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How Cars Work Part 2

The Transmission
Controls the power contained in the crankshaft before it goes to the wheels and allows a driver to control the speed/power of a car by providing different speed/power ratios known as gears.
So, first gear gives plenty of power but little speed whereas fifth gear provides little power but plenty of speed. The principle is the same as on a bicycle.
The crankshaft only connects to the transmission when the car is in gear and the clutch is engaged. If you press down on the clutch the crankshaft disconnects from the gears.
The gears are connected to the drive shaft, which transfers power to the wheels. When the transmission rotates the drive shaft, this turns the wheels. On rear wheel drive cars the drive shaft uses a differential which transfers power to the wheels.

Inside a Ford Focus gearbox

As the engine turns and the clutch is pedal pressed down the link between the engine and transmission comes apart. This enables gear changes and stopping whilst still in gear. When the clutch pedal is brought up slowly the clutch starts to engage and biting point occurs. Biting point is used to push the car until the pedal comes all the way up. Then the link between engine and transmission lock and full power transfers to the wheels.

Other Key Components

Almost like a small generator, it gets turned from the engine via a fan belt and powers the electrical appliances and lights whilst constantly keeping the battery charged. If the battery light comes on or stays on after starting the engine, this usually indicates a problem with the alternator or a broken fan belt.

Cars use either disc or drum brakes. Disc brakes use a calliper to press pads onto a brake disc in order to slow the wheel down. Drum brakes work on the same principle however a drum brake presses against the inside of an enclosed drum. Disc brakes are more efficient than drum and are fitted to most modern cars, especially on the front. The principle is similar on a bicycle.

Controls the opening and closing of the inlet and exhaust valves.

Cooling System
Car engines produce lots of heat. This heat needs to be controlled. To do this water is pumped through passages that surround the cylinders and is then passed through two radiators, one of these radiators is used to heat the interior of the car.

Sends the spark to the spark plug at exactly the right moment. If the timing is off by a fraction then the engine won’t run properly

Exhaust System
Once the fuel-air mix has been burnt the waste gases leave the cylinders via the exhaust valves into the manifold and out through the exhaust pipe. If a catalytic converter is present the exhaust gas passes through it and any unused fuel and harmful toxins are removed.

This is separate from the foot brake. Usually it is mounted on the floor of the car and is connected by a cable to the two rear wheels.

Head Gasket
The cylinder head (a block that seals all the tops of the cylinders) and the engine block (which contains the main bodies of the cylinders) are separate components that need to fit seamlessly together. The head gasket is a piece of metal that sits between them and seals them.

A car engine consists of many moving parts. Oil lubricates these parts and allows them to move smoothly. In most car engines oil is pumped out of the sump through a filter that removes any dirt and then is showered under high pressure onto the bearings and other moving parts. The oil then trickles down to the sump where the process starts over.

Shock Absorbers
Also known as shockers, are fitted between the car’s body and axle in order to prevent excessive bouncing of the car body during motion.

Suspension System
Counteracts the effects of hitting bumps in the road. Without such a system a car would veer of course every time the tyres hit a bump or pothole. The system comprises of springs and shock absorbers. The springs absorb any of the energy released when the tyres roll over a bump and the shock absorbers absorb the energy from the springs. This keeps the the car stable.

Timing Belt
A belt connected to both the camshaft and crankshaft ensuring that they work in tandem with each other. The consequences of not keeping up with the maintenance schedule of the cam belt could mean a new engine.

What is the difference between a Petrol and Diesel Engine?
Diesel engines do not have spark plugs to ignite the fuel and air mixture, the explosion comes from the fuel and air been compressed and the molecules heating up. Diesel engines generate more pulling power than petrol. Hence the reason why trains and lorries are diesel engined.

The M.O.T Test

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