As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINES NR 1 AND NR 3 WERE BEING REMOVED FOR MAINTENANCE. WHEN THE UPPER MOUNT BOLTS, WHICH ATTACH ENGINES TO THE AIR FRAME, WERE BEING REMOVED THE BOLT STOPPED TURNING AND WAS FROZEN SOLID INTO ENGINE MOUNT. BOLT HEAD WAS CUT OFF TO REMOVE ENGINE. BOLT IS MADE OF STAINLESS STEEL. UPPER MOUNT AND BOLT REQUIRED REPLACEMENT. LOWER MOUNT BOLT WAS REMOVED WITH NO THREAD DAMAGE.