Called a rocker cover in most parts of the world, valve covers are a recent invention, as they did not exist on early engines. Today, rocker arms are critical to having the intake and exhaust valves operate properly, so valve covers were created to keep them functioning. Basically, they were first invented to keep the oil in and the dirt out.

The valve cover helps seal the joint between the rocker cover and the rest of the engine. Failure of this gasket can cause oil to leak from the engine. If you are noticing an oil leak in your engine, it might be time to replace that worn down valve cover.