47-12-02: Center Main Bearings

47-12-02 DOUGLAS: (Was Mandatory Note 15 of AD-762-7.) Applies Only to DC-4 and C-54 Series Airplanes Equipped With Pratt & Whitney R-2000-11 Engines. \n\n\tTo be accomplished not later than July 15, 1947. \n\n\tA considerable number of center main bearing failures have occurred in the R-2000-11 engine. These failures include roller bearing P/N 24966 and plain bearing P/N 97387 and 97387B. \n\n\tTo remedy this unsatisfactory condition as soon as possible, the following shall be accomplished: \n\n\tRemove from service at the first opportunity, but in no case later than July 15, 1947, all plain type center main bearings of the above part numbers. Install either the superinspected roller bearing (same part number as above) or incorporate the 2SD13-G or equivalent type main components of the power section crankcase, details of which can be obtained from Pratt & Whitney instructions dated January 15, 1947 and entitled "Power Section Service Fix for R-2000-7 and R-2000-11 Engines". Superinspected roller bearings may be procured through Pratt & Whitney or bearings in stock may become eligible if they are disassembled, inspected, and the inner race magnafluxed. \n\n\tIn cases where operating specifications do not so provide, main oil screen (on right side of rear accessory housing) checks will be accomplished at each routine inspection or at least at every 75 hours of operation to detect failure of bearing. This precautionary inspection must be conducted immediately and also after change to the superinspected roller bearing. However, this precautionary inspection is waived after complete modification has been accomplished to the 2SD13-G or equivalent type components in view of the greatly improved reliability and durability which these components have demonstrated in comparable service.