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

Engine construction and components 125 Engine construction 126 Components of an engine assembly 129 Engine features 130 Working on engines – general 132 Working on the underside of the engine 135 Working on the front of the engine 136 Working on the top of the engine 136 Working on engine ancillaries 138 Working on engine electrical systems 139 Technical terms 141 Review questions 141

Engine construction

and components

Chapter 9

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

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

While multicylinder engines contain parts which

perform the same functions as those of a

single-cylinder 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.

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.

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

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.

figure 9.1 Components at the top of an engine DAIHATSU

figure 9.2 Components at the front of an engine

DAIHATSU

The parts work like this

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.

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:

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

5 crankshaft main-bearing journals

6 pulley and balancer.

figure 9.3 Components at the rear of an engine

DAIHATSU

figure 9.4 Internal components at the bottom of an engine

The parts work like this

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 bottom end of the connecting rod is often

referred to as the big end because it is the larger

end of the connecting rod.

Components inside 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, connect-ing rods, and the flywheel These parts are identified

on the illustration.

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

figure 9.5 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

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).

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

timing chain.

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

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.

Cylinder block

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.

figure 9.6 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

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.

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

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

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 cylin-ders – one for the intake valves, and one for the exhausts The intake camshaft is driven by a toothed

figure 9.7 Cross-sectional view of a basic engine, showing the internal parts MITSUBISHI

figure 9.8 Sectional view of a V-6 engine with a double overhead camshaft

belt, and the exhaust camshaft is driven from the intake

camshaft by a pair of gears.

Horizontal engine

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

in-line 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

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

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

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, power-steering 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.

figure 9.9 Arrangement of a horizontally opposed engine

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

figure 9.10 Basic diesel-engine construction PERKINS

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.

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.

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.

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.

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.

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.

figure 9.11 General arrangement of the components in the engine compartment of a vehicle with a transverse engine TOYOTA

brake fluid reservoir engine oil level dipstick

engine oil

filler cap

windshield washer

fluid tank

engine oil filter

condenser cooling fan radiator cap engine cooling fan

automatic transmission fluid level dipstick

battery

A/C fuse box

fuse block air cleaner

distributor spark plugs

clutch fluid reservoir

power steering reservoir brake booster

engine coolant reservoir

figure 9.12 Use mudguard covers and take precautions

to protect the paintwork of the vehicle