What was found
PILOT OWNER DEPARTED HOME AIRPORT FOR ROUTINE SCENIC FLIGHT. AFTER ABOUT 20 MINUTES INTO CROSS-COUNTRY FLIGHT, ENGINE STARTED RUNNING ROUGH, CARBURETOR HEAT HAD NO EFFECT. RETURN HOME WITH PARTIAL POWER. INSPECTION OF NR 2 CYLINDER ROCKER REVEALED ALL FOUR BOSSES BROKEN OFF REQUIRING REPLACEMENT OF CYLINDER. SUBMITTER SUGGESTS FATIGUE MOST LIKELY CAUSE OF FAILURE. TOTAL TIME ON CYLINDER-ENGINE, 2,100 HOURS SMOH. RECOMMEND DYE PENETRANT CHECK EVERY 500 HOURS.