Valve Cover
The metal or plastic cover bolted to the top of the cylinder head to seal the valvetrain and prevent oil leaks.
The valve cover (also known as a rocker cover) is a removable metal or plastic lid bolted to the top of the cylinder head. Its primary purpose is to seal the valvetrain—including the camshafts, rocker arms, and valves—preventing engine oil from leaking out.
Inside the valve cover, oil is continuously sprayed to lubricate the moving valvetrain parts before draining back to the oil pan. The valve cover also features a oil filler cap where fresh engine oil is added, and often holds the PCV (Positive Crankcase Ventilation) valve.
To prevent leaks, a rubber or cork valve cover gasket is compressed between the cover and the cylinder head. Over time, the gasket hardens and shrinks, causing oil to leak. On overhead cam engines, oil can also leak into the spark plug tubes, causing misfires.
Replacing a leaking valve cover gasket involves unbolting the cover, cleaning the mating surfaces, and installing a new gasket. Plastic valve covers can also crack or warp and must be replaced entirely if damaged.