Serpentine Belt Tensioner Problems - OM603 - PeachParts Mercedes-Benz Forum

a2t · #1 01-28-2007, 10:02 PM

My 87 300D turbo has a squeeling serp belt. Not super loud, but seems to be getting louder. The sound seems to be eminating from the tensioner wheel.

Ive replaced the serp belt, the tensioner spring, and the tensioner wheel.

I notice that the serp belt rides about 1/8" off the FWD edge of the tensioner wheel, as if the tensioner wheel itself is sitting 1/8" too far aft. Now how could that be?? If the lever arm bolt were loose, Id expect the belt to be riding aft of center of the tensioner pulley, not fwd.

Confused...maybe I should replace the lever arm.

And how are you guys (hitman) removing the fan in 5 minutes? Wouldnt the fan shroud need to come off? I thought there was a bolt sitting on the end of the fan shaft, very close to rad. Last time I did a water pump on OM603 I had to remove fan shrould and rad. Im hoping this stupid belt problem wont require the same, but getting the new tensioner wheel on there was a pain with fan in place.

Brian Carlton · #2 01-28-2007, 10:07 PM

Quote:

Originally Posted by a2t

I notice that the serp belt rides about 1/8" off the FWD edge of the tensioner wheel, as if the tensioner wheel itself is sitting 1/8" too far aft. Now how could that be?? If the lever arm bolt were loose, Id expect the belt to be riding aft of center of the tensioner pulley, not fwd.

If it's any consolation, the '86 does the same thing. I'll be following you to see what the culprit is. I'm sure it's related to the tensioner bearing in some way. If the bearing is worn, it allows the entire assembly to tilt slightly downward and the belt will ride forward of the preferred track.

Sixto's got the most experience with these things.

sixto · #3 01-28-2007, 11:52 PM

Is the tensioner pulley sitting on an axis parallel to the crank?

Either the tensioner arm is loose or the tensioner pulley is loose. Should be easy to send a 6mm hex bit into the tensioner pulley to check that. I can send a long 12mm hex bit into the tensioner arm without removing the fan.

There's a thick washer/spacer between the tensioner arm and the front cover. I don't know if the tensioner arm will pivot if that washer/spacer is missing. Do you know for sure that yours is in place?

There is a special tool that holds the belt to the water pump pulley so you can remove the fan. Alternatively there is a hole in the water pump pulley bolt pattern. If you're lucky, your water pump will have a big rib against which you can fit a 3mm hex key to lock the pulley while loosening/tightening the fan.

Release the shroud from the radiator and drape it over the fan for better access to the fan/clutch attachment bolt. Then remove fan and shroud together.

Sixto
93 300SD 3.0

a2t · #4 02-01-2007, 09:37 PM

Thanks for your replies. Here are 2 pics, the 1st shows how the pulley sits with the belt hanging off front half. I cant see in there enough to know if the spacer is present between the tensioner arm and cover. The tensioner arm seems to wobble a little fwd/aft if you press on it with screwdriver (with belt tension released).

I examined the tensioner pulley can see that it is actually making contract with the crank puley. The old one was ground off about 1/8" on aft edge of tensioner pulley. The pulley is sitting too close to engine, for some reason.

So I added 2 washers (.125" thickness total) to move tensioner pulley fwd. Now it clears the crank pulley and doesnt rub, but this makes me nervous. Why is tensioner pulley sitting so far aft? Hmm...

sixto · #5 02-01-2007, 11:06 PM

The EPC shows engine serial number specific part numbers for tensioner arm and tensioner arm washer for .960 and .971 engines. I don't know if that means the tensioner pulley has a different offset or just the redesign from a replaceable to fixed bearing (or was it the other way around?).

The other thing to consider is if you have the right tensioner pulley. The 601/2/3 engines call for pulley 601 200 09 70. The 300E calls for pulley 601 200 07 09. Does anyone have a 300E pulley handy to measure for diameter and offset?

Sixto
93 300SD 3.0

TMAllison · #6 02-01-2007, 11:14 PM

This is the same tensioner system used on the OM606.

Check the motor mounts before tearing into tensioner componets. It's cold out and the rubber can't damp vibrations like it can when it's warmer. Lift the engine 1/4" and look for cracks/separation in the rubber on top.

The above doesnt explain the misalignment yours is exhibiting, but is worth checking as its simple to do. Its also possible the interior sleeve (wear surface) of the tensioner pivot arm is worn allowing the pivot arm to lean to one side causing the misalignment shown in your photo.

