Man you got your moneys worth out of that one on the left didn't you?
The best guess would be you got a hold of a set of junk lifters. There are ALOT of junk engine parts being sold today. You have to watch it or you will be sorry. I build quite a few motors and you really have to pick and choose carefully. Lesson learned I hope. Even some name brand stuff is turning to junk. It is making it tough to get reliability.
Are you using dual valve springs? That would speed up the failure. Hard to say for sure. When the motor was first started when new, did you put enough burnish compound on the lobes and did you run it at 2000+ for the recommended 20 minutes? It is possible the camshaft never mated with the lifters and it just took that long to self destruct. It usually shows up quicker. New cam time!
Roy
