What type of belt synchronizes the crankshaft and camshaft in an engine?

The belt that synchronizes an engine’s crankshaft and camshaft is the timing belt.

A timing belt is a toothed belt whose teeth mesh with toothed pulleys on the crankshaft and camshaft. This keeps the camshaft turning in the correct relationship to the crankshaft, so intake and exhaust valves open and close at the intended points in the piston cycle. In many four-stroke engines, the camshaft turns once for every two crankshaft revolutions.

Timing belts are commonly made from reinforced rubber and operate inside a protective cover. They are quieter and often lighter than timing chains, but the belt material can age and requires replacement at an interval specified by the vehicle manufacturer. If it breaks, the engine may stop immediately; in an interference engine, valves and pistons can collide.

A timing belt is not the same as a serpentine or drive belt. Those external belts usually power accessories such as the alternator, water pump, or air-conditioning compressor. Some engines use a timing chain or gears instead, but those alternatives perform the same synchronization job.