w124 Serpentine adjustment?
 

Really dumb question, I know.

But of all the things I've done I've never replaced or adjusted the serpentine belt on my '89 e-series.

I slipped off the belt when I was replacing my distributor and I forgot to put it back on when I started the car. Now my belt is off one of the pulleys, a little twisted, and too tight to slip back on. I just need to losen the tension to get it back on properly (luckily, the belt still appears to be in good shape).

So, am I just turning the belt tensioner adustment nut which is vertical and just to the drivers side of the head? I haven't been able to find a pic or schematic, and I just want to check with the brain trust here before I do anything stupid.

Advice appreciated. Thanks in advance.

The adjuster is just that, the tensioner is locked down with a bolt through its pivot. Adjusting without loosening it first will just ruin parts. If you've never done anything to it, the likely hood it can be loosened and retightened is less than nil. Plan to buy a tensioner.

Steven, as I recall there is a 10mm allen head bolt that locks the tensioner. Unless you loosen it a few turns before turning the tensioner adjuster you will destroy the tensioner. You can attempt to loosen the tensioner so as to reinstall the drive belt, but don't be surprised if you cannot tension the drive belt afterwards. As duxthe1 mentions, typically the tensioner needs to be replaced ... which is a tedious process.

Where would I find the allen bolt? Is it at the base of the adjuster near the tensioner? (attached schematic I found)

I'm going to give this a try, as I really don't want to have to go thru the process of replacing the tensioner unit. Some good videos on Youtube showing the process, but looks like one really needs small hands to maneuver through all of the parts.

Mine does not contain an allen bolt. Plain hex bolt - see part #56 in diagram. You loosen that first; then loosen/tighten #41. Once belt is snug tighten #56

Already mentioned, but I'll reinforce. Be prepared to replace the tensioner. They do not last long and the more you loosen/tighten, the sooner they lose all ability to hold belt tension.

A terrible design.

Steven, I am unable to see your diagram. The lock bolt is in the center of the tensioner body at the base of the adjuster threaded rod. You will need a flashlight and a mirror to see the lock bolt as it is congested in that area. Gunk on the front of your engine will make it even more difficult to see the bolt head.

I think I now understand. I've have a look in the morning. Hopefully I can get through this by just loosening, and then tightening the tensioner adjuster.

Thanks everyone for your help.

Only buy the OEM tensioner. Aftermarket are garbage.

It sounds like you pried the belt off during the initial repair, this can damage internal cords resulting in a later failure.

If the belt remains twisted without any tension, I would not use it as it has broken cords ( like a broken belt in a tire )

Yup, looks like my Serpentine belt is somewhat frayed. I'm going to buy a new one.

Should I be able to just slip it on over the pulleys once the tensioner is loose, or do I need to remove anything other than the fan shroud?

You will need to first remove radiator shroud to get in there .The adjuster is made to adjust if the bolt is loose .Dont adjust it if the adjuster blot is locked up .

A lot of you guys dont know , that the forum has lots of information on how to do a lot of the jobs on our cars . You just look up above, and on the top header . Look in > HOW TO < articles . Thanks to Pelican Parts and admin

manal 124
 

Hi this manual will help you to replace the serpentine belt .Go to -
Google Search . Put in search box just this - Mercedes 124 Maintenance Manual Index
Then look through it .Let me know if it help you .. Trev

Talking about the fan shroud, if yours has not been updated to the 2 piece one, then it is a good item to look for at the wreckers. It makes life much easier.

Found it. Thx
http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/13-3420.pdf