MP4.2+6.0

I've been posting on recent W12 cooling hose leak diagnostics, tips and possible bad water pump. All resolved and parts replaced with dealer OE. But, the sound I thought was a water pump bearing was ultimately definitively the A/C pulley set up. Classic rumbling bearing noise. Sound clip attached below. And it got worse than that late on actually, including distinct and sickly clicks easily heard anywhere near car. As explained here, the A/C pulley set up is NOT unique to W12's at all, so this can apply to any D3.

Basically, D3's don't have a classic A/C clutch. The on-off control for the compressor is not via the pulley, but internal to the compressor which can vary from 0 to 100% displacement--basically on demand load. For any who want to do a deep dive, it is thoroughly explained in an Audi SSP titled Heating, Air Conditioning and Climate Control Systems, #981203 from 2002. The pulley itself has a sealed bearing for basic spinning and a sacrificial engagement set up. It is basically some interlocking graphite and plastic coated rubber blocks. If the compressor freezes up, the blocks tear out under the force and then let the serp pulley keep spinning so the belt doesn't burn up and leave you stranded.

The pulley is sold as a separate part. About $300 discounted from an on line dealer; somewhat more via an ECS or some others, and not easily found elsewhere or used except with a compressor. And by the way, if you have a port injected 4.2 or W12 you are basically "more in luck" as far as serviceability. If you own an FSI 4.2, an S8 or probably many newer Audi FSI's and this part ever goes, frankly you are pretty screwed if this comes up. The difference is on the port motors it is a conventional pulley set up, while on the others it takes off of a separately driven shaft. They still have the pulley in there of sorts, but now it's just the sacrificial element that has a purpose of protecting the shaft drive. Pretty Rube Goldberg "Art", and now the shaft drive needs to be gotten out of the way to get at it. Way harder than pulling a serp. belt. But to get to that shaft, you get into having to support one side of the motor, pulling a motor mount and various other ugly work. When I searched BTW, these apparently fail sometimes on a variety of VW's, so this isn't some W12 oddity. There are other posts around for non-D3 Audis too. I actually don't remember a post about it in the past for D3's, even though all our D3's in the various motors have them. Port 4.2 pulleys have a different part # than W12's and there are some internal variants Bentley documents. My W12 one had to come from Germany; I had it in hand six days after I ordered it.

In my case, apparently the internal purportedly sealed bearing outright failed. Noise came up from no where to full failure in less than 1000 miles, maybe less than 500. At first when I heard a noise I thought maybe it was the oft discussed air suspension compressor, until I realized it was engine speed dependent and way before I opened the hood. That's when I figured water pump bearing, and it sounds really similar to that from prior failed water pump experience on a variety of older cars.

See the pics. The first time in years where ball bearings literally fell on the concrete floor with zero lubrication as I pulled the part. The compressor is a Denso, as was my 2000 A6 4.2, and the bearing in the replacement one says it is NSK from Japan.

Pic 1.--the crap on the floor as I pulled it out. Wow! Previously it ejected all the rubber when I spun it up to about 4000 RPM. Before that compressor was working and interior was cooling, so I basically knew compressor hadn't frozen. Here the failure was kind of the reverse--the bearing burned up, and so that took out the sacrificial element from the opposite side of where you would normally expect.

Pic 2--Since the bearing totally failed, the inner race was left behind on the compressor. Oh joy... I tried turning it with 18" channel locks and it wouldn't budge. Left it overnight with WD 40 (ran out of LiquidWrench) and it barely turned. Still, a relief. Given it is all tight in there, again a challenge. I went after it with a super specialized set of tools finally--as in a crow bar and hammer. The pictures are for real. I was going to use a large screwdriver, but didn't like the sharp pressure point against either the block and pan area or the power steering pump housing--all of it alloy, expensive and a nightmare if something happened. I could feel a slight groove on the inside of the bearing race so was trying to lever that--visible on the edge of the inner race in pic. 4. The bar had a sharp tip on it and was nicely angled, and the lower part of the bar sat pretty flat to any potential prying/leverage surface. Surprisingly, on about whack three, the race moved halfway off in one single hit. Earlier, I had removed the bearing retaining circlip. Not easy BTW; like the pain in the rear CV joint circlips for anyone who has done those on older Audis. And a lot harder to get in since now pulley was complete and in the way; solved with an external snap ring tool I found on Amazon, tweaked the tips a bit, and got it started about the 15th try, and for keeps the next one where I got it home with a little screwdriver work.

