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CHAPTER ONE

1.0 INTRODUCTION

SIWES is an acronym which stands for Students Industrial Work Experience Scheme.

The idea was conceived in 1973 under the then Colonel Yakubu Gowon led military

government. Owing to financial constraints the idea did not come to life until 1976 during the

short reign of the General Murtala Muhammed Led administration. It is a scheme designed to

expose students with view of earning a Bachelor‟s Degree in the Engineering, Environmental

design and physical sciences to the practical applications of what has been taught and learnt in

class. It actually gives a fore taste of the practical approach in the field of interest.

Students are generally advised to seek placement in a firm/industry whose operation is

relevant to His/ Her course of study. Basics of professional practice are also to be sought after

during this period. An exposure at this level is also meant to prepare the minds of intending

professionals to the demands of the work environment in intellect and human relations.

1.1 OJECTIVES OF SIWES

The Industrial Training Fund‟s Policy Document No. 1 of 1973 (ITF, 1973) which

established SIWES outlined the objectives of the scheme. The objectives are to:

Provide an avenue for students in institutions of higher learning to acquire industrial

skills and experience during their courses of study;

Prepare students for industrial work situations that they are likely to meet after

graduation;

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Expose students to work methods and techniques in handling equipment and machinery

that may not be available in their institutions;

Make the transition from school to the world of work easier and enhance students‟

contacts for later job placements;

Provide students with the opportunities to apply their educational knowledge in real work

situations, thereby bridging the gap between theory and practice;

Enlist and strengthen employers‟ involvement in the entire educational process through

SIWES.

1.2 EXPOSURE TO TRAINING

During my training period at D.W.M.S, Obafemi Awolowo University, Ile-Ife, I was

exposed to the rudiments of automobiles and with little exposure to refrigeration and air-

conditioning. And it was no doubt a wonderful experience to have been there. The mechanical

section of the organization deals majorly with the repairs and maintenance of the institution

vehicles; both hold and new models.

With this I was able to understand the basics of automobiles: engine systems, engine

components/parts, and some maintenance procedures. It cannot be overemphasized that some

little works-tightening and loosening of some parts-done by me are carries out under great

supervision by the supervisors/technician in charge.

The various works done during the training are fully explained in the rest of report

chapters.

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1.3 ORGANISATION PROFILE

ESTABLISHMENT NAME

Division of Works and Maintenance Services

ESTABLISHMENT ADDRESS

Obafemi Awolowo University, Ile-Ife.

NATURE OF BUSINESS

Repairs and Maintenance of the institution properties of various kinds

YEAR OPERATION STARTED

1962

1.3.1 About the Establishment

The establishment was founded by the institution according to rules and regulations to be

met by federal institutions, in view of taking proper care of the institution properties which is to

bring durability, comforts and well suitable environments for both the staffs and students and the

institution properties. In addition, it is also to contribute to students‟ practical knowledge in

different ways.

D.W.M.S is made of different departments which functions together to accomplished the

same goals. They are;

1. Electrical Department: They in charge of the institution electricity supply. They majorly

concentrate on the institution power house.

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2. Civil Department: They in charge of all related civil works in the institution: like roads

maintenance, carpentry works within the institution. Etc.

3. Mechanical Department: Under the mechanical departments, we have sub-units which

are: the automobile units, refrigeration and air-conditioning, fabrication and the electrical

units. The refrigeration and air-conditioning unit takes care of both repairs, maintenance

and installations of refrigeration and air-conditioning in the institution, while others deal

with automobiles

1.4 ORGANIZATIONAL STRUCTURE

VICE-CHANCELLOR

CHAIRMAND.W.M.S

DIRECTOR

D.W.M.S

HEAD OF ELECTRICAL

DEPT.

HEAD OF MECHANICAL

DEPT.

HEAD OF CIVIL

DEPT.

ENNGINEER 1 & SIWES

SUPERVISOR WORKS

FOREMAN

STORE KEEPER SKILLED OFFICER SEMI-SKILLED

OFFICER

VEHICLE TESTER

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CHAPTER TWO

THE ENGINE

2.0 INTRODUCTION

The modern automobile engine converts energy contained in fuel into relatively efficient

inexpensive transportation. With one exception, this chapter discusses the internal combustion

reciprocating engine, which is the engine type in predominant use today. It is called a

reciprocating engine because its power is transmitted through a piston moving back and forth

(reciprocating) in a cylinder. The cylinder is bored into a casting called a blocked. The block

also holds the crankshaft, to which the piston is connected by a rod.

Variations of this basic engine type are used in today‟s automotive vehicles. They include

differences in the number of cylinders, cylinders arrangement and strokes.

2.1 ENGINE TYPES

Most engines are designed with the cylinders in-line, but this is not an invariable rule.

There are, for instance, advantages in having the cylinders arranged in two opposed banks of

two. The design is the only engine design that is dynamically balanced- that is, the movements of

the moving parts balance each other and do not cause vibration. A more or less vibration-free

engine is obviously a good idea, especially when the engine is designed to operate at high

speeds. The „flat four‟ layout also produces a low center of gravity for the car, which improves

handling characteristics.

Engines with a „V‟ configuration of cylinders are also used in six and eight cylinder

versions. The engines are compact, shorter and wider than the in-line engines.

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2.1.1 FOUR-STROKE PETROL ENGINE

In this cycle the piston moves up and down the cylinder twice, each of the four strokes

performing a different task. The cycle is completed in two complete revolutions of the

crankshaft.

Fig 2.1 Engine diagram

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The four strokes, in their correct sequence are;

1. Induction

2. Compression

3. Power and

4. Exhaust.

Fig. 2.2 Four stroke petrol engine

Induction stroke: As the piston starts to move downwards from t.d.c by the momentum

imparted to the flywheel during previous cycles or rotation by hand or starter motor, the inlet

valve opens, the displacing piston causing a partial vacuum, hence drawing in mixture of air and

fuel (petrol) from the carburetor/fuel injector through the inlet port into the cylinder. The

pressure will be below atmospheric pressure by an amount which depends upon the speed of the

engine and the throttle valve opening. The exhaust valve is closed.

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Compression stroke: At bottom dead center (b.d.c) the inlet valve closes sealing the

cylinder. The piston returns, still driven by the momentum of the flywheel, and compresses the

charge into the combustion head of the cylinder. The pressure rises to an amount which depends

on the compression ratio, that is the ratio of the full volume of the cylinder when the piston is at

the outer end of its stroke to the volume of the clearance space when the piston is at the inner (or

upper) end. In ordinary petrol engines this ratio is usually between 6 and 9, and the pressure is

about 620 - 827.4 KN/m2 with full throttle opening.

Power stroke: When the piston is near to the t.d.c. position, both valves being closed, the

compressed gas is ignited by a spark bridging the spark plug electrodes; this ignites the charge

which causes a rise in temperature and subsequent rise pressure, the piston being forced down

the cylinder by the burnt expanding gases. Combustion is completed while the piston is

practically at rest, and is followed by the expansion of the hot gases as the piston moves

outwards.

The pressure of the gases drives the piston forward and turns the crankshaft thus

propelling the car against the external resistances and restoring to the flywheel the momentum

lost during the idle strokes.

Exhaust stroke: At b.d.c. the exhaust valve opens and inlet valve closes, as the piston

rises the exhaust gases escape through the open valve until at t.d.c. this valve closes and the

piston once commences a new induction stroke. The pressure will be slightly above atmospheric

pressure by an amount depending on the resistance to flow offered by the exhaust valve and

silencer. It will thus be seen that there is only one working stroke for every four piston strokes, or

every two revolutions of the crankshaft, the remaining three strokes being referred to as idle

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strokes, though they form an indispensable part of the cycle. This has led engineers to search for

a cycle which would reduce the proportion of idle strokes, the various forms of the two-stroke

engine being the result. The correspondingly larger number of useful strokes per unit of time

increases the power output relative to size of engine, but increases thermal loading.

2.2 ENGINE CONSTRUCTION

As already mentioned, the engine consists of a few large components and many small

ones. Most engines have more than one cylinder. Each manufacturer produces several different

engines, so there are many variations of the basic design but in conformation with the same

working principle. Typical engine construction of the basic type will be discussed below.

2.2.1 CYLINDER BLOCK

This is the main component around which the engine is built. The block is made from

cast iron or, on certain cars, aluminum alloy. The (fig 1.5) cylinder block has the engine

mounting attached to its outside for mounting to the vehicle‟s body or chassis. Bored vertically

into the block are the cylinder bores. Engines are named according to the number of the cylinders

bored into the block, i.e. four, six and eight-cylinder engines. Engines have been made with

sixteen cylinders, but those with more than eight are uncommon. The block must be rigid to hold

the bores relative to each other and to hold the crankshaft in place. The crankshaft runs at right-

angles to the cylinder bores, being retained in what are called main bearings. The block forms

one semi-circular half of the bearing and a semi-circular cap forms the other half.

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2.2.2 CYLINDER HEAD

The cylinder head fits, as its name implies, on top of the cylinder block. The underside

forms the combustion chamber with the top of the piston. Generally the cylinder head is shaped

so that the combustion chamber is actually in the cylinder head, the piston crown forming only

one wall of the chamber. The cylinder head carries the valves, valve springs and the rockers on

the rocker shaft, this part of the valve gear being operated by the pushrods.

Sometimes the camshaft is fitted directly into the cylinder head and operates on the

valves without rockers. This is called an overhead camshaft arrangement. Like the cylinder

block, the head is made from either cast iron or aluminum alloy. The cylinder head is attached to

the block with high-tensile steel studs. The joint between the block and the head must be gas-

tight so that none of the burning mixture can escape. This is achieved by using a cylinder head

gasket.

Fig. 2.3 The Cylinder Head, Head Gasket and Engine Block

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2.2.3 CRANKSHAFT

The crankshaft in conjunction with the connecting rod converts the reciprocating motion

of the piston to the rotary motion needed to drive the vehicle. It is usually made from carbon

steel which is alloyed with a small proportion of nickel. The main bearing journals fit into the

cylinder block and the big end journals align with the connecting rods. At the rear end of the

crankshaft is attached the flywheels for the timing gears, fan, cooling water and generator.

The throw of the crankshaft, i.e. the distance between the main journal and the big end

centres, controls the length of the stroke. The stroke is double the throw, and the stroke-length is

the distance that the piston travels from TDC to BDC and vice versa.

Fig 2.4 Crankshafts

2.2.4 CAMSHAFT

The camshaft can be fitted into the cylinder block or the cylinder head. The former

position, with rocker-operated valves in the cylinder head, is called an overhead valve (OHV)

layout. The latter position, with the camshaft above the valves, is called an overhead cam (OHC)

layout. The camshaft is driven by a chain connected to the front of the crankshaft. The camshaft

has a separate cam for each valve, as each valve only opens once to each two revolutions of the

crankshaft.

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The camshaft must open the valves at the correct time relative to the piston on the

different strokes of the cycle. The chain drive ensures that the camshaft is timed to the engine in

this way.

