As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN-FLIGHT CRUISE, THE HEAD OF THE EXHAUST VALVE BROKE OFF THE VALVE STEM CAUSING INTERNAL ENGINE DAMAGE. THE AIRCRAFT MADE AN EMERGENCY LANDING ON A SHORT GRASS RUNWAY CAUSING SUBSTANTIAL DAMAGE TO AIRCRAFT. THIS INSPECTOR HAS WITNESSED THIS BEFORE ON LYCOMING O-320 AND O-540 NORMAL OPERATED ENGINES. SUGGEST MANUFACTURER COME OUT WITH A BETTER EXHAUST VALVE.