Cylinder head

The cylinder head seals off the cylinders and is made of cast iron or aluminum . It must be strong and
rigid to distribute the gass forces acting on the head as uniformly as possible through the engine block.

The cylinder head contains the spark plug - for
an SI engine - or fuel injector - for CI engine -,
and ,in overhead valve engines, parts of the valve
mechanism.

In the vast majority of four-stroke engines ,the
cylinder head mounts the entire valve gear and is
a basic framework for housing the gas-exchange
valves as well as the spark plugs and injectors.

In car engines , one cylinder head is usually
employed for all cylinders together. The cylinder
heads on water-cooled diesel truck engines are
usually made of cast iron. By contrast,all petrol
and Diesel engines cars use aluminum cylinder
heads due to the superior heat dissipation and lower weight.

In cars , the cylinder head is normally made of aluminum even when the cylinder block is cast iron.
The choice between cast iron or aluminium for the cylinder head is not simple . Aluminium has the advantages of light weight, high Thermal conductivity ,and ease of production to close tolerances
by gravity or low-pressure diecasting.

In trucks and large industrial engines , individual cylinder heads are often used on each cylinder for better sealing force distribution and easier maintenance and repair.

On the other hand, aluminium is more expensive than iron, tooling for large quantity production is costly, porosity in the finished casting can present difficulties, aluminium is more easily damaged in service and rather more prone to Gasket blow-by failure, corrosion may present problems especially where there are copper components in the Cooling system and heat-resistant Valve seat inserts are essential.

The three fluids , combustion gas, coolant and lubricating oil, flow independently in the cylinder head .
Figure below shows a model of the coolant and gas circuits in a cylinder head.

These circuits follow complex three dimensional routes, so cylinder heads are generally produced by casting.

Gravity casting or low-pressure casting using Sand molds or Metal dies are used. These circuits
are cast hollow by using sand cores installed in the holder mold. High-pressure Die casting is not used because the sand cores are fragile and cannot endure the high injection pressure of molten aluminum.