Gaskets and Oil Seals

Gaskets can be made of soft materials such as cork or rubber, or they can be made of soft alloys and metals. Most gaskets are made to be used only once. Oil seals must also be replaced when a component is overhauled.

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, nitrile, paper, heat resistant materials or graphite; or they can also be made of soft alloys and metals such as brass, copper, aluminum or soft steel sheet metal. Such materials may be used individually or in some cases as blends to produce the required functional material.

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. Modern head gaskets have to be constructed to resist high temperatures and engine detonation.

Some modern high temperature head gaskets are called 'anisotropic' in nature. This means that the gasket is designed to conduct heat laterally to transfer heat from the engine to the coolant faster. They are normally constructed with a steel core. Special facing materials are added to both sides of the gasket core to provide a comprehensive seal under varying torque conditions.

With the advent of environmental factors and a reduction in the use of asbestos, replacement materials have been developed. Some of these modern special materials that are now used for the side layers of head gaskets are designed to withstand temperatures up to 2100 degrees F or 1150 degrees C. Such materials are also designed to allow the cylinder head and block, some of which which have considerable distortion rates, to move slightly on the head gasket as they expand during engine warm-up. This feature is vital for preventing head gasket failure.

Some head gaskets also incorporate stainless steel fire rings to help to contain heat and pressure within the cylinder. In addition, many head gaskets also have an added silicone based outer coating on both sides of the side material layers to provide additional cold sealing ability during start-up and warm-up. Head gaskets also seal oil passages, and control the flow of coolant between the cylinder block and head and are fitted with beads or rings to prevent leakage and corrosion.

Some joints between surfaces on modern engines are being sealed with special sealants which eliminate the use of gaskets in some applications. Pure rubber, or conventional cork-rubber is unable to deal with the stresses and pressures in modern engines.

Modern gasket manufacturers are producing improved material combinations such as nitrile and cork blends to deal with 'high tech' engine demands. Such combinations are more able to deal with issues such as compressibility and wicking.

Some materials are designed to 'swell' in application and increase sealing ability. For instance when oil inside a valve cover penetrates the edge of the gasket material, it is designed to swell by approximately 30%. This swelling effect increases the sealing pressure between the head and valve cover sealing surfaces and helps to seal potential leaks.

Some gasket materials are designed to have high tensile strength. They are designed to resist breakage during dismantling or installation processes.

Gaskets around a rotating part would quickly wear out and leak. To seal these parts, oil seals are needed. 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.

Various materials are used in modern oil seals, some being impregnated with special coating materials that are designed to increase their sealing ability on worn shafts.

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