My 606 had a bad vibration at the tensioner for 6 months during whihc time I broke 2 springs, burned up 3 shocks, stretched out 2 belts and ate up one pivot arm before I figured out I had a semi collapased motor mount on the left side that manifested as vibration at the tensioner. Mounts can be sneaky lil devils sometimes.

Hit Man X · #7 02-02-2007, 03:39 AM

Quote:

Originally Posted by a2t

And how are you guys (hitman) removing the fan in 5 minutes? Wouldnt the fan shroud need to come off? I thought there was a bolt sitting on the end of the fan shaft, very close to rad. Last time I did a water pump on OM603 I had to remove fan shrould and rad. Im hoping this stupid belt problem wont require the same, but getting the new tensioner wheel on there was a pain with fan in place.

Yeah I just loosen the shroud, use an 8mm Allen. Takes almost no time, I've done it enough times now.

Aside from that, no clue on your problem. I replaced all my tensioner stuff a while back as it has greater than 200K. Just PM for the cheap. Replaced that tensioner arm, idler as bearing went, belt, spring, and shock.

Hatterasguy · #8 02-02-2007, 10:50 AM

The bearing in the arm is probably worn. Mine is doing the same thing but not quite as bad yet, and I have replaced everything but the bearing in the arm. So thats whats left!

a2t · #9 02-03-2007, 08:35 AM

should you be able to move the tensioner arm fwd aft (with tension removed from belt) ?

Mine kinda wobbles fwd/aft if you push on it with a screwdriver.

Ive also broken a spring a few months back.

Anyway, the washers have pushed it back out so it lines up.

As for the motor mounts....if this whole contraption is connected to the motor, the motor moving should not change relative alignment should it?

How do you remove that tensioner arm? Is it an internal hex bolt like the pulley was? Anyone know the size?

Thanks for all help.

TMAllison · #10 02-03-2007, 12:19 PM

My issue with tensioner vibration drove me crazy and was def a result of a bad mount. Checking them is easy to do to rule this out in your case. Take a big rubber bushing and a 2 x 4 and lift the engine 1/4" and see what happens. I understand it does not seem plausible....thats why it took me 6 months to figure mine out.

My pivot arm does not have any play forward or back.

Mine takes a 17mm hex. Sixto said yours (his?) was 12mm.

If your roller pulley rubbed something wearing one side down its very possible the roller is now beveled to one side and the belt is being pulled off of it.

sixto · #11 02-03-2007, 02:55 PM

Quote:

Originally Posted by a2t

should you be able to move the tensioner arm fwd aft (with tension removed from belt) ?

Should pivot smoothly about the big bolt through the middle. No ckicking or flat spots as it pivots. Shouldn't move in any other direction or axis. If it takes a 12mm hex, torque is 73 lbft.

Sixto
93 300SD 3.0

a2t · #12 02-11-2007, 08:05 PM

Thanks Sixto (and everyone else).

I donno, I guess I will repl the pivot arm and see what happens (hate playing the "replace this and see if its fixed" game).

I rotated all the components (AC, alt, ps pulleys) with belt off and the alt pulley seems to make a little noise while rotating. But it seems like the squeeling is coming from center of engine front, at tensioner wheel.

I bet tensioner is sitting a little crooked and belt is sorta dragging across it sideways, causing squeeling...hopefully all will be fixed with a new pivot arm...

a2t · #13 03-18-2007, 10:37 PM

Hey I was right (for once). I replaced that pivot arm and no more squeel. As Depeche Mode once said...enjoy the silence (ding)

You should see that pivot arm. Massive. Brought it into work (we design aircraft parts) and everyone thought it was jet engine part. Hefty bit. So the old one had about 1/16" play on the main shaft front to back. I guess that was enough to slightly cock the pulley in there so it wasnt aligned with belt. Even with the new pivot arm and new pulley, the pulley is sitting MAYBE 1/16" off crank pulley. Man thats close. I still think the washers uner the tensioner pulley might not be bad idea, but all is well.

$72 at my local benz dealer ($108 retail). Those guys are awesome, if I ever scrape together the cash Im buyin new one from them. Saved me a ton by offering wholesale price, cheaper than online for geniune MB. Do all MB dealers do that? I remember the VW dealers were a-holes about that sort of thing...