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Exhaust springs 912 ULS

in 912 / 914 Technical Questions 10 years ago
At a 100 hr. inspection I found 4 (2 broken 2 missing) exhaust springs. These I understand are 66mm. First question can I use a 63 or 67 MM spring? Would some of the advertised stainless steel springs better and longer lasting. Does anybody have any suggestions to prevent this from happening springs were coated with RTV. Any suggestions for a long term fix?
Mike

  • Re: Exhaust springs 912 ULS

    by » 10 years ago

    Hi Michael,

    Make sure the springs have the proper tension. An easy gauge is to see about a fingernail width space between the coils. Make sure you have enough RTV on the springs. A little pencil width bead of RTV isn't enough. Make the RTV bead on the outside of the spring about 3/8" wide and about 1/4"thick and work it in between the coils of the spring. This gives the RTV some body and strength. Do not fill the springs full in the middle. This causes heat retention and early spring failure. Make sure you safety wire the spring in place. Here is an example picture.


    Exhaustspring.jpg (You do not have access to download this file.)

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Exhaust springs 912 ULS

    by » 10 years ago

    Thanks Roger...as always good advice I have some springs on order.
    Mike
      
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  • Re: Exhaust springs 912 ULS

    by » 10 years ago

    Roger,
    Just as an aside, the springs broke right at the point where the hook bends at the 1st coil...looked like fatigue to me. How will the RTV help to prevent breaking there?
    Mike
      
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  • Re: Exhaust springs 912 ULS

    by » 10 years ago

    What usually kills springs is excessive heat and or excessive vibration. If you have them over stretched that kills them too. Get rid of these and springs can last a long time. The RTV helps dampen the vibration and pulsation from the exhaust.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Exhaust springs 912 ULS

    by » 10 years ago

    Roger,
    Just received from CPS/Aircraft Spruce the new after market stainless steel exhaust springs part # 08-07632. They look great and I am sure will be much better than the original Rotax issue. I have replaced all 8 and then coated them as you suggested with the red RTV...hated to do that since they were all shiny and new!
    Mike
      
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