Using nylon locking nuts / nylocks once

I seem to remember a note saying you may use nylon locking nuts more than once, is this correct? Difference of opinion with a friend. Cant find the reference at the moment.

Situation is that im attaching the ailerons with all hardware but not torquing the nuts, adjusting, removing with plan to finally install the surfaces after wing mounting. Can those same nuts be reused, and if so how many times.

Most A&P's I know use the standard that if the nut cannot be turned by your bare hand, it's OK.

Tony Bingelis and others have suggested that you can re-use 'em as long as they have holding ability. Personally, I wouldn't re-use them on anything that moves (like the hinges for ailerons)...

I bought bags of them as OSH, hundreds of 'em. I use them once and
toss. Why worry about it? Singly they are so cheap and by the gross
not that expensive. I reuse the metal locknuts in the high temperature
areas several times.

Another trick for temporary assembly is to buy none-locking hardware-store nuts, and spray paint them flourescent orange. Use them in the shop when putting things togetehr, taking them apart, putting together, apart, etc....make sure there are no orange parts left during final assembly!

Or, like Walter suggested, buy a bags of the lock nuts, use them once and throw them away...

the book

says if you can turn them by hand to toss them. i never reuse them however and i wouldnt use hardware store bolts either. any thing can be left behind. at the very least i would (and do ) use a batch of used ones for this. paint them orange and reuse them if you want to seperate them. but dont use plain ones. they may sit in the temporay configuration for a year or more.
when final i apply torque seal and go. no torque seal, it gets a new nut for fianl assy.

It is perfectly acceptable to reuse nylock nuts as long as you cannot install them by hand. The locking mechanism is secondary to the nut being torqued. If you want to use them once and throw them away, that's you choice, but it is certainly not necessary.

Use Nylocks Only Once

I've heard but can't confirm that, "you can use a nyloc nut only once." Is it true? If I've turned a nyloc nut on a bolt all the way, but then half to take it off for whatever reason can I re install it or do I need to us a brand new un-used nyloc for flying?

thanks

Reusing nylock nuts

Nylock nuts are routinely reused. If the insert is damaged in any way discard it. Make sure as you spin the nut on that it can't be turned with your fingers once the threads reach the nylon insert.

For temporary fitting of parts where they need repeated removal for adjustment I prefer to use castle nuts - much quicker to spin on and off.
Just make darn sure you use the specified nut for final assembly. Using torque seal after you have torqued the nut in final assembly is a good way to avoid a mistake.

For final assembly of critical parts (such as tail attach) I prefer to use new nylock nuts, bolts and washers.

jimgreen said:

Nylock nuts are routinely reused. If the insert is damaged in any way discard it. Make sure as you spin the nut on that it can't be turned with your fingers once the threads reach the nylon insert.

Click to expand...

Any doubt, replace the nut. They are cheap (relative to effect if the nut comes loose). If it is a nut you take off for routine maintenance (during annual) consider using a castle nut with cotter pin.

Decrease locking feature with every use

Each time you remove / install you decrease the running torque and the effectiveness of the locking feature. I would recommend 3-4 times then trash them.
Alan Jackson
Boeing Mechanical Engineer

Cheap as chips

As previously stated, the nyloks are pennies. I keep a supply of used for trial fitting and then use a brand new one for final fitting. When it is finally torqued, I put on a dab of torque seal which firstly indicates that I have correctly torqued the nut and also breaks if the nut moves. I have read that they can be re-used a couple of times but I am spending something like $175000 on my -10 so why skimp on something so cheap......

nuts

I know it's obvious but since nobody has mentioned it, I will. Nylock nuts are not to be used forward of the firewall. I will spare you the horror stories of things backing off and falling apart because... I don't have any.
I've only once seen a nylock nut with the insert melted out of it.
The choice is up to the builder whether to reuse a nut or install a new one. Some excellent ideas here and indeed using new nuts for final assembly is a good idea. After the assemble, disassemble, repeat involved with building it's good piece of mind.
Phil

Before we get carried away with how cheap nylok nuts are, let's step back and look at "standard practices." If you want to replace lock nuts every time that's fine and you have every right to do so. But let's not condemn those that reuse them. It is perfectly acceptable to reuse nylok nuts as long as you can't put them on by hand. This has been standard practice for many years, and I don't remember ever reading about an accident caused by one coming off.
If you have your personal limits, no problem. But don't make it sound unsafe to follow standard practice.

