New w124 owner need someone to explain the tensioner to me. - PeachParts Mercedes-Benz Forum

hanly2 · #1 06-23-2016, 04:05 PM

Ok here is a little background info. I have a 1990 300e with m103 engine. I noticed the belt was loose so I followed the procedure for adjusting the tensioner. When I was torquing the 19mm bolt back down at 73ftlb, it was not even seated against the washer, so I turned it a little more but not a lot. 2 days later and the belt is loose again. The arrow is still on the left side of the scale. So a few questions I have.
1. If the tensioner is manual, how can it go bad? besides the pulley?
2. Is the tensioner supposed to move up and down when I pull the belt or should it be tight and not moving?
Maybe if I understood how it was supposed to be I could get it right again.
Thanks

lorainfurniture · #2 06-23-2016, 05:26 PM

The big bolt is just a "lock down" bolt. The adjustment part is a vertical nut that is almost next to your power steering pump.

1. Loosen big nut
2. Adjust tension Bolt on top
3. Tighten large bolt.

hanly2 · #3 06-23-2016, 06:31 PM

Yes sir that part is understood, but after I lock it down should it move? is it spring loaded?

Rcktsled · #4 06-23-2016, 07:41 PM

The center of the tensioner is a large rubber bushing that is bonded to the outer perimeter. The normal failure mode is breakage of the bond which lets the outer part rotate freely on the failed bushing. You should really take everything apart and inspect it thoroughly. It is a pain but once you get it right it will stay that way for quite a while.