The engines on most modern cars are equipped with a rubber toothed Belt, the purpose of this is to run the camshaft which in turn opens and closes the inlet and exhaust valves in perfect timing the piston position. This belt has varying replacement intervals which are manufacturer dependant (usually 60,000 miles or a maximum or 5 years) This is usually replaced a kit including all tensioners, idlers and pulleys, it is also recommended that the water pump and antifreeze are replaced at the same time if the pump is driven by the timing belt).

The cost of timing belt replacement varies according the vehicle but will always be cheaper than the consequences of belt failure. If the teeth strip, it jumps or snaps, then the timing between the valves and pistons will not be correct more than likely causing contact between the two, resulting in damage, usually bent valves or broken internal components.