Car Parts and Accessories

Bearingsare used to minimise friction and to support all the rotating parts of a car’s mechanism—parts which are either rotating shafts or wheels on fixed shafts.

They fall into two main types: plain bearings, in which the moving part rotates in a shell or liner, with adjacent surfaces usually separated by a film of oil or grease; and rolling bearings, in which the load is borne by balls or rollers.

Shell bearings

If a plain bearing is in halves for ease of assembly, it is known as a shell bearing. This is the type used on the journals for the crankshaft main bearings, and in the big-ends of the connecting rods. (more…)

In a petrol engine a mixture of petrol and air enters the cylinders and is ignited by an electric spark from the spark-plug. In a diesel engine, only air enters the cylinder on the intake stroke.

Ignition in a diesel engine is caused by compression, which raises the temperature of air in the combustion chamber above the flash-point, or self-ignition temperature, of the fuel.

Diesel fuel, less easily evaporated than petrol, is not drawn in with air as a mixture, but is sprayed under high pressure from an injector into the combustion chamber, where it ignites on contact with the hot, compressed air. (more…)

What the Aut fuel system does

carburetion plays an essential part in a car engine’s performance.

Its job, briefly, is to atomise or break up the fuel particles and mix the right amount of petrol with the right amount of air, so the mixture will burn efficiently in the cylinders depending on the engine’s requirements at the time.

The inlet manifold below the auto carburettor has a twofold task:

* to assist in the vaporisation of the air/fuel mixture – often a ‘hot spot’ is incorporated immediately below the auto carburettor for this purpose; and

* to deliver the correct and preferably equal amount of vaporised mixture to each cylinder – a factor influenced by the length and positioning of the individual manifold tubes or branches. (more…)

The fixed-jet (or fixed-choke) carburettor incorporates various jets and an accelerator pump to alter the mixture’s strength according to engine needs.

As the airstream through a carburettor’s venturi speeds up, the air becomes ‘thinner’ and without some compensating device the mixture would become progressively richer until it was too rich to burn.

The fixed-jet carburettor solves this problem by air correction—mixing some air with petrol before the petrol is drawn into the venturi. On most carburettors, air correction is by means of a perforated tube which emulsifies the mixture. (more…)

A morden carburettor fitted with various emission devices does not differ in principle from the compound carburettor. It is usually a fixed jet carburettor with two or more chokes and a number of anciliary components which control the mixture more accurately than a pre-emission equipped carburettor.

The choke is frequently automatic. A chamber on the end of the choke butterfly spindle contains a bi-metallic coil which is connected to the car’s electrical system when the engine is running. It may be wired through an engine temperature thermostat. This permits current to flow when the engine is warm. Current in the bi-metallic strip changes its spring effect on the choke spindle and opens the choke butterfly as the engine heats up. (more…)

Most modern turbocharged cars and many naturally aspirated cars have petrol injection instead of carburettors.

With a carburettor system, the petrol is mixed with the air as it passes through the carburettor and is then distributed to the cylinders; but with an injection system, the petrol is squirted under pressure through small injector nozzles where it is atomised and vaporised.

Generally injectors are located in the intake passages near the inlet valves. The quantity of fuel injected and the correct timing of the injection varies with the type of system used and the conditions prevailing in the engine at the time. (more…)

Inlet manifolds

There are two jobs the inlet manifold has to do: assist vaporisation of the petrol/ air mixture from the carburettor, and distribute that mixture as evenly as possible to each cylinder.

An even distribution would be straightforward if all the mixture were fully vaporised after leaving the carburettor. But this is not possible under all conditions, and some petrol is still liquid when it reaches the inlet manifold. (more…)

Petrol tanks

Fuel tanks today are positioned well away from the engine, at the rear of a front-engined car or at the front of a rearengined model.

This reduces the risk of fire, and allows the tank to be at a lower level than if it were in the engine compartment. Some full petrol tanks weigh more than 80 kg and the lower this weight is, the less it will affect the car’s handling and stability.

Modern tanks are fitted with baffles, or compartment walls, to restrict the surging of fuel when the car is cornering and braking. The inside of the tank is usually treated to prevent rust being caused by moisture condensation. (more…)

A petrol engine provides power to propel the car by burning a mixture of petrol and air in its cylinders. The ignition system provides the electric sparks that ignite the mixture.

Each cylinder has a spark-plug with two metal points called electrodes, which project into the combustion chamber. When electricity is fed to the spark-plug at a high enough voltage, current jumps across the gap between the electrodes in the form of a spark.

Spark ignition systems are basically the same on all modern cars. (more…)

A car battery normally produces 12+ volts, but a voltage thousands of times higher is needed to produce the sparks which ignite the petrol/air mixture.

It is the coil which boosts the low voltage current from the battery, transforming it into high voltage for the spark- plugs. Depending on the type of ignition system, the coil can produce as much as 60 000 volts for the spark-plugs. (more…)

The distributor is the moving mechanical link between the electrical components of the ignition system and the engine.

