I have a 2006 yz450 that keeps pressurizing the cooling system. I just sent the head off and had it rebuilt I would assume that the shop who rebuilt the head would have checked for cracks and so forth. I installed the head and still have my cooling system getting pressurized, I'm starting to think I need to have the cylinder checked, I have replaced all o rings and seals in the Cooling system along with the radiator cap. Im also wonder if it's possible that the head bolts have been over torqued and stretched? I'm at my wits end trying to track this down. I have put a pressure tester on the system and confirmed that it for sure has a leak I just don't know where??!!