Proper belt tension is essential for efficient power transfer and long accessory belt life. Tensioners are a roller that spins on an internal bearing. The roller pushes against the back of a reinforced rubber belt to keep it properly adjusted.

Automatic tensioners are constantly adjusted by an internal coiled spring that maintains the correct tension, on the fly. Tensioners with weak springs or worn rollers allow belts to slip. This results in noise, poor power transfer, and accelerated belt wear.