When a timing chain breaks, the camshaft stops spinning and the piston can strike open valves. This bends the valves, leading to catastrophic engine failure. Regular maintenance of the timing chain and replacement when necessary prevents engine damage.
A timing chain synchronizes the rotation of the engine's camshaft and crankshaft; a properly functioning timing chain ensures that the valves open and close at the correct times. Timing chains are moving parts that eventually wear out or break, but they are durable enough that manufacturers have no specific guidelines about when to replace them. Rattling in the engine or the check engine light signaling a problem are signs that the timing chain needs to be checked.
In cars manufactured after the 1980s, timing belts are more common than timing chains. Timing belts are cheaper to produce and run more quietly, but are less durable than chains. A timing belt must be replaced every 30,000 to 50,000 miles the car is driven, and due to its quieter operation does not give an auditory warning of imminent failure. Timing chains and timing belts perform the same function, but are not interchangeable; engines designed for timing belts cannot use timing chains and vice versa.