M11 Plus Series Engines Operation and Maintenance Manual – 013-021   Belt Tensioner, Automatic (Alternator)

Every 192,000 km [120,000 mi], 3000 hours or 2 years, whichever comes first, for automotive applications inspect the automatic belt tensioner and every 80,000 km [50,000 mi], 3000 hours or 2 years, whichever comes first, for bus applications inspect the automatic belt tensioner

With the engine turned off, check that neither the top or bottom tensioner arm stop is touching the cast boss on the tensioner body. If either of the stops are touching a boss, the alternator belt must be replaced. Check to make sure the correct belt part number is being used if either condition exists.

WARNING  When using a steam cleaner, wear safety glasses or a face shield, as well as protective clothing. Hot steam can cause serious personal injury.

Check the tensioner pulley and body for cracks. If any cracks are noticed, the tensioner must be replaced. Refer to Procedure 013-021 (Belt Tensioner, Automatic) in Section A for replacement.

Check the tensioner for dirt buildup. If this condition exists, the tensioner must be removed and steam-cleaned.

Inspect the tensioner for evidence of the pivoting tensioner arm contacting the stationary circular base. If there is evidence of these two areas contacting, the pivot tube bushing has failed and the tensioner must be replaced.