Timing Chain

Chains run inside the engine, lubricated by engine oil, and many are designed to last the life of the engine. Hydraulic tensioners and plastic guides keep them taut. Chains can stretch with wear, especially with poor oil maintenance. A stretched chain changes cam timing and, if neglected, can jump a tooth.

Unlike a timing belt, a chain runs in oil inside the engine and is designed to last much longer, though not always for the life of the engine. Some engines use two or more chains, for example one to the camshafts and one to the oil pump or balance shafts. Chain stretch is caused by wear in the pins and links, which is speeded up by long oil change intervals and the wrong oil. Workshops can often measure stretch through the camshaft-to-crankshaft deviation with a scan tool.

Sprockets on the crankshaft and camshafts are connected by the chain. The tensioner uses oil pressure and a spring; guides keep the chain on its path. Tensioners keep the chain tight and guides keep it on track. Hydraulic tensioners rely on oil pressure.

A rattle for a few seconds after a cold start and camshaft correlation codes are typical warning signs. Timing belts work the same way but need replacing at set intervals. A rattling noise at cold start can mean a stretched chain or a weak tensioner. Ignoring it can let the chain jump teeth and cause serious engine damage.