What was found
THIS PROPELLER INSTALLATION UTILIZES 2 SPINNER AFT BULKHEAD ATTACH PLATES, PN A1639-9. BOTH PLATES WERE FOUND TO BE CRACKED WITHIN 50 HR OF INSTALLATION OF PROP AFTER OVERHAUL. BECAUSE BULKHEAD ATTACHMENT PLATES ARE INSTALLED UNDER ATTACHMENT NUTS, PN A1639-9, THAT HOLDS THE PROP TO THE ENGINE IS SUBJECTED TO VERY HIGH CONTACT FORCES DUE TO THE SMALL SHOULDER ON THE NUT(A1639-9). THE LIKELIHOOD OF THIS FAILURE WILL INCREASE WITH THE NUMBER OF TIMES THESE FASTENERS ARE TORQUED. IPC CALLS FOR THE INSTALLATION OF A WASHER BETWEEN ATTACHMENT PLATE AND NUT, EXCEPT THERE IS NOT SUFFICIENT CLEARANCE TO ALLOW THE INSTALLATION OF THE WASHER.