Ok bit of a problem here. this started a couple of posts below when asking advice on valve replacement. I replace the intakes on my 05 exc 400. used OEM valves and had them cut in. did not do anything to the exhaust except remove them to clean. After putting it all back together the exhausts are touching the piston - I could hear it and on tearing into it again tonight you can see very subtle contact, no damage - really just the carbon layers got polished off but still hitting. I timed it this way: -insert TDC bolt on front of case -install cam lobes down -have the two dots level with top of head. *I also installed a new plug I do not have a leak down tester but the compression with a normal gauge was 90. When I took the head off I checked the valves for seal by filling the head with acetone and checking to see if anything leaked through valves - nothing. Good seal. I reused the head gasket and the base gasket. Previous to rebuild the bike ran rough and would generally start and run for a few seconds then die and never start again. This is what it did after the rebuild too , except with the clacking noise that was caused by the contact with the piston. Here are some things that maybe could cause it: -base and head gasket old and too thin and now too thin causing contact? -maybe F-ed up and timed it one tooth off??? can't see how but maybe -cam chain decided to get real long suddenly and put timing out? Other than that I can't figure out what has changed. Help!