If you have the new style spring tensioner, there will be a 15mm nut in the center of the tensioner pulley. IF you have the old style, you will have a tensioning rod. If this is the case, you will have to loosen the clamp bolt (10mm allen) that is just below the pulley and then loosen the adjustment rod.

I usually replace the tensioners on the 119 engine. I have had many, many of them fail at bad times.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS