Timing belt kits contain everything needed to replace the timing belt and its associated parts. The kit generally includes the belt itself, idler and tensioner pulleys which are necessary to maintain or decrease slack as needed, and bolts needed to secure everything in place. When a timing belt is replaced, correct belt tension is critical. A timing belt kit is needed if
the car manufacturer specifies that all parts connected to the belt should also be changed. 

An essential part of car engine efficiency is the drive belt. Apart from its role in driving multiple peripheral devices in an engine such as the alternator, the water pump and the power steering pump, a good quality car drive belt creates less friction in the engine which gives your car an overall better performance.Avoid unnecessary breakdowns by replacing it
with a good quality car drive belts

To ensure that the timing belt is operating at optimum tension at all times, a belt tensioner is needed. This rotating pulley prevents the belt from becoming slack and operating inefficiently or incorrectly. The tensioner may have to be adjusted manually during fitting though many, known as automatic tensioners, have springs which automatically adjust the tension.