Automotive mechanics (volume i)(part 2, chapter9) engine construction and components

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125

Chapter 9

Engine construction
and components

Engine construction
Components of an engine assembly
Engine features
Working on engines – general
Working on the underside of the engine
Working on the front of the engine
Working on the top of the engine
Working on engine ancillaries
Working on engine electrical systems
Technical terms
Review questions


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126 part two engines and engine systems
This chapter deals with the general construction of an
engine and its main components, and also some engine
design features. It uses basic engine dismantling as a
means of understanding how an engine is constructed
and how its parts can be removed and replaced.
■ Engine construction and overhaul is covered in
more detail in Part one of Volume 2.

Engine construction

The parts work like this
The timing belt drives the camshaft pulley, which is
attached to the camshaft. The cams on the camshaft
operate the rocker arms, which pivot on their shafts to
open and close the valves.
The intake valves are opened to admit air–fuel
mixture, and the exhaust valves are opened to
discharge the burnt gases.
Components at the front of the engine

While multicylinder engines contain parts which
perform the same functions as those of a singlecylinder engine, they are more complex and have
many more parts. However, it is easier to understand
how an engine is constructed if it is first broken down

into sections before considering the complete engine.
For our purpose, this will be done by looking at
internal parts at the top of the engine, at the front of the
engine, at the rear of the engine, the main internal
parts, and finally the components of an engine
assembly.

Figure 9.2 shows parts that are located at the front of
the engine, including those in the previous illustration.
These are:
1. piston
2. connecting rod
3. crankshaft
4. crankshaft timing pulley
5. timing belt
6. crankshaft pulley and balancer.

Components at the top of the engine
Figure 9.1 shows the top section of one cylinder of an
engine. These parts, except the piston, are serviced
during what is known as a top overhaul.
Parts that can be identified in the illustration are:
1. timing belt
2. camshaft timing pulley
3. camshaft
4. rocker arms and shafts
5. two intake valves and springs
6. two exhaust valves and springs
7. piston.

figure 9.2

Components at the front of an engine
DAIHATSU

The parts work like this

figure 9.1

Components at the top of an engine

DAIHATSU

The piston is shown on top dead centre (TDC). On the
power stroke, combustion pressure forces the piston
down on the power stroke. Through the connecting rod,
this rotates the crankshaft so that the engine operates.


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chapter nine engine construction and components

The crankshaft timing pulley (or sprocket) drives

the timing belt, and this rotates the camshaft to operate
the valves as described before.
The crankshaft pulley (which is a different one to
the timing pulley) is used to drive parts on the outside
of the engine – the fan, water pump, alternator, power
steering and the air-conditioning compressor (these
parts are not shown in the illustration). The crankshaft
pulley is part of a vibration damper that helps to reduce
engine vibration.
Components at the rear of the engine
A section at the rear of the engine is shown in
Figure 9.3. The parts shown are:

127

1. flywheel
2. starter ring gear
3. piston and connecting rod
4. part of the crankshaft and the crankshaft flange.
The parts work like this
The starter has a pinion which engages with the ring gear
on the flywheel. When the starter is operated, it spins the
crankshaft, the pistons are moved up and down, and fuel
is taken into the cylinders. The fuel is ignited by the
spark plugs so that the engine starts and runs.
The flywheel is bolted to a flange on the rear end of
the crankshaft. The flywheel is a heavy cast-iron disc
that is used to make the engine run smoothly. It does
this by absorbing energy during the power strokes and
releasing energy during the other strokes.

Components at the bottom of the engine
Figure 9.4 illustrates the lower section of the engine.
The parts identified are:
1. four pistons
2. connecting rods
3. crankshaft
4. crankshaft balance weights

figure 9.3

Components at the rear of an engine
DAIHATSU

figure 9.4

Internal components at the bottom of an engine

5. crankshaft main-bearing journals
6. pulley and balancer.


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128 part two engines and engine systems

The parts work like this

Components inside the engine

The crankshaft has four cranks to which the connecting
rods are attached. A bearing between the connecting
rod and the crankpin reduces friction and wear.
The upper end of the connecting rod is connected to
the piston by a large piston pin. This allows the
connecting rod to move in relation to the piston, with a
wrist-like action.
The crankshaft is supported in the crankcase on its
main-bearing journals. During manufacture, these are
accurately ground to produce a fine surface-finish.
The crankshaft has a number of balance weights.
These masses of metal are located opposite the cranks
to balance the crankshaft.
The crankshaft and its bearings are sometimes
referred to as the bottom end because they are located
near the bottom of the engine.

