Engine hits hard stop when rotating by hand

[phalcon51]

I'm cleaning the carbon from the intake ports and valves on my son's '06 Audi A4 3.2 with about 120k miles on it and I've run into an odd problem. He bought the car with about 60k miles and I think this is the first time it's been apart.

First, here's what I've done so far:

Removed the upper intake manifold
Removed the lower intake manifold (air diffusers, left and right)
Removed the high pressure fuel pipes
Loosened the coolant cross-over pipe
Removed the high pressure fuel pump and cam follower cup.
Removed the spark plugs and replaced the coils lightly to block the sparkplug wells
Rotated the crankshaft clockwise (as viewed from the front) to ensure the intake valves on the #1 cyl were closed.
Blocked off intake port #'s 2 - 6 with rags, taped or plugged all open pipes, hoses, injectors, etc.
Used a walnut shell blaster and a vacuum to clean carbon from #1 intake and then vacuumed and blew out all loose debris.

I then rotated the crankshaft clockwise again to open and close the valves on #2 cyl. prior to blasting the carbon out. The #2 valves opened and got about 2/3 closed when I encountered a hard stop. I didn't force it and I hadn't turned the crank counter-clockwise at any point prior. There was no noise or feeling to indicate that the timing chain may have skipped a tooth on the sprocket. The engine was running without any problem prior to this other than some rough running at low speeds, which I attributed to carbon build-up on the valves and intake runners.

Can anyone venture a guess as to what might be stopping the crank from turning?
Also, I've read that you should never rotate the crankshaft CCW as the cam chain tensioners can back off and allow the chain to skip a tooth on the sprocket. Is this true? If not, I was thinking of turning the crank CCW slowly to see if I hit this hard stop at 2 revolutions back which might at least narrow it down to which cylinder may have a problem.

Thanks for any suggestions.

Gary

[phalcon51]

Anybody?

I'm really stuck here. I don't want to go to the expense and time of pulling the heads off if I can avoid it at all.

Does anyone at least know if it's ok to turn the engine backwards without risk of loosening the cam chains?

Thanks again.

[Dmitry at Pelican Parts]

Hi Gary - our VW/Audi community is not as big as our Porsche community. I'm attaching a link to our site's DIY tech articles on the B6 platform - hopefully this helps you out a bit.

https://www.pelicanparts.com/techarticles/Audi_A4_B6_Index.htm