What was found
AFTER A NORMAL FLIGHT AND NORMAL LANDING, UPPER RIGHT ENGINE MOUNT BOLT WAS FOUND BROKEN. THE BREAK WAS ON THE SHANK ADJACENT TO THE SHIMS BETWEEN THE ENGINE MOUNT AND THE FRAME. SLIGHT FRETTING CORROSION AND A VERY SMALL CIRCUMFERENTIAL SCRATCH WAS FOUND AT THE ORIGIN OF THE CRACK. SUBMITTER RECOMMENDS REPLACEMENT OF ALL 4 AN6-37A BOLTS WITH NAS6606-54 WHEN ENGINE RE-SHIMMING IS PERFORMED. ALSO, USE OF CORROSION PREVENTIVE COMPOUND ON THE BOLT SHANK MAY HELP.