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Pre-rotator inspection

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  • Pre-rotator inspection

    The RAF recommended inspection period is 200 hours for the pre-rotator clutch assembly and to replace all three bearings. Since this had never been logged as ever being done on my new 650 hour purchase I inspected mine and am very glad I did. First, everything was "stuck" due to years and hours of neglect. The first photo is the starting reference point. Note the safety wired spring to keep any pieces from flying into your prop if broken. You can also see the internal snap ring I had begun removal by mistake. I could find no help with this effort, which is why I am publishing here. I am not (yet) an RAF expert, and your comments and criticisms are welcome.

    The front clutch plate, which is attached to the flexible shaft with a castle nut is easy. Be sure to catch that 1/4" key. Then the real fun begins! In order press out the pulley from its shaft, I considered leaving the yoke in place, but was worried about scoring it or otherwise damaging the mechanism. So I removed the yoke bolt and the bolt securing the clutch cable end and the tension adjust turnbuckle. Then removed the flexible cable connection. The next thing is to remove the flexible cable. With everything removed, you can use a socket to press the pulley from the shaft. At this point you will have the "empty housing" image where you can see where the large bearing rides on the housing exterior. This is the bearing that spins all the time with your engine. Mine was impossible to spin as removed, but did loosen up when cleaned. No matter, it is going to be replaced. The smaller two bearings only spin when actually pre-rotating. However one of mine has lost its shield and was no longer lubricated except for the excess inner shaft grease that had migrated downwards. Thank you gyro gods!

    Now look at the top and flip sides of the pulley. The "inside" view clearly shows how the larger bearing is nestled in a cup. The "clutch side" shows the three clutch facings, made from Cessna brake linings, and three holes goobered with RTV. If you remove the RTV, then you can see the large bearing outer race and this is how you press that old bearing out as recommended every 200 hours in service. What is not clear is that the brake linings are recessed into the surface of the pulley! This means that you can't measure its thickness to determine wear life. Not a problem. If you can still see the notched "wear pad indicators" than means the rivet heads are not protruding and there is life yet left in those pads.

    Replacing all three bearings with US quality is about $65 - that's just an additional 32 cents per flight hour if replaced per the RAF 200 hour suggestion.

    >>> Now my biggest question is where to find the < 0.120" pull rivets to reinstall that pad! Are these metric rivets? I suppose I could drill out the pulley holes with a #30 drill and install standard 1/8" rivets, but I'd rather get 'er done the RAF way! Anybody help me on this?
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    Last edited by dunc; 01-14-2018, 08:43 AM.
    @ 6450' MSL in W. Colo.

  • #2
    Could you post a picture of the brake rivet.

    Is is the brass, copper or something else.
    PRA member 41204
    PRA Chapter 16


    • #3
      My rivets were aluminum pull type rivets with steel centers. I have not found an authoritative source of what these should be, but will certainly add to this thread. I am also not sure abut whether any of my rivet pullers will do the job. The pads are indeed 66-109 but you can not use the 1/8" brass rivets normally supplied with them without drilling the pulley. Stay tuned!
      @ 6450' MSL in W. Colo.