91 300-SEL-Bent Serp Belt Tensioner Adj Bolt - PeachParts Mercedes-Benz Forum

Mike Murrell · #1 03-03-2010, 08:12 PM

Talking about the bolt used to tighten the serpentine belt tensioner - uses a 13mm socket.

Awhile back found the serpentine belt quite loose. Started looking around and staring down the bolt noticed it was bent.

I know I have work ahead of me and can handle it.

Curious as to why this bolt would have bent all of a sudden.

Thanks for your time.

tinypanzer · #2 03-03-2010, 10:21 PM

It didn't bend all of a sudden. This usually happens when somebody not familiar with that tensioner setup fools with it, usually when replacing a belt or accessory.

Somebody correct me if I'm wrong - the tension is set by the tensioner itself, by where the arrow is pointing on the thing..... There are several different spots to line the arrow up to depending on what accessories you have on the car. The bolt that bent merely releases/engages it for doing work....... Which is why it gets bent up if somebody tries to use it for increasing belt tension...... Which is often necessary if you use an American V-belt which will be slightly longer because it isn't metric......

I think all that is right.... It's been a while since I've fooled with mine, and yes my mechanic bent up my bolt too......

mak · #3 03-03-2010, 10:45 PM

You may like to check the tensioner which is most likely was original fault(internally broken ) which someone tried to compensate by over tightening and bending the rod .

I replaced the tensioner , adjusting rod and a new belt together , in the long run it's the best for reliability. Sometimes even re loosening the tensioner for a belt change causes it to fail .
Surprisingly no alternate solution to this weak point.!

mak
300se

tinypanzer · #4 03-03-2010, 11:10 PM

That's right, it IS an adjusting rod, but its role is rather limited and cannot compensate for a worn-out tensioner.

Mike Murrell · #5 03-03-2010, 11:38 PM

Quote:

Originally Posted by tinypanzer

The bolt that bent merely releases/engages it for doing work.......

I do not believe the bolt releases/engages. It's static in nature.

Yes Mak - likely a hosed tensioner that "backed up".

Car is pushing 20 yrs. of age - tensioner original.

Will be working on this once it warms up a bit.

Have another ride.

Ivanerrol · #6 03-04-2010, 04:02 AM

Read through this thread.

Diagnosing Belt Tensioner M103

Mike Murrell · #7 03-04-2010, 05:26 AM

Thanks for the link.

Missing 19mm bolt! Wow! I'm not there yet.

Much of what's covered in the link is in many others here.

I've had the car since '97 and have replaced the belt a few times + had it off for all sorts of other maint.

Equipped with all the proper factory tools for belt removal/reinstallation - understand the process.

As was mentioned in the link - this system is plagued with issues and sooner or later the tensioner is going to fail.

The one on my car is original - near 20 yrs. old.

I got my $$$ worth out of it.

Thanks for all of the input.

Mike Murrell · #8 12-22-2010, 12:43 PM

Car has been idle for sometime - just now getting around to dealing with this problem.

Got everything off - tensioner is shot - am able to spin it 360 degress from the backside with an adjustable wrench in either direction.

In the following thread - Gilly provides the reason why the adjusting rod was bent. Failure to loosen the 19mm bolt has nothing to do with this. If that bolt is not first loosened - the adjusting rod is going nowhere.

W124 Belt Tensioner ROD

Also look here for a post initiated by KermitF and replied to by Duke2.6

Drive belt tensioner

Duke provides the best insight I've found on getting the 103 belt tensioner replaced.

At benzworld.org - you may also find pdf's for task 13-345 - removing installing tensioning device and 13-342 - replace belt. 13-3450 - similar to 13-345 - but with more complete photos of entire system - all three come in handy.

Drive belt replacement - 13-342 & Tensioner replacement - 13-345

http://web.archive.org/web/20060526115843/mb.braingears.com/201_DISK1/PDF/50008.pdf

124 belt tensioner replacement - 13-3450 - look for post by JackD

http://www.benzworld.org/forums/w124-e-ce-d-td-class/1300944-help-how-replace-belt-tensioner.html

sptt · #9 12-23-2010, 10:48 PM

Just replaced my daughter's tensioner today. The mechanic that replaced her belt before damaged the tensioner and bent the adjusting rod because he did not know how to reinstall it properly. You must first loosen the large bolt that goes through the center of the tensioner first (this locks the tensioner in place once adjusted). Then you can loosen or tighten the tensioner pulley using the brass colored adjustment rod that sticks up vertically (actually a little to the right when facing the car). Her adjustment rod was bent and stripped from someone trying to adjust belt tension without loosening the large center bolt first and the tensioner was blown out and had no spring resistance when I removed it.
Put new one in and it works like a champ now. Had to remove fan pulley (to remove tensioner bracket), power steering pully (to access other bolts on bracket), and water pump pulley (to install new tensioner). Also had to disconnect shock from tensioner at tensioner bottom which is shown in one of the the pictures above.

Mike Murrell · #10 12-26-2010, 09:24 PM

Quote:

Originally Posted by sptt

Her adjustment rod was bent and stripped from someone trying to adjust belt tension without loosening the large center bolt first and the tensioner was blown out and had no spring resistance when I removed it.

The adjusting rod was bent for the reason outlined above in the post made by Gilly - former MB dealer tech.