Heavy Cylinder Damage
We are not sure what started this but a good guess might be a seized or sticking valve. Once a piston strike occurs anything can happen and the entire head of the valve broke off. It is amazing how this engine continued to run with the valve bouncing around in the cylinder. The connecting rod and the piston were very accommodating, don't you think? This type of failure always brings a line of onlookers in the shop. More shock and awe!