GASKETOLOGY 101:


THEY'RE NOT AS SIMPLE AS THEY LOOK

Gasket Function
The environment in which a gasket functions is much more dynamic than most people think. As the cylinder head and engine block are exposed to the heat and pressure of the combustion process, they expand and contract considerably. In addition, the combustion process causes the cylinder head to lift off the block and portions of the head to deflect. This motion is not only hard on head gaskets, but the motion is transferred throughout the entire engine causing the other components to move around and vibrate. This motion creates considerable force on the gaskets and will quickly tear up low quality materials.

A gasket has to be soft enough to conform to mismatched flanges, yet hard enough to resist the motion of the castings, while at the same time maintaining adequate bolt torque. They have to work with cast iron, aluminum and plastic components, as well as combinations of all three.

A gasket designer needs to take all this, and more, into consideration when designing the gasket. That is why the knowledge of experienced gasket engineers, such as Magnum's, is critical to manufacturing gaskets you can rely on.

Gaskets designers must also consider whether the application is for original equipment or aftermarket. OE gaskets are designed to seal between new castings, with close to perfect surface finish, flatness, and precise bolt torque. Aftermarket gaskets, on the other hand, have to seal used, warped, bent, pitted flanges, often with bolts tightened by feel. That's why aftermarket gaskets don't always look like OE. They have a much different role to fill.

Simple or Complex?

Automotive gaskets are definitely not as simple as they may seem. There is a substantial amount of engineering that goes into designing such an ordinary looking piece of material. The gasket designer needs to consider the engine design, it's expected usage, where the gasket is used on the engine, what the casting and covers look like, how many bolts clamp the gasket, bolt torque, flange flatness, flange surface finish, etc.

The mating flanges could be a casting and a cover, or two castings. Castings can be made of aluminum or iron. Covers can be stamped steel, machined aluminum or even molded plastic (nylon composites). Surfaces range from baby smooth to ultra-rough. Each joint on an engine is different, and each engine is different, so you can't use the same design or material for all applications.

Materials and Designs

One basic consideration in gasket design is the choice of thicker/softer material versus thinner/harder designs.

Thicker, softer gasket materials are subject to relaxation and torque loss but have superior conformability. They are generally offered for applications in which:

Thinner, harder gasket materials generally relax less over time and resist torque loss but may not conform to irregular surfaces. They are generally offered for applications in which:

Another basic consideration is whether the sealing material (rubber, cork, paper) needs reinforcement with a rigid core or carrier. The cores and carriers are made of steel, aluminum or plastic (mostly nylon composite). The need for this "backbone" in the gasket design depends on many factors, including size of the gasket, engine component motions, pressure or vacuum the gasket must withstand, etc. Reinforced designs are discussed in detail in the following sections.

PAPER
These gaskets start with an "engineered composite material" that we generally call "paper". It is a complex formulation of polymers, binders, organic fillers, and sometimes Kevlar©. As you can imagine, all papers aren't created equal. Magnum selects premium materials, which cost us a little more, but make a much better gasket.

Plain paper gaskets are generally used on applications where there isn't a lot of motion or clamp load, such as thermostats, timing covers, throttle bodies, etc. When there is a lot of motion in the joint, either a very high density paper material is used or a steel reinforcement is added.

Continue with Gasket Materials
AND DESIGNS