I suspect that if the valves were all the way open, and the piston came up to say hello, carnage would ensue...... Not a real common occurrence though. I would more expect dropped valve seats, or something similar.

 

 

That's really strange. Is your gauge bad?

 

I agree with Heyyou.
How did it sound turning over with all the plugs in trying to start it? Did it sound like it was turning over abnormally fast? If so this would also indicate poor compression. If this is the case its time to take the front of the engine off and check the timing chain and gear alignment marks.

 

 

 

Rent a bore scope, and peek inside some of the dead cylinders. See if anything obvious presents itself.

Did the engine ever overheat??