What was found
ENGINE DISASSEMBLED AT O/H, CRANKSHAFT INSPECTED. FRONT MAIN ID FND WITH NUMEROUS CORROSION PITS, APPROX 2.0 INCHES AFT OF FRONT EDGE OF FLANGE PILOT. CRANK ASSY LW 17676, SN V721 (CRANK AND BUSHING SUBASSY LW17622) HAS ALWAYS OPERATED WITH CONSTANT-SPEED PROP AND IS NOT INCLUDED BY MDL OR DESIGN IN INSP REQUIREMENTS OF LYC SB 505A. THIS REPAIR STATION INSPECTS ALL CRANKS FOR INTERNAL CORROSION REGARDLESS OF MDLS AND THIS IS 2ND CONSTANT-SPEED PROP CRANK SUBMITTER HAS SEEN IN PAST MONTH WITH SERIOUS INTERNAL CORROSION. CRANKSHAFT SUGGESTS ENVIRONMENT AND OPERATION ARE KEY FACTORS IN AFFECTING CORROSION AS WELL AS CONSTANT-SPEED/FIXED PITCH APPLICATION. SUBJECT ACFT OPERATED IN MEXICO AND HAWAII.