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

Automotive Mechanics (Volume I)(Part 1, chapter2) Workshop practices Workshop practices17Automotive service procedures18Workshop operations20Production processes21Fasteners23Locking devices25Screw threads26Vthreads27Workshop manuals28Vehicle identification30Technical terms30Review questions30

Workshop practices

Chapter 2

Automotive service procedures

Workshop operations

Production processes

Fasteners

Locking devices

Screw threads

V-threads

Workshop manuals

Vehicle identification

Technical terms

Review questions

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 spec-ifications 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.

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

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

be re-manufactured to original specifications using the

old assembly Engines and transmissions are often

exchanged in this way to specialist workshops who

re-manufacture 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.

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).

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

figure 2.2 Replacing – parts such as oil filters are

renewed as part of a normal service

figure 2.3 Installing – a special tool is being used to

install an oil seal in a housing

figure 2.4 Adjusting – adjusting screws enable the valve

clearance to be set to the thickness of the feeler gauge MITSUBISHI

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

lubri-cation Engine parts are provided with pressure

lubrication, but some other parts require periodic

lubri-cation 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.

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.

■ 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 valve-refacing 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.

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.

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.

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 trans-mission 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

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.

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.

figure 2.5 Part of a rear suspension showing the manufacturing processes used to produce the various parts HOLDEN LTD

extruding and forming to shape welding

welding

forming and welding

rubber moulding

forming

pressing

forging and machining

pressing and rubber moulding

casting and machining

machining and grinding

pressing

machining and grinding

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

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

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

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 self-locking 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 2.6 Methods of using bolts and stud

figure 2.7 Classes of bolts are identified by markings on

the head

figure 2.8 Various types of nuts

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.

■ Some nuts and bolts are secured with thread-sealing

compounds, which are applied before the nut is

tightened See later section, ‘Locking compounds’.

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.

figure 2.9 Self-locking type nuts

figure 2.10 Types of screw heads

figure 2.11 The points of screws or bolts can be shaped

for particular purposes

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

Self-tapping screws

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.

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,

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.

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

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

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

figure 2.12 Pop rivets are used on sheet metal parts

figure 2.13 Solid rivets shown before installation (top)

and after installation (bottom)

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.

figure 2.14 Keys used between a collar and a shaft

which prevent the nut or bolt from loosening These

are used mainly with smaller bolts and nuts.

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.

Locking compounds

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.

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 left-hand 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

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.

figure 2.15 Lock washers

figure 2.16 Snap rings or circlips

Other locking devices

Other locking devices include:

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