This is the result of a clutch cover gasket that started leaking coolant while riding. It is on a 2011 KTM 250sx. Genuine KTM gasket that was changed 40 hours ago has failed again. The first time I changed it was because it was leaking transmission fluid. This time it leaked out the coolant, causing the head to get extremely hot and melt a head o-ring. Which created enough void to let the combustion exit through. End result is a cylinder and head that have a hole pierced through them. Going to replace gasket with a cometic and cylinder with a 300sx kit. Kind of a bittersweet deal.