The parts shown in the previous illustrations are
combined in Figure 9.5, which shows the internal
construction of the engine. These are the main
operating parts of the engine. They include the valve
mechanism, timing belt, crankshaft, pistons, connecting rods, and the flywheel. These parts are identified
on the illustration.

■ The bottom end of the connecting rod is often
referred to as the big end because it is the larger

end of the connecting rod.

figure 9.5

The parts work like this
There are four valves per cylinder – two intake and
two exhaust.
The camshaft pulley is twice the size of the
crankshaft pulley, so that the camshaft rotates at half
the engine speed. The timing pulleys are connected by
a timing belt. This has teeth which mesh with the teeth
on the pulleys.
The camshaft has a cam for each valve. These are
positioned on the camshaft so that they will open and
close the right valve at the right time. Also, the
camshaft is timed to the crankshaft so that the valves

Internal parts of an engine identified
1 camshaft timing gear, 2 timing belt, 3 rocker shafts, 4 intake rocker arms, 5 exhaust rocker arms, 6 valve
spring, 7 exhaust valves, 8 flywheel, 9 crankshaft, 10 balance weights, 11 connecting rod, 12 piston, 13 crankshaft journal,
14 pulley and balancer, 15 crankshaft timing pulley, 16 belt tensioner, 17 intake valve, 18 camshaft DAIHATSU


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chapter nine engine construction and components

129

open and close at the correct times in relation to the
positions of the pistons.
The pistons are fitted with piston rings which seal
against the cylinder walls. To identify the pistons, they
are numbered from front to rear.
In the illustration, No. 1 and No. 4 pistons are
shown at the top of their stroke (TDC), and No. 2
and No. 3 pistons are at the bottom of their stroke
(BDC).

cylinder head have been cut away so that the internal
parts of the engine can be seen.
The following are parts that are identified: cylinder
block, cylinder head, valve cover, oil pan, exhaust
manifold, intake manifold, throttle body, fan, water
pump, distributor with cables, spark plugs, oil filter,
and the oil pump.

■ While a timing belt is shown, some engines have a
timing chain.

The cylinder block is the largest part of the engine.
The other parts are either fitted into the cylinder block
or attached to it. It has cylinders in which the pistons
operate and bearings which carry the crankshaft. In

some engines, the cylinder block also carries the
camshaft.
The cylinders and pistons are in the upper part of
the cylinder block and the crankshaft is in the lower
part. This lower part is called the crankcase. It has
webs which carry the crankshaft main bearings.

Components of an
engine assembly
Figure 9.6 shows the complete engine. The internal
parts are now installed in the cylinder block and in the
cylinder head. There are also some ancillaries installed
on the outside of the engine. The cylinder block and

figure 9.6

Cylinder block

External components of an engine identified
1 fan, 2 viscous fan coupling, 3 water pump, 4 spark plug, 5 timing-belt cover, 6 spark plug connector, 7 throttle
body, 8 intake manifold, 9 rocker cover, 10 spark plug cables, 11 distributor, 12 cylinder head, 13 exhaust manifold, 14 exhaust
pipe, 15 cylinder block, 16 crankcase, 17 oil pan, 18 oil filter, 19 oil pressure switch, 20 fan belt, 21 timing belt DAIHATSU


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130 part two engines and engine systems
Cylinder head
The cylinder head is bolted to the top of the cylinder
block. A gasket, the cylinder-head gasket, is fitted
between the parts to provide a seal.
The cylinder head is made of aluminium alloy. It is
shaped above each cylinder to form the combustion
chambers in which the air–fuel mixture is burnt. The
cylinder head carries the camshaft, the valves, and the
valve-operating mechanism. Intake and exhaust ports
in the cylinder head are opened and closed by the
action of valves.
Valve cover
The valve cover fits on top of the cylinder head and
covers the valve mechanism. The valve cover is of
aluminium alloy. A gasket is fitted between it and the
top of the cylinder head to provide an oil seal.
Oil pan
The oil pan, or sump, is attached to the bottom of the
crankcase and closes off the internal parts. It also acts
as a reservoir for the engine oil. The oil is circulated
throughout the engine by the oil pump before returning
to the oil pan.
Oil pump and oil filter
The oil leaving the oil pump passes through the oil
filter before it is circulated through the engine. The
filter removes particles of carbon or other foreign
material from the oil.

