These homebuilder's Lycoming valve cover gaskets replace the original cork gaskets which come standard on Lycoming 0-235, 0-320 and 0-360 engines. These new gaskets are molded from high temperature silicone rubber and do not harden over time so they can be re-used again and again. This hi-tech silicone rubber offers a much lower compression set, so it is superior at maintaining an oil-tight seal for the life of the engine. NOT FAA approved. For experimental aircraft only.