The timing chain in an internal combustion engine connects the crankshaft and camshaft. The timing chain ensures that the two shafts remain in sync with one another. Beginning in the mid 1980s, metal timing chains were widely replaced by rubberised timing belts or timing gears. An internal combustion engine will not run with a broken timing chain or belt. Timing chains are rarely known to break during an engine's typical lifetime.
If a timing chain is not properly tensioned, it may develop slack, which can result in chain-slap and premature fatigue. Cracks in the chain may develop, resulting in failure.
An overly tight timing chain is placed under excessive stress. The added tension increases friction and heat within the moving parts of the chain that can result in early failure.
Situations such as an engine overheating or running out of oil can cause a piston to seize within the cylinder. If this happens while the engine is running at a high rpm, the sudden stop in rotation can cause a timing chain to fail.