This tensioner pulley maintains correct belt tension in the engine accessory drive system. It rides against the belt span between the crankshaft pulley and the alternator or fan hub, preventing slip and ensuring consistent power transmission to the driven components. A seized or worn pulley bearing produces a chirping or squealing noise under load and can allow the belt to jump off the drive path. The pulley matches the original assembly's groove profile and bearing preload, so no shimming or adapter spacers are required during replacement. On installation, verify the belt routing matches the original layout and torque the mounting bolt to the specification for the host engine.