Pic 3--looking up toward the race with it now halfway off. A/C compressor race area is the second thing down; the slightly larger one just below is the tensioner, and that pinkish purple you see in background is actually a towel on the handle of the breaker bar I left in there when I undid tensioner; the chrome of the 30mm socket left on the tensioner peeks out of the shadows if you look carefully. The towel idea was an accidental hood close wouldn't leave a big ugly dent in hood since car sat a day + after starting job waiting for yet another Amazon tool for the tricky, large and flexy snap ring. W12 tensioner "how to" explained in my parallel post focused more on the water pump.

Pic 4--the post mortem countertop of the parts. Catastrophic bearing failure and leading to sacrificial clutch failure; compressor itself seems pretty not involved, and confirmed as working immediately on post-work start up and first regular drive/trip with a nicely cooled cabin once again. Those are all the bearings I collected off the floor BTW. I suppose I might have missed a few rollers, but it must have ejected some too; pulley was super wobbly in the end. New one is smooth as silk as expected.

Attached is sound file. And this was in an open parking lot, hood closed. W12's purr, and not remotely like this!

MP4.2+6.0

I ran out of attachments in original post, so here are some shots of what a new pulley looks like, including the sacrificial part inside, and the bearing trade markings.

Mister Bally

Thanks for the writeup and photos.

Not looking forward to this. I figured that the clutchless compressor just used a solid pulley so I would never have to worry about anything in this area. Amazing how A/C problem only arise when it is hot outside.

Your summary: "If the compressor freezes up, the blocks tear out under the force and then let the serp pulley keep spinning so the belt doesn't burn up and leave you stranded." is spot on.
Not that I know anything about a serpentine belt failure. Especially with a newer *OEM Quality* component. Especially a thousand miles away from home.

dvs_dave

Interesting. Would the job have been any easier if the pulley/bearing were still intact?

MP4.2+6.0

Net, my guess is harder if it were intact. The reason is the retaining circlip. Because it fell apart, one thing I had to do incrementally was hold the plate where it bolts up to the compressor center shaft with a 10mm bolt. Leaving belt on until I pulled it was of no use because pulley spun separately from shaft now that it had torn out internally. Generic pin tools are available to fit into the holes in the plate they provide. I happened to have the viscous fan pulley holding tool my C5 4.2 used, which has the same basic set up and identical pin hole size. Later with new one, I just reinstalled serp belt and used that belt-pulley resistance to snug the bolt.

What was way easier with the destroyed one was pulling the circlip that retains the main bearing. I just had to get a long screwdriver blade wedged up in there and pry it just right. By contrast, getting the new/good one was no picnic. The circlip is maybe 30mm even relaxed, very thin and spring steel. So it wants to twist as you open it with a tool. Not only that, where it needs to go is a recessed groove that is barely 1mm wide/ < 1/16", AND it is recessed about ½" inside the outer face of the pulley. That recessing in a tight working space where you have to come in from below and not face on is what makes it a challenge. You wouldn't have to deal with the springy nature of the steel releasing it, but I find those clips often kind of hang up in the groove and not come out freely; plus to even see the two tiny punched holes where you attach the circlip pliers with the pulley on, you pretty much have to use an inspection mirror.

Bottom line, it was designed more to be serviced with compressor off the car, or with motor out, or front clip completely off, or to bolt it up easily in an assembly line situation (BINGO...). But it was ultimately do-able, completely in the vehicle, no front clip pull, and no need to pull refrigerant lines and all that.

