What was found
AIRCRAFT ANNUAL INSP- 2 WEEKS PRIOR- REPLACED EXHAUST AND INTAKE VALVES ON NR 2 CYLINDER DUE TO LOW COMPRESSION. FLEW 6 HOURS PRIOR TO INCIDENT. IN CRUISE FLIGHT, ENGINE SUDDENLY RAN VERY ROUGH WITH VIBRATION. VFR WITH FLIGHT FOLLOWING. DECLARED EMERGENCY AND LANDED AT NEAREST AIRPORT(3F3), 18 MILES AWAY. POST FLIGHT INSPECTION: NR 2 CYLINDER BROKE INTO 2 PIECES- SEPARATED AT TOP OF BARREL AND JUNCTURE OF HEAD. HEAD WAS HELD ON BY VALVE COVER AND PUSH RODS. THIS CYLINDER IS REPORTEDLY NOT SUBJECT TO EXISTING ADS OR MANDATORY SB THAT COVER OTHER ECI CYLINDERS WITH SIMILAR PROBLEMS. (SW05200502730)