2.2.5 OVERHEAD CAMSHAFT

In this system the valves and the camshaft are both fitted to the cylinder head. There are

several ways in which an overhead camshaft can be made to work the valves but the most

common method is shown in Fig 2.6

Fig 2.5 Valve operated by a pushrod system

Here the cam pushes the valve down from directly above. A tappet is fitted over the end

of the valve assembly to stop the cam from pushing the valve sideways and bending it. When the

cam has passed the tappet, the spring closes the valve.

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An overhead camshaft is better than a pushrod system in that it acts directly on the valves

and does not need pushrods and rocker arms. On the other hand it is much easier to connect the

camshaft to the crankshaft when both shafts are in the cylinder block.

Fig 2.6 Valve operated by an overhead camshaft

2.2.7 FLYWHEEL

The flywheel is a large diameter, heavy disc, usually constructed of cast iron. It is bolted

to the engine‟s crankshaft. The flywheel smooth out, or damps engine vibrations caused by firing

pulses. It also acts as a friction surface and heat sink for one side of the clutch disc. The teeth

around the circumference of the flywheel form a ring gear, which when engaged to the starter

motor pinion gear, are used to start the engine.

Vehicles with automatic transmission do not have a flywheel. Instead, they use a drive

plate or flex plate. These lightweight, stamped steel discs are used only to bolt the torque

converter to the engine‟s crankshaft. They have no clutch friction surface and will not

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interchange with manual transmission flywheels. They do have a ring gear, for the engine

starting.

2.2.8 PRESSURE PLATE

The pressure plate or clutch plate is a large spring-loaded clamp that rotates at flywheel

speed. It consists of a sheet-metal cover, multiple, high-rate coil springs, and levers.

2.2.9 CLUTCH DISC

The clutch (friction) disc is a steel plate that fits between the flywheel and the pressure

plate. It has friction material riveted or bonded to both sides. Like brake lining material, the

friction disc lining wears as the clutch is engage. Some high-performance clutch assemblies use

multiple friction discs.

2.2.9 PISTON

The piston runs in the cylinder bore, going up and down on stroke. Its purpose is to keep

the gases above and below it tightly sealed in their place and to transmit the pressure of the

burning gases on the power stroke to the gudgeon pin. Pistons are made from aluminium alloy,

which is light, strong and a good conductor of heat. They look quite simple but are extremely

complicated. They run at speeds up to 13m/s (2500 ft/min) with a temperature range being as

high as 20000C at the crown and as low as freezing point where the gudgeon pin fits. The skirt is

the lower half of the piston, being the same shape as the garment it is named after. Piston

crowns come in different shapes: flat top, dishes and domed. These give different combustion

chamber shapes.

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The skirt holds the piston crown level by stopping the piston from turning vertically in

the bore of the cylinder. The movement of the piston in the bore is a slapping side-to-side

motion, called piston slap. This can be heard clearly inside the car. Split skirt pistons are the

same size all the time. The expansion of the piston simply closes the split in the skirt.

Fig. 2.7 Piston

2.2.10 GUDGEON PIN

The gudgeon pin, which is inside the piston transfers the force produced by the

expanding petrol vapour and air from the top of the piston to the connecting rod. The gudgeon

pin is hollow to reduce weight. In many modern engines the fit of the gudgeon pin into the

cylinder is called a „thermal fit‟. This means that the gudgeon pin can only be removed when the

piston is heated in boiling water to expand it. Sideways movement of the gudgeon pin must be

prevented otherwise the cylinder may become scored. This possible movement is prevented by

fitting circlips in the piston.

2.2.11 CONNECTING ROD

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The connecting rod little end is connected to the gudgeon pin. A bush made from a soft

metal, such as bronze, is used for this joint. The lower end of the connecting rod fits the cycles

we implied that the valves opened and closed instantaneously at TDC and BDC.

Fig. 2.8 Connecting rod

2.2.12 VALVE TIMING

If the timing gear has been disturbed in any way it will be necessary to reset the timing.

Incorrect fitting of the timing chain or belt or positioning of gear wheels will lead to the

relationship between movement of the piston and the valve opening periods to move out of

phase, causing erratic running and loss of power. As valves can neither open nor close straight

away and as more power can be obtained by moving the opening and closing time, we have

slightly different valve timing. To get more gas into the cylinder the inlet valve starts to open

about 10 degrees before top dead centre and stays open until 40 degrees after bottom dead centre.

The early opening is called the valve lead. The exhaust valve opens at about 40 degrees before

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BDC and closes 10 degrees after TDC so that the cylinder is thoroughly cleared of exhaust gases.

The delay in closing is called valve lag. As the inlet stroke follows the exhaust stroke there is a

period where both valves are open, i.e. 10 degrees before TDC to 10 degrees after TDC. This is

called valve overlap.

It is usual to mark the t.d.c. position of number one cylinder on the rim of the flywheel so

that it can be viewed through an aperture I the clutch housing. For ease of access many

manufacturers indicate the t.d.c. position on the crankshaft pulley or the damper by means of a

pointer, notch, or hole which must be in-line with a pointer on the timing chain cover or on the

sump. Having set the piston to its t.d.c. position, the sprockets or gear wheels should then be set

to their timing marks and the chain or mating gear replaced with care. If the sprockets or gear

wheels are not marked, it is necessary to do that before dismantling the engine.

Unmarked engines will require the manufacturer‟s timing diagram in order to accurately

set the valve timing if suitable precautions have not been taken before dismantling the engine. In

such cases the following procedure is recommended.

1. Set the valve clearance to the manufacturer‟s specification, which may state a larger valve

clearance than the normal for timing purposes.

2. Set the number one piston to its t.d.c. position, either by observing the piston or using a rod,

where possible through the plug hole. Mark t.d.c. position on the flywheel also. It should be

noted on a six-cylinder engine; numbers 1 and 6 are at t.d.c. when numbers 2, 3, 4 and 5 are

equidistance down the bore.

3. Calculate the angular rotation in inches of the flywheel from t.d.c to the position where the

inlet valves opens. The movement in degrees can be obtained from the timing diagram. This

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method is suggested, as it is easier to measure round the rim of a flywheel with flexible steel

rule than attempt to measure the movement in degrees. The latter would entail the attachment

of a protractor to the front end of the crankshaft.

4. Move the flywheel at the calculated amount and rotate the camshaft until the inlet valve

begins to open.

5. Connect together the crankshaft and the camshaft using the timing chain or belt as the case

might be.

2.2.14 OIL AND FILTER

The single most important part of engine maintenance is checking the oil. In this regard,

self-service gas stations are a threat in disguise. Many drivers will put gas in the car and never

check the oil level in the engine. The oil should be checked after the car has been parked on a

level surface for several minutes with the engine off. This allows the oil in the engine upper parts

to drain down and provide a true measurement. The dipstick is used in checking the oil level; it

has index marks identifying the minimum and maximum amount of oil required for the engines.

Many manufacturers suggest changing the oil at intervals of 4800-19200km. to help the

engine last, the engine should be changed at the manufacturer‟s specified time; also the

manufacturer‟s oil requirements should never be exceeded. The oil filter separates from the oil

dirt which tries to get into the engine, but one cannot rely totally on the oil filter to keep the oil

clean at all time; the filter element do fail at times. The oil filter does not filter out acid, the most

corrosive elements suspended in used oil.

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2.2.15 SUMP

The sump is fitted at the bottom of the engine to collect and retain the lubricating oil. It is

made of either steel pressings or cast aluminium. It store the oil until it is needed and catches the

oil as it falls back from the various parts of the engine after it has been used. A dipstick is fitted

to hang into the oil in the sump.

2.2.16 HEAD GASKET

The cylinder head and cylinder block must mate perfectly and not allow leakage of gases,

oil, or water. Normal production machining cannot produce a perfect mating. To do so, a head

gasket is normally used to seal the surfaces between the head and the block.

Gasket materials must possess certain qualities. First, a gasket must be resistant. This

means that any change in temperature, pressure, or anticipated conditions under which the gasket

will be used must be considered when designing a gasket. Gaskets musts conform to the surface

they are used on, including surfaces that may warp slightly or that are rough from machining. A

resilient gasket must remain sealed even when a temperature, pressure, or vibration change

causes a joint to loosen. A gasket must be impermeable, i.e. it must be able to keep all fluids

from leaking or seeping out.

Holes are cut out of each head gasket to allow for the bolts, valves, cylinders, and water

passages in the head and block. The head bolts are tightened down on the head gasket after it is

installed. This squeezes the gasket metal which is soft and seals the mating surfaces between the

head and the block. A head gasket will normally be marked „front‟ or „top‟ to make sure it is

installed correctly. If the gasket is not marked, is should be installed with the trade mark facing

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up. Incorrect installation can block off the oil or coolant passages. It is necessary to make sure

that the matching holes in the head and block are also matched by the head gasket.

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CHAPTER THREE

ENGINE SYSTEMS

3.1 TYPES OF COOLING SYSTEM

The purpose of the cooling system is to keep the engine at a constant temperature whilst

preventing overheating of any specific components. The average car petrol engines runs most

efficiently at between 800 and 85

0 C. diesel engines run at 5

0 cooler. A typical 4 cylinder vehicle

cruising along the highway at around 50 miles per hour, will produce 4000 controlled explosions

per minute inside the engine as the spark plugs ignite the fuel in each cylinder to propel the

vehicle down the road. Obviously, these explosions produce an enormous amount of heat and, if

not controlled, will destroy an engine in a matter of minutes. Controlling these high

temperatures is the job of the cooling system.

The modern cooling system has not changed much from the cooling systems in the model

T back in the '20s. Oh sure, it has become infinitely more reliable and efficient at doing its job,

but the basic cooling system still consists of liquid coolant being circulated through the engine,

then out to the radiator to be cooled by the air stream coming through the front grill of the

vehicle.

Today's cooling system must maintain the engine at a constant temperature whether the

outside air temperature is 110 degrees Fahrenheit or 10 below zero. If the engine temperature is

too low, fuel economy will suffer and emissions will rise. If the temperature is allowed to get

too hot for too long, the engine will self-destruct.

There are two types of cooling systems: water cooling and air cooling systems.

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3.1.1 WATER COOLING SYSTEM

Water has natural tendency to circulate when heated up in the cooling system-hot water

rises. This is called thermo-syphoning. As the cooling water is head up in the cylinder block it

rises through the top hose into the radiator header tank. The water then falls through the radiator

core into the bottom tank. As it falls it is cooled by the incoming air which passes through the

radiator from the front of the car. The weight of the water in the radiator forces it through the

bottom hose back into the engine. The water can then continue thermo-syphoning provided that

there is enough water in the system. The water level must be kept above the top hose connection

to ensure that a constant circulation is maintained.

3.1.2 AIR-COOLING SYSTEM

Air-cooling systems are used on certain light cars and most motor cycles. Air cooling has

the advantages of not using water and needing less moving parts. Having no water, it cannot

freeze or leak. However, air-cooled engines tend to be noisy than water-cooled ones. The system

operates by entering through the flap valve. The fan, which is driven by a crankshaft pulley,

forces the air over the fins of the cylinder. The air is then discharged backed into the atmosphere.

