This belt tensioner maintains the correct tension on the accessory drive belt that powers the engine-mounted pumps and the alternator. It is mounted on a bracket on the front of the engine block and uses a spring-loaded arm to press a pulley against the belt. A failing tensioner allows belt slip, which causes undercharging of the electrical system and reduced hydraulic pump output. The manufacturer machines the pivot bore and pulley face to the same tolerances as the original assembly, so the tensioner arm aligns with the belt path without shimming. When replacing, inspect the belt for glazing or cracking and replace it if worn.