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Thread: Broken Jackscrew

  1. #41
    KJC's Avatar
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    It won’t be any cheaper next year and it’s really not that hard. If you find someone who knows how to do it, you’ll be done by lunchtime.
    PA-12 N418BS
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  2. #42
    Kodiakmack's Avatar
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    Broken Jackscrew

    Quote Originally Posted by KJC View Post
    It won’t be any cheaper next year and it’s really not that hard. If you find someone who knows how to do it, you’ll be done by lunchtime.
    It won’t be cheaper but I’ll be more flush. I’m a federally employed fire pilot in the lean part of the year facing a government shutdown. I’ll have a local cub guy come have a look if he has time. Was hoping one could tell function/condition sans tail feathers removal.


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  3. #43
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    Quote Originally Posted by Kodiakmack View Post
    I really appreciate that and will make it so. I see you have a zerx for the liner tube. I don’t have this and doubt this liner tube has seen any love for several years minimum. Recommendations on making sure everything in this area is moving?
    Judging by all that you've said, you really ought to remove the entire tail. The front where you have been looking does need attention as has been discussed. You also need to look at the pivot tube which connects the two stabilizers at the tail post. Piper just drills an oil hole which rarely gets lubricated with other than moisture. Rust slowly builds in the tube eventually "freezing" the cross connector tube in place. You don't realize this because the angular motion when you move the trim is very small. Because of this design and the fact the stabilizers are rarely removed for any reason, the connector tube becomes rusted into both the stabilizers and the cross tube in the fuselage. Many have welded a short tube or nut over the oil hole in order to install a zerk fitting for regular greasing. Just be certain the zerk doesn't interfere with the elevator control horn. Squirting oil in the hole may make you feel good, but it does a poor job of completely lubricating the entire movable joint. Thus the rust build up.

    Do not be surprised to find the stabilizers both rusted to the connector tube and the tube rusted to the fuselage. Sometimes when this has not been addressed for years a hacksaw will be required. A liberal use of Kroil may save some grief.
    N1PA
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  4. #44
    Steve Pierce's Avatar
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    Run the trim and see if the rear liner tube rotates or bends the stabilizer. Pretty easy to tell in my experience. If you watch the Annual Inspection videos I did here a few months ago there is a whole section on the tail. The play you have between the yoke and the carry-thru tube just needs shims and lube. Up and down play there can be a loose screw in the yoke or the screw could be loose on the fuselage and just need the nut on the bottom tightened a flat or two. The side to side play comes from the stabs being fit to the liner tubes with paint and stuff in between, it wears and they get sloppy side to side. safety wire in the groove fixes that. Also check your elevator bushings for play. Tension of tail brace wires. One worn thing seems to compound wear on everything else in short order.
    Steve Pierce

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  5. #45
    Steve Pierce's Avatar
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    Quote Originally Posted by KJC View Post
    The inner part of the yoke which is cut for the acme thread just wears out after years of riding on that steel screw.
    The Dakota Cub jack screw uses an Acme thread which is more threads per inch than Piper or Univair. Takes more turns than stock to trim but lasts a lot longer.
    Steve Pierce

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  6. #46
    Kodiakmack's Avatar
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    Thanks Steve. I’ll watch those videos. Your advice as always much appreciated. The play is minimal but I’m all about minimizing even that.


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  7. #47

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    A quick easy check for the rear liner tube being stuck or not moving freely is to pull the 2 bolts that attach the front liner tube to the yoke assembly, when you are shimming them, then move the yoke assembly as far to the top of the travel as you can. You can now grab the front of the stabilizer and try to move it up and down by hand. Watch for the rear of the stabilizer to move and it should move freely. It could be rusted solid, but also could be gummed up and moving harder than normal. If not moving freely you can attempt to free it up with some kroil and exercising it up and down. If you can't free it up, removing the horizontal stabilizers is highly recommended.
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  8. #48
    Kodiakmack's Avatar
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    Today I removed the bolts connecting the trim yoke to the horizontal, oiled the liner tubes both front and back and made sure they both have free movement. At first they were pretty tight but after working them a bit and re-oiling they freed up pretty well. Will install new bolts and shim as advised and she should be good to go back there for some time : )


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  9. #49
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    Broken Jackscrew

    Well we get to take the horizontal off anyways. As we were re-assembling this “weld” broke off. Weld or new part? We will see.


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  10. #50
    mike mcs repair's Avatar
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    Just weld it...

    but be careful of making to much extra penetration on inside of tube you will need to grind off. Not fun grinding.


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  11. #51
    mike mcs repair's Avatar
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    What brand trim pulley is that in picture? Experimental?


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  12. #52
    Kodiakmack's Avatar
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    Good question. As I mentioned this is our first cub type plane so we are learning as we go. I was told a double pulley -18 trim setup was installed at rebuild.
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  13. #53

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    Dakota cub double groove pulley
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.

  14. #54
    Kodiakmack's Avatar
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    You’re the man Mike
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