When idling in the garage the other day I noticed a new sound being produced from the engine compartment of my '85 928 S 5 sp. It was very noticeable at idle and seemed to diminish with revs (or the sound was just drowned out).

The sound it's self is hard to describe but sounded like a belt rubbing on plastic or metal. I initially though I must have a loose accessory belt. I inspected the belts and they looked good, but I proceeded to remove ALL accessory belt and fire the car up on battery power alone (no alternator).

The noise persisted. Using a vacuum hose to locate the sound it seemed amplified at the Drivers side timing belt inspection hole in the t-belt cover.

Next I pulled the drivers and passengers side T-Belt covers and every thing looked fine. Checked T-belt tension with the after market tool and it registered in the window just toward the tight side. cam marks lined up with the cover notch at TDC.

BTW I replaced the T-belt one month ago...so on the plus side every thing was clean and relatively easy to remove.

Proceeded to take the middle lower cover off (inspected and no visible signs of rubbing or wear) and re-install the Drivers side and Passenger side covers so I could install the distributors and fire the car up on battery again. Listening around the front of the exposed parts in the front of the car with a length of vacuum hose the noise seemed to be generated from behind the vibration dampener. CRAP

Reluctantly I installed the flywheel lock (I have to actually disconnect the slave cylinder from it's feed line...which is why I really hate installing the flywheel lock...) and removed the vibration damper.

I'm thinking the T-belt is rubbing on the thrust washer ( pt # 928 102 125 02) that is installed behind the damper. The washer it's self seemed quite worn ( note sure if this is normal / Should have been replaced with T-belt change or irrelevant), and when the T-belt leaves the main drive gear, it seems to be a couple of millimeters forward ( toward the front of the car) off the gear. The belt then proceeds over the tensioner roller where it also seem to be too far forward on the roller.

Any thoughts before I replace the washer and button this thing back up...I'd really hate to miss some thing and have to so this again!! On the plus side I'm getting reallt good at checking tension and pulling the front of the engine off.

Picture of the Washer:


http://www.momentoffame.com/snapshot...ame/l45364.jpg


Micture of the main drive gear (behind the damper) with the belt slightly forward in the gear


http://www.momentoffame.com/snapshot...ame/l45365.jpg

 

Are you sure you installed the washer right side round? IF, (and I stress IF), I remember correctly the washer is supposed to have the convex side towards the damper.

 

ErnestSw

I believe that the convex side is oriented toward the gear and the concave side toward the balancer. This is how the thrust washer was installed.

I didn't give it much thought at the time of re-assembly but due to the unmistakable wear pattern of the gear notches, the convex side (which was originally toward the gear) was replaced in the same orientation.

 

I woukd trust your logic more than my memory. Do you trust your torque wrench?

 

Something is kicking your belt foward. The noise is probably caused by the belt rubbing the washer, but whats causeing the belt to rub the washer? There in lies your problem.

Did you replace the plastic bushings on the tensioner arm? If so, did you get the right ones?

How are the idles, expecaly the tensioner idler? If they turn realy easily, their worn. That will allow the idlers to wabble, and when that happens, the belt can move foward or backward, and you get your problem.

OK, there could also be other problems. Are any of your pullys worn? If one is worn in a mannor that could kick the belt off, it needs to be replaced.

Good luck.

 

Rich,

If it were me and I didn't have a definite idea where to look I think I would check that plastic guide that sits under the crank gear. Maybe one of the clips came loose?

 

Rich:
You only have until the second week in September to get this sorted!

Did you put the belt on the right way? So that the letters are readable from the front of the car.........

When are you home? I'll call and we can discuss what the differences were in what we did.

 

Thanks for the suggestions!

ErnestSW - torque wrench..I used a snap on T-Wrench and torqued to 220 ft-lb on the crank bolt (first attempt with an inferior wrench @ 150 ft-lb resulted in crank bolt backing out while accelerating to highway speed!! Loss of alternator due to no accessory pulley caused me to shut down ASAP...and get a bigger wrench)

ViribusUnits:

I replaced the idler on the water pump with new due to minor damage I inflicted trying to remove it. The tensioner Idler and the small idler next to the crank gear turn with mild resistance and no noise so I assume they are good ( just pulled and checked the tensioner one tonight to make sure).

The other gears have very slight wear and appear to be in good shape.

I did replace the plastic bushings in the idler pivot...They fit snug and I placed a small amount of grease on the bolt prior to installation.


Mitch: checked the back plastic cover which guides around the crank and it is tight. No loose movement and I stuck my head between the rad and the T-belt for a close inspection...no apparent rubbing, all clearances look good!

ViribusUnits I like your thinking.. Why is the belt moving forward on the crank gear?? All other gears seem to be fine with clearance between the end of the gear and the start of the belt.

