I havea 92 500sl. The belt is loose and i dont know how to tighten it up can anybody tell me?? Thanks.

 

I had the same problem with mine, there is an adjustment on my tensioner that as I remember involved a 10mm socket with a small wratchet. If you look closely there are graduation marks on the pulley and you can actually see how much adjustment you have left if any. I do know those tensioners eventually loosen up to the point where they can no longer sustain enough pressure to hold the belt tightly enough. Mine was even slipping on the alternator slightly without my knowledge, after tightening the battery stayed full and the dreaded " dash Flash" went away. Hope this is of some help.