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horizontal axial play on the reduction gear bax prop shaft


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C-130 world, we have an engine which broke down 4 starters and 3 generators, all  where broken similar.

due to this problem, we did an investigation,

  • no debris was found on the magnetic pick-ups.
  • Compressor damage was found on the 5th and 10th rotor where trailing edge blade tip curling was seen ( bent down in the rotation sense)
  • oil filters where not abnormal dirty, but little bit more carbon dust

 B) can the axial horizontal play of the propeller shaft in the RGB cause the problems, the parts, starter and generator, broken down and the compressor damage?

on the METS (mobile engine test stand) we can see that the pump housing is going FWD and BWD when changing the power lever. the largest impact is low-normal speed and vice-versa, GI to FI and vice-versa and pulling to reverse. you can compare it with a drill machine making hole in concrete.


any idea's...

br bob

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This is a new one...

The gear box inner bearing diaphragms/ bearings are obviously moving causing the idler gear and gears for the starter generator to move. That movement in turn causing failures; the compressor may be a separate issue.

If the internal gearbox movement is being transmitted thru the torque shaft to the engine it (for/aft travel) should be stopped at the air inlet housing as it has a "ball" bearing and should prevent the for aft movement prior to the compressor...

Edited by NATOPS1
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Interesting to say the least, but yes, any movement that can be seen I would say is a problem 

and operation should be discontinued. I had an engine come in recently where the starter mounting

nuts were turning loose. There had been a mention (no write up) by the crew of some vibration. When

I checked my records for the zero-time run, I had annotated higher than expected vibration in

the RGB and compressor at 1.2mils. 1000hrs later both were 2.5.



The tip curl on the compressor blades is normal, especially if aircraft has been spending time

in the desert

Edited by pjvr99
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