Pajinek

I'm at a loss guys. The motor is a 2000 LS1, bottom end was just rebuilt, used heads with yellow springs. The motor has a misfire, I was hoping it was an ignition problem but after doing a compression test, cylinder 6 makes 0 compression. After removing the rockers (to relieve any pressure on the valve springs), the cylinder made 90 psi compression. I tried swapping rockers and pushrods from a different cylinder, but again it made no compression. Something is preventing the valves from closing entirely, or at least that's my best guess. I purchased the heads with valves and springs already installed by the seller, I suspect the fault may be in his assembly but lack the experience to be certain. The rest of the cylinders made 140-160 psi cold.
Any advice would be greatly appreciated, thanks guys.

A.R. Shale Targa

iTrader: (2)

valve tip height is too tall and this causes the pushrod to bottom out in the lifter plunger, essentially making it a solid and holding the valve open
you can take all the rockers off on that side and use a straight edge to verify this

nzgreenfox

What Tony said and try this
http://www.gregsengine.com/cylinder-...n-testing.html
re putting oil in no 6 clyinder to check leakage around the rings.
Also if you have a depth gauge remove the pushrods and check the lifter height ensuring the cam lobe is on the base circle. Check the pushrod length on cylinder 6 with another cylinder.