system. The engine in Figure 9.6 has a variable-speed
fan that is belt-driven, but electric fans are also used.
Water pump
The water pump is driven by the fan belt from the
crankshaft pulley. It circulates coolant throughout the
engine and radiator assembly.
Distributor, cables and spark plugs
The distributor is at the rear of the cylinder head and is
driven by the camshaft. It distributes high voltage to
each spark plug at the right time. This provides the
spark which ignites the air–fuel mixture.
The cables from the distributor are connected to the
spark plugs which, on the engine in Figure 9.6, are
located in the centre of the cylinder head.
The firing order for a four-cylinder engine is 1-3-4-2
or 1-2-4-3. This is the sequence in which the pistons
deliver the power strokes.

Engine features
Some of the different engine design features can be
seen in the following illustrations. While the basic
operation is the same for all engines, there are many
variations in actual engine design.
This can be in the engine configuration, whether it
is mounted transversely or longitudinally in the
vehicle, the type of fuel used, number of valves per
cylinder, number of camshafts, and so on.
Sectional view of an engine

Intake manifold and exhaust manifold
The intake manifold carries the air–fuel mixture into
the engine. The engine illustrated in Figure 9.6 has
electronic fuel injection (EFI), and this has a throttle
body attached to the intake manifold. On carburettor
engines, the manifold is of a different shape and it has
the carburettor mounted on top.
The exhaust manifold is on the opposite side of the
engine to the intake manifold. It is flange-mounted to
the cylinder head over the exhaust ports. Pipes or
branches of the manifold carry the burnt gases away
when the exhaust valves open. The exhaust manifold is
made of cast iron to resist heat.
Fan
The fan at the front of the engine provides a flow of air
through the radiator as part of the engine’s cooling

Figure 9.7 shows a cross-sectional view of a basic
engine. This has been cut right through the valve
cover, cylinder head, cylinder block and oil pan to
show the construction of the parts.
Items that can be identified are: water-jackets in the
cylinder head and cylinder block, intake and exhaust
valves and their ports, the camshaft and rocker arms,
the cylinder-head gasket, the piston, the crankshaft,
and the connecting-rod.
Sectional view of a V-type engine
The engine shown in Figure 9.8 is a V-6 engine. It has
two banks of cylinders at an angle of 60°. Each bank
contains three cylinders.

There are two camshafts for each bank of cylinders – one for the intake valves, and one for the
exhausts. The intake camshaft is driven by a toothed


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chapter nine engine construction and components

figure 9.7

Cross-sectional view of a basic engine, showing the internal parts

figure 9.8

Sectional view of a V-6 engine with a double overhead camshaft

MITSUBISHI

TOYOTA

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132 part two engines and engine systems
belt, and the exhaust camshaft is driven from the intake
camshaft by a pair of gears.

cylinder head. It also has long pistons, which have a
combustion chamber in the piston head.

Horizontal engine

■ The components of a diesel engine carry greater
stresses than a petrol engine and so diesel engines
are generally of heavier construction.

The arrangement of a horizontal engine, often referred
to as a flat engine because of its construction, is shown
in Figure 9.9. This is a four-cylinder engine with its
cylinders horizontally opposed. Its various features are
identified in the illustration.
This has a different dismantling sequence to an inline engine. There are two cylinder heads to be
removed, and two cylinder blocks that are separated at
the crankcase.
Diesel engine
The basic construction of a diesel engine can be seen

in Figure 9.10. This is an overhead-valve engine with
the camshaft mounted in the cylinder block. Cam
followers operate on the cams of the camshaft, and
pushrods transfer movement to the rocker arms on top
of the cylinder head.
The camshaft of this engine is driven by timing
gears, which also drive an auxiliary shaft. This, in turn,
drives the injection pump and a vacuum pump.
Being a diesel engine, injectors are fitted to the

figure 9.9

Arrangement of a horizontally opposed engine

Working on engines – general
Modern engines have a lot of ancillary equipment
attached to the engine. Usually, some of this has to be
removed to gain access to the actual engine component
that is to be removed or dismantled.
Preliminary work on an engine could include
removing items such as: engine covers, the air cleaner
and air ducts, coolant hoses, drive belts, powersteering pump, air conditioning compressor, alternator,
starter, parts of the fuel system, or emission controls.
There is also equipment mounted in the engine
compartment – the general arrangement of an engine
compartment of a transverse engine is shown in
Figure 9.11, with some of these components identified.
Some engine parts are accessible only from
underneath and the vehicle has to be raised on a jack or
hoist. With transverse engines, some parts are

accessible from under the mudguards and the wheels
have to be removed to provide working space.