The flap valve is controlled by the thermostat, which opens the flap when the engine is hot, so

allowing air in it. The flap is closed when the engine is cold, so restricting air flow and allowing

the engine to warm up quickly. Air cooled engines are found on a few older cars, like the original

Volkswagen Beetle, the Chevrolet Corvair and a few others. Many modern motorcycles still use

air cooling.

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3.1.3 COMPONENTS OF A COOLING SYSTEM

Water Pump

To circulate the water quickly a water pump is fitted. This forces the water to circulate

around the engine in the same direction as the thermo-syphoning. The water pump is fitted on to

the front of the engine. The bottom hose from the radiator is connected to the water pump and

the water outlet from the pump is connected to the engine‟s water jacket. The pump is driven by

the engine through one of the following.

1. A fan belt that will also be responsible for driving an additional component like an alternator

or power steering pump.

2. A serpentine belt, which also drives the alternator, power steering pump and AC compressor

among other things.

3. The timing belt that is also responsible for driving one or more camshafts.

The water pump is made up of a housing, usually made of cast iron or cast aluminum and

an impeller mounted on a spinning shaft with a pulley attached to the shaft on the outside of the

pump body. A seal keeps fluid from leaking out of the pump housing past the spinning

shaft. The impeller uses centrifugal force to draw the coolant in from the lower radiator hose and

send it under pressure into the engine block. There is a gasket to seal the water pump to the

engine block and prevent the flowing coolant from leaking out where the pump is attached to the

block.

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Fig. 3.1 Water Pump

Radiator

The function of the radiator is to receive hot water from the top of the engine and return it

to the lower part of the engine after having cooled it considerably. The heat is taken away from

the coolant whilst passing from the top to the bottom of the radiator. This is achieved by the

coolant passing through numerous copper tubes, each one separated from the next by cooling

fins. Cool air passing across the large surface area of the copper tubes take away the unwanted

heat from the coolant.

The radiator consists of brass or carbon fibre top and bottom tanks: the top tank being

adapted with a filter-cap neck, top-hose fitting and over-flow pipe; the lower tank being adapted

with a bottom-hose fitting and occasionally with a drain-plug. The assembly of copper or

aluminium tubes and fins (known as the matrix) is secured by soldered joints between two tanks.

Several types of matrix design have been used in radiator construction according to their

requirements. Basically there are four popular designs in use; three vertical-type, one horizontal-

type.

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Fig. 3.2 Radiator

Pressure Cap and Reserve Tank

As coolant gets hot, it expands. Since the cooling system is sealed, this expansion causes

an increase in pressure in the cooling system, which is normal and part of the design. When

coolant is under pressure, the temperature where the liquid begins to boil is considerably

higher. This pressure, coupled with the higher boiling point of ethylene glycol, allows the

coolant to safely reach temperatures in excess of 250 degrees.

The radiator pressure cap is a simple device that will maintain pressure in the cooling system up

to a certain point. If the pressure builds up higher than the set pressure point, there is a spring

loaded valve, calibrated to the correct Pounds per Square Inch (psi), to release the pressure.

When the cooling system pressure reaches the point where the cap needs to release this

excess pressure, a small amount of coolant is bled off. It could happen during stop and go traffic

on an extremely hot day, or if the cooling system is malfunctioning. If it does release pressure

under these conditions, there is a system in place to capture the released coolant and store it in a

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plastic tank that is usually not pressurized. Since there is now less coolant in the system, as the

engine cools down a partial vacuum is formed.

The radiator cap on these closed systems has a secondary valve to allow the vacuum in

the cooling system to draw the coolant back into the radiator from the reserve tank (like pulling

the plunger back on a hypodermic needle). There are usually markings on the side of the plastic

tank marked Full-Cold, and Full Hot. When the engine is at normal operating temperature, the

coolant in the translucent reserve tank should be up to the Full-Hot line. After the engine has

been sitting for several hours and is cold to the touch, the coolant should be at the Full-Cold line.

To prevent the loss of water, and hence the need for topping up the radiator, a sealed

system is sometimes used. An overflow tank is fitted on the side of the radiator and a rubber tube

from the pressure cap connects to the overflow tank. Thus any water allowed past the radiator

can go into the overflow tank. When the radiator cools and water contracts, the water in the

overflow tank is drawn into the radiator to fill the space available.

Radiator Fan

Mounted on the back of the radiator on the side closest to the engine is one or two electric

fans inside a housing that is designed to protect fingers and to direct the air flow. These fans are

there to keep the air flow going through the radiator while the vehicle is going slow or is stopped

with the engine running. If these fans stopped working, every time there is a stop, the engine

temperature would begin rising. On older systems, the fan was connected to the front of the

water pump and would spin whenever the engine was running because it was driven by a fan belt

instead of an electric motor. In these cases, if a driver would notice the engine begin to run hot

in stop and go driving, the driver might put the car in neutral and rev the engine to turn the fan

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faster which helped cool the engine. Racing the engine on a car with a malfunctioning electric

fan would only make things worse because you are producing more heat in the radiator with no

fan to cool it off.

The electric fans are controlled by the vehicle's computer. A temperature sensor monitors

engine temperature and sends this information to the computer. The computer determines if the

fan should be turned on and actuates the fan relay if additional air flow through the radiator is

necessary.

If the car has air conditioning, there is an additional radiator mounted in front of the

normal radiator. This "radiator" is called the air conditioner condenser, which also needs to be

cooled by the air flow entering the engine compartment. As long as the air conditioning is turned

on, the system will keep the fan running, even if the engine is not running hot. This is because if

there is no air flow through the air conditioning condenser, the air conditioner will not be able to

cool the air entering the interior.

Fig. 3.3 Radiator Fan

28

Thermostat

The thermostat is a temperature operated water valve. It is fitted between the top of the

engine and the top hose. A connection, usually a separate casting called thermostat housing, is

used to locate it. The thermostat housing attaches to the engine, usually with two bolts and a

gasket to seal it against leaks. The gasket is usually made of a heavy paper or a rubber O ring is

used. In some applications, there is no gasket or rubber seal. Instead, a thin bead of special

silicone sealer is squeezed from a tube to form a seal. When the thermostat is closed the water

cannot flow; when it is open the water can flow. The thermostat allows a quick warm-up period

by remaining closed until the engine has its required temperature and keeps the engine at a

constant temperature by opening and closing as the engine becomes hot or cools down.

The thermostat is simply a valve that measures the temperature of the coolant and, if it is

hot enough, opens to allow the coolant to flow through the radiator. If the coolant is not hot

enough, the flow to the radiator is blocked, and fluid is directed to a bypass system that allows

the coolant to return directly back to the engine. The bypass system allows the coolant to keep

moving through the engine to balance the temperature and avoid hot spots. Because flow to the

radiator is blocked, the engine will reach operating temperature sooner and, on a cold day, will

allow the heater to begin supplying hot air to the interior more quickly.

The thermostat is usually located in the front, top part of the engine in a water outlet

housing that also serves as the connection point for the upper radiator hose. The thermostat

housing attaches to the engine, usually with two bolts and a gasket to seal it against leaks. The

gasket is usually made of a heavy paper or a rubber O ring is used. In some applications, there is

29

no gasket or rubber seal. Instead, a thin bead of special silicone sealer is squeezed from a tube to

form a seal.

There is a mistaken belief by some people that if they

remove the thermostat, they will be able to solve hard to find

overheating problems. This couldn't be further from the

truth. Removing the thermostat will allow uncontrolled

circulation of the coolant throughout the system. It is possible

for the coolant to move so fast, that it will not be properly

cooled as it races through the radiator, so the engine can run even hotter than before under

certain conditions. Other times, the engine will never reach its operating temperature. On

computer controlled vehicles, the computer monitors engine temperatures and regulates fuel

usage based on that temperature. If the engine never reaches operating temperatures, fuel

economy and performance will suffer considerably.

3.1.4 COOLING SYSTEM MAINTENACE

An engine that is overheating will quickly self-destruct, so proper maintenance of the

cooling system is very important to the life of the engine and the trouble free operation of the

cooling system in general.

The most important maintenance item is to flush and refill the coolant periodically. The

reason for this important service is that anti-freeze has a number of additives that are designed to

prevent corrosion in the cooling system. This corrosion tends to accelerate when several different

types of metal interact with each other. The corrosion causes scale that eventually builds up and

begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually

Fig. 3.4 Thermostat

30

overheat. The anti-corrosion chemical in the antifreeze prevents this, but they have a limited life

span.

Newer antifreeze formulations will last for 5 years or 150,000 miles before requiring

replacement. These antifreezes are usually red in color and are referred to as "Extended Life" or

"Long Life" antifreeze. Most antifreeze used in vehicles however, is green in color and should be

replaced every two years or 30,000 miles, whichever comes first. The new long life coolant can

be converted to, but if only the old antifreeze is completely flushed out. If any green coolant is

allowed to mix with the red coolant, shorter replacement cycle must be reverted to.

The National Automotive Radiator Service Association (NARSA) recommends that

motorists have a seven-point preventative cooling system maintenance check at least once every

two years. The seven-point program is designed to identify any areas that need attention. It

consists of:

a visual inspection of all cooling system components, including belts and hoses

a radiator pressure cap test to check for the recommended system pressure level

a thermostat check for proper opening and closing

a pressure test to identify any external leaks to the cooling system parts; including the

radiator, water pump, engine coolant passages, radiator and heater hoses and heater core

an internal leak test to check for combustion gas leakage into the cooling system

an engine fan test for proper operation

a system power flush and refill with car manufacturer's recommended concentration of

coolant

31

3.2 FUEL SYSTEM

The fuel system supplies the engine with fuel (petrol or diesel) for it to be able to its work

efficiently. There are three main parts to the system- the tank, the pump, and the

carburetor/injector.

The tank stores fuel until it is needed by the engine. It is normally fitted as far away from

the hot engine as possible to reduce the risk of fire. For example, in a front-engine car the tank is

usually at the back. The tank is fitted with a sensor unit to measure how much petrol is in the

tank. This is connected to the petrol gauge of the dashboard, so that the driver can see at any time

how much petrol is in the tank. This sensor device is referred to as a tank unit. At the bottom of

the tank is a drain plug which allows for the draining of the petrol if necessary. As an extra safety

precaution, most systems now also incorporate a rollover valve. The valve is located in the

vapour vent line; it prevents fuel flow if the vehicle should be turned over in an accident. The

average valve will hold pressure to about 3 psi

The pump draws fuel from the tank and delivers it to the carburetor. It is usually fitted with

a filter to stop dirt from the tank entering the carburetor. The carburetor mixes the petrol with

air to form a spray, which is suitable for the engine to draw in and turn.

32

Fig. 3.5 Fuel System Diagram

3.2.1 MAJOR COMPONENTS OF A FUEL SYSTEM

A fuel of some kind is needed to pump petrol from a low level in the petrol tank to a

higher level in the carburetor float chamber. A fuel pump may be mechanically or electrically

operated. In the majority of fuel pumps, the pumping action is supplied by a diaphragm. The

main chamber of the pump is sealed by a rubber fabric diaphragm which comes way to lower the

air pressure. Atmospheric pressure forces fuel from the tank to the pump chamber. The

diaphragm is then returned by a spring which pumps petrol through the outlet valve and at the

same time closing the inlet valve. The pump delivery pressure is controlled by the diaphragm

spring at between 10-20 KN/m2.

