What was found
THE INSTALLED EXHAUST ROCKERS WERE PN 534398. THEY EXPLAINED THAT THOSE ROCKERS DID NOT HAVE THE HOLE DRILLED TO SQUIRT OIL ON THE EXHAUST VALVE STEM. THE NEW EXHAUST ROCKER HAS THAT SQUIRTER HOLE TO AID IN LUBRICATION. THIS WAS CAUSE OF FAILURE, PER MFG. NEW EXHAUST ROCKER IS PN 641682 (2 PIECE BUSHING) OR PN 652130 (1 PIECE BUSHING). SOME REPAIR SHOPS MODIFY OLD PART NUMBER ROCKER ARM BY DRILLING THE SQUIRTER HOLE. OLD ROCKER ARMS (PN 534398) WERE INSTALLED IN THE ENGINE FOR AT LEAST THE PREVIOUS 1400 HOURS PRIOR TO THE OVERHAUL AND DID NOT CAUSE PREMATURE VALVE OR GUIDE WEAR.