ENGINES
HMM – What procedure would you recommend to eliminate this problem? PT – Following the instructions in the Rolls-Royce 250 operations and maintenance manual (OMM), lubricate the tach drives as instructed and at the proper intervals. If the N1 and N2 tach drives are lubricated as called out in the OMM, the reduced wear and tear will prolong engine life and reduce maintenance costs, as the tach drives cost approximately $6,500 each to replace. HMM – What other inspection items have proven to be a concern? PT – Another lesson learned on the 100-hour inspection is
N1 Female Tach Drive – Photo Courtesy of Premier Turbines
a low torque value on the compressor and turbine mounting stud nuts. The OMM calls for 80 inch pounds and the mechanics tend to forget to add the drag torque value on the nuts. When this is added in, the actual torque value is closer to 110 inch pounds. This ensures the nuts stay tight. The area of concern is where the turbine and gearbox come together. If the nuts holding the turbine in place are not torqued to the proper value, they vibrate loose and wear the mounting pads of the turbine. This necessitates the gearbox cover and exhaust collector to be re-worked back to specifi cation, and is an additional maintenance cost. Just looking at them and saying they look tight isn’t good enough. Another lesson learned is on the 300-hour inspection of
N1 Male Tach Drive – Photo Courtesy of Premier Turbines
the engine fuel nozzle. The nozzle should be removed, cleaned and re-installed during the 300-hour inspection. However, if your aircraft has no airframe fuel fi lter, it is required to be done at the 100-hour inspection. Depending on the quality of the fuel that is being used, this may have to be done more frequently.
M250 Engine Fuel Nozzle – Photo Courtesy of Premier Turbines
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HelicopterMaintenanceMagazine.com December 2014 | January 2015
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