CYLINDER HEAD

The internal combustion engine comprises of many parts and the most important part is the cylinder head which is positioned above the cylinders on top of the cylinder block. The head seals off the top of the piston cylinders, forming the combustion chambers. The cylinder head and block are joined together with a seal called the cylinder head gasket. The cylinder head also provides spaces for the passage ways that feed air and fuel and air/fuel mixtures to the cylinders aswell as passages that allow the burnt exhaust gasses to escape called inlet and exhaust ports.

The cylinder head ports allow the fuel/air mixture to travel into the combustion chamber through the inlet valves from the intake manifold and for burnt exhaust gasses to travel out from the combustion chambers exhaust valves to the exhaust manifold and exhaust. In a water cooled engine, the cylinder head also contains ducts and passages for water/coolant to circulate thus cooling the cylinder head and engine block which also has water passages, and therefore cooling the engine in general.

In the overhead valve (OHV) design, the cylinder head contains the poppet valves and the spark plugs, along with tracts or ports for the inlet and exhaust gases. The operation of the valves is initiated by the engine's camshaft, which is sited within the cylinder block, and its moment of operation is transmitted to the valves pushrods, and then rocker arms mounted on a rocker shaft, the rocker arms and shaft also being located within the cylinder head.

In the OHC design, the cylinder head contains the valves, spark plugs and inlet/exhaust ports just like the OHV engine, but the camshaft is now also contained within the cylinder head. The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and still also utilizing rocker arms (but without any pushrods), or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing 'cam bucket' tappets also called ‘cam followers’.

Almost all in-line straight engines use a single cylinder head that serves all the cylinders. A ‘V’ engine has two cylinder heads, one for each cylinder bank of the 'V' form. For a few compact 'narrow angle' V engines, such as the Volkswagen VR6, the angle between the cylinder banks is so narrow that it uses a single head spanning the two banks. A flat engine where the angle between the cylinder banks is 180° has two heads. Most radial engines have one head for each cylinder.

Some engines, particularly medium and large capacity diesel engines mostly have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. The design of the cylinder head is key to the performance and efficiency of the internal combustion engine, as the shape of the combustion chamber to piston, inlet port passages and exhaust ports.

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