FYI: After I took the tensioner off to inspect the idler and re-installed it I spun the engine by wrench to get a base T-belt tension setting. After 4 more revolutions and adjusting I was back into spec. I pulled the vibration damper off and the thrust washer and the belt was sitting slight BEHIND the end of the gear where I would expect it and where it probably wouldn't rub.

I'm going to order an new thrust washer tomorrow, but am tempted to remove the flywheel lock tool and spin the engine with the starter as it sits to see if the belt move to the outer position with higher rev than I can produce by hand.

Just a thought

 

Rich..... you do have 2 of those "thrust washers" don't you? One on each side of the belt-drive sprocket.

From my pics, I can't see any influence on belt position other than the tensioner pulley. Did you check the tightness (torque) of the bolt that locates the large pulley on the tensioner as well as the torque and fit of that idler-pulley's shoulder bolt on the new bushings? Apparently there are 2 different bushings and I don't recall what the transition event was........maybe it was the 32v engine.

 

Rich, do you have a good clutch and parking brake?

On my car, that was sufficent to hit the 220 ft/lb for the crank shaft. I put her in 5 gear, and set the brake. It held more than enough. It saved me from screwing around with the flywheel lock, and the 35 bucks, plus risking stripping the screw.

Are the washers on the outside water pump pulley eating at the edges of the belt? If not, something VERY weird is happening.

You pullys are worn if the dark annoizeing coat has been worn, and replaced with a shiney aluminum surface.

Is the tensioner arm bent at all?

Did you include that washer on the tensioner arm bolt? To keep the arm further from the water pump?

Does your belt hang "straight" or is it kinds sideways? (I've never heard of something like that, but it could happen. Doughtful, but it could happen.)

Does your crank have excessive play in it? Camshaftes? Water pump? Oil pump pully?

Good luck.

 

Brian: I do have both thrust washers (one on each side of the crank gear). Since I never pulled the crank gear the rear one has not been disturbed and shows no belt rubbing wear as the front one does. I also never removed the tensioner pulley from the arm so I'll double check it's torque tonight along with the pivot bolt torque.

ViribusUnits:

Now I find out I can use the park break and 5th gear. I have the lock tool, but my issue is disconnecting the slave feed line every time I use the lock tool. This of course allows a bunch of air into the slave and my clutch pedal slams to the floor when pressed until I bleed it properly ( which is no small feat in it's self)

The belt fits well with in the water pump pulley guides and does not appear to rub.

All of my gears exhibit the shiny aluminum look to some degree and only where the belt does not ride are the surfaces colored beige. Other than that they seem in very good condition.

The pivot bolt was (is) installed against the tensioner arm lightly greased with the washer between it and the idler pulley.

I believe the plastic bushings were updated in '85. Brian I believe this is what Andrew sent us in-the group order, but I'll double check the list when I get home tonight. The pivot bolt fits well inside the busings with good movement and no lateral play.

Tensioner Arm is fairly robust and does not appear to be stressed so the assumption is it's OK ( not really sure how to confirm though)

More to come!

 

The only thing that makes sense to me is the alignment of the tensioner. My analysis indicates that there are only 2 likely candidates at the tensioner......... the tensioner arm itself (meaning the bushings/mounting bolt), and the main pulley itself (meaning the bearing). I believe that the bushings were right for both of us, upon checking with Andrew.

I think that the only issue that is different between our individual projects was that I replaced that tensioner pulley (when I screwed mine up trying to replace the bearing) and you didn't. Does the pulley run true with the new bearing? Is it possible that the new bearing that you installed is not located "on center" in the pulley and that such a shift in the centerline induces some forward-walk force to the belt?

 

HI Rich,

Could it be a bearing? Can you run the engine in neutral? Then use a mechanic's stethoscope to isolate the source.

 

Thom: I performed your suggestion in order to isolate the noise to the front of the car, and my wearing thrust washer seemed to indicate the problem. It could be an engine bearing (shudder), but I have no way of quantifying that it this point.

Brian: Actually I replaced the entire idler at the tensioner mounting point to the water pump. Not that it does much on a regular basis, but it was damaged from removal.

When I took off the main idler last night it seemed to have wear on the main body but not on the "back" of the body closest to the car. This may be enough to move the belt to the forward position and it looks like the idler is not reversible ( flip it the other way around to move the belt to the back of the car). Thus I have a new thrust washer and tensioner pulley en route..should be in on Wednesday. Hopefully this does the trick.

When replacing the tensioner idler on the arm I will be sure to torque to spec (once I look it up) and the pivot bolt (once I get the new idler on).

Hopefully this does the trick.

Thanks again!

 

Rich..... be careful with the torque setting on the tensioner-arm mounting bolt!! That's the one I broke off in the block by setting the torque wrench to the setting for the shoulder shaft diameter rather than the thread diameter.......... duh!!


Can you have Andrew ship a few (6) of those smaller idiot-light bulbs with your stuff??