51-12-01 WRIGHT: Applies to All Models C9GB, C9GC, C9HD and Military R-1820 Series Engines.
Compliance required as soon as possible, but not later than April 1, 1952.
To preclude piston pin failures, piston pins P/N's 68827, 117691, and 131061, which have not been carburized, must be replaced at each engine overhaul. Piston pins P/N's 117691 and 131061 retain the same part number when carburized, but may be identified by the symbol "C" on the recessed end of the pin. Piston pins P/N 68827 were never carburized and therefore should not be reused. It is suggested that orders for carburized piston pins be placed well in advance of required delivery date.
(Wright Service Bulletin No. C9-156A covers this same subject.)