What is a Rocker Cover Gasket?

This image shows just one example of a rocker cover gasket, of which there are hundreds of designs, shapes, and constructions, each of which is specific to a particular engine or application. Before we get to the specifics of this example though, we need to discuss rocker covers, and what they do.

In some ways, rocker covers, aka tappet covers, valve covers, or even engine covers can best be thought of as a kind of lid that performs much the same function as the lid of a pressure cooker. On the one hand, a rocker cover seals off an engine from the open air, while on the other hand, a rocker cover helps to contain the volatile gases that arise from normal engine operation.

On most modern engines, rocker covers are made from cast aluminium, which ensures that it expands and contracts at the same rate as the cylinder head, which is typically also made from cast aluminium, although in some cases, rocker covers are made from various types of plastic and/or injection-moulded resins. Nonetheless, in both cases, the rocker cover is bolted to the cylinder head with several small bolts or screws, but to prevent oil from seeping out of the joint, all rocker covers are fitted with highly engineered gaskets such as the example shown here, to provide a positive seal between the rocker cover and the cylinder head.

You may wonder why rocker cover gaskets need to be “highly engineered” to be effective, given that most engines have a slight vacuum in them. The answer to this question is highly technical in nature and therefore, the finer details of this subject fall outside the scope of this article. Nonetheless, suffice to say that the vibrations that are inherent to all engines are the single biggest reason why rocker cover gaskets on older engines fail, so all rocker cover gaskets on modern engines feature one or more mechanisms that damp out or absorb engine vibrations.

Moreover, since rocker covers are not as tightly bolted down onto cylinder heads as cylinder heads are bolted down to engine blocks, rocker covers tend to vibrate at significantly higher frequencies than cylinder heads. Therefore, if rocker cover gaskets did not have features like ribs, grooves, or ridges as shown in the example above, to absorb engine vibrations, it would be impossible for even the most advanced polymeric gasket compounds to provide a positive seal between rocker covers and cylinder heads.

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