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Thread: Engine and tail shimmy question

  1. #1

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    Engine and tail shimmy question

    I am the proud new owner of a 1993 PA-18
    I have two questions hoping you guys can help with.

    1st: The engine is a 150hp with a2b. It had horrible compression on two cylinders so I bought the stc and have the cylinder kits from Lycoming on my desk to make it 160hp b2b. My question is about cylinder removal. My IA and I are going to do them this weekend, but I have not seen any Lycoming service instructions for removal of one cylinder and then torque and so on... or do you remove 4 cylinders at once and just retorque per service 1029d. Does Lycoming make any suggestions?

    2nd: I have mad tailwheel shimmy on the baby bush tailwheel that was pretty severe. I have gone thru most issues from tailwheel angle to all adjustments. I have not flown it yet with all my adjustments but I am pretty confident I have fixed some of the problems. I have not been able to solve this mystery in the picture....where the rudder connects to the spring... is that factory? It has about a 1/4 of play in that bolt and wondering if that is contributing to any shimmy from the start...not sure because my other cub is not rigged like that.
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  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Never seen 2 eye bolts per side. None is stock. I use 1 per side. Can’t say I dislike what you have, kinda neat looking...hmmmmm


    Sent from my iPhone using SuperCub.Org

  3. #3
    www.SkupTech.com mike mcs repair's Avatar
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    Change all 4 cylinders. Inspect cam BEFORE opening cylinder boxes......


    Sent from my iPhone using SuperCub.Org

  4. #4

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    Good advice !! Thanks Mike

  5. #5
    behindpropellers's Avatar
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    The spring in your hand will not determine tailwheel shimmy. The primary cause is the arch in your spring. If you do a search on it, you will get a bit more detail.

  6. #6

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    Quote Originally Posted by mike mcs repair View Post
    Never seen 2 eye bolts per side. None is stock. I use 1 per side. Can’t say I dislike what you have, kinda neat looking...hmmmmm


    Sent from my iPhone using SuperCub.Org
    A quick easy way to adjust tension- interesting...
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  7. #7

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    Not a fan of baby bushwheel.
    Weight penalty, drag penalty, AOA penalty, pocketbook penalty.
    and prone to shimmy.
    Cub has a very light tail.

  8. #8

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    The Bushwheel is designed for off pavement work. Put a 2:50x2:80x4 wheel and tire on there for pavement work. Bushwheel needs a locking device for pavement ops. Opinion.

    Not opinion: the kingpin needs to be vertical when loaded. You can tell - the interface between castings needs to be parallel to the pavement under load. We use tapered shims, but you can re-arch the springs in a hydraulic press.

  9. #9

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    Quote Originally Posted by bob turner View Post
    The Bushwheel is designed for off pavement work. Put a 2:50x2:80x4 wheel and tire on there for pavement work. Bushwheel needs a locking device for pavement ops. Opinion.

    Not opinion: the kingpin needs to be vertical when loaded. You can tell - the interface between castings needs to be parallel to the pavement under load. We use tapered shims, but you can re-arch the springs in a hydraulic press.
    ^^^ This. One (the only one I can think of) advantage to the Baby Bushwheel on pavement is that it forces one (to avoid as much shimmy as possible) to touch down very straight and very slooowww. With the current work at MRI, putting the -12 with it's BBW down on gravel is not an option for me, so get to practice some real slow landings. I've found that a good, just about edge of the energy/airspeed/vertical speed envelope, can't-do-it-everytime, slow landing pretty much eliminates shimmy, at least enough to take out the holy c**p feeling.
    Back In Alaska
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