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Thread: "Grating" or "scratchy" throttle feel from metal on pitted metal when using the throttle

  1. #1

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    "Grating" or "scratchy" throttle feel from metal on pitted metal when using the throttle

    I've had to divert from my original "fixer upper" list on my PA-12 to attend to some unexpected and bigger issues and am now very fortunately back to my list of "things to make the user experience better"!!

    The aircraft has the original side trims and as there's been some surface corrosion and pitting of the frame, plus possible dents and bends in the side trims, the throttle lever is now basically dragging, metal to metal, against the side trim lip on one side and the frame horizontal member on the other at certain points when moving the throttle open and shut, giving an unpleasant scratchy and grating feel and not the smooth action I'd prefer and expect from the bottom mounted pivot.

    Before I dive in and cut more out of the side trim (which I'm loathe to do) I'm hoping other people have found answers to this problem I could borrow I've thought about using strips of thin but stiff mylar or similar on the surfaces the lever is sliding against, so it's sliding on smooth, non metallic and uniform surfaces to take away the grittiness, but I'm completely open to any ideas!!

    Thank you!!

    Philly

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    round the edges of lever with a file?

  3. #3
    Gordon Misch's Avatar
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    There is steel guide material on both sides of the throttle lever, underneath the aluminum trim. The inboard piece is thin and easily deformable. Take the trim off and examine this before midifying the trim.
    Gordon

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  4. #4

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    Quote Originally Posted by Gordon Misch View Post
    There is steel guide material on both sides of the throttle lever, underneath the aluminum trim. The inboard piece is thin and easily deformable. Take the trim off and examine this before midifying the trim.
    Yes, Iíve seen this, but itís such a small gap between the side trim and frame and the guide steel looks so low down, rickety and wide gap that Iíd pretty much discounted using it, without widening the top throttle gap. Does everybody primarily set up the throttle movement down here?


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  5. #5

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    Quote Originally Posted by mike mcs repair View Post
    round the edges of lever with a file?
    I am considering putting some kind of finish around the lever, so IT becomes the non metallic piece, filing some rounds would definitely add to this


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  6. #6
    skywagon8a's Avatar
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    Perhaps place a piece of "heat shrink" tubing over the throttle arm? This will give a non metallic bearing surface. Has the throttle arm become twisted over time thereby causing the rubbing?
    N1PA

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    Try a little squirt of silicone or LPS 1.

  8. #8
    55-PA18A's Avatar
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    Are you sure it's the lever and not the cable?

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    Quote Originally Posted by stewartb View Post
    Try a little squirt of silicone or LPS 1.
    Quote Originally Posted by skywagon8a View Post
    Perhaps place a piece of "heat shrink" tubing over the throttle arm? This will give a non metallic bearing surface. Has the throttle arm become twisted over time thereby causing the rubbing?
    Great idea! However I put some fairly strong electrical tape over the side trim surface, hoping for a similar effect and on looking at this yesterday, a slit had been cut down the middle of the tape by the lever and side trim surfaces rubbing together and acting like scissors

  10. #10

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    Quote Originally Posted by stewartb View Post
    Try a little squirt of silicone or LPS 1.
    Great idea, I'll give it a go

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    Quote Originally Posted by 55-PA18A View Post
    Are you sure it's the lever and not the cable?
    Yes, definitely not the cable - if I remove the side trim top screws and increase the gap, the throttle lever moves full movement REALLY smoothly

  12. #12

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    Quote Originally Posted by skywagon8a View Post
    Perhaps place a piece of "heat shrink" tubing over the throttle arm? This will give a non metallic bearing surface. Has the throttle arm become twisted over time thereby causing the rubbing?
    I checked the lever today and it's pretty much in line with the slot, it's just that the slot is narrow and can catch the lever.

    I ground ran the engine today, having applied the Piper Service Bulletin to the Fuel Selector (MASSIVE difference!!!), having widened the slot by flexing the trim panel on Sunday and the throttle action was much easier, although still with the occasional scratchy dragging, which isn't the smooth as greased silk user experience I'm looking for (which I'm now getting from the fuel selector

  13. #13
    hotrod180's Avatar
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    Quote Originally Posted by Philly5G View Post
    Yes, definitely not the cable - if I remove the side trim top screws and increase the gap, the throttle lever moves full movement REALLY smoothly
    How about adding some spacers behind the trim / screws,
    to widen that gap without shaving anything off the trim.
    Cessna Skywagon-- accept no substitute!
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  14. #14

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    Quote Originally Posted by hotrod180 View Post
    How about adding some spacers behind the trim / screws,
    to widen that gap without shaving anything off the trim.
    Great idea, but unfortunately the top screws are pointing down and next to the side windows, so Iíd need to elongate the fixing holes to move the side panels out.

    Whatís the usual throttle gap width? and do most people use the throttle guide rails down towards the pivot point?


