This V-belt tensioner pulley maintains the correct tension on the accessory drive belt in the engine. It is mounted on a pivot arm or bracket and presses against the back of the belt to prevent slippage and ensure consistent power transmission to the driven components. A seized or worn pulley bearing causes belt squeal, reduced alternator output, and eventual belt failure. The pulley is machined to the same diameter and profile as the original component so the belt tracks correctly and does not ride on the edge of the pulley. When replacing the pulley, inspect the belt for glazing or cracking and replace it if necessary.