Timing Belt

Timing belts are made of reinforced rubber with teeth that mesh with pulleys. They run outside the engine behind a cover, unlike timing chains which run in oil. Manufacturers specify a replacement interval in kilometres or miles and years. Some newer engines use belts that run in oil.

Engines are either interference or non-interference designs. In interference engines, valves and pistons share space at different times, so a broken belt lets them collide.

The crankshaft pulley turns the belt, which turns the camshaft pulleys at half crankshaft speed. A tensioner keeps the belt tight, and on many engines the belt also drives the water pump.

A broken timing belt stops the engine immediately and, on interference engines, can cause serious damage. Replace it on time, usually together with the tensioner and idlers. Because the job requires removing many parts, the water pump is often replaced at the same time when it is driven by the belt. Keep the invoice as proof of replacement.