The timing belt connects the crankshaft to the camshaft(s), which in turn controls the opening and closing of the engine's valves. In some engine designs, the timing belt may also be used to drive other engine components such as the water pump and oil pump. When a timing belt is replaced, correct belt tension is critical. Too loose and the belt will whip, too tight and it will whine and put excess strain on the bearings of the cogs. In either case belt life will be drastically shortened.

For this reason it is important to replace all the timing components, rather than just the timing belt. As mentioned above this may include tensioners, idlers and the waterpump.The timing belt should always be replaced within the manufacturers specified period to ensure no problems with the timing system.