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Product Improvement Test of Mast

a. c The established time between overhaul (TBO) of the standard 
mast assembly, P/N 204-040-366, was 300 hours due to a history of 
excessive wear of the main mast bearing. Action was taken to modify 
main mast bearings to reduce bearing wear and increase the T BO of the 
mast assembly. The manufacturer modified the mast assembly by 
incorporating hardened steel (M -50) ball bearings in the main mast 
bearing. The modified mast assembly (P/N 204-040-366-7) is the test 
item for this report. This test item was operated for a total of 1239 
flight hours during the conduct of the YUH- ID logistical evaluation test.

The test item was removed at the completion of 1239 hours and the mast 
bearing was analytically inspected during November and December of 
1904. Several discrepancies were found during this inspection; however, 
the mast bearing was serviceable. 
b. For the purpose of continuity, the following are the results 
of the November / December 1964 inspection of the mast bearing (flight 
time 1239 hours): 
(l) The first ball to the right of the ' 'S/N 10" etched on the 
cage had a roughness when the ball was pressed away from the center 
of the cage and rotated. The same condition existed in the ball 80 
degrees opposite. 
(2) The first, seventh, eighth, and ninth balls to the left 
of the 'S/ N 10" etched on the cage had one-to-several discoloration 
marks. These marks represented minor corrosion; however. no pitting 
or roughness in the area could be determined. The largest of the marks 
measured I / 1 6-inch in diameter.

c. A decision was made to reinstall the test item for further 
testing with a scheduled inspection 50 hours after installation. The 
reinstallation of the test item was accomplished on 13 February 1965.