A vehicle's timing belt controls the camshaft and crankshaft rotation, opening and closing the valves to smoothly operate the vehicle. It is so named as it turns the camshaft in sync timing with the crankshaft. On some engines, a timing belt failure causes catastrophic damage to the engine.
The timing belt times the opening and closing of the valves so that they are closed when the piston is dead center. In a four-stroke engine, the valves open and close once for every revolution of the crankshaft.
Timing belts are located under timing belt covers and may be in hard-to-access places in the engine. For this reason it is recommended that the belts be replaced on a schedule following a vehicle owner's manual. In some engines, the timing belt also runs the water and oil pumps. When the belt is replaced, it is recommended that these pumps be replaced also, due to where they are located.
In a type of engine called an interference engine, more than one valve may open into an area where the pistons travel. If the piston makes contact with the valve due to timing belt failure, it can severely damage the engine. A non-interference engine is one where an open valve never enters into an area where the pistons travel.