'95 S600 V12 Belt Tensioner Issue - Assistance requested...
 

Hello all,

This is my first post, as I recently acquired a 1995 S600 (W140) for better or worse :)

For brevity sake, I will get to the issue at hand, as follows -

1) Serpentine belt begins squeaking
2) Squeaking turns into horrendous grinding sound
3) Lift the hood and as pictured, it appears my Belt Tensioner is failing and has now "moved" or "fallen" forward and is now dangerously in the way of my fan blade (You can see chipping on the fan blade tip in the picture, as the blade has brushed up against the now canted tensioner pulley).
4) Not sure exactly how the pulley came to fall forward and in such a precarious position (center bearing failure?)however I am hoping someone may have experience with this issue and/or repair on the V12 model?
5) I have found many videos, etc. online for a belt tensioner repair for just about everything but the V12 - In particular, I am trying to find the best way to access the belt tensioner, so I can remove and replace it - It looks substantially easier to access in the 6 & 8 cylinder engine bays. For example, do I need to remove the fan and/or perhaps [dreadfully] the coolant hose currently in the way. Is it accessible from the bottom with the car raised?
6) My local dealer is estimating 3.7 hours of labor for this repair, leading me to believe this model may require a bit more work as compared to the shorter repair videos I've seen on other models, at least from an access perspective.

Any help would be greatly appreciated and thank you in advance for the assist.

Peace,
-dLo.

dLo, I have no experience with any MB engines other the Inline 6 and V6, but you will need to remove the fan and fan cowling to access the belt tensioner … not sure about the coolant hose … avoid touching that, if possible. Once you remove the tensioner and belt turn all the accessory pulleys to ensure that something (alternator, A/C compressor, power steering pump, etc.) has not frozen. Wear gloves so you don't cut your hands.

Thank you @FerdMan -

Yes, I have seen a combination of either just the cowling being removed on some models and both the cowling and fan being removed on others. I just have not found any videos, pics or otherwise as of yet reflecting the V12 and/or what it took to gain access. I am beginning to wonder if I have to go as far as removing the radiator as well, in order to gain access to the belt tensioner - Looks fairly tight even with the fan removed (not done as of yet). Might be why my local dealer is quoting 3.7 hours labor for the replacement. Grrrr….

Appreciate the response none-the-less,

Peace,
-dLo.

If the tensioner arm spring is in good condition, you can change just the pulley as that is lots less work.

This thread has some out of car engine pictures.

https://www.peachparts.com/shopforum/tech-help/361625-easy-questions-m120.html

Thank you @ 97 SL320 -

Appreciate the link and pic attached. Yes it would be nice, if it turns out to be just the pulley vs. the whole assembly. Unfortunately, I cannot currently see it clearly and suspect I am going to have to remove the assembly anyway before I can determine the extent of the failure. That or alternatively leaving the fan on and removing the radiator for "theoretical, unadultered" viewing and repair [+ lots of profanity]. Good times...

Thanks again,
-dLo.

As an initial step, I'd pull the fan shroud to see if there is enough access for a pulley change.

This era of car uses a locking tab you pull to allow a shroud ring to be rotated a bit and disengaged. ( the shroud is marked lock / unlock ) Lay the ring against the engine and disengage the two clips that hold the main shroud to the rad. The will allow you to lift the main shroud out of the car. ( Assuming there is not a hose in the way. ) Be sure to remove the locking ring too.

Thanks @97 SL320 -

I spent some additional/limited time on her today -

1) I "spun" the smaller 1/2 of the fan cowling (the 1/2 closest to the windshield) into the open position, then hung it on the fan.

2) I then removed the two top tabs from the second 1/2 of the fan cowling and while twisting it for removal (around that damn coolant hose), it broke in the process being ~25 year old plastic, but looks [hopefully] repairable and removed it accordingly.

3) I then looked to remove the remaining 1/2 cowling (from Step #1 above), only to find that someone was kind enough [sic] to have zip tied said cowling to a tab at the bottom of the radiator. I cannot currently/readily cut the tie as the fan is in the way, so this 1/2 of the fan cowling currently remains hanging on the fan.

4) I then tried to get a 15MM socket on the tension pulley bolt, I believe it fit, however when trying to remove the socket to get a ratchet on it, the socket then fell on to what I assume was the underbody panel.

With that said - It looks like I am going to jack the car up and try to remove that underbody panel tomorrow, so that I can both get my 15MM socket back and in the likely event anything else falls during the repair, I can more readily retrieve it.

At this point, I am -

a) Trying to avoid removing the radiator at all costs if feasible.
b) Hoping to get at & remove the pulley asap, so I can determine if I need to order just the tensioner pulley or the whole belt tensioner assembly
c) Looks like there is no way around replacing the serpentine belt and/or pully without removing the fan (other then possibly removing the radiator instead). I did find a vid or two showing the fan removal on a similar model (non-V12) - Looks like the fan is best removed with a breaker bar and a hex socket/bit on the end, followed by an allen wrench by hand. Though I did also note the use of various specialty tools (depending on the video) used to "lock" the pulley/pulleys in place so that they do not spin when trying to remove the fan bolt. Not sure I can readily access one of these tools.

I am certainly open to any additional suggestions, tips, etc. should anyone have experience with the fan removal and/or tensioner pulley repair, preferably on the V12.

Thanks in advance!

Peace,
-dLo.

This site has some good articles and information that may help. To include removing the fan. v12uberalles.org I would just remove the radiator to make your life easier and reduce the possibility of damaging anything else. The key is to remove as much crap out of the way as possible. I have also have a 1995 S600... great car just a little quirky.