Im in the middle of putting my PnP'd head back together with crower camshafts. I get the motor all the way back together before I noticed one of the cylinders valves arent closing all the way. If I rotate the crankshaft, I get compression, compression, compression, SSSHHHH. Meaning all my compression is leaking past those valves. What should I be looking for here? Im taking the motor apart again after work, Might try swapping in the valves from the old head.

Bent valve. It is possible that valve is bent to the point you can hardly notice. A quick glance and you will miss it

You should know which cylinder its in (this is, of course, provided you put your cams in correctly). If you still got it together, you can also figure out if its an exhaust or an intake valve. When you have it off, just use water into the ports to narrow it down to which valve (with the amount of PSSHH, that you describe it should be easy enough to pick out).

Once you have the valve identified try hitting it with a soft mallett on the top of the retainer. Then check to see if it still leaks. Sometimes (rarely, but sometimes) you can get a piece of dirt etc. between the seat and the valve. If that's the case (and she doesn't leak now) just pull out the offending valve and re-lap it in. Then check again when its back together.

If not then take out the valve and see if it slides up and down freely in the guide (possible sticky valve guide/ valve situation) Or, if its not sticky, check the valve to see if its bent (usually bent at the head). I just spin the valve in my fingers (by the stem) and do a visual check. You could actually chuck it into a drill chuck (carefully) if you want.

It was actually 2 valves on the exhaust side of cyl 2. Not sure what was up. Took the head off, cams out, camshafts out, checked the valves, put it all back together and its sealing now. I guess Ill try firing her up and post the results..