VOLKSWAGEN


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chapter nine engine construction and components

figure 9.10

Basic diesel-engine construction

133

PERKINS

When working under the bonnet, protect the
paintwork by using covers on the mudguards
(Figure 9.12). Liquid spills should be cleaned up
immediately, particularly hydraulic brake fluid and
coolant additives, as these can remove paint.
■ Before dismantling an engine, its construction

details and features must be known, and these
should be obtained from the appropriate workshop
manual.
Engine repairs
During an engine repair job, attention should be paid to
the following items:
1. Small parts. Parts such as fuel lines and emission
hoses should be tagged so that they can be easily
replaced in their original position.
2. Fuel lines. These should be removed carefully so
that they are not damaged. The fuel lines for

electronic fuel injection systems hold pressure,
even with the engine stopped. This has to be
released slowly so that fuel does not spray
everywhere.
3. Holes and pipes. These should be covered or
plugged to keep out dirt and foreign objects.
4. Air conditioning parts. Refrigerant-recovery
equipment should be used if air-conditioning pipes
have to be disconnected. Refrigerant cannot be
released into the atmosphere as it causes pollution.
5. Dismantled parts. After parts are removed or
dismantled, they should be laid out in some form
of order so that they can be easily identified. After
cleaning, parts should be arranged ready for
reassembly.
Cleaning and inspecting
1. Cleaning. Parts can be cleaned by washing in
solvent, by using a scraper on flat surfaces, by

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134 part two engines and engine systems
power steering reservoir
spark plugs
brake booster
clutch fluid reservoir
brake fluid
reservoir

distributor

air cleaner

engine oil
level dipstick

fuse block

engine oil
filler cap

A/C
fuse box

battery

windshield washer
fluid tank

engine coolant reservoir

engine oil filter

automatic transmission fluid level dipstick
condenser cooling fan

figure 9.11

radiator cap engine cooling fan

General arrangement of the components in the engine compartment of a vehicle with a transverse engine

TOYOTA

Parts should be replaced in their original
positions. Parts should not be forced when being
installed. Look for a reason if any part does not fit
into place easily.

Use mudguard covers and take precautions
to protect the paintwork of the vehicle

2. Gaskets and seals. These must be correctly
positioned when being installed. The use of sealant
is recommended for some parts. Seals should be
lubricated.

brushing, or by immersing in a cleaning tank. After
cleaning, parts that could rust should be coated with
oil. Small parts, such as bearings, should also be
wrapped to keep them clean.

3. Tightening. Bolts and nuts must be tightened in the
correct sequence and to the correct torque.
Overtightening could damage the bolt or strip a
thread. Undertightening could cause leaks or allow
a part to come loose.

figure 9.12

2. Inspecting. Parts are inspected for serviceability
and must be clean so that this can be done properly.
Some parts have to be measured for wear. Other
parts are checked visually for cracks, damage,
corrosion, or distortion.
Installing
1. Installing parts. Before installing a new part, it
should be checked against the old part to make sure
that both parts are identical.

Adjusting and checking

1. Adjusting. Some parts have to be adjusted to
specifications. These include drive belts, some
valve clearances, and throttle cables.
2. Checking. After reassembling, a final check should
be made to be quite sure that everything that should
be done, has been done. The engine has to be
started and run for some checks, and the vehicle
road-tested for others.


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Working on the underside
of the engine
Oil pan
The oil pan, or sump, is secured to the bottom of the
cylinder block by a number of bolts. Figure 9.13 shows
the general procedure for removing and replacing an
oil pan.
Removing the oil pan