Fuel Lines

Steel lines and flexible hoses carry the fuel from the tank to the engine. When servicing

or replacing the steel lines, copper or aluminum must never be used. Steel lines must be replaced

33

with steel. When replacing flexible rubber hoses, proper hose must be used. Ordinary rubber

such as used in vacuum or water hose will soften and deteriorate. Be careful to route all hoses

away from the exhaust system.

Fuel Filters

The fuel filter is the key to a properly functioning fuel delivery system. This is truer with

fuel injection than with carbureted cars. Fuel injectors are more susceptible to damage from dirt

because of their close tolerances, but also fuel injected cars use electric fuel pumps. When the

filter clogs, the electric fuel pump works so hard to push past the filter that it burns itself up.

Most cars use two filters. One inside the gas tank, and one in a line to the fuel injectors, or

carburetor. Unless some severe and unusual condition occurs to cause a large amount of dirt to

enter the gas tank, it is only necessary to replace the filter in the line.

Fig. 3.6 Fuel Filter Exploded Diagram

34

Petrol Injection

The majority of racing cars and some production cars introduce petrol vapour and air

mixture into the cylinders by petrol injection. With a carburetor system the petrol vapour and air

is sucked into the combustion chambers by the downward movement of the piston.

With a petrol injection system, petrol is squirted, under pressure through small injector

nozzles directly into each cylinder. The injectors are positioned near the intake valves. This

system gives improved engine power, acceleration and fuel consumption because distribution of

petrol is accurately controlled and is more efficient than the carburetor system. The disadvantage

of this system is its high cost.

The Carburettor

The carburetor is the unit which:

1. Turns petrol into vapour.

2. Mixes this vapour with air in the correct proportion, to be burnt inside the engine.

3. Helps the car engine to start easily.

4. Enables the car to accelerate.

5. Enables the car to cruise economically.

The air filter and silencer, inlet manifold and inlet valves are involved in the process

called carburation.

How the carburetor basically works

35

A carburetor is that part of a gasoline engine which provides the mixture of gasoline and

air that the engine burns. The carburetor must mix the gasoline with about 15 times its

weight in air for the engine to run smoothly at all speeds. A driver controls the engine

speed by increasing or reduction the flow of the fuel mixture. Carburetors are called

updraft or downdraft according to their position. If the carburetor is below the intake

manifold's input, it is updraft. If it is above, it is a downdraft.

The float chamber of the carburetor stores a small amount of gasoline, which is gravity-

fed from the fuel tank. When the carburetor bowl chamber is filled to the proper level, a

float resting on top of the gasoline closes a valve restricting flow from the tank fuel line.

As the engine consumes gasoline, the float drops. This opens the valve and lets more

gasoline flow into the bowl chamber.

Air and gasoline are mixed in the Venturi, which sits in the carburetor throat area. The

Venturi is a tube, which narrows to a small size and then widens out again, which

increases the speed of the air rushing through the carburetor, and lowers its pressure. The

higher air pressure in the float chamber then forces gasoline through the jets into the

Venturi. The air picks up the gasoline and turns it into a vapor. Vacuum from the engines

intake manifold draws the air and gasoline vapor into the engine.

The throttle plate valve controls the engine speed by letting more or less of the air and

gasoline vapor to enter the intake manifold. The driver presses the accelerator pedal to

open the throttle valve and let up on the accelerator to close it.

The choke plate valve looks similar to the throttle valve, but it controls the amount of air

entering the carburetor. When it partly closes the carburetor input opening, more gasoline

36

and less air flow into the engine. Choking the carburetor makes it easier for the spark

plugs to ignite the air-gasoline mixture when the engine is cold.

Fig. 3.7 Carburettor

3.2.2 FUEL SYSTEM MAINTENANCE TIPS

Chang fuel filter every 20,000 miles or 1 year

Clean idle passage every 20,000 miles

Clean throttle blades every 20,000 miles

Clean back of fuel distributor plate (primarily on German manufactured vehicles) every

20,000 miles

Check air temperature sensor at 10,000 miles

Check throttle bolt torque (if applicable) at 20,000 miles

Check fuel lines for signs of deterioration and cracking every 2 years or 20,000 miles

Change oxygen sensor every 30,000 miles

Clean fuel injectors every 30,000 miles

Change gas cap every 30,000 miles

37

3.3 IGNITION SYSTEM

The purpose of the ignition system is to create a spark that will ignite the fuel-air mixture

in the cylinder of an engine. It must do this at exactly the right instant and do it at the rate of up

to several thousand times per minute for each cylinder in the engine. If the timing of that spark is

off by a small fraction of a second, the engine will run poorly or not run at all.

The ignition system sends an extremely high voltage to the spark plug in each cylinder

when the piston is at the top of its compression stroke. The tip of each spark plug contains a gap

that the voltage must jump across in order to reach ground. That is where the spark occurs. The

voltage that is available to the spark plug is somewhere between 20,000 volts and 50,000 volts or

better. The job of the ignition system is to produce that high voltage from a 12 volt source and

get it to each cylinder in a specific order, at exactly the right time.

The ignition system has two tasks to perform. First, it must create a voltage high enough

(20,000+) to arc across the gap of a spark plug, thus creating a spark strong enough to ignite the

air/fuel mixture for combustion. Second, it must control the timing of that the spark so it occurs

at the exact right time and send it to the correct cylinder.

The ignition system is divided into two sections, the primary circuit and the secondary

circuit. The low voltage primary circuit operates at battery voltage (12 to 14.5 volts) and is

responsible for generating the signal to fire the spark plug at the exact right time and sending that

signal to the ignition coil. The ignition coil is the component that converts the 12 volt signal into

the high 20,000+ volt charge. Once the voltage is stepped up, it goes to the secondary circuit

which then directs the charge to the correct spark plug at the right time.

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3.3.1 MAIN COMPONENTS

Ignition Coil

The ignition coil is nothing more than an electrical transformer. It contains both primary

and secondary winding circuits. The coil primary winding contains 100 to 150 turns of heavy

copper wire. This wire must be insulated so that the voltage does not jump from loop to loop,

shorting it out. If this happened, it could not create the primary magnetic field that is required.

The primary circuit wire goes into the coil through the positive terminal, loops around the

primary windings, then exits through the negative terminal.

The coil secondary winding circuit contains 15,000 to 30,000 turns of fine copper wire,

which also must be insulated from each other. The secondary windings sit inside the loops of the

primary windings. To further increase the coils magnetic field the windings are wrapped around

a soft iron core. To withstand the heat of the current flow, the coil is filled with oil which helps

keep it cool.

The ignition coil is the heart of the ignition system. As current flows through the coil a

strong magnetic field is built up. When the current is shut off, the collapse of this magnetic field

to the secondary windings induces a high voltage which is released through the large center

terminal. This voltage is then directed to the spark plugs through the distributor.

39

Fig. 3.8 Ignition Coil

Ignition Wires

These cables are designed to handle 20,000 to more than 50,000 volts, enough voltage to

toss you across the room if you were to be exposed to it. The job of the spark plug wires is to get

that enormous power to the spark plug without leaking out. Spark plug wires have to endure the

heat of a running engine as well as the extreme changes in the weather. In order to do their job,

spark plug wires are fairly thick, with most of that thickness devoted to insulation with a very

thin conductor running down the center. Eventually, the insulation will succumb to the elements

and the heat of the engine and begins to harden, crack, dry out, or otherwise break down. When

that happens, they will not be able to deliver the necessary voltage to the spark plug and a misfire

will occur. That is what is meant by "Not running on all cylinders". To correct this problem, the

spark plug wires would have to be replaced.

Spark plug wires are routed around the engine very carefully. Plastic clips are often used

to keep the wires separated so that they do not touch together. This is not always necessary,

40

especially when the wires are new, but as they age, they can begin to leak and crossfire on damp

days causing hard starting or a rough running engine.

Spark plug wires go from the distributor cap to the spark plugs in a very specific

order. This is called the "firing order" and is part of the engine design. Each spark plug must

only fire at the end of the compression stroke. Each cylinder has a compression stroke at a

different time, so it is important for the individual spark plug wire to be routed to the correct

cylinder.

For instance, a popular V8 engine firing order is 1, 8, 4, 3, 6, 5, 7, 2. The cylinders are

numbered from the front to the rear with cylinder #1 on the front-left of the engine. So the

cylinders on the left side of the engine are numbered 1, 3, 5, 7 while the right side are numbered

2, 4, 6, 8. On some engines, the right bank is 1, 2, 3, 4 while the left bank is 5, 6, 7, 8. A repair

manual will tell the correct firing order and cylinder layout for a particular engine.

The next thing to know as well, is what direction the distributor is rotating in, clockwise

or counter-clockwise, and which terminal on the distributor cap that #1 cylinder is located. Once

we have this information, we can begin routing the spark plug wires. If the wires are installed

incorrectly, the engine may backfire, or at the very least, not run on all cylinders. It is very

important that the wires are installed correctly

41

Fig. 3.9 Typical V8 Firing Order 1, 8, 4, 3, 6, 5, 7, 2

Spark Plugs

The ignition system's sole reason for being is to service the spark plug. It must provide

sufficient voltage to jump the gap at the tip of the spark plug and do it at the exact right time,

reliably on the order of thousands of times per minute for each spark plug in the engine.

The modern spark plug is designed to last many thousands of miles before it requires

replacement. These electrical wonders come in many configurations and heat ranges to work

properly in a given engine.

The heat range of a spark plug dictates whether it will be hot enough to burn off any

residue that collects on the tip, but not so hot that it will cause pre-ignition in the engine. Pre-

ignition is caused when a spark plug is so hot, that it begins to glow and ignite the fuel-air

mixture prematurely, before the spark. Most spark plugs contain a resistor to suppress radio

interference. The gap on a spark plug is also important and must be set before the spark plug is

42

installed in the engine. If the gap is too wide, there may not be enough voltage to jump the gap,

causing a misfire. If the gap is too small, the spark may be inadequate to ignite a lean fuel-air

mixture, also causing a misfire.

Fig. 3.10 Spark Plug

Servicing of the spark plug consists of cleaning them to remove any carbon deposits

every 7500 km (5000 miles) and resetting their gaps. To clean the plugs effectively, a plug-

cleaning machine should be used. Before replacing them, they should be gapped, i.e. the gap set

to the manufacturer‟s figures using gap gauge and tested in the plug-cleaning machine. Every

1500 km (1000 miles) the plugs should be replaced with new ones with correctly adjusted gaps.