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  15. #15
    aktango58's Avatar
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    push the throttle handle away from the trim, sounds like it got bent slightly. bend it back
    I don't know where you've been me lad, but I see you won first Prize!
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  16. #16

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    Quote Originally Posted by aktango58 View Post
    push the throttle handle away from the trim, sounds like it got bent slightly. bend it back
    Thatís what I did on Sunday, along with flexing the trim to get as much gap as possible. The lever easily flexes laterally and touches the trim/frame, hence my questions on using the lower guide and lining the edges of the trim and frame, as without these, the gap would need to be REALLY wide to allow the lever flex NOT to touch the sides


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  17. #17
    www.SkupTech.com mike mcs repair's Avatar
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    Remove trim. Tighten nut at bottom of lever. Re cotter key


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  18. #18
    Stew's Avatar
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    Friction washers

    Just a thought......

    The PA18 throttle has a pair of friction washers (PN 81342-20, "Vellumoid" Washer) that sit either side of the base of the throttle lever.

    When you torque up the castle nut (A310-5)/throttle friction lug as necessary, the lever is held pretty firmly in the lateral plane and smoothly slides accurately up and down the channel without undue fouling. The friction washers stop metal to metal contact between the throttle lever faces and the bracket face/friction lug.

    Your friction washers may be worn/missing or worse still, the friction lug may have been "lost".

    Univair list the friction washers and lugs, the image of the friction washer looks like a metal washer when it is actually fibre/fiber.

    https://www.univair.com/piper/piper-j-3/view-all/u81342-020-piper-friction-washer/


    https://www.univair.com/piper/piper-...-friction-lug/
    Last edited by Stew; 10-18-2018 at 05:42 AM.
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  19. #19

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    Quote Originally Posted by Stew View Post
    Just a thought......

    The PA18 throttle has a pair of friction washers (PN 81342-20, "Vellumoid" Washer) that sit either side of the base of the throttle lever.

    When you torque up the castle nut (A310-5)/throttle friction lug as necessary, the lever is held pretty firmly in the lateral plane and smoothly slides accurately up and down the channel without undue fouling. The friction washers stop metal to metal contact between the throttle lever faces and the bracket face/friction lug.

    Your friction washers may be worn/missing or worse still, the friction lug may have been "lost".

    Univair list the friction washers and lugs, the image of the friction washer looks like a metal washer when it is actually fibre/fiber.

    https://www.univair.com/piper/piper-j-3/view-all/u81342-020-piper-friction-washer/


    https://www.univair.com/piper/piper-...-friction-lug/
    Thanks for this Stew. Iíll definitely check out the washers!!

    The channel definitely needs some work though and Iíll be looking at other Cubs and seeing how wide their channels are, in fact it would be great if I could get feedback via the forum on typically the width of the throttle channels in use?


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  20. #20
    Stew's Avatar
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    Throttle Channel

    I was at the hanger yesterday and got out the relevant bits and pieces to get a few images for you.

    When I had it assembled and torqued up so that the friction was about right, there is virtually no lateral movement in the throttle. The channel will need a bit of "dressing" as will the throttle itself but the short answer is that the throttle will run in a narrow channel without fouling the sides if using the proper components and correctly torqued.

    Have to say that it is not unknown for people to hang on like grim death when they are "exploring the envelope" and the throttle lever can get bent and distorted.

    Kind regards

    Stew
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    Last edited by Stew; 10-31-2018 at 05:29 AM.
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  21. #21

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    Quote Originally Posted by Stew View Post
    I was at the hanger yesterday and got out the relevant bits and pieces to get a few images for you.

    When I had it assembled and torqued up so that the friction was about right, there is virtually no lateral movement in the throttle. The channel will need a bit of "dressing" as will the throttle itself but the short answer is that the throttle will run in a narrow channel without fouling the sides if using the proper components and correctly torqued.

    Have to say that it is not unknown for people to hang on like grim death when they are "exploring the envelope" and the throttle lever can get bent and distorted.

    Kind regards

    Stew
    WOW!!!! Thanks Stew and first thing(s) to say-your workshop, Cub and workmanship look ABSOLUTELY BEAUTIFUL!!!! I'm looking forward to flying down and visiting you!!!

    THANK YOU for posting the pics and your throttle lever looks just like mine!! The slot it's sliding in looks a bit wider than the slot I've managed to create in the PA-12, but great news-when I test flew on Monday, the changes I've made obviously worked as the throttle action was MUCH smoother!!! Not perfect YET but well on the way

    I'm ordering some parts from Univair this week and I'll be adding the friction washings to the order

    Thanks again Stew

  22. #22
    www.SkupTech.com mike mcs repair's Avatar
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  23. #23
    www.SkupTech.com mike mcs repair's Avatar
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    actually the -12 is slightly different arm and channel(s) wise.... 2 channels it could be rubbing on...

  24. #24

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    Quote Originally Posted by mike mcs repair View Post
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    Thanks Mike!! I guess my aircraft is somewhere between that one and Stew's

  25. #25
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Philly5G View Post
    Thanks Mike!! I guess my aircraft is somewhere between that one and Stew's
    that was some of the "before" pictures as I started a rebuild

    here's more of the "done" and during that project photo albums

    https://goo.gl/photos/GRXyyNHPoUik2V44A

    https://goo.gl/photos/PuiR5ha2aBDbkUBS8


    PS shameless plug, someone send me a rebuild job!! my shops been empty since mid June basically....

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