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Thread: Gearbox Maintenance

  1. #1
    Super Moderator Av8r3400's Avatar
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    Default Gearbox Maintenance

    I've been wanting to change the gear ratio in my gearbox from the 80 hp 2.27:1 to the 100 hp 2.43:1 in order to get a little more crankshaft RPM. Last Sunday I had the opportunity to finally do this.

    I got a gear set from Hal Stockman and a slipper clutch from a parts engine a member of my EAA chapter had, so I proceeded to take the gearbox apart to re-shim it and change the ratio.


    I found a little more than I was expecting...
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  2. #2
    Super Moderator Av8r3400's Avatar
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    Default Re: Gearbox Maintenance

    Photos of my surprise...

    72CE71CE-A5BD-4961-B1EE-5DB85CCF51BC.jpg
    The back of my prop had a "dry check" -- term used by Lonnie Prince, that make me a little concerned. I sent the prop back to Ohio for repair and they tell me it will be fine. It is from the wood core drying along the grain line.


    Then, after getting it all apart I discover this damage to the prop shaft!

    7322F25B-9456-40D0-A69E-BCEF8451CC3C.jpg
    A2A9F34E-E1EB-4887-830D-50C8C692273D.jpg
    C8410877-C9B0-4E97-AEFE-1843EB6AD350.jpg

    Luckily I have the prop shaft from the parts engine. But I am now replacing the bearings and seals as long as I have it this far apart.

    I have not had a prop strike or any other impact or vibration on this engine. All that I can think of is it was from an incident by the previous owner. The paperwork had a GSC prop listed but the plane had an IVO on it when I got it...
    Last edited by Av8r3400; 03-26-2018 at 09:53 AM.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  3. #3
    Senior Member efwd's Avatar
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    Default Re: Gearbox Maintenance

    What kind of Cliff Hanger is that?. what did you find?

    Oh, just needed to wait 1 more min.
    Last edited by efwd; 03-26-2018 at 09:47 AM. Reason: incomplete

  4. #4
    Super Moderator Av8r3400's Avatar
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    Default Re: Gearbox Maintenance

    I needed to add photos from my phone...
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  5. #5
    Senior Member efwd's Avatar
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    Default Re: Gearbox Maintenance

    wow, if you weren't a tinkerer Larry, this could have ended up with you landing off field sometime soon. Glad you found that and that scenario was averted.
    Eddie

  6. #6
    Senior Member Dave S's Avatar
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    Default Re: Gearbox Maintenance

    Larry,

    just out of curiosity, any idea how much time the engine with the damaged shaft had on it; or, if it had the rotax recommended mid time overhaul?
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  7. #7
    Super Moderator Av8r3400's Avatar
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    Default Re: Gearbox Maintenance

    The engine has about 350 TT on it. I was going to do the gearbox re-shim when I was assembling the plane but ran out of time. That was another reason for doing this now, I wanted to get that "mid time maintenance" done.
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
    YouTube Videos

  8. #8
    Senior Member Av8r_Sed's Avatar
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    Default Re: Gearbox Maintenance

    It isn't because of all that extra HP you're carrying around from the Zipper?

    -- Just me being jealous of the stupendous climb rate you get.
    -- Paul S
    Model III SN910
    582 IVO Med

  9. #9
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    Default Re: Gearbox Maintenance

    Quote Originally Posted by Av8r_Sed View Post
    It isn't because of all that extra HP you're carrying around from the Zipper?

    -- Just me being jealous of the stupendous climb rate you get.
    How about that huge prop as well?? Maybe I'm just being jealous as well. :-) Maybe it doesn't put any more pressure on the gearbox than a heavy 3 blade Warp drive??? Hope you get it sorted out and back in the air soon. JImChuk

  10. #10
    Super Moderator Av8r3400's Avatar
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    Default Re: Gearbox Maintenance

    I was worried about that during the build so I did the MOI test. The whole hang the prop from a string and swing it back and forth, deal.

    My calculations showed something like 4900 cubic meters per lunar rotation or what ever the units are. 6000 is allowable.

    Now the 400hp, plus nitrous mega-zipper 912 has nothing to do with it...
    Av8r3400
    Kitfox Model IV
    The Mangy Fox
    912UL 105hp Zipper
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