The engine

The parts of an overhead-camshaft engine Camshaft The camshaft has pear-shaped lobes whichactuate the valves - usually one inlet and oneexhaust valve for each cylinder. Piston The piston is fitted withsteel rings which fill thegap between it and thecylinder wall. Flywheel The flywheel is a heavy disc attached to the end ofthe crankshaft. It helps to transmit the enginepower and to smooth out the individual impulsesof the pistons so that the power flows evenly. Connecting rod The connecting rod converts theup-and-down movement of thepistons into rotary motion through atreadle action. Crankshaft The crankshaft transmits power to theroad wheels through the gearbox. Sump The sump contains the lubricatingoil for the engine's moving parts. Apipe from the oil pump draws up theoil through a strainer. Camshaftdrive belt A toothed belt - oftencalled the timing belt -drives the camshaftfrom a sprocketmounted on the end ofthe crankshaft. Thecamshaft rotates at halfengine speed.

The parts of an overhead-camshaft engine

The engine is the heart of your car. It is a complex machine built to convert heat from burning gas into the force that turns the road wheels.

The chain of reactions which achieve that objective is set in motion by a spark, which ignites a mixture of petrol vapour and compressed air inside a momentarily sealed cylinder and causes it to burn rapidly. That is why the machine is called an internal combustion engine. As the mixture burns it expands, providing power to drive the car.

To withstand its heavy workload, the engine must be a robust structure. It consists of two basic parts: the lower, heavier section is the cylinder block, a casing for the engine's main moving parts; the detachable upper cover is the cylinder head.

The cylinder head contains valve-controlled passages through which the air and fuel mixture enters the cylinders, and others through which the gases produced by their combustion are expelled.

The block houses the crankshaft, which converts the reciprocating motion of the pistons into rotary motion at the crankshaft. Often the block also houses the camshaft, which operates mechanisms that open and close the valves in the cylinder head. Sometimes the camshaft is in the head or mounted above it.

The cylinders in which the pistons operate are cast into the block, as are mountings for ancillary equipment such as a filter for the oil which lubricates the engine, and a pump for the fuel. An oil reservoir, called the sump, is bolted underneath the crankcase.

Both block and head are usually made of cast iron. But sometimes aluminium is chosen for the head, because it is lighter and dissipates heat more efficiently.

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