the game drive vehicle - mechanics - wildlifecampus

– Game Ranging / Field Guiding Course

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Field Guiding Skills © Copyright

Module # 12 – Component # 3

The Game Drive Vehicle - Mechanics

Introduction

Major Parts

A car consists of 9 systems:

Engine

Electrical system

Fuel system

Cooling system

Lubrication system

Transmission system and wheels

Braking system

Suspension system

Steering system.

All these parts are mounted on a steel frame called a chassis and surrounded by

bodywork.

It is very important that every field guide is very familiar with all aspects of the vehicle under his / her care. There will come a time when you will be

required to repair the vehicle in the bush.

Your practical training will teach you the rudimentary points of vehicle repair and

maintenance.




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The Engine The engine can be divided into four parts: the cylinder head, the cylinder block,

the crankshaft assembly and the sump.

Cylinder head

Made of cast iron.

Houses combustion chamber, valve ports and valves.

Running along the top of the cylinder head of most engines are the camshafts.

Camshafts are attached to the rockers which open the valves.

Around the head of each valve is a spring which closes the valve after opening-

there are two valve ports and two valves for each cylinder.

The petrol/air mixture is drawn in through one set of valves known as the inlet

valves and exhaust gases are expelled through the other set of valves known

as the exhaust valves.

The combustion chamber where ignition of the fuel mixture takes place is

usually situated in the bottom of the cylinder head.

Along the sides of the cylinder head are inlet ports through which the petrol/air

mixture is sucked as the valves open.

There are passages around the cylinder head through which water passes, to keep the engine cool.

The lower face of the cylinder head is flat to enable it to mate with upper face

of cylinder block.

The two parts are joined and sealed by means of a gasket.

Cylinder block

This is the main part of the engine.

Has cylinders, tunnels for the crankshaft, and oil-ways to allow the flow of oil through the engine.

Made of cast iron.

Mountings for various engine components such as petrol pump, distributor, oil

filter and water pump are all incorporated into the cylinder block.

Crankshaft assembly

Situated at base of cylinder block.

Pistons are connected to the crankshaft.

Pistons slide into cylinders in cylinder block.

When ignition starts, fuel mixture in combustion chamber ignites and pushes

each piston downwards in turn.

Power is then transferred from the pistons via the crankshaft to the transmission, and then to the wheels, so allowing the vehicle to move forwards.

Sump

Situated at base of engine block.

Is reservoir for oil which is responsible for lubricating all the moving parts of the engine.




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The Electrical System The Battery

Supplies electricity to the ignition system and other electrical components.

Made up of 6 cells each cell producing 2 volts of electricity, making a total of

12 volts.

Each cell has 2 sets of plates called electrodes. One electrode is made of lead dioxide, the other of spongy lead.

Electrodes sit in a solution of dilute sulphuric acid called the electrolyte.

Acid reacts with the electrodes, creating electrical energy from chemical

energy.

As chemical reaction continues, lead sulphate builds up on the electrodes and the acid turns to water. When the plates are covered in lead sulphate, the

battery is flat.

Re-charging the battery with an electric current restores the electrodes to their original state.

Heaviest demand is made on the battery when engine is started.

Most batteries are earthed by means of the negative terminal being attached

to the chassis or bodywork of the vehicle.

The Coil

The car battery produces 12 volts.

Thousands of times more voltage is needed to produce sparks in the spark

plugs.

Purpose of the coil is to convert 12 volts to as much as 60 000 volts.

This is accomplished by means of a complex system of wiring around a central

soft iron core within the coil.

This high voltage is then sent to the distributor.

The Distributor

Is the link between the electrical components and the engine itself?

Distributes the coil’s high voltage to the spark plugs in a specific order by means

of a rotor arm.

Consists of a body and a cap.

The cap has five terminals, a central one carrying power from the coil, which is connected to the centre of the rotor arm, and 4 outer terminals which lead to

the spark plugs.

Power from the coil enters the distributor at the central terminal.

As the rotor arm turns, it connects the central terminal to the spark plug

terminals in rotation.

In this way, the electrical current is “distributed” to the various spark plugs.

The body of the distributor contains the contact breaker “points” and the

condenser.

Purpose of the “points” is to interrupt the flow of electricity through the system

which is necessary for high voltages to be attained.

The condenser prevents excessive arcing from taking place.




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The Spark Plugs

Produce the sparks needed to ignite the petrol/air mixture in the engine’s

cylinders.

Consist of central electrode passing through centre of insulator with another

earthed electrode on the outer edge of the bottom of the plug.

The 2 electrodes are separated by a small gap.

High voltage electricity runs down the central electrode and jumps across this

gap in the form of a spark.

The spark must be big enough to light the petrol/air mixture efficiently, which

means that the gap must be larger. The larger the gap, the more voltage

required.

The gap measures 0,6 - 0,8mm.

The electrodes erode and deposits build up as time goes by and the gap must therefore be checked regularly.

