There is 1 major component rotating in an internal combustion engine. It is the crankshaft. It transfers power from the cylinders and rods to the transmission to power the vehicle. It also drives the camshafts, which move the valves to bring in air and take exhaust gasses from the cylinders. The crankshaft and camshaft are connected by a Timing Chain on most vehicles but on some vehicles a Timing Belt does it. The name Timing refers to one of its major functions. It keeps precise timing of the camshaft and crankshaft. If this timing is off engine performance suffers. If the timing gets off by too far it can cause major engine damage from the valves hitting the pistons. A timing chain is designed to last virtually for the life of the engine. A timing belt requires periodic replacement. There are still several new vehicles that are equipped with timing belts. We recommend these vehicles have their timing belt replaced every 60,000 miles.