53-01-01 BELL: Applies to Model 47D1 Helicopters, Serial Numbers 477 to 625, Inclusive.
Compliance required at next 300-hour teardown inspection but not later than February 28, 1953.
In order to improve the method of mounting the tail rotor gearbox assembly and to avoid the possibility of distorting the S10R bearing when tightening the existing clamp, install sleeve P/N 47-640-058-1 on assembly 47-640-044-3. Clamping ring P/N 47-644-197-1 and clamp P/N 47-640-046-1 are replaced by the riveted sleeve.
(Mandatory Service Bulletin No. 90, Revision B, dated December 8, 1952, covers this same subject. Service Bulletin No. 90, Revision A, also covers the same subject but Revision B simplifies the installation and completes the parts called out.)