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Spinning and unremoveable nylock. Any tips?

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SamP

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Nov 4, 2016
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28
Hello All,
I've got an An3 bolt with an nylock nut that I was attempting to tighten on some metal parts. For some reason, I couldn't achieve the appropriate tension. When I tried to remove, I noticed the nut would spin, but not descend down the thread. Yes, I held the bolt stationary.

I'm trying to understand why this is happening, and more important, how to remove the nut without damage to the rest of the plane. Did i bottom out on the thread?That would explain why I couldn't tighten, but why is it not letting me back out?

Thanks
 

SamP

Active Member
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Nov 4, 2016
Messages
28
Thanks, I'll try cocking the nut while trying to rotate it out. Hoping to not have to get the grinder out since it's in a tight location
 

BoKu

Pundit
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The torque specs on AN3 are pretty modest. You might consider using a torque wrench to calibrate your "mechanic's feel" for how much you can tighten them. Of course, using a torque wrench on every would be the best practice...

I've also had them strip like that when I chose a too-long bolt and had the nut come up against the unthreaded shank before clamping against the part. So maybe double-check the length before you just throw another bolt into the hole.
 

Dan Thomas

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Sep 17, 2008
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5,650
One can sometimes drill into a flat on the nut to weaken it, then split it with sidecutters or something. You might have to hold it still with visegrips so you can drill it. Use as big a drill as you can fit---an AN3 nut might accommodate a 7/32" bit---and drill right through into the bolt to get as much of the nut removed as possible.
 

wktaylor

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Its probable You 'bottomed' the nut on the bolt threads [in the thread-runout to the shank area]... then over-torqued/stripped threads... nut and/or bolt at that location.

However You remove the nut from the bolt threads [several ideas, noted]... both the bolt and nut are unserviceable.
WARNING: be careful about pulling the damaged-bolt out of the hole. Damaged threads [stripped, chipped, splintered, distorted, etc] WILL score the hole on the way-out!!!! The automotive/household 'trick' of turning-out a tight bolt/screw using what-ever-is-left-of-the-threads [as 'thrust']… is guaranteed to 'rifle-score [spiral-score] the hole wall'. Scoring of any type destroys the integrity of the hole.

Check bolt length and shorten... or add washers if the thread-runout is showing outside the material stack-up.
CAUTION: A good practice [structural or mechanical] is to install all nuts with a washer against the primary structure.

Also. Verify that the nut threads are a true match to the bolt threads. Thread-miss-matches... or excessive looseness between nut and bolt/screw threads... can lead to 'cross-threading'.

BoKu had an important point... the installation torque on low strength bolts [AN3] per FAA-H-8083-30 AMT General handbook Figure 7-34. Standard torque table (inch-pounds) [for tensile nuts on 125-KSI FTU bolts] is ONLY 20-to-25 INCH-POUNDS!
 
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speedracer

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Feb 4, 2020
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Heat it up with a small propane torch to melt the plastic, then just use vicegrips to pull it off?
 

rv7charlie

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A 'three handed' approach: use a cheap (worthless) chisel or thin screwdriver ground to an edge, and wedge it under the lip of the nut. A pair of 'dykes' (diagonal cutters) can work, as well; sometimes better than the chisel. Hold the nut, and turn the bolt 'out', maintaining pressure with the wedge device to force the joint open. If you're lucky, the damage is to the bolt, and once the nut's threads get to good threads on the bolt, it'll bite & turn the rest of the way off without the wedge. Even if it's completely stripped, it will eventually back off if wedge pressure is maintained as the bolt is unscrewed.

The '3rd hand' can be a pair of vise grips on the nut, in some cases. Clamp them on the nut, and rotate until the handle contacts nearby structure.

And the others are right; if you've never torqued a -3 nut using a torque wrench, you'll scare yourself on how untorqued it seems after torquing to spec.

Charlie
 

gtae07

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Are you sure you didn't twist the bolt apart? I've snapped the heads off AN3s before by accidentally overtorquing them...
 

Dan Thomas

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Sep 17, 2008
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The usual stripping rips the threads off the bolt and mashes them over where they meet the stripped section so that the nut is trapped on the bolt and ain't gonna come off without a fight. That fight can damage the structure. I prefer to carefully surgically remove that nut. Takes time to do that but a lot less time than having to repair damaged structure.

Depending on access, drilling the nut can weaken it so it can be split off. Or the bolt's threaded end can be cut off through the nylock section to remove the remaining threaded section so the nut can fall off. Or a die grinder and carbide burr can mill off enough nut to remove it. If the bolt head is accessible you can drill though the center of it until the head pops off and the bolt is pulled out at the nut end. Sometimes I have very carefully taken the head off with a die grinder and carbide burr or sanding disc.
 

Hot Wings

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That fight can damage the structure. I prefer to carefully surgically remove that nut.
Good advice.
If this was a Chevy truck I'd recommend a chisel and hammer to split the nut.....But any aircraft structure that is held together with a -3 is probably not robust enough to be pounded or pried on.

The Dremel with a cutoff wheel mentioned above would be my preference - if there is room/access. Slice down the bolt centerline and cut the nut in half at the same time. The AN-960 should give plenty of protection to the underlying structure.
 

SamP

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Nov 4, 2016
Messages
28
Thanks for all the tips. I wound up taking the grinder to the head. Behind it was a bracket that could be sacrificed. Fortunately I didn't scuff it up.

I was torquing the nylock to ~42 in pounds, which is what the RV-12 Vans manual says for a AN3 nut with nylon insert (Yes, it seems higher than what other people are saying). I've seen other people mention torquing to ~35 in pounds. Basically adding 10-15 lbs to the base torque mentioned above. Adding the actual drag torque specific to that nylock to the base is the best
 
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SamP

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Nov 4, 2016
Messages
28
Thanks for linking and the healthy discussion. My copy dated 2013 has a different value there. I wonder why they would increase it to what is beyond what people are typically doing and calculating

 

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