Gaskets form a seal by being compressed between stationary parts where liquid or gas could pass. Most gaskets are made to be used only once. They can be made of soft materials such as cork, rubber, paper, asbestos. They can also be made of soft alloys and metals such as brass, copper, aluminium or soft steel sheet metal.

Choosing which material and design to use depends on the substance to be sealed, the pressures and temperatures involved. And, the materials and mating surfaces to be sealed.

Head gaskets seal and contain the pressures of combustion within the engine, between the cylinder head and block. They also seal oil passages between block and head. And control the flow of coolant between the block and the head.

Some gaskets provide or adjust clearances. Some joints between surfaces on modern engines are being sealed with special sealants which eliminate the use of gaskets in some applications.

Gaskets around a rotating part would quickly wear out and leak. To seal these parts, oil seals are needed. Many different kinds have been developed, including oil slinger rings. The most widely used is the lip type dynamic oil seal. It has a shaped dynamic rubber lip that’s held in contact with the shaft to be sealed by a circular coil spring called a garter spring.

A similar sealing principle is used to seal the valve stem to prevent oil entering the engine combustion chamber.

Rotating or sliding shafts can also be sealed by using “O” rings, but generally they are not as durable in most applications as the lip-type seal.

As a general rule, oil seals must be replaced when a component is overhauled.