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 must always be replaced when the cylinder head is removed and refitted. In addition, when refitting a cylinder head, it is important that the manufacturer’s information is sought and applied with respect to replacement of cylinder head bolts where necessary. Correct torque and a tightening sequence of cylinder head bolts must be followed

Cylinder heads are cast from aluminium alloy or iron. Aluminium alloy is lighter but cast iron or steel valve seats and guides must be installed in the head . Cast iron heads generally have valve seats

The combustion chamber is formed in the cylinder head such that, on assembly, it is located directly over the cylinder bore in the engine block. There are numerous designs in use depending on engine type, optimization parameters and application. The evolution of petrol engines can be seen in the design of combustion chambers that has been developed over the years to improve efficiency.