
When fitting a split pin, the head should fit neatly
into the slot on one side of the nut. One end of the pin

is bent over the end of the bolt and the other end is
bent back on to the flat of the nut. The ends should be
trimmed neatly to length.
Self-locking nuts
Some nuts have a built-in locking feature which
prevents them from working loose (Figure 2.9).
The nut in Figure 2.9(a) has a slot cut in the side
which has been partly closed to distort the top two or
three threads. These bind on the bolt and prevent the
nut from loosening.
The interference nut in Figure 2.9(b) has a collar of
nylon or soft metal. This binds against the thread of the
bolt and is tight enough to prevent the nut from
unscrewing.
The self-locking nut with vertical slots in
Figure 2.9(c) is made so that the top threads are tight
on the bolt. This holds the nut in position.
The palnut in Figure 2.9(d) is a thin nut which is
pressed to shape. It acts as a lock nut to prevent a
larger nut from loosening.

figure 2.10

Types of screw heads

broad heading of screws. These are sometimes referred
to as setscrews or capscrews in particular locations.
The points or ends of screws are also made in
various shapes for particular purposes (Figure 2.11).
A grub screw, sometimes referred to as a setscrew, is

used to secure a pulley or collar to a shaft, and so has a
cone point to fit into a small hole. A cup point is used
to grip against a shaft.

■ Some nuts and bolts are secured with thread-sealing
compounds, which are applied before the nut is
tightened. See later section, ‘Locking compounds’.

figure 2.11

The points of screws or bolts can be shaped
for particular purposes

Self-tapping screws

figure 2.9

Self-locking type nuts

These have coarse, tapered threads which are hardened
to enable them to cut their own thread through sheet
metal parts. A hole is drilled or punched through the
sheet metal that is large enough for the point of the
self-tapping screw to enter and the screw cuts a thread
as it turns.

Screws
Screws used for securing metal parts are threaded right
up to the head. The heads have various shapes, with
different types of slots or recesses for driving the

screw. Some are shown in Figure 2.10. Special
screwdrivers or spanners are required for the special
heads.
Certain bolts with hexagonal heads are also
threaded for their full length and classed under the

Rivets
Rivets are used to hold parts together. They are used
where parts do not normally have to be dismantled.
Pop rivets are commonly used on thin material. The
rivet is hollow, but it has a thin wire shank that enables
it to be installed with a riveting tool (Figure 2.12). The
tool grips the shank of the rivet and pulls it to spread
the hollow end of the rivet. After spreading the rivet,


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chapter two workshop practices

figure 2.14

figure 2.12

Pop rivets are used on sheet metal parts

the shank then breaks off as tension on it is increased.
Solid rivets have a head which is flat, countersunk
or oval in shape (Figure 2.13). After being installed in
the hole, the end of the rivet is formed to shape. There
are special tools to form oval heads, but a ballpein
hammer would probably be used for the occasional
small job. Forming the head also spreads the rivet in
the hole and this helps to hold the parts securely
together.

25

Keys used between a collar and a shaft

Square-section keys are also used. With these, the
shaft has a long groove (keyway) to accommodate
the key and a corresponding groove in the collar which
fits onto the shaft.
A nut or bolt and washer is used on the end of the
shaft to retain the collar or other part in place.
Splines
Splines are grooves cut into a shaft and its mating part
so that parts can be fitted together. The splines of a
shaft are known as external splines and those in the
gear or other part as internal splines. Splines can be
parallel or tapered.
A part mounted on parallel splines can slide, such
as parts of a manual transmission. With tapered

splines, such as some steering wheels on the steering
column, the parts are held firmly together.

Locking devices

figure 2.13

Solid rivets shown before installation (top)
and after installation (bottom)

Various types of locking devices are used to prevent
nuts and bolts from working loose. The type of locking
device used will depend on the importance of the part
being secured by the bolt or nut and the likelihood of it
working loose.
Lock washers

Keys
Keys and splines are used, in conjunction with other
fasteners, to secure gears, pulleys, collars and similar
parts to shafts (Figure 2.14). The key fits into a recess
or slot in the shaft, but projects above the shaft. The
collar or other part has a keyway that fits over it.
A Woodruff key is a sector-shaped key which fits
into a recess in the shaft.

Lock washers (Figure 2.15) are used under nuts and
under the heads of bolts.
Spring washers are used with larger bolts. They
compress when the nut or bolt is tightened and so

provide a spring loading which prevents the nut or bolt
from working loose.
Other types of lock washers do not compress as
much as spring washers, but they have small teeth


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part one introduction to motor vehicles

Locking compounds

figure 2.15

Lock washers

which prevent the nut or bolt from loosening. These
are used mainly with smaller bolts and nuts.

