How do I figure out this M104 belt tensioner???!!!
 

I was going to post pics of my alternator and serpentine belt replacement, but my de-install is not going very smoothly.

Got the fan shroud and fan off okay, but I am either short on tools (MB seems to like those allen bolts) or I am looking at the wrong places.

I gave up last night and just pulled the old belt off of one of the pulleys by hand and then slid the rest off. So now the alternator swap will be a cinch, but I am fearful of how to get the new (tighter) belt back on.

The Haynes manual was of no help, as the idler pulley bolt it specifies didn't exist, etc. etc.

I can't imagine that it is much different from the M103.

You need to loosen the large allen bolt (6 or 8 mm key needed) that is located under the tensioner, then back off the tensioner adjustment. That will allow the idler to move and the belt to be removed.

When you put it on, you push the indicator to the end of the scale and tighten the adjuster until the indicator moves to the mark.

There are a lot of good posts on this - try a search.

Good luck.

DOH! Oh yeah...the search...us veterans should know better!:rolleyes:

I guess I'm going to get an allen socket set tonight. Otherwise, I figure there may be more show stoppers as a result of lack of proper tools (what ever happened to just plain ole bolts???)...

ctaylor738: thanx... just stared at that bolt and tried to figure out what to do about it. Saw the pointer as well, but didn't know how that worked either. I guess I will get to play with those when I get ready to put the new belt on...

Glad to help.

You need hex bit sockets and allen wrenches from 1 mm-8 mm at least. Get good ones. There are some cheap ones that are not very well hardened and they will quickly round off. Sears is OK, but MAC or Snap-On are better.

Is your belt tensioner secured with an allen head or a 19mm socket? On a 103, after you loosen the 19mm holding the belt tensioner snug, you loosen a tensioning rod on top of the tensioner with a 13mm socket. The 103 motors use a special 8mm Stahlwille and ft. long metal rod bent slightly at one end for fan removal. Somehow, you got through this.

If you'd like, I can email you the 103 belt replacement process off the MB CD-Rom. Like Chuck, I don't think this process differs much between the 103/104.

I can eyeball the top of the tensioner (spring, shock, whatever) BOLTED on, not an allen head bolt. Doesn't appear to be much larger than about 15mm.

The allen head bolt (as I feel around with my fingers) takes a hex size that is way larger than I have in my current tool collection. This bolt sits just left and behind the coolant pump pulley and seems to mounted on a bracket of some sort.

I am guessing the tensioning rod must be that long hollow thingy (accepted a 13mm socket) that sits between the coolant and the power steering pump (or was that the A/C compressor)? Didn't seem to do anything when I loosened it, and the pointer stays at the same position.

As far as the fan, I used a hex key wrench and a little grunt to get the three bolts off to remove the fan blade. The clutch is still intact.

God I hope this doesn't turn into the "try to replace the rear brake pads but end up dismantling the calipers instead" kind of repair!!!


And YES, I would like the instructions off the CD-ROM...it's gotta be more explicit than the Haynes manual (hey, I just got an idea of what I want for Xmas...).

I like the manual, but when they try to explain a process using three different engine configurations as examples, it gets kind of confusing...:confused:

If it is an allen, it is a 10mm. You loosen it and then the tensioning rod. After this, you will retension with car as not to break the tensioner.

G-Benz

I would stop the party for a moment and verify what you have. If you have a 19 mm hex head bolt securing the tensioner in place, as the M103s have, and mistakenly loosen an allen bolt holding the tensioner bracket in place, then attempt to tension/detension the tensioner with it still held tight, you are going to strip the threads on the tension adjuster. This is the 13 mm octagonal, long device sticking up at about 15 degrees toward the driver's side from vertical and directly in front of the coolant pump.

If you strip the threads on the tensioner adjusting device, you will now be into the r/r of the tensioner to remove this device and replace it. The bracket for the tensioner also has one bolt hole on the far left (passenger) side that is open to the engine and needs sealant to prevent a steady leak from beneath the bolt.

Someone with a scanner offered to send you ac section of the manual. If you don't have the manual, this appears to be very good advice for ensuring you know where you're going.


someguyfromMaryland who has been all over the tensioner and coolant pump on an M103 and doesn't want to see someone have to go there without a good reason

Thanks for the warning!

I am awaiting the CD-ROM info, but here's what I have done:

I have not loosened ANY tensioner bolts that I have found so far, but I DID play with that tension adjuster (recognized what I did based on your description). Loosening it didn't seem to do anything, so I then tightened it back up the way it was before. This was with the belt still in place.

Hope I didn't do any damage...

Anyway, I just hefted the old belt off with my bare hands. SO I left the tensioner alone and concentrated on the alternator.

It is held on with 2 15mm bolts (bolts! it's got bolts, praise God). Well, it turns out that I didn't have a 15mm socket (got 14, 16, 17, and 19, but no 15), so I had to use a 15mm crescent wrench. Mine is short, so no way to get the necessary torque to work those tight bolts off! Had to invent some levers with other tools to get the grunt I needed to work those bolts off...2 hours later, alternator is now off!

Oh yeah...halogen shop light decided to blow out early in the process...so I worked with a little flashlight.

Then realized I don't even have a socket big enough to get that alternator pulley bolt off to swap the pulley! Looks like a 22mm?

I am in serious need of tools! What I have could get me through a VW engine overhaul, but MBs are a different breed!

For now, I'm just going to take the alternators to the local indie and have them swap out the pulley...might even do it for free!

Maybe I will post pics anyway...good for a few laughs!!! :p