A mechanic I paid for service left the oil.

Thank you for your reply. It helps a lot. If the lifter came out the bore which the tech did state I have a bad lifter( claims not his fault) and it caused loss of oil pressure couldn't that cause the cam not to lubricant properly and fail? The lifter and cam lobe damaged is in the same cylinder as the rocker that shifted off the push rod. The was nothing wrong with the cam or that cylinder at all.I'm just having trouble with figuring out why the cam would fail when there was no issue with it before and I know this as fact as I changed the valve cover gasket and all rockers and rods were sound. The research I've done says to much play in the rocker and lifter or damaged, the cam running dry or over tightening of the rocker can cause a cam to go flat.I need to find the source of why the cam failed and move forward from there. And I greatly appreciate your knowledge and help in the matter thank you!

It's still in the shop. He couldn't get the rod to seat on the lifter, and couldn't pull oil up when priming it. The motor was completely sound before he worked on it not a tick at all. Hell I don't even know if its flat its what he's saying.I took the truck to him because I couldn't check the heads for a crack. He said he "look at the heads and didnt find a crack" replaced the head gasket and pour some stuff in the radiator to seal up the crack if there was a small one, didnt work still had water in the oil, so he replaced the heads, that solved it but there was excessive ticking, so I told him of it and he took the truck back said he use a "timing gun" and that the rockers were all tight, I know you don't use a timing gun for this. He gave the truck back and I drove it for a week and the knocking got worse. So I myself went to tighten down the rockers knowing how and notice the rocker pushed of the rod and hitting the valve cover. It been about 8 months since he started working on the truck