Special chemical compounds are used as locking
devices. These products are available in a range of
strengths, suitable for various purposes. The compounds

can be used for locking the threads of bolts, nuts and
studs, or helping to retain pulleys or gears on shafts.
To prevent the bolt or nut from loosening, a small
quantity of locking compound is applied to the thread
or other part during assembly. Some compounds also
act as sealers.

Snap rings or circlips
These are rings of spring steel which spring or snap
into place when installed. Smaller rings, often called
circlips, are made of round wire. Larger snap rings are
usually flat. There are external and internal snap rings
(Figure 2.16).
External snap rings are used on shafts to hold
bearings, gears or collars in place. They fit into a
groove in a shaft and have to be expanded with special
circlip pliers when being installed or removed.
Internal snap rings are used in grooves in housings
to retain bearings or other parts. They have to be
contracted when being installed or removed so that
they can pass into the hole in the housing and then be
allowed to spread into the groove.

Screw threads
There are external threads and internal threads.
Screws, bolts and studs have external threads, nuts and
threaded holes have internal threads. Threads are
produced by special machines in the manufacturing
industry, but by taps and dies in the workshop.
There are also right-hand and left-hand threads.

Most threads are right-hand, where the nut can be
screwed on to a bolt, or a bolt screwed in to a hole by
turning clockwise.
Left-hand threads are used for special purposes
where a right-hand thread is liable to work loose, such
as on some axles. The spindle of a bench grinder
usually has a right-hand thread on one end and a lefthand thread on the other.
■ Threads are not only used for fastenings, but they
are also used for transmitting motion or power, as
in a screw jack; for gauging, as in a micrometer; or
for adjustments, as for valve tappets.
Basic thread forms

figure 2.16

Snap rings or circlips

Other locking devices
Other locking devices include:

There are four common screw thread forms, which
take their name from the shape of the thread section
(Figure 2.17).
1. V-thread. This is the most common, and is used
for bolts, nuts and other fastenings. It is easily
produced in the workshop by taps and dies.

1. Tab washers. These fit under the bolt or nut and
have a tab that can be bent against a flat side of the
bolt or nut.

2. Locking wire. This is threaded through holes in two
or more adjacent bolt heads so that they hold each
other.
3. Locking plates. These have tabs and are used
between two bolts or nuts.
4. Staking. The end of the bolt or nut is staked with a
centre punch or small chisel.

figure 2.17

Types of threads


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chapter two workshop practices

2. Square thread. This is rugged in design, and used
for screw jacks, vices, clamps and similar tools.

27

V-threads

4. Buttress thread. Where there is a thrust against the
screw in one direction only, a buttress thread can be
used. Some vice threads and clamp threads are of
this form.

A number of different forms of V-thread have been
used for bolts, nuts and similar fastenings. The major
manufacturing countries developed their own thread
system, and so there were different thread forms which
were not interchangeable.
The heads of bolts and nuts also presented a
problem because their size was related to the particular
thread system. Different spanners were required for
use with the different systems.

Thread terminology

Coarse and fine threads

Special terms are used to describe the various parts of
threads. These are shown in Figure 2.18 and explained
below.

Coarse threads and fine threads are generally used for
different purposes. Coarse threads may be used
for threaded holes in castings, where the metal is fairly
brittle and requires a larger amount of metal in the
thread.
Fine threads are mostly used for bolts and nuts
where the material is tougher and greater strength is

obtained by using a larger number of fine threads.

3. Acme thread. This is used particularly on lathe lead
screws. The sloping sides of the thread allow the
half-nuts, which are used as a form of clutch, to be
easily opened and closed on the thread.

1. Thread form. This is the shape of the particular
thread.
2. Crest. The top of the thread. This can be flat or
round for the particular thread form.
3. Root. The bottom of the thread. This can also be
curved or flat for a particular thread form.
4. Angle. The angle of a V-thread.
5. Major diameter. The outside diameter.
6. Minor diameter. This is the smallest diameter of the
bolt (measured at the root of the thread).
7. Pitch. The distance from a point on the crest of one
thread to a corresponding point on the crest of the
next thread.
8. Lead. The lead or distance that the screw moves for
one turn. For a single-start thread, the lead and the
pitch are the same. For a two-start thread, the lead
would be twice the pitch.

