2003 440 sno pro. Has about 2000 miles on it. Has not been raced. Belongs to a friend. We tore it down because of a head o ring started leaking. The bore looks like it has no wear. No scuffing on pistons but both pistons have cracked skirts. They are the stock pistons. The only thing I found wrong was the exhaust valves were both stuck closed. Gummed up really bad, we about couldn't even pull them out. Can that cause alot of heat in the combustion chamber?