What was found
(CAN) ENGINE WAS SENT FOR INVESTIGATION AFTER OPERATOR REPORTED A SUSPECTED #4 BEARING FAILURE. DISASSEMBLY FOUND THE #4 BEARING AREA FAILURE WAS THE SPLITTING OF THE HP IMPELLER BEVEL GEAR. ONE OF THE MOST COMMON CAUSES OF THE #4 BEARING AREA FAILURE IS THE BACKING OFF OF THE IMPELLER BEVEL GEAR RETAINING NUT. THIS RESULTS IN UNUSUAL STRESSES AND EXCESSIVE FRETTING AND RUBBING BETWEEN PARTS. UNUSUAL RUBBING AND FRETTING WAS SEEN BETWEEN THE COMPONENTS IN THE #4 BEARING STACK-UP.