2000 A6 4.2 L timing belt issue
I chose not to remove the pulleys and just use the winged pieces and the alignment tool T40005 to get the cams in the right spot before installing the new belt. I also used the crankshaft locking pin. Initially, I didn't want to purchase the extra tools, but I am really glad I did because my car starts and runs great.
I had alot of concern about the eccentric cam because as you described it affects the timing. (I didn't fully understand the affect until I got it back together and discussed it with my fellow engineer, then I read your comment and it was confirmed.) I didn't have the tool used to torque it into place, so this is probably an area that is not perfect on my replacement. It also doesn't seem like the most precise method to tell the mechanic to line it up with the pulley on the waterpump. Regardless, my belt was really loose on both sides when I removed it. After, it was very tight.
Is there an adjustment period for the ECU to adapt to the new belt or is it set where it's set? It seemed like the MPG gauge was lower after the change, but that was the only noticable change.
All in all I am glad I did the change myself, but I had several doubts throughout the process particularly with the oil cooler that made me question the attempt. I had trouble with the front and rear bolts on the top of the cooler. I stripped both hexes on these bolts (call it OE if you want but those things were welded in there) but I was able to get them out by praying. Anyway, I did raise and lower the engine off the mounts in order to remove the cooler. I don't see how this procedure is possible without this step since the cooler is part of the mount. Anyway, I would be glad to answer questions about the process if anyone wants amateur advice. I am just thankful I survived and the car runs so well.

The good! My 4.2L A6 reassembled and running

The bad. The plastic coolant pipe... in three pieces.

The ugly! Stripped bolts from the front and rear of the oil cooler housing

The engine with cooler removed. Looks like loads of room...right.

Oil cooler off
The 'winged' pieces that the cam lock tool attaches to are keyed to the cams, but will be free to move a bit when the cam bolt is loose. The cam gear itself is not keyed to the camshaft, hence the infinite adjustability and requirement for the tools to do this right. The winged piece will always be physically aligned to the cam/cam lobes when the cam bolt is in place & snug.
Cam Tool aligns the wings, wings are physically aligned with the cams, Belt & Cam sprockets align the cams to the crank when tension is set & the bolts are tightened.
When you are ready to set timing, Take the cam lock tool off if it is on, put the belt on, re-align the keyed 'wings' on the cam, tighten the bolts slightly, so the 'wings' set into the keyed protrusion on the cam (trapezoid), put the cam lock tool on the cam that is not in line & gently pull the bar down to line up with the opposite cam. Make sure your belt tension is good & tighten the two cam bolts.
As far as which method to use (by the book w/ the tools or by counting teeth), I'm of the opinion that every rotating part of the timing belt routing should be changed to do the job correctly & that includes the eccentric pulley. Changing that pulley means you are changing/setting the tension on the belt. If the eccentric pulley isn't replaced at precisely the same angle and/or the belt is not nearly identical in flex to the old belt on the car (when that belt was new), the right hand side tension & as a result, timing, will be different. ECU is doing its best to burn fuel as efficiently as possible by changing spark timing, so 'slight' variations might not be obvious.
hp is one argument for being exact, maximizing mpg is another.
If anyone is in north west NJ or would like to drive there I will happily loan out my tools (cam bar, crank lock plug, cam chain tensioner tool) to a fellow AWN 4.2 owner.
Good luck w/ the oil cooler & post a picture of the stupid broken plastic pipe.
Other folks can correct, but I don't think the ECU does much in the way of 'learning'; it should be working ignition timing to maximize fuel burn based on feedback from the 02 sensors. Keep an eye on your mileage, there might be something else going on.
Since you have the 4.2L, you might want to check the variable length intake runner mechanism (front of the intake manifold has two vacuum bellows that rotate shafts inside the manifold that change the route air takes depending on engine RPM) They can get 'stuck', the little plastic links can break, etc. Car off the springs should pull the bellows into the extended position, when you start the engine I think both should close once the engine warms up, RPM settles down & engine goes into closed loop. (vacuum is applied or removed from the bellows by two small electronic valves controlled by the ECU) If this isn't working correctly, you could be running at slightly lower power/efficiency.
Your oil cooler looks somewhat different than mine; I don't recall removing the oil filter housing/mount.
My experience with this was that the chain and sprocket won when the tensioner messed up and got stuck between meaning the plastic just came apart. But there might be a different failure scenario that could cause the damage to the sprocket. I opted to get rid of the vehicle rather than replace the intake manifold because I don't have a garage to work on it and I needed transportation sooner than I could get to it. I don't think this helps you much, but I did watch videos on youtube for replacing the tensioner that seemed pretty straight forward. This required the removal of the cam shaft which would allow you to replace the sprocket. You still have to reset the timing correctly. In my case, I suspected my valves were damaged and possibly the pistons, so I would have needed to overhaul that side of the block. I gave up. Hope you can fix yours.
For the cam belt, etc., using Elsawin and a couple of online sources it all went fairly easily. When removing the front panel some of the bolts on the RH side of a RHD car cannot be reached from below, but access is possible from above.
I've just changed the transmission filter and fluid - at 163000 kms it seemed a good move. As you might expect the fluid was dark and there was a thin layer of fine sludge in the pan. Not sure if it was needed, but happier that I know what's in there.
I am working on my 2000 4.2 A6. Long story short timing was off bad and have a bunch of bent valves. I haven't seen any timing marks for crankshaft. I have the locking pin but can't seem to find the correct TDC to get it in. Is there a way I can do this with the cylinders since the cams are off? Im not sure whether cylinder 1 or 3 should be at TDC when crank is lined up. Thanks all.
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Just FYI. My timing got off as well, and that is why I parted ways. Mine didn't have anything to do with the belt. It was the internal cam tensioner that failed and allowed the cam chain to skip teeth. I didn't try to fix, because I didn't have the money to risk failure of installing new heads. I hope you find success in your endeavor.
I am working on my 2000 4.2 A6. Long story short timing was off bad and have a bunch of bent valves. I haven't seen any timing marks for crankshaft. I have the locking pin but can't seem to find the correct TDC to get it in. Is there a way I can do this with the cylinders since the cams are off? Im not sure whether cylinder 1 or 3 should be at TDC when crank is lined up. Thanks all.







