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Thread: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

  1. #1
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    Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Car = 1992 500e

    I was running a bunch of errands yesterday (stop, start, stop, start), and at the end of the day, as I fired the car up, I noticed that I had a belt squeal. Pretty classic squeal (starts out high pitched, settled down, then squeals at the same "RPM" as the motor, then, after a couple seconds, it goes away).
    Huh... I got home, and of course it wouldn't do it, so I parked it and figured I'd take a look this morning when it was cold.

    Sure enough, I fire it up, and it squeals right off the bat. I have the hood popped, and it looks/sounds like the far left (left standing in front of the car, so that is actually passenger side... so maybe MB people call this "left") side of the Serpentine belt routing. Feels like Power steering, but I have no leaks... So I shut the car off, and start feeling around the belt, and it is SUPER loose. Like loose enough that I could probably take it off by hand if I wanted to. Hmmm...

    At first I thought it might be one of those "the belt only tensions under power" things, but it doesn't look like it. I came inside and read up a little, and it seems like the 1992 has a manual tensioner? Looking at the marks on the body of it, I have a couple of "hashmarks" to go, but do you have any advice about tightening it?

    Also, if I have a squealing belt, I realized it is a good idea to have a spare. What is the correct belt for the engine in that car? Is it the 1992?

    it looks like the correct tensioner is P/N 119 200 02 70?
    Looks like 230.00 through Parts.com?



    Is there a special trick to tensioning it? I went out and cranked it a little with a big long 19mm wrench, and it seemed to work a little, but I am thinking replacing it is the best plan.

    Any advice on this one?

    Which belt is the correct one?

  2. #2
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    Re: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Howdy Dan,

    What you describe sounds a lot like a failed tensioner. The early style tensioner is known to have a fairly short life span, at least compared to the later spring-style tensioner. The early tensioner is just a rubber bushing that twists to provide tension to the belt. Factory setting is to have the pointer at the "far" mark with no tension, then you tighten until the pointer is in the middle of the four "close" marks. I usually tension it a bit less (about at mark #2 of the 4) to reduce stress on the tensioner. Over-tensioning can drastically shorten the life of the tensioner assembly. Your part numbers are correct, btw:

    119-200-02-70 = manual tensioner for all 1992 models
    009-997-87-92 = serpentine belt, 8-groove, 2465mm long

    The 19mm hex bolt locks the tensioner in place. The actual adjustment is via the 13mm hex on the tensioner rod, that pokes up through the power steering pump bracket. You loosen the 19mm hex about 1/2 turn or so, then twiddle the 13mm hex and watch the pointer. Once it's tensioned properly, you tighten the 19mm hex to 100Nm. DO NOT try to adjust the tension (via 13mm hex) without loosening the 19mm center bolt!! And, don't forget to tighten the 19mm bolt after adjustment.


    FSM procedure to R&R the belt (may not be necessary) :
    http://www.w124-zone.com/downloads/M...19/13-3420.pdf

    FSM procedure to R&R the tensioner from the car - see pages 1 and 2:
    http://www.w124-zone.com/downloads/M...19/13-3450.pdf

    FSM procedure to 'test' the tensioner if removed from the car - basically clamp in a vise, and make sure it snaps back when you try to rotate it:
    http://www.w124-zone.com/downloads/M...19/13-3452.pdf


    Tip: When removing the tensioner, make a careful note of the orientation of the the washer on the back side, relative to the tensioning rod+ring. The manuals do not show which goes on first (i.e., if the spacer washer goes against the block, or against the tensioner). It must go back together in the correct order.

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    Re: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Stellar! I have an OEM tensioner and a new belt on order now. I <3 Parts.com.


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    Re: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Quote Originally Posted by Dbreid View Post
    I <3 Parts.com.
    Me too !

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    Re: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Quick update on this (I always hate it when people don't come back and post how things went on threads they start).

    I ordered the parts through Parts.com on Monday, July 22nd. They arrived today (Friday, August 2nd). Not exactly speedy, but oh well.

    The part numbers above were spot on, and the belt and tensioner were OEM, and VERY nice.

    Some notes:

    1.) The washer Dave speaks of above goes to the BELT side of the assembly, and the eccentric (flat inner sided washer) with the bolt connected to it for the adjuster goes to the BLOCK side (closer to the engine).
    2.) It was a little bit of a hassle to line everything up to reassemble, and it is possible to get the adjuster washer (the thing that connects to the 13mm adjuster rod) flipped around. Don't do that. It won't work well that way.

    This was one of those jobs that inexplicably took me an hour, but if I had to do another one right now, I'd be done in 6 minutes. Just seeing how everything went together, and double checking my belt routing took a little time.

    But everything is working well now, and I have spare (used) belt for the trunk. Lastly, I will say that in some ways, I kinda like the design of the 1992. I was expecting the "chevy V8 style" of tensioner where you crank on it to loosen. But the manual adjust is kind of a neat feature. It isn't executed perfectly, but overall, I see where they were going...

    -Dan

  6. #6
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    Re: Dealing with Squeaking belt and 1992 manual tensioner for serpentine belt

    Cool! Glad you were able to get it all back together successfully. Any sign of what the OEM is for the tensioner, btw? Speculation was Laso, but there may not have been any logo on it, so we may never know...


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