Valve train geometry
After seeing this problem for literally years I can tell you all exactly what the problem is, but you're not going to like it. It's the JUNK Crane 'gold' rocker arms. If you have this problem get rid of the rockers to someone who doesn't mind tearing their hair out, and simply buy a set of Hughes rockers, instantly the problem will disappear. Perfect tip alignment will be the order of the day, although in my experience it's not that big of a problem. I've got my own engine apart for a freshen up at the moment it's done 10 HARD years and I swapped the inlet valves for another set I liked better [Eddy heads] the stem dia. was about half a thou larger than the originals and I had to get the guides honed because some wouldn't even go into the guides, and yes this engine is using 1.6 Crane gold rockers with the rubbish tip alignment that they all come with and guess what virtually no guide wear in 10 years. I hope this helps someone.