got an emergency. need help please. 124 belt tension
 

good people
i just replaced my water pump (day and half. never again i hope!) and now my belt is too loose. i had three different writeups from this site, on the procedure taped to the wall and followed them as much as possible.
ive reassembled everything and for some reason theres no belt tension. ive turned the adjusting nut all the way one way and all the way the other but no change. it was working fine before i removed it.

can someone definitively tell me about the long adjusting nut. is it supposed to be "mounted on" the backing plate so that adjusting it moves it relative to the backing plate, because mine just kinda seems to be sticking through the hole. which begets my question; how does it them adjust tension if it isnt pulling/ pushing on anything.

also, i dont see this arrow/ mark/ pointer that everyone seems to be mentioning. is it on the pulley, body of the tensioner, somewhere else???

id appreciate any advise. thank you.
im perusing the results for a search on "300e belt tensioner" as we speak, but i dont have time to go at this again. i absolutely have to be home by friday, im 400 miles from home in a borrowed garage and dead broke. thank you.

bump

First thing I would do is check your tensioner to make sure it works. Grab the tensioner pulley and move it to see if the rubber twists and returns to normal.
If it does, then the tensioner is OK.
As far as the pointer goes, it is on the top side of the tensioner assembly and when the tensioner is in the relaxed position, you are suppose to move the pointer to the left...at the starting point. Then proceed to tighten the tensioner adjusting bolt until the pointer moves to the maximum mark on the scale.

Make sure your lock down bolt is loose and then tighten it back down after adjusting the tensioner.

If all you did was replace the water pump, then everything should go back like it was.

Good luck,

Dave

In a bind, to get you home, you may be able to get some kind of lever in there to push the tensioner pulley to tighten the belt, then tighten the hold down bolt. Kinda like we used to do before there were belt tensioners.

This is what the part you are asking about looks like:

Your tensioner may be shot. Do a search here, somebody took a failed one apart and determined that the poor design is prone to having the rubber material lose shape and distort early.

Make sure your belt is routed correctly. If not, you will not be able to tighten the belt to proper tension.

I had to replace one for that exact reason. The rubber was torn and shredded and wouldn't hold tension.

One reason why I now no longer mess with the tensioner when doing any work under the hood. Not so much on the W124 but especially on the W210 I just "lift" the belt off the top pulley with my bare hands and leave the tensioner in place so as to disturb it as little as possible.

I put the relevant docs from the service manual up at

www.pauldrayton.com/uploadfiles/merc/13-1202hw.pdf
www.pauldrayton.com/uploadfiles/merc/13-3200hw.pdf

Hopefully they will be of some help.

the tensioner wouldnt budge. i had to break out the credit card and buy a new one and a tensioner rod nut thingamajig.

i really do appreciate your help. really, i cant say that enough.

im slappin it together right now and trying to figure out the marks that are supposed to align with the planets when the moon is blue and pluto is resplendent over mars. or some crazy talk like that.

When you install it, put the pointer at the left line with the tightening bolt still a bit loose. Adjust the tensioning nut until the pointer is between the two center lines.

One trick that got me a few more miles (while the rubber part was still good) was to remove the tensioner, adjusting nut plate, and spacer that is on the shaft. You will probably find that the aluminum shaft flats are worn from the adjusting nut plate flats. Flip the plate over, and swap its position with the space, so that it now rides on an unworn section of the shaft, and is pushing with the opposite flat sides of the adjusting nut plate. If it's wear there, that will get you a few more miles.

That said, my last one was a case of sheared rubber inside the tensioner. Pushing the idler 30 degrees with the shaft held in a vice showed that it would not come back to its original position.

Gerry