Hi All;

I just changed the timing belt on my 2001 4.2L Audi A6. I really appreciated the help I got from looking at posts on this board.

I didn't want to rent the cam sprocket locking tool so I figured out how to make one for almost free.

What i did was take two breaker bars with the correct socket for the cam sprocket bolt and tie them together with hose clamps. I then zip tied the "tool" to the sprockets.

When I released the timing belt, the left cam moved less than one tooth an the right didn't move at all. I completed the job (TB, Water Pump and T-Stat) without incident and the car runs great.

I consider this method of locking the cams a success.

Also, as a note to everyone with a 4.2 engine, I found (just by chance) that one of the links that actuate the variable geometry intake manifold (called the IMT link) was broken. The dealer wants $400 for re-build kit but I was able to order a nice set of machined aluminum ones for about $80. Still expensive for what it is but really nice pieces. If you are working on your motor, check these links. The IMT system really increases low end torque!

 

The problem with this approach is that it is far easier to put the timing belt on if the toothed cam sprockets are able to spin freely. The rental or "official" cam locking tools work by holding the trapazoidal washer between the bolt and the sprocket in place; the sprockets can spin freely but the cams themselves stay put.

 

seriously? it only moved less than 1 tooth! thats less than 1 tooth too much. do it right, you will like your car much better when its done right, feels like a completely different car!

 

Less than one tooth which way? How do you know that both cams are now in synch with each other and with the period of the crank rotation?

 

The main reason for doing it right with the tool is that the timing belt stretches. By creating infinitely variable positioning of the sprockets, slop or mis-match in the position of the teeth after tension is applied to the new belt is accounted for. Without this step, the best you can get is the same positioning as the old belt, which stretched out of shape during it's lifetime. Many owners have remarked at how much better the engine runs after changing the timing belt due to this.
Jim

 

I did my timing belt and then had a leak from the thermostat, because blauparts sent me a thermostat o-ring that was just a little too thin. I drove for almost a week hoping it was just the water pump break-in or the thermostat o-ring needing time to expand from heating, but it still leaked, so i took it all apart again, and had to take off the timing belt (so at this point it had a whole week to stretch out to what it will hopefully remain at, after I fixed the leak the engine ran better with a VERY VERY noticable increase in power and smoothness of the power band. I feel like its even better than a new car now, seriously, If I ever buy a new car with a timing belt, I'd redo the timing just to make sure its perfect after the belt stretches after a thousand or 2 miles.

 

I have changed many timing belts. This is the first Audi 4.2 engine I have done but I have done dozens of other cars and never had a failure, never had one come back and never had to take an engine apart a second time.

Locking tools are not always used in DOHC V style engines. To my understanding, the purpose of the locking tool for this particular motor is to make sure the cam sprockets don't rotate when you remove the timing belt. In most cars, the cam sprockets won't rotate on their own. However, in the Audi 4.2, the specialists I talked to told me that the sprockets can spin on their own as much as 30 degrees when you release the tension from the timing belt.

There was some debate among the experts that I talked to regarding whether or not letting the sprockets move would cause a problem as long as they were reset correctly with the new belt. Some said it would do damage since the movement is stopped by a valve contacting a piston. Others told me it wasn't a problem since the movement happened slowly and wasn't driven. Better safe than sorry in my opinion.

Now, when I say "the sprocket only moved less than 1 tooth," I mean that when I removed the belt, the sprocket only rotated less than 1 tooth before my makeshift locking bar stopped it from rotating further. When I installed the new belt, I aligned it exactly the same as the old belt. This was done by marking the old belt on all three sprockets, transferring those marks to the new belts and setting the new belt to match the marks on the sprockets.

I should note that I didn't change the camshaft seals or loosen the camshaft sprocket bolt. I believe when the bolt is tight, there is no difference in locking the sprockets via the specialized tool or via affixing the bolts. Does anyone believe those are not the same? I also believe the new Timing Belt should be aligned the same as the old timing belt (e.g. the teeth should all line up the same places). Does anyone think that is not true?

The motor runs great and has plenty of power so the operation was a success in any case.

 

>> I also believe the new Timing Belt should be aligned the same as the old timing belt (e.g. the teeth should all line up the same places)

Maybe - if there was no stretch or mis-alignment of the old belt.

The whole idea of the Audi tools for the TB is that you lock the crankshaft with the locking pin at TDC. Then you lock both camshaft assemblies with the bar so that all three (the two/four camshafts and the crank) are exactly aligned regardless of the belt. Then when you put the belt back in place, release the tensioner, and lock the moving sprockets with the nuts, the timing is exactly right to within fractions of a degree regardless of belt length, stretch, or tooth position. While this may sound like overkill, it gets things exactly right.

These cars are overengineered in some places, but they run so well in part because the engineers didn't leave anything to chance. And it's not just Audi - my Infiniti J30 uses the same system for TB alignment (except that instead of a bar there's a tool that engages flats on the camshaft pairs directly).

If yours is running great, that's wonderful. But they did design the TB that way system that way for a reason.
Jim

 

the sprockets MUST SPIN FREELY!!!!! It doesn't matter where the sprockets are, it matters where the cam is positioned, to make sure its positioned correctly you need to use the cam locking back, loosen the cam bolts and pull the sprockets so they rotate FREELY!!! If you did NOT do that, the tension of the belt will be different between each of the 3 sprockets!!!!! that will cause problems!!! Essentially, its just wrong!

 

Think about it, a rubber/material belt on 3 sprockets, with different tensions between them. The belt is being stretched then loosened then stretched, etc etc over and over again. Then imagine whats going on at 7000rpm, its a disaster waiting to happen.