Distributor

When the distributor cap is removed from the top of the distributor, the points and

condenser are seen. The condenser is a simple capacitor that can store a small amount of

43

current. When the points begin to open; the current flowing through the points looks for an

alternative path to ground. If the condenser were not there, it would try to jump across the gap of

the points as they begin to open. If this were allowed to happen, the points would quickly burn

up. To prevent this, the condenser acts like a path to ground. It really is not, but by the time the

condenser is saturated, the points are too far apart for the small amount of voltage to jump across

the wide point gap. Since the arcing across the opening points is eliminated, the points last longer

and there is no static on the radio from point arcing.

The points require periodic adjustments in order to keep the engine running at peak

efficiency. This is because there is a rubbing block on the points that is in contact with the cam

and this rubbing block wears out over time changing the point gap. There are two ways that the

points can be measured to see if they need an adjustment. One way is by measuring the gap

between the open points when the rubbing block is on the high point of the cam. The other way

is by measuring the dwell electrically. The dwell is the amount, in degrees of cam rotation, that

the points stay closed.

On some vehicles, points are adjusted with the engine off and the distributor cap

removed. The fixed point is loosened and moved slightly, then retighten it in the correct position

using a feeler gauge to measure the gap. On other vehicles, most notably GM cars, there is a

window in the distributor where a mechanic can insert a tool and adjust the points using a dwell

meter while the engine is running. Measuring dwell is much more accurate than setting the points

with a feeler gauge.

Points have a life expectancy of about 10,000 miles at which time they have to be

replaced. This is done during a routine major tune up. During the tune up, points, condenser, and

44

the spark plugs are replaced, the timing is set and the carburetor is adjusted. In some cases, to

keep the engine running efficiently, a minor tune up would be performed at 5,000 mile

increments to adjust the points and reset the timing.

Distributor Servicing

1. Checking of contact breaker points for excessive pitting and renew as necessary, the correct

gap setting is best stated by the manual.

2. Inspection of insulating washers and bushes for wear and cracks.

3. Checking of serviceability of internal low tension leads.

4. Cleaning of the cap inside and out with a dry clean rag and inspect for;

a. Freedom of movement and wear of the carbon brush.

b. Cracks.

c. Signs of tracking.

5. Inspection of the rotor arm for;

a. Cracks.

b. Brass segment security

c. Correct fit on cam.

d. Signs of tracking

Contact Breaker Fault.

1. CB gap too wide

a. Engine too far advanced

b. Dwell period reduced, giving misfiring at high revolutions

45

2. CB gap too close

a. Engine too far retarded

b. Misfiring at low revolutions

3. Weak CB restoring spring. This will cause the CB points to sluggish in closing, so reducing

the dwell period. This will cause misfiring at high engine revolutions.

3.3.2 MECHANNICAL IGNITION SYSTEM

The distributor is the nerve center of the mechanical ignition system and has two tasks to

perform. First, it is responsible for triggering the ignition coil to generate a spark at the precise

instant that it is required (which varies depending how fast the engine is turning and how much

load it is under). Second, the distributor is responsible for directing that spark to the proper

cylinder (which is why it is called a distributor).

The circuit that powers the ignition system is simple and straight forward. When the key

is inserted into the ignition switch and turned to the Run position, current is sent from the battery

through a wire directly to the positive (+) side of the ignition coil. Inside the coil is a series of

copper windings that loop around the coil over a hundred times before exiting out the negative (-

) side of the coil. From there, a wire takes this current over to the distributor and is connected to

a special on/off switch, called the points. When the points are closed, this current goes directly to

ground. When current flows from the ignition switch, through the windings in the coil, then to

ground, it builds a strong magnetic field inside the coil.

The points are made up of a fixed contact point that is fastened to a plate inside the

distributor, and a movable contact point mounted on the end of a spring loaded arm. The

46

movable point rides on a 4, 6, or 8 lobe cam (depending on the number of cylinders in the

engine) that is mounted on a rotating shaft inside the distributor. This distributor cam rotates in

time with the engine, making one complete revolution for every two revolutions of the engine.

As it rotates, the cam pushes the points open and closed. Every time the points open, the flow of

current is interrupted through the coil, thereby collapsing the magnetic field and releasing a high

voltage surge through the secondary coil windings. This voltage surge goes out the top of the coil

and through the high-tension coil wire.

Now, that is voltage necessary to fire the spark plug, there is need to get it to the correct

cylinder. The coil wire goes from the coil directly to the center of the distributor cap. Under the

cap is a rotor that is mounted on top of the rotating shaft. The rotor has a metal strip on the top

that is in constant contact with the center terminal of the distributor cap. It receives the high

voltage surge from the coil wire and sends it to the other end of the rotor which rotates past each

spark plug terminal inside the cap. As the rotor turns on the shaft, it sends the voltage to the

correct spark plug wire, which in turn sends it to the spark plug. The voltage enters the spark

plug at the terminal at the top and travels down the core until it reaches the tip. It then jumps

across the gap at the tip of the spark plug, creating a spark suitable to ignite the fuel-air mixture

inside that cylinder.

47

Fig. 3.11 Ignition System Diagram

3.3.3 ELECTRICAL IGNITION SYSTEM

In the electronic ignition system, the points and condenser were replaced by electronics.

On these systems, there were several methods used to replace the points and condenser in order

to trigger the coil to fire. One method used a metal wheel with teeth, usually one for each

cylinder. This is called an armature or reluctor. A magnetic pickup coil senses when a tooth

passes and sends a signal to the control module to fire the coil.

Other systems used an electric eye with a shutter wheel to send a signal to the electronics

that it was time to trigger the coil to fire. These systems still need to have the initial timing

adjusted by rotating the distributor housing.

The advantage of this system, aside from the fact that it is maintenance free, is that the

control module can handle much higher primary voltage than the mechanical points. Voltage can

48

even be stepped up before sending it to the coil, so the coil can create a much hotter spark, on the

order of 50,000 volts instead of 20,000 volts that is common with the mechanical systems. These

systems only have a single wire from the ignition switch to the coil since a primary resistor is no

longer needed.

On some vehicles, this control module was mounted inside the distributor where the

points used to be mounted. On other designs, the control module was mounted outside the

distributor with external wiring to connect it to the pickup coil. On many General Motors

engines, the control module was inside the distributor and the coil was mounted on top of the

distributor for a one piece unitized ignition system. GM called it High Energy Ignition or HEI for

short.

The higher voltage that these systems provided allow the use of a much wider gap on the

spark plugs for a longer, fatter spark. This larger spark also allowed a leaner mixture for better

fuel economy and still insure a smooth running engine. The early electronic systems had limited

or no computing power, so timing still had to be set manually and there was still a centrifugal

and vacuum advance built into the distributor.

On some of the later systems, the inside of the distributor is empty and all triggering is

performed by a sensor that watches a notched wheel connected to either the crankshaft or the

camshaft. These devices are called Crankshaft Position Sensor or Camshaft Position Sensor. In

these systems, the job of the distributor is solely to distribute the spark to the correct cylinder

through the distributor cap and rotor. The computer handles the timing and any timing advance

necessary for the smooth running of the engine.

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Fig. 3.12 Magnetic Distributor

3.3.4 DISTRIBUTORLESS IGNITION SYSTEM

Newer automobiles have evolved from a mechanical system (distributor) to a completely

solid state electronic system with no moving parts. These systems are completely controlled by

the on-board computer. In place of the distributor, there are multiple coils that each serve one or

two spark plugs. A typical 6 cylinder engine has 3 coils that are mounted together in a coil

"pack".

A spark plug wire comes out of each side of the individual coil and goes to the

appropriate spark plug. The coil fires both spark plugs at the same time. One spark plug fires on

the compression stroke igniting the fuel-air mixture to produce power while the other spark plug

fires on the exhaust stroke and does nothing. On some vehicles, there is an individual coil for

each cylinder mounted directly on top of the spark plug. This design completely eliminates the

high tension spark plug wires for even better reliability. Most of these systems use spark plugs

that are designed to last over 100,000 miles, which cuts down on maintenance costs.

50

3.4 BRAKING SYSTEM

The typical brake system consists of disk brakes in front and either disk or drum

brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to

the master cylinder. Other systems that are connected with the brake system include the

parking brakes, power brake booster and the anti-lock system. There are two types of the

brake system which are; the mechanical and the hydraulic brake systems.

Early cars were fitted with mechanical brakes, both the foot-brake pedal and the hand-

brake lever being connected to the brake drums by a series of rods and cables. Current vehicles

use mechanical linkages only for their hand-brake mechanism. However, mechanical linkages

are commonly used on trailers, motor cycles and specialist vehicles like works truck.

Hydraulic type of braking system will be discussed in this report as they were mostly

done during the periods of the training.

Fig. 3.13 Braking System Diagram

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3.4.1 HYDRAULIC BRAKING SYSTEM.

With hydraulic brakes the transmission of force from the brake pedal to the brake shoes is

through hydraulic fluid. The system works on the principle that as the brake fluid is a liquid it

cannot be compressed, and that any pressure applied to a fluid in one direction is transmitted

equally in all direction. This principle is called Pascal‟s Law.

Working Principle

When the brake pedal is pressed, there is actually pushing against a plunger in the master

cylinder, which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the

braking unit at each wheel. Since hydraulic fluid (or any fluid for that matter) cannot be

compressed, pushing fluid through a pipe is just like pushing a steel bar through a pipe. Unlike a

steel bar, however, fluid can be directed through many twists and turns on its way to its

destination, arriving with the exact same motion and pressure that it started with. It is very

important that the fluid is pure liquid and that there is no air bubbles in it. Air can compress

which causes sponginess to the pedal and severely reduced braking efficiency. If air is suspected,

then the system must be bled to remove the air. There are "bleeder screws" at each wheel

cylinder and caliper for this purpose.

On a disk brake, the fluid from the master cylinder is forced into a caliper where it

presses against a piston. The piston, in-turn squeezes two brake pads against the disk (rotor),

which is attached to the wheel, forcing it to slow down or stop. This process is similar to a

bicycle brake where two rubber pads rub against the wheel rim creating friction.

52

With drum brakes, fluid is forced into the wheel cylinder, which pushes the brake shoes

out so that the friction linings are pressed against the drum, which is attached to the wheel,

causing the wheel to stop. In either case, the friction surfaces of the pads on a disk brake system

or the shoes on a drum brake convert the forward motion of the vehicle into heat. Heat is what

causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require

replacement.

Fig. 3.14 Hydraulic Braking System

3.4.3 CLASSIFICATION OF BRAKES

There are majorly two classifications of brake which are; disc brakes and drum brakes

Disc Brakes

The disk brake is the best brake we have found so far. Disk brakes are used to stop

everything from cars to locomotives and jumbo jets. Disk brakes wear longer, are less affected

by water, are self-adjusting, self-cleaning, less prone to grabbing or pulling and stop better than

53

any other system around. The main components of a disk brake are the Brake Pads, Rotor,

Caliper and Caliper Support.

Fig. 3.15 (a) Brake Pads (b) Caliper Support (c) Fluid flow in the disc brake

Drum Brakes

While all vehicles produced for many years have disk brakes on the front, drum brakes

are cheaper to produce for the rear wheels. The main reason is the parking brake system. On

drum brakes, adding a parking brake is the simple addition of a lever, while on disk brakes, there

is need for a complete mechanism, in some cases, a complete mechanical drum brake assembly

inside the disk brake rotor.

