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Thread: Jack Screw movement

  1. #1

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    Default Jack Screw movement

    Hello all. N5773H is finally flying 1 year and 10 days later -- picture to follow. I have always heard that the jack screw should have a 1/4" or so movement in it -- and mine had that before rebuild. My IA on the rebuild said there should be NO movement and tightened it (how?) so that it is completely tight and absolutely no movement. How should it be and how did he tighten it anyway? Thanks.

  2. #2
    Administrator Steve Pierce's Avatar
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    Default Re: Jack Screw movement

    Beth Ann, There should be no play in the jackscrew however it should turn freely. The picture shows my daughter removing the nut that you tighten to take the play out of the jackscew if the play is not worn threads between the jackscrew and the yoke.

    100_3771 (Medium).JPG
    100_3808 (Medium).JPG
    Last edited by Steve Pierce; 06-11-2013 at 11:29 AM.

  3. #3
    Gilbert Pierce's Avatar
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    Default Re: Jack Screw movement

    Quote Originally Posted by clipquito
    Hello all. N5773H is finally flying 1 year and 10 days later -- picture to follow. I have always heard that the jack screw should have a 1/4" or so movement in it -- and mine had that before rebuild. My IA on the rebuild said there should be NO movement and tightened it (how?) so that it is completely tight and absolutely no movement. How should it be and how did he tighten it anyway? Thanks.
    The Drawing CD is supposed to do away with "I have always heard" dogma. See Piper drawing 11825 Tail Installation note 2. Piper used 0.015" clearance max as their desgin criteria. Since you propbably have a new jack screw and yoke I would expect no more then 0.015" clearance between the horizontal stabilizer and the airframe

  4. #4

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    Default Re: Jack Screw movement

    Yowie, STEVE! There HAS TO BE A STORY about the upper rightt longeron!!!

    ...and, how come SHE gets to do that on one that isn't COVERED??? I always have to slither down in there from the baggage compartment, and have to "bridge" on my belly button for 15 minutes (or until I turn purple and have to take a break, which doesn't take NEARLY that long, these last few years???)

    Yeah, what Gilbert said. Before you "commit", have somebody on the OTHER SIDE "wiggle the stab up and down" while you squint in there from the opposite side with your bright light, and spot where the "loososity" actually is. If it's where the jack screw itself passes through the airframe, up top, you simply need to "adjust the clearance" back (1/4" is WAYYYY TOO MUCH slop) with a spacer (washer, or shims) to the obligatory .015" Max (or less, IF the trim doesn't "bind" when you operate the trim handle). If it is the aluminum casting flopping ON THE THREADS of the jackscrew, well...you missed you're Golden Opportunity to do this like Steve's Daughter is in the pic. NOW somebody'll have to flop around in their on their belly (like ME, most times!). [hint, if this is the case...it is 300%!!! easier to do this task if -adjust shims- you make the fuselage LEVEL (or even a few degrees "up" at the tail) than to attempt it with the tailwheel on the ground!!! The blood doesn't RUN to your head.]

    There is no "published max" for end play at this location for "in-service Inspection", and there IS some question about whether Piper intended the Production Drawing to be the "final in-service limit" (I think NOT, I think that was "off the Production Line" limits)...but I like to "re-shim them" if the stabs more more than 1/8" (.125") travel due to the jackscrew upper spacers having worn, and renew parts if more than "just noticeable play" shows where the yoke winds on the jack screw.

  5. #5

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    Default Re: Jack Screw movement

    Thanks guys for the good info. Looks like my IA followed the drawing after all.

  6. #6
    pa20's Avatar
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    Default Re: Jack Screw movement

    I am currently replacing my trim cable, and while there am intent on addressing the play in the trim system. I currently have much more than the .015 movement (stab to fuselage), but it is clear that most of that is jackscrew movement, i.e. washer wear. As I will be down in the tail anyway, it seems prudent to replace the washers. When searching UnivAir's site, the 81342-005 washer is clearly labeled as a "elevator trim washer". However 80122-041 washer is simply labeled as a "Piper Washer". Is this the correct P/N for this application? There is a slight differential on the O/D of the washers also, however the I/D appears to be the same (3/8").
    I can call UnivAir, but am holding off until I can determine if my yoke and jackscrew assy is worn. There appears to be not much vertical movement of the yoke on the jackscrew, but there is definitely "wobble" if the jackscrew is held and vertical pressure is applied from the horns. If there is a need to replace the yoke & jackscrew, I plan on going with the Dakota Cub STC. Does anyone know if Dakota Cub carry's the washers, so as to avoid 2 separate orders?
    Mark Ohlau
    PA-20 N7744K 2020 Donation Paid

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    Administrator Steve Pierce's Avatar
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    Default Re: Jack Screw movement

    Mark, I run into this quite often. Remove the cotter key on the castellated nut and snug it just enough to take out the slop. I believe it wears the tube welded into the fuselage just a bit.

    Also Dakota does have all the associated parts however I have never found washers that could not be reused.

  8. #8
    pa20's Avatar
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    Default Re: Jack Screw movement

    I have decided to replace the entire assembly while I am doing the cable. The jackscrew can be tightened, but there is (wobble for lack of a better term) of the yoke on the jackscrew. I ordered the Dakota Cub assy this morning. While I have searched the threads, I have not been able to answer my questions about the exact process for removing it.
    Is it possible to disassemble the unit and remove it without cutting the fabric ahead of the dorsal fin?
    Also, to allow the installation of the cable on the front pulley (the one the crank mounts on) , I need to be able to get the shaft out. It appears that I will need to make a small hole in the fabric to get it out. Is this correct?
    Thanks!
    Mark Ohlau
    PA-20 N7744K 2020 Donation Paid

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    Administrator Steve Pierce's Avatar
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    Default Re: Jack Screw movement

    Mark, Take the nut off of the jack screw and you can unscrew the jack screw from the yoke and it will all come out the bottom. A Cub is not as easy as it all goes out the top and you must cut a hole in your fabric. As far as the front trim handle shaft I have been able to push it far enough up that it allows me to get the shaft out of the pulley to change the cable. Do you have the new cable yet. I will post some part numbers and particulars later when I have a bit more time.

  10. #10
    pa20's Avatar
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    Default Re: Jack Screw movement

    Thanks Steve!
    I do have the new cable having obtained it from Tony Cesare, Millinocket Me. 207-723-9491, whom you recommended. I have the Dakota Cubs assy on order.
    It seemed that it was possible to get the assy out by unscrewing the jackscrew, but I wanted to ask. It seems that I am a master at making a small project a big one!
    Last edited by pa20; 03-06-2013 at 03:52 PM.
    Mark Ohlau
    PA-20 N7744K 2020 Donation Paid

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