Here is a timing belt tensioner which had started to fall apart notice the missing bit on the outside. It is of the type with a plastic surround which when breaks up allows the timing belt to slip several teeth with disasterous results for the engine. This one is from a Vw Golf 1.4 16v engine which came in for an unusual tapping sound from the front of the engine. In this case the customer was lucky and a timing belt and tensioner kit was fitted to get the vehicle back on the road