■ Tables 2.1 and 2.2 show the thread pitch for metric
sizes and the threads per inch for common bolt
sizes for other systems.
Metric threads
The metric thread system is an international standard

system for V-threads which is now used on all motor
vehicles.
Table 2.1 shows the pitch, the tapping size, and the
spanner size for various diameters. The sizes are all
shown in millimetres.

table 2.1 Metric threads, international pitch showing
sizes in millimetres
BOLT DIAMETER

4
5
6
8
10
12
12
14
16
20
24

PITCH

TAPPING SIZE*

0.70
0.80
1.00
1.25

1.50
1.25
1.75
1.50
2.00
2.50
3.00

3.5
4.0
5.0
7.0
8.5
10.0
10.0
12.0
14.0
17.5
21.0

* Approximate size for workshop use

figure 2.18

Parts of a screw thread

SPANNER SIZE

7
8

10
13
17
19
19
21
24
30
36


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part one introduction to motor vehicles

Unified threads

Thread-pitch gauge

Before the introduction of a standard metric thread
system, a Unified thread system was used in Englishspeaking countries. Vehicles from Britain, North
America and Australia all had this thread.

There are two unified threads: Unified National
Coarse (UNC) and Unified National Fine (UNF).
Originally, both Britain and the USA had their own
standard thread systems. Vehicles produced in Europe,
other than in Britain, used metric threads.

A gauge for measuring the pitch of threads is used as
shown in Figure 2.19. The gauge has a number of
blades with teeth which are the shape of various
threads. The blades are marked with the pitch of the
thread and can be used on external and internal
threads. When the correct blade is selected, it will fit
neatly into the thread.

British standard threads
British Standard Whitworth (BSW) is a coarse thread
of British origin which has a similar pitch to the UNC
thread. British Standard Fine (BSF) is a finer thread.
The sizes are in inches.

■ A bolt can be used in a similar way. Place their
threads together and hold them up to the light. If
they have the same pitch and thread, they should be
a neat fit.

table 2.2 British and Unified threads, showing threads
per inch
BOLT SIZE (INCHES)

1/8

3/16
1/4
5/16
3/8
7/16
1/2
9/16
5/8
3/4
7/8
1

BSW

BSF

UNC

UNF

40
24
20
18
16
14
12
12
11
10

9
8

–
32
26
22
20
18
16
16
14
12
11
10

–
–
20
18
16
14
13
12
11
10
9
8

–

–
28
24
24
20
20
18
18
16
14
12

figure 2.19

A thread-pitch gauge has a number of blades
for different threads

Workshop manuals
American National Fine (ANF)
This thread was originally developed by the Society of
Automotive Engineers (SAE) and known as the SAE
thread. It was later adopted as an American standard.
It is similar to the UNF system.
Pipe threads
Threads on pipes, also referred to as gas threads, are
often tapered throughout their length. The taper is used
to form a seal between the pipe joints. The size of pipe
threads refers to the inside diameter of the pipe on
which it is normally used and not to the outside
diameter of the pipe. Some plugs on transmissions and

rear axles used tapered threads.

Vehicle manufacturers publish workshop manuals for
their vehicles. In some instances, technical information
is also available on compact discs. As well as this, an
owner’s manual is supplied with each new vehicle.
Workshop manuals are divided into a number of
sections, each covering a major part of the vehicle.
There are procedures for major and minor repairs as
well as information on maintenance, adjustments, fault
diagnosis and specifications.
Manuals are often divided into a number of
volumes, with separate volumes for the engine,
transmission, body and so on. An automotive
mechanic must be able to refer to workshop manuals
and interpret the information that they contain.
Workshop manuals have a contents page at the
front of the book and a contents list at the start of each


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chapter two workshop practices

29

section. These should be the starting point when
looking for information.

this book. There are a number of different types of
illustrations.

■ Workshop manuals are also known as service
manuals or repair manuals.

1. Line drawings. These show only one view of an
object and so have only two dimensions – width
and height, depth and height, or depth and width.

Technical information

2. Pictorial drawings. These have three dimensions –
width, height and depth. They show the full shape
of the object.

The following types of technical information can be
found in workshop manuals.
1. Descriptions. The features and construction of a
component or a system are often described at the
start of a section as a means of introducing a
component.
2. Principles of operation. The principles of operation
of various components and systems are described –
it is necessary to know how things function before

they can be properly serviced, particularly when
diagnosing problems.
3. Maintenance and service. These are procedures that
should be carried out at regular intervals to
maintain the vehicle in a sound condition.
4. Service adjustments. Manuals include descriptions
of how adjustments are carried out and when they
should be done.
5. Tune-up procedures. These are the services that
should be done periodically to maintain engine
efficiency.

3. Photographic illustrations. These are photographs
of the actual object.
4. Exploded views. This type of illustration is used to
show the parts of a component that has been
dismantled. The parts are laid out in the correct
order for reassembly.
5. Sectional views. These have a section of the object
cut away to show the internal parts. Cross-hatched
lines drawn across the housing show where it has
been cut. (Figure 2.13 is an example.)
6. Schematic drawings. These are simplified drawings
in which parts are not drawn to their true shape.
Instead, outlines of the parts are drawn, or the parts
are represented by symbols. Wiring diagrams are of
this type.
7. Block diagrams. Block diagrams are used to show the
relationship of parts of a system. The actual parts are
not drawn to shape, but rectangles (blocks) are used

to represent the parts. (Figure 2.20 is an example).