1. Raise the front of the vehicle, or raise the complete
vehicle on a hoist.
2. Drain the engine oil.
3. Remove the oil pan retaining bolts.
4. Carefully insert a screwdriver or special tool
between the oil pan and the crankcase to separate
the oil pan (Figure 9.13(a)).
5. Remove the oil pan completely (Figure 9.13(b)).
6. After removing the oil pan, inspect it for damage
and check the condition of the thread in the drain
plug hole. Check the oil pump screen and clean it if
necessary (Figure 9.13(c)).
7. Clean the oil pan and remove all the old gasket or
sealing material from the mating surfaces of the oil
pan and the crankcase. Fit the drain plug, use a new
washer if necessary.
Installing the oil pan
1. Fit a new gasket to the flange of the oil pan and
retain it with grease; or apply a 3 mm bead of liquid
silicone gasket material to the flange of the oil pan
as shown in Figure 9.13(d). The silicone must form
a continuous bead around the flange and must be
inside the bolt holes to prevent leaks.
2. Install the oil pan to the crankcase, fit the bolts and
tighten them to the correct torque.
3. Refill the oil pan with oil, run the engine and check
for oil leaks.
■ Where silicone is used, the oil pan has to be
reinstalled and the bolts tightened within about
fifteen minutes. The material cures when exposed to

air and parts must be assembled within a limited
time.
Oil pump
Some oil pumps are chain-driven, some are shaftdriven, and some are driven directly by the crankshaft.

figure 9.13

General procedures when removing and
installing an oil pan FORD

Figure 9.14 shows the location of a chain-driven oil
pump that is secured to the crankcase by two bolts and
is accessible with the oil pan removed.
Where the oil pump is driven by the crankshaft, the
timing cover and housing will have to be dismantled
from the front of the engine before the oil pump can be
removed.


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136 part two engines and engine systems

figure 9.14

Location of an oil pump at the front of the
crankcase – the pump is held by two bolts

figure 9.15

FORD

Using a screw-type puller to remove a crankshaft pulley FORD

Working on the front of the engine

Fitting a timing-cover oil seal

Parts located at the front of the engine include the
water pump (on most engines), the crankcase pulley
and vibration damper, the timing cover, and the timing
chain or timing belt.
Engines with a timing chain have a cast-metal or
pressed-metal cover. The timing chain is lubricated by
engine oil and the timing cover has to be oil-tight to
retain oil within the engine.
Engines with a timing belt have a plastic timing
cover. This keeps out dirt but does not have to retain
oil, because the timing belt runs dry.

A lip-type seal is used between the crankshaft and the
timing cover. It must be renewed if it leaks. The seal is
punched out and a new seal installed with a suitable
tool as shown in Figure 9.16.

Before the seal is installed, grease should be packed
behind the seal to provide initial lubrication.

Removing a crankcase pulley
The pulley assembly fits on the end of the
crankshaft. It is keyed to the crankshaft and retained
by a bolt or nut. A puller is needed to remove some
pulleys. After removing the bolt or nut securing the
pulley, a puller is fitted to the pulley as shown in
Figure 9.15.
Removing the timing cover
Metal timing covers are retained by a number of bolts
and can be removed after the crankcase pulley has
been removed. There will be a gasket or sealing
material between the timing cover and the cylinder
block. The timing cover is removed and treated in a
similar way to the oil pan.
Timing-belt covers are made of plastic material
and are retained by fewer bolts than metal covers.
They have no gaskets or sealer, and so are easier to
remove.

figure 9.16

Installing a timing cover oil seal

FORD

Working on the top of the engine
Before removing components from the top of the

engine, accessories such as the air cleaner or air ducts
will have to be removed, as well as items such as
vacuum tubes for emission controls, fuel pipes, spark
plug cables and spark plugs.
Engine components at the top of the engine are the
valve cover, the timing cover, timing belt, the camshaft


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chapter nine engine construction and components

pulley, the valve mechanism, the camshaft, and the
cylinder head.
Dismantling sequence
Figure 9.17(a) to (d) shows the general sequence for
dismantling the components at the top of the engine.
1. In Figure 9.17(a), the valve cover has been removed
to expose the valve mechanism. The timing-belt
cover is still in place on the front of the engine.
2. In Figure 9.17(b), the upper part of the timing-belt
cover has been removed to show the timing pulley
and the timing belt. These have to be removed
before the valve mechanism can be removed. The

engine is turned with No. 1 piston on TDC, so that
the timing mark on the pulley will align with the
timing mark on the timing case.
3. Figure 9.17(c) shows how the rocker assembly,
consisting of the rocker shafts and rocker arms, can

figure 9.17

137

be removed. This is unbolted from the cylinder
head and lifted away complete with the camshaft
bearing caps.
4. Figure 9.17(d) has the camshaft sitting in its bearings in the cylinder head ready to be lifted out.
Cylinder head
The cylinder head is bolted to the engine block by a
number of special high-tension bolts.
When the cylinder head is being removed, the bolts
must be loosened progressively in a sequence to
prevent head distortion (Figure 9.18). When the
cylinder head is replaced, the bolts must also be
tightened progressively in sequence as shown.
■ The practice of loosening and tightening in a
sequence should be used on most parts, particularly
castings, both aluminium alloy and cast iron.

