Mr. Gasket Valve Cover Gasket is made from high-density cork and rubber gasket material bonded to a steel core for extra rigidity in order to prevent the gasket from being sucked in or blown out. It is 0.313 thick and the steel core construction averts the gasket from being drawn inside or pushed out of engine at a high RPM. The valve cover builds a positive seal by controlling the swelling of gasket material when exposed to hot engine oil. A black latex rubber coating is applied to the exterior of the gasket to help seal minor flange irregularities. Its extra thickness also adds clearance between the valvetrain and the valve cover.