This multi-ribbed belt tensioner maintains the correct drive-belt tension on the alternator drive of the host tractor. It is mounted on the engine front cover and presses against the belt span between the crankshaft pulley and the alternator pulley. A worn tensioner allows belt slip, which reduces alternator output and can cause the belt to overheat and crack. The tensioner is manufactured to the original spring-rate and damping specifications, so it holds the belt at the designed tension without requiring manual adjustment. When replacing, inspect the belt for wear and replace it if necessary.