General sequence for removing components from the top of an engine

MITSUBISHI

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138 part two engines and engine systems
the piston comes out of the top of the cylinder. Care
must be taken not to damage the connecting-rod
bearing or mark the crankshaft journal.
The general method of removing and replacing a
piston is shown in Figure 9.19. When replacing the
piston, the piston rings have to be compressed with a
special ring compressor so that they will enter the
cylinder. This must be done carefully because piston
rings can be easily damaged or broken.

Working on engine ancillaries
figure 9.18

Cylinder-head bolts
(a) loosening and (b) tightening

Pistons and connecting rods
With the cylinder head and sump removed, the pistons
can be removed from the cylinder block. To do this,
the connecting rods have to be disconnected from the

crankshaft.
The connecting rods are then pushed upwards until

figure 9.19

There are various components attached to the engine
which have to be removed for servicing, or to obtain
access to other parts. These include: the water pump,
power steering pump and air-conditioning compressor.
These are all belt-driven from a pulley on the front of
the crankshaft.
The drive belt, or belts, have to be removed before
the components can be removed from the engine.
When the parts are replaced, the tension of the drive
belts will have to be adjusted.
The engine in Figure 9.20 has a single belt which
drives a number of pulleys.

General method of removing and installing a piston

FORD


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chapter nine engine construction and components

Working on engine
electrical systems

139

Many vehicles have engine management systems
that use electronic control units to operate and monitor
a range of engine functions.

The main engine electrical components are:
Ignition system

1. the ignition system components
2. the battery
3. the starter
4. the alternator
5. the electrical wiring system that is used to connect
these various parts.
(Items 1, 3 and 4 are identified on the engine in
Figure 9.20.)
The above five components form the basic starting,
charging and ignition systems that are needed to start
the engine and keep it running. However, there are
many other electrical and electronic components.
Some are attached to the engine, others are located in
the engine compartment.

alternator

Ignition system service includes removing and replacing spark plugs and checking the ignition timing.
Distributors with electronic ignition and other
electronic ignition systems which do not have a
distributor do not require routine servicing. Older
vehicles have distributors with breaker points and
these need regular service.
■ Hands should be kept clear of the ignition system
when the engine is running because very high
voltages are produced.
Spark plugs
Removing and inspecting spark plugs is a routine
service item for ignition systems. Spark plugs are

ignition coils

tensioner

valve cover

drive belt
H.T. cables
power steering
pulley

spark plug connectors
exhaust manifold
water pump
pulley

starter

idler
crankshaft pulley
and balancer
oil pan

figure 9.20

External components of a V-6 engine – the single belt drives a number of pulleys

HOLDEN LTD


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140 part two engines and engine systems
screwed into threaded holes in the cylinder head. They
are removed and replaced using the following procedure:
1. The cables should be removed from spark plugs by
holding and pulling the connector and not the cable
(Figure 9.21). Pulling the cable will cause it to
stretch and it will be permanently damaged.

figure 9.21

Remove spark-plug connectors by pulling
and twisting MITSUBISHI

2. A special spanner is used to remove spark plugs. It
should be used carefully to avoid breaking the
ceramic insulator, which is very brittle.
3. The condition of the spark plug should be checked
after it has been removed. The deposits on the spark
plug can indicate the condition of the plug, how
well it has been firing, and possibly the condition of
the engine (Figure 9.22).
4. Spark plugs can be cleaned with a spark plug
cleaner, but if the electrodes are eroded or the
insulator is cracked or burnt, the plug will have to
be renewed.

