98613441 automobile engines
TRANSCRIPT
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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
CHAIRMAN
D.W.M.S
DIRECTOR
D.W.M.S
HEAD OF ELECTRICAL
DEPT.
HEAD OF MECHANICAL
DEPT.
HEAD OF CIVIL
DEPT.
ENNGINEER 1 & SIWES
SUPERVISORWORKS
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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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.
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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,
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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
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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
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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
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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
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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
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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
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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.
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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
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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.
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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
http://www.familycar.com/brakes.htm#Disc%20Brakehttp://www.familycar.com/brakes.htm#Disc%20Brakehttp://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Brake%20Lineshttp://www.familycar.com/brakes.htm#Brake%20Lineshttp://www.familycar.com/brakes.htm#Brake%20Lineshttp://www.familycar.com/brakes.htm#Master%20Cylinderhttp://www.familycar.com/brakes.htm#Parking%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Anti-Lock%20Brakeshttp://www.familycar.com/brakes.htm#Anti-Lock%20Brakeshttp://www.familycar.com/brakes.htm#Anti-Lock%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Power%20Brakeshttp://www.familycar.com/brakes.htm#Parking%20Brakeshttp://www.familycar.com/brakes.htm#Master%20Cylinderhttp://www.familycar.com/brakes.htm#Brake%20Lineshttp://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Disc%20Brake
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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.
http://www.familycar.com/brakes.htm#Brake%20Fluidhttp://www.familycar.com/brakes.htm#Disc%20Brakehttp://www.familycar.com/brakes.htm#Rotorhttp://www.familycar.com/brakes.htm#Rotorhttp://www.familycar.com/brakes.htm#Disc%20Brakehttp://www.familycar.com/brakes.htm#Brake%20Fluid
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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
http://www.familycar.com/brakes.htm#Drum%20Brakehttp://www.familycar.com/brakes.htm#Brake%20Padshttp://www.familycar.com/brakes.htm#Brake%20Shoeshttp://www.familycar.com/brakes.htm#Brake%20Shoeshttp://www.familycar.com/brakes.htm#Brake%20Padshttp://www.familycar.com/brakes.htm#Drum%20Brake
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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-whee