As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN NORMAL CRUISE FLIGHT, THE PILOT/OWNER REPORTED THE ENGINE BEGAN RUNNING ROUGH WITH ASSOCIATED LOSS OF POWER. EXECUTED AN UNSCHEDULED LANDING AT PWM AIRPORT AND WE TOOK IN SUBJECT AIRPLANE FOR REPAIRS AND RETURN TO SERVICE. INSPECTION REVEALED THE #2 CYLINDER ASSEMBLY HAD CRACKED AND A PORTION OF THE EXHAUST VALVE HEAD AREA HAD SEPARATED BUT WAS STILL HELD PARTIALLY IN PLACE BY 1 ROCKER BOX COVER SCREW. THE ROCKER BOX COVER WAS SLIGHTLY DAMAGED AS WELL.