It interrupts the current to the coil’s primary windings and distributes the coil’s high voltage output to the spark-plugs in the required firing order by a rotor arm. In older cars, the current is switched on and off by ignition points, but mechanical distributors are steadily being replaced by solid state electronic ’switches’. (more…)

How a spark-plug works

The ignition system produces the correctly timed high voltage pulses of electricity necessary to produce sparks. The spark- plugs provide the means for the electric sparks, which ignite the petrol / air mixture in an engine’s cylinders, to occur.

A spark-plug consists of a metal electrode passing through the centre of a ceramic insulator. Surrounding the lower portion of the insulator is a metal casing that is screwed into the cylinder head. (more…)

A CAR exhaust system has two main functions. Firstly, it takes hot, waste gases from the engine to a point where they can be released into the atmosphere without danger to the occupants of the car. Secondly, it reduces the noise made when used gases are expelled by the engine. This is done by a muffler, or silencer.

The gases produced in an engine expand with great force and are released into the exhaust system under pressure. Each time the gases pass into the exhaust manifold, a shock wave is set up. With shock waves occurring at the rate of several thousand a minute, the noise from cars would be socially unacceptable if it were not moderated. (more…)

Water circulation

Only about a quarter of the heat energy developed in a spark-ignition engine is converted into useful work.

The remainder of the heat has to be disposed of without causing any engine part to become so hot that it ceases to work. At full throttle, about 36 per cent passes out of the exhaust system, some 7 per cent is lost to internal friction and heating the lubricating oil, and a further 33 per cent is dissipated in the cooling system.

There are two types of cooling system: Fins direct and indirect. In the direct system, air is blown over fins on the outside of the cylinders and cylinder heads. In the indirect system a coolant, usually water, flows through passages inside the engine. (more…)

Where Auto Part Engine heat is lost

The function of the radiator is to dissipate heat from the hot water circulating in the cooling system. It normally consists of a. header or top tank and a bottom or receiving tank, with a core, usually of metal tubes, between them.

Hot water enters the header tank through the thermostat from the water jacket, and flows through the core, where it gives up its heat. The tubes are fitted with fins to provide a greater contact area for the cooling air.

The cooled water passes into the receiving tank and is then returned to the auto part engine through the water pump. (more…)

Temperatures in the engine vary widely. The engine must be able to start below freezing point; yet an ideal sump temperature when running is about 82`C because this evaporates moisture formed by the process of combustion. The temperature in the main and big-end bearings will be about 11°C above the sump temperature, but the piston-ring temperature may reach 232°C when the car is at full throttle.

All auto car oils get thinner as they are heated, but some thin out more rapidly than others. The rate at which they thin out is known as the viscosity index; the less the viscosity changes with the temperature, the higher the viscosity index number. (more…)

Auto Car Oil pumps

Two kin ofauto car oil pump are in general use —the gear type and the rotor. Each is usually driven from the camshaft or the crankshaft. The gear type has a pair of meshing gears. As the gears rotate the spaces between the teeth are filled with auto car oil from the sump. When the teeth come together, or mesh, the auto car oil is forced out under pressure. The rotor pump consists of an inner and an outer rotor in one cylinder, with auto car oil filling the gap between them. As in the gear-type pump, auto car oil is first drawn in from the sump then delivered under pressure to the engine. (more…)

How the engine turns the wheels

The transmission channels power from the engine to the road wheels. With a frontmounted engine and in rear-wheel drive vehicles transmission starts at the flywheel and continues through the clutch, gearbox, propeller shaft and final drive to the rear wheels.

Cars with front engines and front drive, or rear engines and rear drive, do not need a propeller shaft; power is transmitted through short drive-shafts to the driving wheels.

The clutch allows the engine power to be disconnected from the transmission to free it from torque (turning effort) when gears are engaged or changed. (more…)

What the Auto Clutch has to do

A motor vehicle’s clutch takes the load off the gears when they have to be changed, by disconnecting the driveline between the engine and the driving wheels. The clutch also permits the engine to be revved up to develop sufficient power to move the vehicle before the drive is engaged.

Disengaging the clutch separates three parts of the clutch assembly the flywheel, the driven plate (also known as the centre plate or clutch plate) and the pressure plate. The flywheel is bolted to the end of the crankshaft and rotates with it; the driven plate is splined to the gearbox input shaft so that they rotate together; and the pressure plate clamps the driven plate to the flywheel. (more…)

Why a car has a gearbox

Road wheels turn at about 1000 rpm if a car is to cover 110 km in an hour. At this speed the engine may be turning at 4000 rpm. The relationship between the rotation speeds of the engine and wheels is the axle ratio. In this case it would be 4:1. As long as the car is driven at a steady 110 km/h on the level, this gearing is satisfactory, but when the vehicle is confronted by a hill, a lower gear must be selected or the engine will begin to falter and eventually stall as little power is developed at low engine revs. Selecting a lower gear enables the engine to turn faster in relation to the road wheels and also multiplies the torque. (more…)