I have a 2001 Evinrude 250 FICHT. I just rebuilt the engine after losing compression on two cyliinders due to overheating (trash in the thermostat). I bored all six holes, new wiseco pistons, etc. Got it back together. Went out on Sunday and after about an hour of running, I burnt a hole in the #5 piston right at the exhaust port. Plenty of oil in the cylinder that burnt. Any ideas on what happened?