Bad cam or bad lifter,how to tell

[HARLEY696969]

This past fall I re-did everything on the top end of my truck,454. It's got all crane stuff like cam,springs,lifters and arms. I started having a miss and thought it was a spark plug. Changed em and still missed. I climbed under truck to look for a oil leak I had,gave up with the miss for now. I saw that my valve cover was leaking bad on the pass. side. Took valve cover off and it did have a bad gasket. Was happy cause I thought it was a rear seal. Before I put the cover back on, I just wanted to make sure the rocker's were adjusted right,again. So I started shacking them while they were on the bottom of the lobe and found the very back one shook alot,I mean alot. I adjusted it but knew something was bad cause the lock nut went down more then the other's. Turned it over and that back valve isn't opening like all the other's. I mean you can see it plan as day. It's not been in the truck that long and maybe 800 miles,if that. We broke it in just like we have in the past and can't figure out what happened. How can I tell if it's a lifter or a cam? I got a bad feeling it might be both but don't want to go through all this work again,plus spending more money.

[Thunderbolt]

My guess would be a collapsed lifter. I would think if a lobe on the cam went bad at 800 miles there would be a lot of metallic debri in the oil. are you sure the push-rod is seated in the lifter and not off of it?? Take the rocker arm off and use your hand to see if you can collapse the lifter. If you had the valve lash too tight you could have bent the push-rod also.