As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN CRUISE, EXHAUST VALVE BROKE APPROXIMATELY ONE-HALF WAY UP THE STEM. THE CYLINDER HEAD AND THE PISTON WERE RENDERED UNSERVICEABLE DUE TO THEIR COMBINED EFFORT TO BREAK THE VALVE INTO SMALL ENOUGH PIECES TO BLOW THEM OUT THE EXHAUST SYSTEM.