The timing chain keeps internal engine components in sync with each other by causing valves to open and close at the proper time. It is durable and generally needs no maintenance. However, timing chain failure can result in serious internal engine damage.
In order to maintain the mechanical integrity the engine needs to operate, engine components must be in precise synchronization. If the timing chain is loose or improperly adjusted, it may "jump time" (skipping a tooth or more, usually on the cam gear). This results in a loss of synchronization and engine performance.
Due to their inherent long life, timing chains usually have no specific replacement or maintenance intervals. Abnormal engine noise originating at the front of the engine (a rattle or rumble, associated with engine speed) is a good indicator of a failing timing chain. Timing chain faults can cause poor engine performance with or without Check Engine Light illumination. Some engines cannot tolerate any deviation in precise valve control. Any timing chain problem—a loose, noisy, or broken timing chain—can have disastrous consequences. Repairs can range from simple timing chain replacement to major engine repairs for damaged pistons and bent valves.
To replace the timing chain, remove the fan belts, pulleys, crankshaft pulley, and timing covers. The mechanic will inspect components inside the timing cover and, if necessary, replace oil seals, tensioners, and idler bearings. On certain engines, a water pump replacement should be done at the same time as the timing chain. The timing chain, its tensioner, and sprockets are considered a unit and should be replaced at the same time.