Drum brakes consist of a backing plate, brake shoes, brake drum, wheel cylinder,

return springs and an automatic or self-adjusting system. When the brakes are applied, brake

fluid is forced under pressure into the wheel cylinder, which in turn pushes the brake shoes into

contact with the machined surface on the inside of the drum. When the pressure is released,

return springs pull the shoes back to their rest position. As the brake linings wear, the shoes must

travel a greater distance to reach the drum. When the distance reaches a certain point, a self-

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adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that they

are closer to the drum.

Fig. 3.16 (a) Drum Brakes (b) Drum brakes parts diagram

3.4.4 POWER-ASSISTED BRAKES

The power brake booster is mounted on the firewall directly behind the master cylinder

and, along with the master cylinder, is directly connected with the brake pedal. Its purpose is to

amplify the available foot pressure applied to the brake pedal so that the amount of foot pressure

required to stop even the largest vehicle is minimal. Power for the booster comes from engine

vacuum. The automobile engine produces vacuum as a by-product of normal operation and is

freely available for use in powering accessories such as the power brake booster. The power

brake booster derived its vacuum from the low pressure in the inlet manifold. If there is a failure

in power brake booster, the footbrake will work normally, but will need harder pressure on the

pedal.

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Fig. 3.17 Power Brake Booster

3.4.5 ANTI-LOCK BRAKES (ABS)

Maximum braking happens right before each tyre locks (stop running) and starts to slide.

It is very difficult to manually maintain such fine control over braking, especially when the tyres

have a different amount of traction. Traction varies due to sand, snow, ice, bumps, vehicle

loading, and weight transfer. Special anti-lock braking systems (ABS) can sense wheel lockup

and modulate braking at that wheel many times per second. Such systems use electronics to

sense wheel rotation versus the car‟s speed. A computer then tells a hydraulic modulator to

release or restore brake line pressure as needed.

The system consists of an electronic control unit, a hydraulic actuator, and wheel speed

sensors at each wheel. If the control unit detects a malfunction in the system, it will illuminate an

ABS warning light on the dash to let you know that there is a problem. If there is a problem, the

anti-lock system will not function but the brakes will otherwise function normally.

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3.4.6 BRAKE BLEEDING

. Contaminated brake fluid is removed by flushing. Flushing is simply forcing out all the

old fluid while adding new. Any contaminants will be removed with the old fluid. Air is removed

from the system by brake bleeding.

Bleeding forces out air bubbles but not necessarily all the brake fluid. There are two ways

of bleeding, pedal and pressure. Pedal bleeding begins by topping the master cylinder reservoir

with fresh fluid. Brake fluid must never be reused during this process, fluid spillage must be

avoided on the vehicle body else ruin the paint where the fluid spills on. First, the farthest brakes

from the master cylinder are best to start with, usually the rear right. The bleeding valve is loosed

and may be attached to it a hose which is suspended at the other end into a clean jar partially

filled with fresh fluid.

It should be noted as well that the bleeding can be done without the attachment of the

hose. Bleeding at least is a two man job; one who presses the pedal and the other that do the

bleeding at the wheels. The bleed valve is opened while a helper slowly depresses the brake

pedal. While the pedal is depressed, brake fluid flows through the hose into the jar. When clean

air-free fluid flows from the hose, the helper stops the pumping of the pedal but completely

depressed.

The master cylinder reservoir fluid level must be monitored during the bleeding process.

Otherwise the reservoir will run dry causing air to be sucked into the system, which amounts to a

double work.

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The bleeder is closed, the hose is removed and the brake pedal is released. The usual

bleeding order is RR, LR, RF, and LF. This order may vary, however. A shop manual is

consulted for specific instructions and orders.

3.4.7 BRAKE DEFECTS

Excessive Brake-Pedal Travel

1. Low fluid level in reservoir.

2. Excessive clearance between linings and drum.

3. Excessive push-rod clearance.

4. Air in system.

5. Leak in system.

6. Cracked brake drum.

Brake pedal feels hard

1. Seized piston in wheel cylinder.

2. Oil or brake fluid on linings.

3. Binding brake pedal.

Brakes drag

1. Pull-off springs broken or weak.

2. Pedal return spring broken or weak.

3. Binding pedal

4. Master cylinder by-pass port choked.

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5. Seized piston in wheel cylinder.

6. Shoes seized on anchor pins.

7. Handbrake mechanism seized.

8. Master cylinder reservoir overfilled, together with a choked atmospheric port

9. Handbrake cables over-adjusted.

10. Pedal to pushrod adjustment small.

Noisy brakes

1. Weak shock absorbers.

2. Axle supports insecure.

3. Broken springs.

Brakes inefficient

1. Linings not bedded-in.

2. Linings greasy.

3. Incorrect type of lining.

Brakes grab

1. Linings not bedded-in.

2. Wrong type of linings.

3. Oil or brake fluid on linings.

4. Loose back plate on anchor pins.

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Braking is unbalanced

1. Oil or brake fluid on linings of one brake

2. Distorted brake drums.

3. Tyres unevenly inflated.

4. Back plate loose on the axle.

5. Bolts connecting axle to road springs loose.

6. Front spring broken.

7. Worn steering connections.

8. Lining of different types or grades fitted.

3.5 THE WHEELS AND TYRES

For the wheels and tyres to be able to carry out their functions efficiently they must be

made and maintained to the following basic requirements:

1. They must be perfectly round. If the wheel and tyre are not round then the vehicle

will bounce and shake as it goes along the road.

2. They must be stiff, i.e. not able to flex from side to side. A stiff wheel gives precise

steering and smooth running.

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3.5.1 FUNCTIONS OF WHEEL AND TYRES

The functions of the wheels and tyres are:

1. To allow the vehicle to roll freely along the road.

2. To support the weight of the vehicle.

3. To act as a first step part of the suspension.

4. To transmit to the road surface the

(a) Driving force, (b) Braking force, (c) Steering force.

3.5.2 TYRES

The function of the pneumatic tyre is to provide a cushion of compressed air as a shock-

absorbing medium. It may, therefore, be considered as part of the suspension system; in addition,

the tread provides the necessary friction between the road and the wheel for braking and static

forces. The air in the tyres may be contained inside the inner tube which is protected by outer

cover, but recently on modern cars, the tubeless tyre is now widely used.

The tyre is constructed of a number of layers of rayon or nylon cords. In this country

synthetic rubber has superseded natural rubber for the treads of car tyres to give longer life and

better grip on wet surfaces. Tyres are produced in three basic constructions which are:

Bias.

Bias/Belted.

Radial.

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The tread pattern is usually a compromise between slow rate of wear and grip. Thus a

tyre with pronounced tread will probably have a good adhesion, especially on wet roads, but its

rate of wear and also its noise level may be objectionable. Another factor which has made the

design of tyres difficult is the tendency of designers to use smaller diameter wheels in order to

gain a lower centre of gravity and also less interference of the rear wheel arches in the body.

Other markings might be found on the tyre such as; M & S for mud and snow. In areas

where it snow, chains are required unless the car is equipped with mud and snow tyres.

3.5.3 HYDROPLANNING

Rainwater that lingers in the ruts of roads places demands on driving. When the ruts are

deep, the risk of hydroplaning is high, but anticipatory driving and good treads can reduce the

risk. New tyres are the best weapons against hydroplaning. A tread pattern that channels water

out from between the tyre and the road is the most effective means of preventing hydroplaning.

According to test results, hydroplaning starts at 76 km/h (47 mph) when cornering on worn out

tyres (groove depth below 1.6 mm), whereas the corresponding speed for new tyres is 96 km/h

(60 mph).

3.5.4 TYRE MAINTENANCE

Tyre Inflation: The most important item in a tyre maintenance program is a sound,

regular inflation maintenance program. Inflation supports and carries the load. Inflation must be

maintained as specified for the load and service condition. Tyres are designed and built to deflect

in service. Inflation pressures are established to assure tyres deflect properly. The pressures

required vary with the load, speed and type of service. When inflation pressure is too high or too

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low, the tyre does not deflect within design limits. Tyres deteriorate quickly under these

conditions. Generally, low speed off-the-road operations allow heavier loads at a given inflation.

At high speeds, loads must be decreased.

Over inflation of tyres can:

Reduce the ability of the tyre to absorb road shocks, resulting in a much harsher ride

Cause excessive wear of the centre of the tyre.

Under inflation can:

Cause excessive flexing in the tyre, building up internal heat and causing rapid and

irregular tread wear.

Create more rolling resistance which will have a negative impact on your vehicle‟s fuel

efficiency.

Tyre Rotation: Different vehicles will wear their tyres at different rates. For example, a front-

wheel drive car will wear its tyres very differently from a rear-wheel drive. Wagons and utilities

– because of the lack of weight over the rear wheels – will also wear at varying rates.

One of the best ways to look after the tyres is by rotating them regularly. Swapping the

rear tyres to the front and vice-versa ensures that tyres wear evenly and last significantly longer.

As a guide, tyres should be rotated every 5,000 to 8,000 km even if there is no sign of uneven

wear. Tyre should be rotated in a definite pattern, and the same pattern should be followed every

time they are rotated.

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Tyre Storage: Proper tyre storage can slow down the ageing of the tyres. Below are the

conditions for proper tyre storage.

1. Temperature: The storeroom temperature should be below +25 ºC, it should preferably be

dark and below +15 ºC. The properties of rubber may change, affecting the final service

life of the tyre, if the temperature is above 25 ºC or below 0 ºC. Cool storage does not

have any adverse effect on rubber products.

2. Humidity: Extremely humid conditions should be avoided. Humidity in the storeroom air

must not be so high that condensation occurs on the tyres. Tyres must not be stored in

conditions where they are exposed to rain, splashes, etc.

3. Light: Tyres must be protected from light, particularly from direct sunlight and intense

artificial light with a high ultraviolet content.

4. Oxygen: Ozone has a very strong deteriorating effect on tyres. The storeroom must not

contain any ozone-producing equipment, such as fluorescence lamps or mercury vapour

lamps, high-voltage electrical equipment, electric motors or any other electrical

equipment that may generate sparks or silent electric discharges

5. Deformation: If possible, tyres must be stored freely in their natural form, so that they are

not under stress, pressure or torsion. Strong deformities developed during long-time

storage may break when pressurized.

6. Solvent, oil, greases, heat: Tyres must be particularly protected from any contact with

solvents, oils or greases, however short-term. Tyres must also be protected from powerful

emitters of light and spatter from electric welding.

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7. Tyre handling: When handling tyres in warehouse it is detrimental to drop tyres higher

than 1.5 m. Tyres could damage on drop from bead area. Typical consequence could be

kinked bead.

Tyre Inspection

Tyre inspection includes:

Checking of tyre pressures regularly.

Inspection during each rotation and at regular intervals between rotations. Any tyre that

has a tread depth of less than 1.6 mm should be replaced.

Inspection of rolling direction during rotation or fixing of tyres.

