A timing cover is a component typically found in internal combustion engines and is designed to protect components such as the timing gears and chain or belt. In applications that use a timing chain, the timing cover usually seals the front end of the block, while engines with timing belts typically have timing covers that are less integral. Timing covers can be made from either metal or plastic. Engines with timing chains usually have a metal cover, while those with a timing belt may utilize covers made from a variety of different materials.
Timing chain covers are typically designed to seal the front end of the engine block. This is generally so the timing gears and chain can be lubricated with engine oil. These covers will usually be sealed to the block with a timing cover gasket, which may be responsible for engine oil leaks if it fails. Additionally, the crank shaft will typically pass through a seal set into the timing cover that may potentially leak. Replacing a timing cover gasket is typically a time intensive job, while replacing a crankshaft oil seal is sometimes possible without removing the cover itself.
Timing covers are also used in conjunction with timing belts. In these applications the front of the engine will typically be sealed with oil seals that are set into the block or head where the crank and cam shafts extend. With the engine otherwise sealed, the function of a timing belt cover is simply to protect the belt from damage. These covers may be constructed of either metal or plastic and may be comprised of several different pieces. Multi-piece timing belt covers may even contain both metal and plastic pieces.
Timing cover gaskets are also often used with timing belt covers, though they are designed to keep contaminants away from the belt. If an oil leak develops at a crank or cam shaft seal, oil may contaminate the timing belt and require its replacement. Oil may also contaminate the cover gasket, causing it to swell and become unusable. In these cases, the seal, belt, and gasket are often replaced at the same time.
In some cases, timing belt covers will use special timing cover bolts. These bolts will typically have a thick shoulder that allows them to tighten without cracking the plastic cover. In other cases the cover may have metal bezels in the bolt holes that are designed to perform the same function.