The serpentine belt on my 1992 W124, (139,000), is squeeling like a stuck pig when the car starts and I'm tired of people staring at me! I did a topic search on this, but the past posts mainly discuss the eventual need, and cost, to replace faulty tensioners, which may be what I need, but none seem to explain the procedure for tightening the tensioner if it's not stripped. Upon examination, the belt is loose. I found a bolt at the end of a rod beside what I think is the power steering resevior, but when I turned it, both clockwise and then counter-clockwise, there was no change on the tension of the belt. I turned it carefully and not far each way because I feared stripping the threads, but I may have done so anyway because on other cars I've owned, there was always some other bolt that had to be loosened first, but I can't tell if this car has the same set up.
Also, I'm thinking I should replace the belt, (bought the car three years ago and have never touched the belt). but it seems that in order to get to any of the lower pulleys I'll need to remove the fan shroud and maybe even the fan in order to get my hands down there and to see what I'm doing. Is there a preferred method/procedure for replacing the belt? And is it easier to access all this stuff from under the car or down from the top? Thanks.

1962 MB 220SEb "Fintail" Sedan
1963 Vespa VNB4T Motor Scooter
1992 MB 300TE 4Matic Wagon
1995 Subaru Wagon AWD

Check out this thread.

The procedure to release/tighten the tension is explained by a fellow 124 owner.

Good luck.

Covered over and over in the archives. I'll summarize but please do yourself the favor of researching the matter.

The long nut on the threaded shaft that you turned is the adjuster for the belt tensioner. You're right in assuming that it does nothing except ruin threads if you force it against a torqued tensioner.

Look down into the engine just to the right of the power steering reservoir. You should see something like in the picture -- a pointer along some sort of scale. In a good tensioner, proper tension is achieved when the pointer is at the gap or the heavy vertical line (not sure which anymore). If your indicator shows proper tension but the belt is loose, the tensioner is shot. If the indicator is further down the ramp, there's room for adjustment.

Some models have a ramp as in the picture, some models have a graduated tick marks, and there are probably other adjustment indicator schemes. Don't be surprised if you don't see a ramp, but the intent is the same.

I've never worked on a 124 but I assume it's tighter than a 126. You can probably get away with replacing the belt without removing the fan and shroud (they have to come off together in some cases) but the difficulty is in getting a proper 19mm wrench or socket on the tensioner bolt with the shroud in place.

Going back to the picture, you can see the head of the 19mm head tensioner bolt. It's the gold colored piece between the bracket and the grooved pulley (belt is off for clarity).

To adjust the tensioner, whether to loosen it to remove the belt or tighten it, loosen the 19mm head tensioner bolt a half turn to a turn. Don't pull it out or you'll have to reset the tensioner adjuster and that's just too much fun for one day. Once the 19mm head bolt is loose you can move the tensioner by hand. Clockwise on the long adjusment nut tightens the tensioner, counterclockwise loosens the tensioner, just as you'd expect.

Tightening torque for the 19mm head bolt is 75Nm.

I won't go into removing the fan and shroud here because there are variations in M103 applications with regards to chassis, year, RWD/AWD, etc. and I just don't know them all.

I won't go into replacing the tensioner either because I don't know how the hydraulic pump of a wagon complicates matters.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Oops. I forgot the attachment.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Attached Thumbnails

 

Tensioner fails when the the rubber bush inside, which acts as a torsion spring, breaks up. When this happens adjustment is futile as the adjuster twists the inner part of the bush so the torsion acts on the tensioner arm into which the bush is fitted. The danger is that attempts to turn the adjuster cause the rod to break either because the bush inner cannot turn because the big 17mm bolt running through it has not been released or because the crank has already rotated to the top.

Anyway it's fairly easy to take it all apart and see whats happened, you may have to remove the radiator to gain access. I did see a post about fitting a turnbuckle in place of the damper but if the bush is too badly broken up the pulley alignment will be wrong and cause excessive belt/pulley wear.

__________________
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)

Hydraulic pump on the estate models is on the back of the steering pump so makes no difference. I managed to unbolt the pump assembly and move it out of the way without disconnecting any of the hoses.

That was with a 4 cylinder engine with loads of room at the front which is why I thought you may have to remove the rad on a 6.

__________________
Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)