Checking of old tyres for uneven wears.

Tyre-changing: The sequence below must be followed when changing a tyre on a wheel:

1. A key is used to unscrew the valve and so deflate the tyre.

2. The tyre bead is pressed away from the wheel-rim edge on both sides of the tyre.

3. One side of the tyre is levered off the wheel.

4. The other side of the tyre is levered off, thus removing the tyre from the wheel. The

procedures are reversed for refitting.

3.5.5 WHEEL ALIGNMENT

In its most basic form, a wheel alignment consists of adjusting the angles of the wheels so

that they are perpendicular to the ground and parallel to each other. The purpose of these

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adjustments is maximum tyre life and a vehicle that tracks straight and true when driving along a

straight and level road.

Wheel Alignment is often confused with Wheel Balancing. The two really have nothing

to do with each other except for the fact that they affect ride and handling. If a wheel is out of

balance, it will cause a vibration at highway speeds that can be felt in the steering wheel and/or

the seat. If the alignment is out, it can cause excessive tyre wear and steering or tracking

problems. The three primary angles of adjustment are camber, caster and toe.

Camber

Camber is the angle of the wheel, measured in degrees, when viewed from the front of

the vehicle. If the top of the wheel is leaning out from the center of the car, then the camber is

positive, if it's leaning in, then the camber is negative. If the camber is out of adjustment, it will

cause tyre wear on one side of the tyre's tread. If the camber is too far negative, for instance, then

the tyre will wear on the inside of the tread.

If the camber is different from side to side it can cause a pulling problem. The vehicle

will pull to the side with the more positive camber. On many front-wheel-drive vehicles, camber

is not adjustable. If the camber is out on these cars, it indicates that something is worn or bent,

possibly from an accident and must be repaired or replaced.

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Fig. 3.18(a) Camber Angle (b) Camber Angle Effect on Tyres

Caster

When the steering wheel is turned, the wheels of the vehicle turn on an upper and a lower

pivot. Caster is the angle of the line between these two pivot points and a vertical line. If the top

pivot is leaning toward the rear of the car, the caster is positive. If it is leaning toward the front of

the car, the caster is negative. If the caster is different from side to side, the vehicle will pull to

the side with the least positive caster. If caster is equal but too negative, the steering will feel

light and vehicle will wander over the road. If the caster is too positive, the steering will feel

heavy and the steering wheel will pull hard to center coming out of a turn. Caster has little effect

on tyre wear.

Toe

Toe is a measurement in fractions of an inch of the difference in distance between the

front of the wheels and the rear of the wheels. This setting is close to zero or very slightly in.

This means the wheels are parallel. Toe in means the front of the wheels are closer together than

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the rear of the wheels. This will cause wear on the outer portion of the tread, this type of tyre

wear is called a saw-tooth wear pattern. Toe out means the front of the wheels are farther apart

than the rear of the wheels and this condition will cause wear on the inside of the tread. Toe is

adjustable on the front wheels of all vehicles and on the rear wheels of some vehicles.

Fig. 3.19 (a) Toe-in and Toe-out (b) Caster Effects on Tyres

3.6 CLUTCH ASSEMBLY

The purpose of the clutch is to transmit the torque, or turning force, from the engine to

the transmission. It is designed so that the drive can be engaged and disengaged smoothly and

easily. By disengaging the drive, the clutch allows the gears to be changed smoothly and it

provides a temporary neutral position. This allows the transmission gears to be engaged or

disengaged whilst the engine is running.

To understand how a clutch works, it helps to know a little bit about friction, which is a

measure of how hard it is to slide one object over another. A clutch works because of friction

between a clutch plate and a flywheel.

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The clutch assembly is contained in the bell-housing between the engine and the gearbox.

The main components of the clutch are the pressure plate, the flywheel, clutch disc, clutch

release bearing, pilot bushing and transmission front bearing retailer.

Fig. 3.20 Clutch Assembly

3.6.1 CLUTCH MAIN COMPONENTS

Flywheel: The flywheel provides a friction surface for the clutch disc, a mounting surface for the

pressure plate, a mounting for the starter driven gear, and on some engines, the flywheel is a

factor in engine balance.

The condition of the friction surface of the flywheel is important for proper clutch

function. The surface should be smooth and free of burned spots and surface cracks. Used

flywheels can be re-surfaced. This should be done by grinding rather than lathe turning as less

material is removed. The amount of material removed from the face can affect which clutch

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release bearing should be used. A flywheel should always be checked for run out on the engine it

will be used on. Face run out should not exceed .005 (five thousandths) of an inch.

Fig. 3.21 Flywheel

Pressure Plate: This is the "driven" part of the clutch. It has a friction material riveted to each side of a

wavy spring (called a marcel). This is attached to a splined hub that the transmission input gear

protrudes into.

There are basically two types of friction material used for clutch lining. These are organic

and metallic. The organic is best for all around use. The metallic is preferred by some for severe

duty applications but requires high spring pressures and is hard on the flywheel and pressure

plate friction surfaces. Avoid solid hub clutches and clutches without marcel as they will always

chatter when used in vehicles with a rear differential mounted on springs (as opposed to a

transaxle design).

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Fig. 3.22 Pressure Plate

Clutch Disc: The clutch disc, or driven disc, transfers engine torque from the flywheel to the

transmission input shaft when engaged. In normal use, the disc is replaced when its friction

facing wears thin.

Usually, the friction facing is riveted to the disc, sometimes it is bonded with riveted

facings, and the disc must be replaced before the friction material is worn flush with rivets, or

rapid pressure plate and flywheel scoring will occur.

Fig. 3.23 Clutch Disc

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Pilot Bushing: In most cases, this is a porous bronze, pre-lubed bushing rather than an actual

bearing, as it is often called. A few applications still use an actual bearing and others use a needle

roller type bearing, but by far, the most common type is bronze. a roller bearing cannot be used

on a transmission shaft originally designed for a bronze bushing due to different type of heat

treatment on the shafts.

The pilot bushing is seldom thought of as a part of the clutch system but it is one of the

most vital parts of the system. It pilots the end of the transmission input gear in the crankshaft. If

it is worn or not running "true", it can cause serious clutch problems or transmission failure. Pilot

bushing bore run out should always be checked with a dial indicator and should be within .002

total. The bronze bushing type should be a press fit in the crankshaft bore. It must be installed

carefully. It should have between .001 and .003 clearance on the transmission shaft when

installed. The pilot bushing is only functional when the clutch is disengaged but it is a factor in

input gear alignment at all times.

Clutch Release Bearing: As its name implies, this is the bearing that releases the clutch. It is

often referred to as a "throw-out" bearing. They come on a number of different style carriers. The

carriers, in some cases, vary considerably with the particular engine. Because the release bearing

only works when the clutch is being released it usually lasts quite a long time. However,

improper linkage adjustment or riding the clutch with your foot when driving can wear the

bearing prematurely. Normally there should be a minimum of 1/16" clearance between the face

of the bearing and the three release fingers or diaphragm spring of the pressure plate when the

clutch is engaged.

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Fig. 3.24 Clutch Release Bearing

Transmission Front Bearing Retainer: This great device has three critical functions. This first

is as its name implies. The second is to provide a register on which the bell housing must center.

This is feature is sometimes overlooked with expensive consequences. Thirdly, its tubular snout

is the surface on which the throw-out bearing rides on its way into to depress the springs of the

pressure plate. Conversions often require special and modified retainers to achieve compatibility.

Fig. 3.25 Transmission Front Bearing Retainer

3.6.2 OPERATING MECHANISMS

The clutch is engaged and disengaged with the left-hand pedal. The pedal can be

connected to the thrust race assembly by one of several methods:

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Mechanical operated clutches need a direct linkage which is subjected to movement of

the engine on its mountings and results in judder being transmitted to the clutch. This problem is

particularly aggravated by the remote position of the clutch and clutch pedal.

Hydraulic Clutch

Both the rod and the cable clutches rely on mechanical linkages and therefore on the

lengths of the levers for their mechanical advantage. The hydraulic clutch uses hydraulic fluid,

like that used in hydraulic brakes, to transmit the movement form the clutch pedal to the clutch

cross-shaft in the bell-housing. This system has its mechanical advantage ( the difference

between the pressure applied by the foot on the pedal and the actual pressure moving the clutch

thrust race) built into the hydraulic system.

The clutch pedal moves a pushrod which pushes a hydraulic piston into the master

cylinder. The hydraulic fluid above the piston is forced along the connecting tube. This fluid in

turn forces the slave cylinder piston against the operating rod which moves the clutch cross-

shaft. These systems are very efficient and smooth in operation, being used on modern cars and

trucks. It is essential that the fluid in the master cylinder reservoir is kept topped to the right

level.

3.7 SHOCK ABSORBERS

The function of shock absorbers, however, is not primarily to increase the resistance to

deflection but to damp out small vibration and prevent them from being transmitted to the

chassis, and to check rebound which would otherwise cause a violent pitching of the car in a

fore-and-aft direction.

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Rebound is when the axle moves downwards after the spring has been compressed by the

wheel surrounding an obstacle. This up-and-down movement, if undamped, will continue for

some time, getting less and less. Efficient shock absorbers will retard the speed at which the axle

returns and minimize any further oscillations.

The most widely used shock absorbers in today‟s modern cars are the hydraulic ones; it

makes use of hydraulic pressure which will not vary in the same way with wear as occurs on

other types. Another advantage is that it is possible to have a different resistance on the rebound.

Telescopic Shock Absorber

The telescopic shock absorber gets its name from its telescopic-like shape and action. The

cylinder is filled with oil or, as it is generally called, shock absorber fluid. The cylinder is

connected to the axle or suspension with a mounting eye. The piston and valve assembly, which

are able to move in the cylinder, are mounted to the vehicle‟s chassis with the upper mounting

eye or a bolt arrangement. When the wheel hits a bump the suspension travels upwards,

shortening the distance between the mounting. Therefore the piston travels down the cylinder.

The resistance of the oil slows the movement of the piston, so damping the shock load on

the suspension. When the wheel has gone over the bump the suspension rebounds, i.e. the wheel

travels down again and the piston travels up the cylinder. The resistance of the oil dampens the

suspension movement, so preventing the car from bouncing along the road.

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CHAPTER FOUR

REFRIGERATION AND AIR-CONDITIONING

4.1 BASIC CONCEPTS AND DEFINITIONS

4.1.1 REFRIGERATION

Refrigeration is the withdrawal or removal of heat from a substance or within a space,

resulting in a temperature lower than that which would exist under the natural influence of the

surroundings. This withdrawal of heat may be accomplished by the use of ice, snow, chilled

water or mechanical refrigeration. Several types of mechanical refrigeration are available.

4.1.2 AIR-CONDITIONING

Air-conditioning is the treatment of air in an enclosure with a view to controlling its

temperature, humidity (moisture content or water vapour), motion and air quality (cleanliness) to

meet the requirements of the enclosure. These requirements are usually for human comfort or/

and industrial process control.

