|
Upon close inspection I found the culprit. The cam was advanced too far for the build and at high rpm was allowing the intake valve to contact the piston crown. I found some slight scuffing in the valve reliefs on the crown. The repeated contact would have caused enough shock over time to crack the guide. Valve is still straight somehow and retainer looks fine as well. Bad news is I think the piston has a hairline crack at the base of the pin... and the top ring journal is compacted down pinching the top ring on one side. Looks like I'll be needing a new piston. So the moral of the story kids is dont deck it too much or advance the cam too far. Found another 78mm piston on Ebay and will be ordering that along with some new guides and all should be good.
|