Had similar thing happen with a truck I bought that came with a recent (5000 mile) reman engine from a well known supplier. It was a 400, ran decent but couldn't get idle as smooth as I wanted. Almost no compression on #1. Couldn't see anything wrong (didn't look hard enough) and pulled pan, head, piston thinking it had to be ring sealing issue. Replaced rings, piston etc. Eventually discovered intake valve stem was TOO LONG by a fraction, holding intake valve open. But just barely.

 

Well thanks for all the advice.the rockers are pedestal mount.had to shim because no clearance at valve stem. Heads were machined. Pulled the valve covers back off and the ones I shimmed were so loose they weren't opening the valve.pulled all the shims and everything is in tolerance.not sure what happened there. Realized the damn distributor was 180 degrees out ( stupid mistake). Tries to crank now but dies immediately. Pulled plugs and of course they are gas fouled. Pick up new ones tomorrow and we will see. Wish me luck.

 

Installed new plugs and truck cranked right up.did the break in run on it.everything is good nonow.thanks for everyone's help

 

Good job on finding out what was wrong!