Factors that can cause erratic sparking include: crack in insulator, film of oil or

water on outer surface, defective plug wire or connection.

The Ignition Switch

By turning the ignition switch using a key, a connection is made between the

battery and the rest of the electrical system.

This starts the flow of electricity through the system.

The Starter

Starter motor turns the engine over until it fires.

Engines must turn at 250-300 rpm to start.

This needs large amount of electrical power and therefore drains more electricity from the battery than any other component.

Because of this high current, the starter needs a heavy-duty switch to connect

it to the battery.

This switch is called a solenoid and is controlled by the ignition switch.

Starter is connected to engine crank-shaft by a pair of gears, one small one on the starter motor called a pinion, and a larger one called a flywheel which is

directly connected to the crank-shaft.

When the ignition switch is turned, the pinion engages with the flywheel, the starter motor rotates, so rotating the fly-wheel which in turn rotates the crank-

shaft.

As soon as the engine fires, the pinion disengages from the flywheel, to prevent damage to the starter motor.




5


The Alternator

Generates electricity whilst the engine is running, so keeping the battery fully-

charged.

Is connected to the drive-shaft of the engine by means of a fan-belt.

Power from the engine is transferred to the alternator by means of the fan-belt, which then spins the alternator, so allowing it to generate current.

This current then re-charges the battery.

Instrumentation

The main instruments on the dashboard to note are the charge warning light,

oil pressure warning light, fuel gauge and temperature gauge.

The charge warning light lights up if the alternator isn’t charging the battery. This could be because of a faulty alternator or a loose or broken fan-belt.

Oil pressure warning light lights up if oil pressure or level is too low.

Fuel gauge monitors the amount of fuel in the tank.

Temperature gauge monitors the engine temperature. If gauge indicates

“high”, then overheating is taking place. This could be because of low coolant level in the radiator or a loose fan-belt.




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The Fuel System The fuel system consists of the tank, where fuel is stored; the fuel line, which

transports the fuel from the tank to the carburettor; the fuel pump, which pumps

fuel from the tank along the line to the carburettor; and the carburettor which

mixes air and petrol and then delivers this mixture to the cylinders for firing.

Fuel tank

Positioned far away from engine and at lowest level possible to reduce risk of

fire and improve handling.

Has compartment walls that reduce surging of fuel around tank during

cornering.

Inside of tank lined with rust-proofing.

Tanks contain from 25 to over 100 litres and allow cars to travel a minimum of

300kms on a full tank.

Filler pipe must be wide enough to allow nozzle from petrol pump to fit in and at the same time allow for the escape of air as the tank fills up.

Fuel filters

Prevent dirt from entering the fuel line and the carburettor.

There is usually a coarse filter in the fuel tank, mostly at the bottom of the inlet pipe.

The fuel pump contains a filter.

There is often a plastic in-line filter between the pump and the carburettor. This

filter can be cleaned out by removing it from the line and then blowing into the

filter in the opposite direction to the flow of petrol.

Some engines have an additional fine filter with a glass sediment bowl below.

Sediment filtered out of the petrol sinks to the bottom of the glass bowl and

the bowl can be removed and emptied.

Fuel pump

Needed to pump fuel from the tank to the carburettor.

Can be mechanical or electrical.

Mechanical pumps are situated next to the engine which gives them their power.

Electrical pumps are usually next to the tank, away from engine heat.




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Carburettor

Purpose is to break up fuel particles and mix this with air to form a vapour

which will burn efficiently in the cylinders.

As the engine turns, the pistons move downwards inside the cylinders, creating

a vacuum and causing air to be sucked through the carburettor into the

cylinders.

The amount of air drawn into the carburettor is controlled by a flap called a

throttle valve, which in turn is controlled by the accelerator.

As the amount of air flowing into the carburettor increases, so the flow of petrol

also increases.

The carburettor therefore controls the amount of petrol that is released into the airstream.

In the carburettor is a float chamber which contains petrol that is released into

the chamber by means of a drip valve.

Petrol from the float chamber is released into an air chamber called a venturi,

where it is mixed with the air before entering the cylinder.

In the cylinder, this mixture of petrol vapour and air is ignited by the spark

plug.

Air cleaner

The air cleaner is situated on the air intake on top of the carburettor.

Its purpose is to filter dust out of the air before it enters the carburettor.

It consists of a housing unit with an air intake attached to the carburettor and

containing a pleated paper filter.

The filter removes any dust particles from the air before it enters the

carburettor.

This dust accumulates in the paper filter and can eventually block the flow of air into the carburettor.

The filter therefore must be replaced every 20 000 km [12500 miles] or so.

In dusty conditions, it would have to be replaced more regularly than that.




8


The Cooling System

Engines develop a large amount of heat and therefore must be cooled in some

way.

Most engines have a water-cooled system consisting of a jacket, radiator, fan, hoses, water pump and thermostat.

The jacket consists of passages passing through the hottest parts of the engine.

