A6Gary

viewed from the front. That being the case, your rear passenger cylinder photo shows that the exhaust lobe (rearmost lobe) is about to depress the exhaust valve, meaning that the piston is at or near the bottom of its power stroke, and is about to exhaust the cylinder. Then the intake engages on the downward stroke, as shown in your photo, by following the exhaust stroke. Again, clockwise rotation.

Regardless which cylinder is at it top position when the TDC is aligned with the mark on the harmonic balancer, the crank/cam timimg is set correctly when the crankshaft lock tool and the camshaft locking bar are installed adn the timing belt is tensioned correctly.

FYI, Bank #1 is passenger side, Bank #2 is driver's side (based on O2 sensor IDs in the Bentley Manual).

DMW96A6

The rear cam lobe (exhaust) in the picture will not begin to open the exhaust valve until the piston reaches the bottom of its travel. Anyone who has ever adjusted mechanical lifters including the old Audi 5000s knows that this is the position for TDC for that cylinder.
<img src="http://pictureposter.audiworld.com/88502/img_1127.jpg" />

If you look at the next image of the Driver's Side Middle Cylinder, you will see that the intake valve (farthest in this image) is just beginning to open the intake valve while the exhaust valve is just closing. This is called overlap which is a period where both the intake and exhaust valves are both open slightly at the same time.
<img src="http://pictureposter.audiworld.com/88502/img_1128.jpg" />

This is also the cylinder that the spark from the same coil that fires on the passenger side rear cylinder also fires on this cylinder which does nothing. This is how 3 coils can run a 6 cylinder engine without a distributor. One spark is used and the other is wasted. This method allows each coil one complete revolution of the crankshaft to charge to it's fullest voltage.

The whole point of this cylinder numbering and firing order issue is the fact that there is no diagram that shows what the cylinder numbering is. It can only be derived by looking at the high voltage wiring diagram on the coil (if it is there) and tracing the wires to the cylinders. Aligning the marks on the crankshaft pulley and with the camshaft tool in place, I assumed that I would be able to do the cylinder leak down test (which requires each cylinder to be at TDC compression stroke) starting at what I assumed to be cylinder #1 (front passenger side). However, when I tried the leakdown test, I discovered that the exhaust valve was wide open. I did not have the valve covers off to determine what stroke the cylinder was on. It was not until I removed the valve covers that I discovered that the passenger side rear (#3) was at TDC compression. So the resulting firing was 3-6-2-5-1-4. I was then able to do the leakdown test and determine which cylinders were leaking into the water jacket.

Like I said before, with the Audi v6 being the only exception, every engine made by Porsche (street and race), Mercedes, BMW, Audi, Ferrari, Chevrolet (street and race), and Toyota, that I've worked on, have all had cylinder #1 at TDC with the crankshaft mark lined up and the camshaft(s) lined up with their marks (or tool installed). Audi apparently had a design problem that was not enough of an issue to justify the redesign of the cams and crankshaft. All engine timing is based on the alignment of the camshafts with the crankshaft based on the timing mark and the cam alignment tool. I suspect that if you remove the crankshaft position sensor CPS, that you would see the magnetic slug (or whatever they use) in the position that would cause the CPS to send a pulse to the ECU. This means that the cylinder numbering with #1 at the front is only for identification of components that cause OBD errors. But mechanically and electronically, all engine timing is based on the alignment of the passenger rear cylinder. And the cylinder that all timing is based off of has always been designated as cylinder #1.

MrGoodbytes

OR... the marks on the balancer don't mean TDC but are there for timing belts only.

DaveInSaltLake

"engine" as opposed to any given cylinder. On several rare occasions it even associates engine TDC with cylinder #1, but we've seen that is not accurate.

I have to believe that there is additional factory service information regarding this issue.

mulsannekink

They have #3 at TDC so the crank can be locked on the cyl #2/4 crank counter weight.