What was found
DURING CRUISE FLT RT ENG NR 2 CYL PISTON CONN ROD BROKE LOOSE FROM CRANKSHAFT, PENETRATED UPPER CRANKCASE. NR2 CYL SEP FROM ENGINE, RESTED IN COWLING. THE FORCE OF CONNECTING ROD COMING THROUGH THE CASE BROKE LEFT MAGNETO OFF ITS BASE AND PUNCHED A HOLE IN THE UPPER COWL. PILOT SECURED ENGINE AND FLEW TO A MAINTENANCE BASE. UPON REMOVING PIECES AND LAYING THEM OUT ON TABLE IT WAS NOTICED ONE OF THE CONNECTING ROD CAP BOLTS DID NOT HAVE THE REMAINS OF A COTTER PIN IN EITHER OF THE SAFETING HOLES. BOLT HEAD HAD BEEN BROKEN OFF(SUSPECTED FROM THE HAMMERING WHEN THE NUT WAS LOOSE). IT WAS ALSO NOTED THAT THREADS OF SAME BOLT, NOT AS DAMAGED AS BOLT ON OTHER SIDE , INDICATING IT UNSCREWED ITSELF.