Van's Air Force
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How many times can you re-use MS21042 nuts?
- Thread starter bertschb
- Start date
I believe as long as the running drag is more than what your fingers can overcome, they are still good.. but I don’t remember where I read that.. as for changing the bolts too, when you scrape off the Cad plating, the bolt can rust.. that’s why nylon lock nuts are better as long as you aren’t in a high heat environment. Funny how even Lycoming specifies and uses nylock nuts for the fuel injection line clamps on top of the engine..
Toobuilder
Well Known Member
In the AF I was taught that if the nut is 1/4 or smaller and you can turn it through the self locking portion with fingers, then its junk. Otherwise, keep using it. Larger nuts have a minimum prevailing torque specification to determine if it still can be used.
I see table 7-2 in the ac43.13, which is referenced in 7-64f for nylon or fiber, the section before on metal (e) does not reference the table, but does say the locking action depends on the resiliency of the metal. I would infer the table would apply here as well, but that’s just my take.
Agreed. I just deleted my earlier post which was "as I recall" and not definitive.
The definitive answer is in AC43-13B, section 7-122 (c): Self-locking nuts are used in applications where they will not be removed often. Repeated removal and installation will cause the self-locking nut to lose its locking feature. They should be replaced when they are no longer capable of maintaining the minimum prevailing torque. (See table 7-2.)
Table 7-2 is in the AC, ref. https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf
I wonder how may people, industry wide, actually check the torque of their used lock nuts each time it gets reused.
Although it does not say Table 7-2 applies to plate nuts, i believe it does since Table 7-2 is located in Section 7-64 which addresses all self-locking nuts (and Table 7-2 does not specifically call out nylon lock nuts.)
Surely someone has tested nylon lock nuts and platenuts to get an average number of uses before they no long meet the torque criteria.
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cvairwerks
Well Known Member
Our company standards limits on most locknuts are a maximum use of 5 times. We have some, in various areas of high loads and stresses, that are single use only. Once they come off, they get tossed into the scrap boxes.
HFS
Well Known Member
The problem with that table, of course, is that it starts at 7/16 - 20 and goes up from there - so for the most part is not applicable. I have done testing on "prevailing" torque on fasteners down to 8-32 size, and it doesn't take many cycles for them to lose a significant portion of their retention capacity. And, there is a great deal of difference in how strong our thumbs are between when we were 25 (anybody remember what they were doing then?) and now (75), so even that "spec" is quite variable.
If anybody has any interest in the actual numbers vs sample size vs no. of cycles, I can dig some of that info out and offer it ...
HFS
As a generalization - if you would torque to the high end of the spec; and, subtract the empirically derived prevailing torque, you would still be above the lower torque limit, for first time use.
Would love to see the data.
Over the past three or four decades, I have tossed more MS21042 nuts because I did not like they way they look than for ones that had lost resistance to turning and still looked good. For the all metal lock nuts, I will reuse them as long as they look good and have resistance when threading them on to a bolt.
David Paule
Well Known Member
Here are some recommended torques for screws and for the locking elements:
These were taken from MSFC-STD-486B, Nasa's "Standard, Threaded Fasteners, Torque Limits For."
Dave
These were taken from MSFC-STD-486B, Nasa's "Standard, Threaded Fasteners, Torque Limits For."
Dave
OK...what about nut plates? 
When I have a fastener that backs out on its own from a platenut, I replace the platenut with a new one. In other words, when the fastener will not stay tight and will get loose on it own, I will remove and replace the platenut with new.OK...what about nut plates?
I was being sorta facetious, that is, I don't think anybody checks the running torque on fasteners when they are reinstalling into a platenut. Maybe, I don't know. Never had one that didn't grip well enough that I drilled it out and replaced it, but that's just by "feel".
HFS
Well Known Member
FredMagare
Well Known Member
For ANY self-locking nut, if you can run it on with your fingers past the locking feature - REPLACE IT! If it binds up while running it on - it's still good.... If you have reservations - just replace it. Peace of mind is worth every dollar!
HFS
Well Known Member
I deleted my post of my test on AN365- ... NyLok nuts when I noticed variables between what I had done (2015), and the tests done on nuts still sitting in my inventory (up to 9 years later) yesterday.
Nylon ages over time, and the results of todays tests show significant increases in the prevailing torque for those nuts tested. Also to be considered, over the long term, is what "set" is taken by the nylon in its installed condition, possibly compromising its reuse? I'm going to get a fresh batch of stop nuts from AC Spruce and have a "do over" on my initial findings.
Also, will start long time testing, of changes over time of installed nuts (all south of FW - so elevated heat not an issue) of their retention values when compared with tested the first time.
Stay tuned ...