The radiator is usually mounted in the front part of the engine compartment.

The jacket passages are connected to the radiator by hoses.

Mounted on the front end of the cylinder block is a water pump which is responsible for pumping water in a circular route from the jacket, through the

radiator and thermostat and back into the jacket.

mounted behind the radiator and in front of the cylinder block is a fan which sucks air through the radiator.

The core of the radiator is made up of tiny tubes surrounded by numerous fins which provide greater contact with the air.

As the air is sucked through the radiator, it cools the water in the radiator

before it is pumped through the jacket where the cooled water keeps the engine parts cool.

The purpose of the thermostat is to shut off the flow of cold water through the

engine when the engine is cold, and to allow the flow of water again when the engine gets warm.

The water in the cooling system can be replenished through an opening in the

top of the radiator.




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The Lubrication System

When metal surfaces rub together, friction takes place and this generates heat

and wear.

Oil reduces this friction, and thus reduces heat and wear and tear.

Oil is pumped from the sump by means of a pump, through a filter into the

spaces where the moving parts of the engine operate.

The oil pump is usually mounted on the side of the cylinder block with the oil

filter attached to its base.

The oil level in the engine must be checked regularly, by means of a dip-stick.

The oil filter must be changed regularly.

The oil in an engine also must be changed on a regular basis, usually every 5

000 to10 000 Km [3000- 5000 miles].




10


The Transmission System The transmission system consists of the gearbox, the clutch, the prop shaft, the

final drive and the half-shafts. Its purpose is to transfer power from the engine to

the wheels.

The clutch

Is the connecting point between the engine and the gearbox?

Part of the clutch is connected to the flywheel on the cylinder block and part is

connected to the gearbox shaft, so allowing power from the engine to be transferred to the transmission.

Depressing the clutch pedal in the driver’s compartment disengages the clutch

and allows the driver to change gears. Releasing the clutch pedal again engages the clutch.

The gearbox

Contains a series of gears that allow the driver to choose the most suitable ratio

of engine speed to road-wheel speed.

Usually a choice of 4 or 5 forward speeds as well as reverse and neutral.

The prop shaft and universal joints

Prop shaft connects the gearbox to the final drive on the back axle, so transferring power from the gearbox.

The universal joints at either end of the prop shaft allow flexibility and

movement as the car rides over bumps.

The final drive

Consists of several gears connecting the prop shaft to the half-shafts and

mounted inside housing in the centre of the rear axle.

The pinion gear attached to the end of the prop shaft connects at right angles to the crown wheel and this transfers power to the half-shafts via the

differential.

The differential is another set of gears which allows the half-shafts to rotate at different speeds when the car is turning corners.

The half-shafts

Each rear wheel is attached to an independent half-shaft which transfers power

from the final drive to the wheels.

The wheels are attached to the half-shafts by means of a hub.




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The Braking System

Brakes slow the car down by causing friction between a non-moving part of the

vehicle and a drum or disc which turns with the wheel.

The braking system consists of a fluid reservoir attached to a master cylinder containing a piston, which in turn is connected to a series of pipes leading to

brake cylinders at each wheel.

When pressure is applied to the brake pedal, the piston in the master cylinder forces the hydraulic fluid in the system through the brake pipes under pressure

to the wheel cylinders, where a pair of pistons are then forced outward.

These pistons then force the brake pads on the inside of the drum outwards so

that they meet the drum. This friction then causes movement of the drum to

slow.

The brake fluid reservoir must be checked on a regular basis to ensure that

there is sufficient fluid.




12


Suspension System

Purpose is to give car a smoother ride consists of shock absorbers and springs

attaching the wheel axles to the chassis.

Some cars have leaf springs, others have coil springs.

Springs give the car “springiness”, and shock absorbers absorb the bouncing

effect of the spring.




13


Steering System

Consists of steering wheel, steering column with universal joints, either a rack

and pinion steering gear, or a steering box, and ball joints next to the wheels.

The steering box and the system of gears and linkages that connect the steering wheel to the front wheel are designed to give the driver directional control with

the minimum of effort.

The steering gearbox converts the turning motion of the steering wheel into a to-and-fro movement of the steering linkages.




14


Functioning of Major Parts

The turning of the ignition key starts the flow of electricity through the electrical

system of the car. At the same time, the accelerator pedal is depressed to start

the flow of petrol into the fuel system.

Electrical power is sent to the starter motor and to the distributor at the same

time.

The starter motor turns the engine over, creating suction which sucks the petrol-air mixture into the combustion chamber of the cylinder head.

At the same time an electrical spark ignites the petrol-air mixture in the combustion chamber.

This explosion causes expansion in the cylinder and pushes the piston

downwards.

Each piston is pushed downwards in turn in this way.

The movement of the pistons is transferred to the crankshaft which in turn

transfers power to the gearbox and hence to the rest of the transmission system and to the wheels.

The vehicle moves forward.

the game drive vehicle - mechanics - wildlifecampus

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