6. Repair operations. These are the detailed descriptions and illustrations of both major and minor
repairs. They include methods of dismantling,
repairing, installing and adjusting the various
components and systems.
7. Special tools and equipment. Information is
provided on special tools and equipment needed to
service the particular model of vehicle.
8. Technical data. This is important information
which includes specifications, torque settings,
capacities (fuel, oil and coolant), sizes, wear limits,
clearances and other information that is needed
during servicing or repairs.
9. Wiring diagrams. These show the electrical wiring
for the various parts of the vehicle. They include
the colour code for the wires and the connections to
all the electrical components.
Technical illustrations
Illustrations are used in workshop manuals to support
the text and the same types of illustrations are used in

figure 2.20

A block diagram which shows the flow of fuel
in the fuel system

Tables and charts
Tables and charts are used to show specifications,
pressures, thread sizes or other data. They provide

information in a form for easy reference. (Tables 2.1
and 2.2 are examples.)
Some charts are known as tree charts because they
have branches which lead from one item to another.
A chart used for diagnosing problems is shown in


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part one introduction to motor vehicles

Figure 2.21. This shows a logical sequence to follow
when trying to solve a problem.

CATEGORY
APPROVAL NO.
MOTOR VEHICLE MANUFACTURER
GVM

KG
VIN

THIS VEHICLE WAS MANUFACTURED TO COMPLY
WITH THE MOTOR VEHICLE STANDARDS ACT 1989

MOTOR VEHICLE MANUFACTURER
MODEL

figure 2.21

BODY No.

Tree chart shows a path to follow when
diagnosing a problem

TRIM

A/C

PAINT
BUILT

Vehicle identification

ENG

SUSP
TRANS

Manuals have general information about the vehicle,
including vehicle model identification. All vehicles are
fitted with a compliance plate and a data plate. These

metal plates are fixed to a body panel in the engine
compartment and must never be removed.

figure 2.22

Compliance plate

Technical terms

A compliance plate (Figure 2.22(a)) shows the make,
model and the vehicle identification number (VIN). It
also states that the vehicle was built to comply with the
Motor Vehicle Standards Act.
Vehicles must conform to Australian Design Rules,
which cover safety, emission control and consumer
protection. All vehicles are built to these standards and
must carry a compliance plate.
Data plate
A data plate (Figure 2.22(b)) contains a manufacturer’s
information about the vehicle, such as model, body
type, trim, colour code, suspension and transmission type.
These are shown as codes consisting of letters and
numbers. The date the vehicle was built is also shown.
This is the date that the vehicle is driven from the
production line.
Manuals explain this data and also show where to
find the body number, the engine number and the
transmission number. Serial numbers stamped on these
parts are used for identification purposes.
■ Data from this plate is used to identify the vehicle

and components when obtaining replacement parts.

AXLE

Compliance plates and data plates are fitted
to every vehicle

Specifications, serviceable, unserviceable,
replacement part, assembling, installing, adjusting,
lubricating, diagnosing, reconditioning, fitting,
reaming, machining, fabricating, welding, arc, flux,
soldering, casting, diecasting, moulding, forging,
self-locking, spline, snap ring, circlip, screw thread,
left-hand thread, V-thread, metric thread, unified
thread, pitch, maintenance, technical data, exploded
view, sectional view, schematic drawing, compliance plate, data plate.

Review questions
1.

There are a number of basic service procedures.
What are they?

2.

What is meant by installing?

3.

What are replacement parts?

4.

What is meant by serviceable and unserviceable?

5.

What are specifications?

6.

What is diagnosing?


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chapter two workshop practices

7.

A part has been machined. What does this
mean?

8.

What is a casting?

9.

Name some parts produced by casting.

10.

What is an extrusion?

11.

What process would be used to produce a body
panel?

12.

What are the commonly used methods of
welding?

13.

What are the basic safety precautions that relate
to welding?

14.

What is a forging?

15.

Name some parts produced by forging.

16.

Where is soldering used?

17.

List various types of locking devices and consider where each is used.

18.

What is a spline?

19.

What is a snap ring?

20.

What are the four basic thread forms?

21.

What is the pitch of a thread?

22.

From the appropriate table, find the pitch of the
threads for a 10 mm bolt.

23.

List five types of technical information that
would be found in a workshop manual.

24.

In this book, find an example of each of the
following: a line drawing, a circuit diagram, a
pictorial view, a sectional view and an exploded
view.

25.

What is a compliance plate, and where is it
likely to be located?

26.

What type of information is a data plate likely to
have?

31


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