Thinking about that, the valve could hit there because as it moves toward closed it moves back away from the center of the piston. Bewing out of time could indeed allow it to hit there. I gotta go to the Dr. so I must run. To verify that the timing is correct pull the back plate and watch as the piston rises on the exhaust stroke, at TDC both valves should be open slightly, (overlap) byt the same amount.