Two types of air conditioning are available: summer air conditioning and winter air

conditioning. Summer air conditioning involves cooling and dehumidification (removal of

moisture) of air in an enclosure while in winter air conditioning, the reverse situation exists, that

is, heating and humidification (addition of moisture).

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4.2 APPLICATIONS OF REFRIGERATION

Modern refrigeration has many applications. For convenience, these applications can be

classified into six groups thus;-

a. Domestic Refrigeration: Household refrigerators and home freezers: for production of

ice, beverage cooling in restaurants and in general for food preservation.

b. Industrial Refrigeration: Food-packing plants (meat, fish and frozen foods industries),

breweries, creameries; industrial plants such as oil refineries and rubber plants.

c. Marine Refrigeration: This involves refrigeration on ship vessels as in fishing boats.

d. Transportation Refrigeration: This applies to trucks for delivery of refrigerated

commodities.

e. Comfort Air conditioning: Refrigeration provides the cooling part in the conditioning of

air for human comfort at homes, stores, public buildings, automobiles and aircrafts.

f. Industrial Air conditioning: Refrigeration has special applications in manufacturing and

construction industries. For instance, in such industries, its functions include;-

I. Governing the rate of chemical and biochemical reactions

II. Producing low temperatures used in industrial operations for production and

protection of precision components.

4.3 REFIGERANTS

A refrigerant is a working fluid used in a refrigerating mechanism. It is a heat carrier

which absorbs heat from the evaporator as it changes phase from liquid to vapour and releases

this heat in the condenser by condensing from vapour to liquid.

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4.3.1 PROPERTIES OF A REFRIGERANT

For a working fluid to be used as a refrigerant, it must possess certain properties. The

following, though not arranged in order of importance, are some of the essential requirements of

a refrigerant:

1. Non-toxic, non-poisonous and odorless

2. Non-expensive and non-corrosive

3. Ease of leak detection

4. Low cost

5. Chemically stable i.e. no reaction with lubricating oils

6. High latent heat of vapourization at evaporator temperature for good cooling effect

7. Low freezing point

8. Low condensing pressure

Some refrigerant application

Name Cylinder Colour Application

R-12 (Freon 12) White Domestic refrigerator, domestic food freezers,

auto. air-conditioning, vending machines,

shipboard air-conditioners, water coolers, room

and window air conditioners

R-22 (Freon 22) Green Food freezing plants, window air conditioners,

public building air conditioning, frozen food

delivery service vans

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R-717 (Ammonia) Silver Ice plants, large storage facilities, absorption

refrigeration systems.

4.3.2 REFRIGERANT CYLINDERS AND CARE IN HANDLING

Refrigerant cylinders are usually made of steel or aluminium materials. They are

available in three forms viz:

i. Service cylinders

ii. Supply cylinders and

iii. Disposable (throw away) cylinders

Refrigerant cylinders should always be stored in cool dry place and should not be

exposed to excessive temperatures and pressures otherwise may explode. The cylinder should

not be completely filled with refrigerant. Space must always be allowed for expansion otherwise

high pressure developed by expanding refrigerant may burst the cylinder.

4.4 BASIC COMPONENTS OF A REFRIGERATION SYSTEM

All the principal parts and path of refrigerant flow are indicated. A refrigerant system

consists essentially of two different pressure conditions: the low-pressure side and the high-

pressure side. The evaporator, suction line, the inlet of the compressor and the outlet to the

refrigerant control are on the low-pressure side. The condenser, filter drier, liquid line, the outlet

to the compressor and the inlet to the refrigerant control are on the high-pressure side.

(a) Compressor: The compressor is the heart of a compression refrigeration cycle. It is a

mechanism which draws low pressure refrigerant from the suction line, compresses the

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vapourized refrigerant and discharges it at high pressure to the condensing side of the cycle.

Details of the common types of compressors used are discussed in the later part of this report.

(b) Condenser: This part of the refrigeration system receives hot high pressure refrigerant

vapour from the compressor, removes heat from the refrigerant until it returns to a liquid phase.

(c) Filter-drier: This device contains desiccant for the removal of moisture from the

refrigerant. Moisture, if not removed, will combine with oil to form sludge and stops the flow of

refrigerant. A new liquid line filter-drier must be installed in a system whenever a major repair

work is done on the system.

(d) Capillary tube: the word capillary means “hair-like” that is, very small in diameter. A

capillary tube, therefore, is a very small tube of sufficient length to produce the metering effect

desired. The capillary tube is usually soldered or clamped to the suction line for heat exchange

processes. Capillary tubes with internal diameters of 0.66mm to 1.4mm are common, and the

lengths may be anywhere from a few meters to several meters, depending upon the application.

The internal wall of the capillary tube is rough thus offering frictional resistance to the

flow of refrigerant which results in a pressure drop along the length of the tube. Due to this

pressure drop the liquid refrigerant at inlet to the evaporator is considerably reduced in pressure

with corresponding drop in temperature.

(e) Evaporator: This is the part of the refrigeration system where the refrigerant absorbs

heat from the compartment and vapourizes to produce the desired cooling effect.

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(f) Motor Control Thermostat: The motor control thermostat is an electromechanical

switch to control the starting and stopping of the compressor motor. It operated by a

temperature/pressure sensitive gas or liquid. The gas or liquid is trapped inside a bulb and a tube

attached to the outlet of the evaporator.

4.4.1 COMPRESSORS FOR REFRIGERATING SYSTEM

There three basic types of compressors in use in vapour compression refrigerating

systems. They are:

a. Reciprocating compressor

b. Rotary compressors and

c. Centrifugal compressors

However, within the scope or this report, only the reciprocating compressors would be

discussed.

Reciprocating Compressors

A reciprocating compressor uses a piston and cylinder arrangement to provide

compression action. The corresponding unit of the reciprocating compressor draws in vapour

refrigerant from the low pressure side of the system, compresses and discharges it at high

pressure to the condenser. There are three basic types of reciprocating compressor in use:

i. Hermetic compressor: It consists of the compressing units and the electric motors which

are hermetically sealed (welded) in a domed housing.

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ii. Semi-hermitic compressor: The compressing unit and the electric motor are sealed in

housing by means of bolts. The cylinder head can be lifted so that valves and pistons can

be serviced.

iii. Open type compressor: The crankshaft of the open type compressor extends from the

housing and is externally driven by a pulley/belt assembly or through an electric motor.

Open-type reciprocating compressors are used in cars and for commercial systems.

Possible Compression Damages and Prevention

a. Broken discharge pipe

b. Electric shock due to naked wire

c. Damage or wear of internal valve

d. Damage of the electric motor due to erratic power supply

The compressor is prevented from damage through the following

Use of overload protector

Use of relay

Gauging of the refrigerant level in the compressor

Rubber stopper are used at the base of the compressor to reduce vibration and noise.

Oil lubrication of the compressor to prevent wear.

Refrigerant charging in case of low refrigerant gauge of the compressor

Leakages detection and repairs.

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4.5 AIR-CONDITIONING SYSTEM

An air-conditioning system consists of components and equipment arranged in sequential

order to heat or cool, humidify or dehumidify, clean and purify, attenuate objectionable

equipment noise, transport the conditioned outdoor air and recirculate air to the conditioned

space, and control and maintain an indoor or enclosed environment at optimum energy use.

The types of buildings which the air-conditioning system serves can be classified as:

Institutional buildings, such as hospitals and nursing homes

Commercial buildings, such as offices, stores, and shopping centers

Residential buildings, including single-family and multifamily low-rise buildings of three

or fewer stories above grade

Manufacturing buildings, which manufacture and store products

4.5.1 BASIC CLASSIFICATIONS

The purpose of classifying air-conditioning systems is to distinguish one type from

another so that an optimum air-conditioning system can be selected according to the

requirements. Proper classification of air-conditioning systems also will provide a background

for using knowledge-based expert systems to help the designer to select an air-conditioning

system and its subsystems.

Since air system characteristics directly affect the space indoor environmental parameters

and the indoor air quality, the characteristics of an air system should be clearly designated in the

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classification. The system and equipment should be compatible with each other. Each system has

its own characteristics which are significantly different from others.

Air conditioning or systems can be classified as individual, space, packaged, and central

systems.

1. Individual System: Individual systems usually have no duct and are installed only in

rooms that have external walls and external windows.

2. Packaged Systems: In packaged systems, air is cooled directly by a DX coil and heated

by direct-fired gas furnace or electric heater in a packaged unit (PU) instead of chilled

and hot water from a central plant in a central system. Packaged systems are different

from space conditioning systems since variable-air-volume supply and air economizer

could be features in a packaged system. Packaged systems are often used to serve two or

more rooms with supply and return ducts instead of serving individual rooms only in an

individual system.

3. Central Systems: Central systems use chilled and hot water that comes from the central

plant to cool and heat the air in the air-handling units (AHUs). Central systems are built-

up systems. The most clean, most quiet thermal storage systems, and the systems which

offer the most sophisticated features, are always central systems.

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4.5.2 AIR-CONDITIONING SYSTEM COMPONENTS

The air-conditioning systems have almost the same components as the refrigeration

system only that there are some components in the air conditioning system that cannot be found

in the refrigeration systems. They are;

The fan blower inside the evaporator compartment

The fan blade in the condenser compartment

The capacitor that gives power to the compressor and the fan motor

The fan motor which drives both the fan bade and the fan blower

The expansion valve that controls the refrigerant flow into the evaporator.

Fig. 4.1 Car Air-Conditioning Flow Diagram

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CHAPTER FIVE

RECOMMENDATION AND CONCLUSION

SIWES was established to provide opportunities for students to be involved in the

practical aspect of their respective disciplines in the industrial working environments.

During the 12-weeks industrial training, the trainee gained a wide range of experience

from the various repairs and maintenance undertaken such as the ability to handle some

equipment in the workshop and learning the principles through which they operate. All the

experience gained help to fulfil the objectives of SIWES.

From all these, it is evident that good design results when there is harmony among the

artistic, the technological and the practical facets of mechanical engineering.

RECOMMENDATIONS

Having gone through the 8-weeks industrial training, I the trainee has the following

suggestions for the effectiveness of SIWES:

Trainees should endeavour always to be involved in practical work and discovery works.

This really goes a long way to ensure the completeness of one‟s experience in this

profession.

Companies should show more commitment to the training of technology students so as to

improve the quality of training given.

Government should endeavour to improve automobile works by providing more research

facilities through the use of improved modernize equipment

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REFERENCES

Fundamentals of Refrigeration & Air-Conditioning. By O.A. Osore, IPS Educational

Press, NIG; 1st Edition, (2000)

Understanding Automotive Engineering (Principle). J.A Odunnaike & Bayo Otuyemi,

IPS Educational Press, NIG; 1st Edition, (2004)

Motor Vehicle Technology. By J.A Odunnaike, Pius Debo [Nig.] Press, Ijebu-Ode;

(2005)

Wang, S.K. and Lavan, Z. “Air-Conditioning and Refrigeration” Mechanical Engineering

Handbook. Ed. Frank Kreith Boca Raton: CRC Press LLC, 1999

http://www.civiccenterauto.net/services/alignment-steering-and-suspension/

http://www.familycar.com