5. Before installing a spark plug, the gap should be set
(Figure 9.23). This applies to new plugs as well as
existing plugs.
6. The gap between the electrodes is checked with a
feeler gauge and the earth electrode carefully bent
if the gap has to be adjusted. Any force applied to
the centre electrode will crack the nose of the
insulator and the plug will be worthless.

figure 9.23

The spark plug electrodes have a specified
gap

7. When replacing a spark plug, start the first few
threads by hand and make sure that the plug is not
cross-threaded. Tighten the plug until it seats
firmly, but do not overtighten. The tightening
torque is about 15 to 20 Nm.
Distributor cap, coil and cables
Where a distributor is fitted, the outside of the
distributor cap and the ignition coil should be kept
clean and free from oil and dirt. The cables should be
pushed firmly into their sockets.
Ignition timing
Figure 9.24 shows timing marks of an engine. There
is a timing mark on the crankshaft pulley and a
degree scale on the timing cover. The scale has ‘T’
for TDC of No. 1 piston, as well as a scale for
ignition timing.
The spark is advanced a specified number of
degrees. That is, it is arranged to occur before the
piston reaches TDC. Timing marks are used for
ignition timing and also for valve timing when the
engine is being dismantled and reassembled.
Battery

figure 9.22

After removal, the spark plugs should be
examined – they can provide useful

information

Batteries require regular checks of the electrolyte level,
although some batteries are classed as being
maintenance free or low maintenance. The top of the


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chapter nine engine construction and components

141

figure 9.25

figure 9.24

Timing marks on a timing cover and on the
crankshaft pulley FORD

battery should be kept clean and the battery terminals
should be clean and free of corrosion.

The negative battery terminal should

normally be disconnected when working on
or near electrical components HYUNDAI

some vehicles, disconnecting the battery might
cause loss of data or diagnosis information.

■ Dirty battery terminals can prevent the starter from
operating. They are one of the most common of all
electrical problems.

2. Disconnect electrical connectors carefully to avoid
damage. Pull the connector, not the wires. Some
connectors have a small catch which must be
released before the parts can be separated.

Starter

3. Keep wiring away from hot manifolds and
exhausts.

The starter draws a high current when turning the
engine for starting. Starter operation depends on good
battery maintenance – it needs a good, well-charged
battery with clean terminals.

■ Particular caution is needed when working on or
near electrical wiring or sensors connected with air
bags. An error could cause an air bag to deploy.

Alternator

The alternator drive belt must be correctly adjusted to
prevent slip. A loose belt could allow the battery to run
down. A quick check of the alternator can be made
using a voltmeter as follows:
1. With the engine stopped, connect a voltmeter
across the battery terminals.
2. The voltmeter should read approximately 12 volts.
3. Start the engine and run it at a speed above idle.
4. The reading on the voltmeter should be higher than
before, and around 14 volts.
■ When carrying out this check, the voltmeter must be
connected with correct polarity.
Electrical wiring and connectors

Technical terms
Timing belt, timing pulley, sprocket, balancer,
crankshaft pulley, balance weight, main bearing,
journal, piston pin, big end, cylinder block, cylinder
head, oil pan, throttle body, distributor, water pump,
reservoir, exhaust manifold, intake manifold,
carburettor, water-jackets, horizontal engine,
injection pump, stress, refrigerant, electronic fuel
injection, EFI, silicone, vibration, vibration damper,
air cleaner, air duct, emissions, emission controls,
sequence, ceramic, insulator, electrode, terminal,
ignition timing, valve timing.

Review questions

When servicing electrical parts, take the following

precautions:

1.

Name the main components that are located at
the top of an engine.

1. Disconnect the battery as a safety precaution where
‘live’ wires or components could cause a problem
(Figure 9.25). This is a general safety rule but, in

2.

Name the main components that are located
at the front of an engine.


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142 part two engines and engine systems

3.

Why is a flywheel needed?

12.

4.

What is the function of the connecting rods and
crankshaft?

How would you go about removing an oil
pan?

13.

How is a crankshaft pulley removed?

5.

What is the purpose of the timing belt?

14.

6.

Why is an engine ‘timed’?

7.

How are the valves operated?

In what sequence would components be

dismantled from the top of an engine? (Refer to
the illustrations.)

8.

In the illustrations, locate and identify the
following parts: camshaft, camshaft pulley or
sprocket, timing belt, intake valves, exhaust
valves, rocker shafts, crankshaft, balance weights.

15.

Why are cylinder-head bolts loosened and
tightened in a specified sequence?

16.

How could a faulty spark plug be identified?

17.

How can a spark plug be serviced?

18.

What is meant by ignition timing?

19.

Why is it important to keep battery terminals

clean?

20.

What is the likely effect of badly corroded
battery terminals?

9.

How does a diesel engine differ from a petrol
engine?

10.

What is the main difference between an EFI
engine and a carburettor engine?

11.

How would sealant be applied to a part, such as
an oil pan?