Many cars are equipped with belt driven camshafts. A timing belt is a toothed belt, running over toothed gears. Of course, it is essential that the teeth on the belt can't jump over the teeth of the gear, because that would change the timing, resulting in poor engine performance or even damage to pistons and valves. So the belt tension should never be too low and never be too high, as that would cause the belt to break, causing severe engine damage too.

On most cars, a tensioner adjusts the belt. This is a pulley, rotating on a bearing and mounted on a slider, so it can be pushed towards the belt to increase the tension.

Belt tensioners are wear parts. The surface of the pulley will wear down and get rough, the bearing inside the pulley may run dry or develop excessive play, resulting in noisy operation, vibration and eventually seizing. That will cause the belt to snap, resulting in severe engine damage.

The tensioner pulley should be replaced when replacing the timing belt. Most people prefer to buy a kit, containing the belt, the tensioner and other pulleys. Some people prefer to buy the parts separately. That's why Nipparts offers a wide range of individual tensioner pulleys for Japanese and Korean cars.  tensioner pulleys are made to OE specifications and are manufactured from first grade steel and top quality bearings, resulting in a top quality pulley for an affordable price.