YMMV - mine did, hence the "do over"!
HFS
Nylon ages over time, and the results of todays tests show significant increases in the prevailing torque for those nuts tested. Also to be considered, over the long term, is what "set" is taken by the nylon in its installed condition, possibly compromising its reuse? I'm going to get a fresh batch of stop nuts from AC Spruce and have a "do over" on my initial findings.
Also, will start long time testing, of changes over time of installed nuts (all south of FW - so elevated heat not an issue) of their retention values when compared with tested the first time.
Stay tuned ...
YMMV - mine did, hence the "do over"!
HFS
Thanks for sharing the results. I saved a copy of them after you posted before they were deleted. I have NOT done a test like this but your findings were pretty much would I would have guessed. Understand that like a lot of things, it is a SAMPLE of one and others could get different results.
AlexPeterson
Well Known Member
There are many nuts FWF in my plane that after 22 years, 1800 hours are still providing way more drag than I can move with my fingers. And some have been off a lot of times. I recall that 10-32 non-fiber nuts need about 15in-lbs, while a new fiber nut takes about 10in-lbs just to turn, resulting in the proper torque being about 25in-lbs. Don't quote me on these numbers...
AlexPeterson
Well Known Member
I'd love to see the log books on this...
cvairwerks
Well Known Member
LOL...No logs on the hardware. Certain installations have notes within the maintenance instructions about one time use fasteners. Even the specific instructions will say " Remove the xxx nuts and discard. These are one time use only."
A lot of the hardware gets changed before reaching the five time limit, if an item is going in and out more than once or twice. Bolts and nuts get damaged, or filled with sealant or something else causes them to not be reusable.
Dugaru
Well Known Member
They should check!
The brackets holding my cowl inlet baffling in place were secured with nutplates. Of course I never paid any attention to them, including during preflights… On one of them (the upper passenger side) literally all the screws backed out over some unknown period time. One day during a run up the bracket fell on top of my alternator! Made a super ugly noise and trashed the bracket, but fortunately no other damage. Interestingly the baffling stayed stuck to the cowling inlet.
I’m not the builder, and had always assumed nutplates were sort of permanent. I had no clue this sort of thing was even possible. The leading theory is that it had simply been installed/reinstalled too many times under previous ownership.
Desert Rat
Well Known Member
Blue loctite maybe, but that red stuff makes the bond semi-permanent. On something like a #8 or #10 screw if you ever want to take it apart again your going to need a heat gun and a broad swear vocabulary for all the stripped screw heads youre going to have to deal with. On something like baffles where you've presumably got easy access, it would be much better to just replace with new nutplates.
This is the most likely explanation, IMO. I think most of us have had to do this, but you have to be very gentle to relieve *just a bit* (unless you want it to be much easier to remove, like this ones on the outermost floor ribs that hold the seat pans in, as per Van's construction manual).
Sam Buchanan
been here awhile
I've never used a tap on a platenut, just a dab of Boelube or toilet wax (works great!) on the screw threads. In 25 years of service on the RV-6 the only time I've replaced a platenut is in the rare aftermath of needing to drill out a screw that got wallowed out due to lack of attention of the service tech.....otherwise the vintage platenuts still have sufficient grip to secure the screw.
For those who discard nyloc nuts after one use, if you will toss those nuts into a can I'll swing by and pick them up.
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I've never used a tap on a platenut, just a dab of Boelube or toilet wax (works great!) on the screw threads. In 25 years of service on the RV-6 the only time I've replaced a platenut is in the rare aftermath of needing to drill out a screw that got wallowed out due to lack of attention of the service tech.....otherwise the vintage platenuts still have sufficient grip to secure the screw.
For those who discard nyloc nuts after one use, if you will toss those nuts into a can I'll swing by and pick them up.
Construction Manual, RV-7/7A, p. 8-5.
Sam Buchanan
been here awhile
I built an RV-6.
Good for you.I built an RV-6.
You can have mineFor those who discard nyloc nuts after one use, if you will toss those nuts into a can I'll swing by and pick them up.
I followed the plans and tightened an AN365-624A nut and later removed it (again, per the plans). It took all my might to remove that nut.That isn't the first time I've had trouble with nyloc nuts getting "stuck" on bolts (not on my airplane build thankfully). I was told this could have been caused by trying to tighten the nut too quickly which heated and expanded the nylon. Since that happened I now tighten and loosen nyloc nuts veeeeery slowly to prevent a reoccurrence. Even with that precaution, this AN365-624A nut "locked up" on me a few days ago on my -14 build (lower gear brace). I'm replacing that nut and the bolt it was attached to since it was probably compromised by the amount of force it took to remove the stupid nut.
