Timing Cover

A timing cover is a protective metal, aluminum, or plastic cover bolted to the front of the engine block and cylinder head. Its primary purpose is to fully enclose the engine's timing belt or timing chain assembly, shielding these critical components from road dust, water, oil leaks, and debris.

The function of the timing cover differs depending on whether the engine uses a timing belt or a timing chain. On timing belt engines, the cover is typically made of plastic and runs dry, simply acting as a dust shield. On timing chain engines, the chain is bathed in pressurized engine oil for lubrication. In this case, the timing cover is made of cast aluminum or iron and acts as an oil-tight seal, using a gasket and silicone sealant to prevent oil leaks.

The timing cover also houses the front crankshaft oil seal, which seals the rotating crankshaft where it exits the engine block. Over time, the timing cover gasket or the crankshaft seal can degrade, leading to oil leaks at the front of the engine. On plastic belt covers, the plastic can warp or crack, potentially rubbing against the timing belt and causing premature belt wear.

Replacing a timing cover gasket or repairing a cracked cover requires removing accessory belts, the crankshaft pulley (harmonic balancer), and unbolting the cover. It is common to replace the timing cover gaskets during a timing chain or water pump service.