Engine components

This explores various different engine components found on modern road vehicles

Engine components

Engine block and liners

Engine cylinders, when cast in a single housing, are known as the engine block. Usually, the engine block is manufactured from cast iron or aluminium alloy. In the latter case, cast iron or steel liners form the cylinder bore. The engine block forms the major component of a ‘short’ motor.

The cylinder bores are formed via a machining process with a boring tool to give the correct form to the cylinder within closely specifi ed tolerances. Cast iron is a mixture of iron with a small amount of carbon (2.5–4.5% of the total). The carbon added to the iron gives a crystalline structure that is very strong in compression. In addition, it is slightly porous and this helps to retain a fi lm of lubricating oil on working surfaces. This property makes cast iron particularly suitable for cylinder bores that can be machined directly into the casting. On many engines cylinder liners are used.

Pistons and connecting rod

Pistons are generally manufactured from an aluminium alloy, which reduces weight and increases heat dissipation. There are numerous designs to accommodate thermal expansion according to engine type and application

Piston features: 1, fi re land; 2, crown;
3, piston pin bore; 4, skirt diameter; 5, skirt; 6, piston rings

Aluminium has greater thermal expansion than cast iron used for the block and cylinder liners. This means that the piston expands more than the block
as the engine temperature increases. When the engine is cold, the working tolerances are greater to allow for expansion. The piston has design features to allow for expansion and correct tolerances at running temperatures; for example, a cold piston is slightly oval and tapered inwards towards the crown

Piston dimensions: 1, crown diameter;
2, skirt diameter; 3, diameter in piston pin direction;
4, diameter at right angles to the pin


The crankshaft of a four-cylinder engine usually has fi ve main bearings. At the front of the crankshaft provision is made to locate and drive the crankshaft pulley and timing gear via keyways and securing bolts . The oil pump drive is located behind this, and then the first or front main bearing as important Engine components.

Crankshaft pulleys

Cylinder heads

The cylinder head gasket has to form a gas-tight seal at the interface between the cylinder head and the cylinder bores. In addition, it must seal and separate the cooling water supply jacket and the oil supply and return drillings. Traditional head gaskets were constructed from copper and asbestos. Modern material technologies allow head gaskets to be made from composite materials which have superior sealing and heat transfer performance

Head gaskets


Inlet and exhaust valves are poppet-type valves with a circular sealing face recessed in the cylinder head . The valves are located via the stem and slide inside valve guides mounted in the cylinder head. Valve heads are exposed to full, combustion chamber temperatures and pressures; the temperature of the exhaust valve can be as high as 800°C. The incoming gas charge has a cooling effect on the intake valve but, generally, heat dissipation from the valves is via the stem and guides to the cylinder head. Combustion and fuel deposits can cause problems on the valve; this can be avoided by the use of good quality fuels and oils.

Valves in position on a cutaway engine.


The camshaft, on most modern engines, is mounted in bearings formed into the cylinder head via an in-line boring process . The camshaft is forged from steel or cast iron and the bearings and cam surfaces are a smooth, machined fi nish. The camshaft has cam lobes for each valve and to ensure the correct sequence of valve timing, the camshaft is timed and synchronized with the crankshaft position as Engine components.

Engine components
cylinder head with two cams in position.

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