Thanks for the reply. No contact with the valves, valve timing was spot on, all marks lined up perfectly. As a bit of background, this was a routine maintenance exercise, Piston change at 30 hours ready for the new season. Bike was running sweet 2 weeks ago, so no internal damage prompted the piston change. I am waiting delivery of KSE-670 (2007-2011) piston, will post on here if this solves the issue.