AD 50-20-01

50-20-01 CONTINENTAL: Applies to All Model C145 Engines, Serially Numbered 3000 to 5031 Inclusive, Except: Nos. 3612, 4650, 4652, 4654, 4671, 4676, 4679, 4683, 4690, 4710, 4855, 4889, 4904, 4996, 4997, 5002 Through 5021, 5023 Through 5029. Compliance required by June 1, 1950, and each 25-hour period of operation thereafter. To minimize possible engine operation difficulty due to crankcase and/or cylinder barrel failures, the following inspection procedure should be accomplished as indicated. (1) Visually inspect crankcase for cracks giving special attention to those areas around each cylinder base. This portion of the inspection need not be accomplished or new type crankcases (P/N 530836 and 530837) which are incorporated on all serially numbered engines above No. 4383, and on all engines overhauled by the manufacturer after September 1, 1949. This new type crankcase can be identified by throughbolts (extending through both halves of crankcase) located ahead of the frontcylinder and adjacent to nose oil seal. The old style crankcase (P/N 6642 and 6643) requiring inspection has studs at this location extending through one crankcase half only. (2) Visually inspect cylinder barrels for cracks at the base flange fillet. New flanged-typed cylinder base nuts, P/N 531001 and 531003 have been made available for service operation. This portion of the inspection may be discontinued upon accomplishing one additional 25-hour inspection including a torque check after installation of these new flanged nuts. During installation of new cylinder base nuts, special attention should be given to the removal of paint and burrs from the cylinder flange nut seat and to compliance with the engine manufacturer's torque limits of 500 plus or minus 10 inch-pounds for the 7/16 studs and through bolts, and 420 plus or minus 10 inch-pounds for 3/8 studs. Improperly torqued nuts are a major contributing factor to cylinder barrel, cylinder base studs, and crankcase failures. The engines exempted from this inspection, as indicated above, have had the new flanged nuts installed at the manufacturer's plant. Since small cracks are more easily detectable by oil leaks, it is recommended that each inspection include a run-up with a clean engine. (Continental Motors Corp. Service Bulletin No. M50-2 covers this same subject.) This supersedes AD 50-18-04.