Timing belt or chain

The timing gear synchronises the crankshaft with the camshaft so the valves open at the right moment. That is done with a toothed belt or with a chain. A timing belt has a prescribed replacement interval, depending on the engine often in the order of tens of thousands of kilometres or a number of years, whichever comes first; if it is exceeded and the belt breaks, serious internal damage follows on many engines.

A timing chain is designed to last the engine's lifetime in principle and usually has no fixed replacement interval, but is not maintenance-free: on certain engine families chain stretch is a known point of attention. Which solution an engine has, and on a belt which interval applies, differs per engine and model year.

We name the type of timing gear as a factual characteristic where that is known. The exact replacement interval is in the manufacturer's service schedule for that specific engine; our mention is a concept explanation, not maintenance or buying advice.