SO, i had a upper timing chain break on my xk8, and i removed the head to have a machine shop check for bent valves. they reported that there were no bent valves and no leaks after a pressure test was done. THere were no dings or contact marks on any of the cylinders on this side of the motor. After reinstalling the head and setting the timing, i have 130psi on all 4 cylinders on bank A (the side i removed the head from) and 170psi on all 4 cylinders across bank b. What did i do wrong?

 

Just speculation here ...

I can think of only two things that could do this with such uniformity among cylinders in the A bank: if the head gasget were not sealing properly, or if there were a problem with valve timing.

New gasget, right? Is there any chance the valve timing is not correct? (Either primary chain or secondary chain.)

 

I second the valve timming

 

have you had the engine running yet or did you do the compression test right away?
Could make a big difference as you might not have had a proper oil pressure yet.

 

I second everyone, especially Jochem00. If you don't have oil up on the cylinder walls yet, the air will just slide right past the rings and into the crankcase, reducing your compression. If you want to check the compression before running the engine, just take out the spark plugs and squirt a dab of oil into the cylinders.

 

Besides compression effects, lack of oil will skew your timing somewhat, since the hydraulic tensioners are not tensioned.

 

Jog my memory, didn't you change the head gasket because you had low compression on that bank, or was that someone else.

 

Sorry about the dumb post. I read it more completely and anwswered my own question.