BTW, for the serp belt and timing belt pulley and other debates, this could be a wake up call--for the 4.2's that is. On the 6.0, the only service called for is a periodic (on the vehicle) serp. belt inspection. This was an outright sealed bearing failure to the point of disintegration at 114K miles, and it came out of no where in only 500-1K miles. The crux of the bearing is very much like those found in the various accessory pulleys, tensioners and the like in the 4.2 timing belt and serp drive pulley. The A/C compressor housing actually even has sort of a shield cast into it the protects the upper part of the pulley shaft area, unlike any of the timing belt or serp tensioner pulleys on a belt motor. It may be a more stressed pulley axial load wise than any of the other accessory or even tensioner pulleys given the constant compressor on/off/variable, quasi full time A/C use, etc. But meantime, I always wondered about all those various other helper pulleys and how far to go in a 2.8 or 4.2 belt job. Not so much any more...

dvs_dave

Fortunately it seems like a rare failure given the lack of previous posts on it. And I just took a glance at my 4.2 and the AC compressor is bottom left (car left) and is the lowest unit so access on the face of it may be a little easier from below?
See below pic (copyright Mishar, I think)


Although whilst you have the debris on the bench, any clues as to why you think the bearing failed in the first place? You say the lube was gone so do you think the seals failed or it got water into it? Is there anything on the W12 that perhaps has the assembly located in an area more susceptible to spray or a coolant leak?

Here is a good bearing failure diagnosis guide that may help identify the root cause and if it's something for us more "fastidious" owners to keep an eye on.

http://www.schaeffler.com/remotemedi...ures_us_en.pdf

MP4.2+6.0

Yes, as I think I recall from my C5 4.2, the A/C is down toward the bottom corner opposite the alternator and the P/S is higher up; sort of reversed on the W12. The Audi picture below (ignoring cutaway elements) is accurate to my field experience with various parts of the motor, including even the detailing of the front of the A/C pulley and the whole serp. driven components.

The bearings were completely dry when they fell on the floor. No lubricant. But the week before when I found the pulley loose, I tried flushing out w/ brake cleaner. At the time I thought it was rubber debris external to the bearing. But since it wobbled at that point, I think bearing was gone even then and it was just wishful thinking it might still be okay and smooth out.

The bearing was unmistakably failed, since out came only one small chunk of some kind of identifiable race piece, and not nearly enough bearings to be a non race set up unless a bunch were ejected. I have lost Audi wheel bearings before where you often used to have to press them out and they sometimes came apart, plus a few old tapered drum brake type bearings. This was way gone and really looked like seal had been compromised at some point so lubricants were scarce. Since I am pretty sure one part was a race cage, the race could have broken first and then churned around metal fragments that tore at the seals. Perhaps the coolant leak from just above accelerated it when it dripped down, but the seal would have had to have been compromised for it to enter. Also a large circular metal ring fully intact came out, which seemed to be part of the outer edge inside seal from comparing it to the new one. Yes, the coolant leak was above there, but as I mentioned there is some casting material surrounding the upper part of the shaft area (apparent in the picture from the 9-12 o clock positions if you look carefully), so it seems pretty sheltered. And with the compressor higher up, it is completely protected from any road spray issues, it is fully behind main body of radiator and way above the belly pan area.

When I ran a search, having not heard of it myself I was somewhat surprised with the volume of hits I seemed to find, mostly VW motors. And unless it fails all the way like mine, I can see on a timing belt motor how if it was noisy people would probably assume something else in the belt drive unless they spun the compressor with the serp. belt off. It does say to me clearly to check the compressor pulley with any serp. belt pull, be very suspicious of any wobble or lateral movement, and replace at first sign of roughness or noise.

AEightSilver

That's a great write up.

I am chasing this weird noise (I can't explain it, like a little groan) that happens a few seconds after startup that kinda sounds like the accessory belt slipping. But it seems to mainly go away after that. When driving there is a slight noise I can hear but nobody else can . I have already changed all the pulleys, belt and tensioner, and ps pump not long ago which eliminated the 'other' noises and this one is whats left. I do remember rolling that pulley by hand and didn't detect anything; but I didn't try to rock it or pull on it to find play. Based on your write up, I suspect the compressor pulley is starting to fail and will take the belt off and start the car as well as examine the pulley more thoroughly to be sure.

AEightSilver

Ebay OEM pulley arrived https://www.ebay.com/itm/184990526288 for $70.

I'm there now with my job and its tight on the BFM motor to get the circlip out. Coolant hoses are in the area I can't get either set of pliers I have properly seated in the holes to expand it. In fact you really cant see much the circlip at all, I only see what I think is one hole. Will keep fighting with it.

But I'm pretty sure its my problem. No side to side play but I can ever so slightly hear the bearing grinding when I roll it fast enough by hand.