Difference between aviation and cheap locknuts

Hi guys,
This is a good time to remind all about the difference between cheap lock nuts and aviation/space lock nuts. Cheap lock nuts just crimp the end of the nut so there is friction when installing the threads; this is fine for your tractor but not for your airplane/spacecraft.
Aviation/space lock nuts hold the nut threads properly engaged with the bolt. This is what causes the friction and prevents them from backing off.
When working on race cars, I have found many metal lock nuts that are of the non aviation type that just create friction but do not hold the threads engaged, and have found a few of these that backed off after a race, even though they passed the turn-with-the hands test.
Just my experience.

Johnny Stick
RV10 wannabe

Gotta jump in on this one. Alan and Mel are both correct in use of ANY locking nut. All properly made fasteners (to SAE/ASTM standards), whether nylon or all-metal lock configuration are typically tested to an application standard that sets limits for first on, first off, and fifth off torque values. This is not a clamping test (thread/strength test), but is rather to determine consistency in the locking element. All metal locks rely on elasticty of the metal to maintain locking ability. Nylocks are typically used in appclications that will see repeated on/off usage and help to minimize thread galling on the mating part. They represent a very small percentage of fasteners used in industry, primarily beause they are more expensive to manufacture. Temperature is another, but smaller consideration.
I know of no standard that tests any of these nuts to more than 5 uses. Further, the test standard does not accout for over-length bolts, where long thread run-down will further degrade the locking element. Don't use more than 3-4 times. If it runs down easily (by hand, for example), don't reuse.
Terry

I'll reuse them a few times. My criteria is once the cadmium plating starts getting scratched up by the use of a wrench I'll toss em. This is to help prevent rust from appearing in the future. Using this method disposes of the nut long before the nylon locking mechanism even starts to get suspect.

Where's the actual spec?

Our EAA chapter had a presentation by our FSDO rep this evening regarding homebuilt certification. One of the items he indicated is that fiber locknuts cannot be reused. I thought I remembered looking this up previously to find the rule "they can be used but only if they can't be tightened by hand" and so I asked him about it.

He indicated the wording on his slide was right out of AC 43.13-1B, Section 4 Paragraph 7-64f:

DO NOT reuse a fiber or nylon locknut

I don't believe he included the rest of the sentence:

, if the nut cannot meet the minimum prevailing torque values (See table 7.2).

Looking at the table provides guidance for large sizes, but not the smaller sizes that are most abundant on our RVs.

Table 7.2:

FINE THREAD SERIES
THREAD SIZE - MINIMUM PREVAILING TORQUE
7/16 - 20 8 inch-pounds
1/2 - 20 10 inch-pounds
9/16 - 18 13 inch-pounds
5/8 -18 18 inch-pounds
3/4 - 16 27 inch-pounds
7/8 - 14 40 inch-pounds
1 - 14 55 inch-pounds
1-1/8 - 12 73 inch-pounds
1-1/4 - 12 94 inch-pounds

COARSE THREAD SERIES
THREAD SIZE - MINIMUM PREVAILING TORQUE
7/16 - 14 8 inch-pounds
1/2 - 13 10 inch-pounds
9/16 - 12 14 inch-pounds
5/8 - 11 20 inch-pounds
3/4 - 10 27 inch-pounds
7/8 - 9 40 inch-pounds
1 - 8 51 inch-pounds
1-1/8 - 8 68 inch-pounds
1-1/4 - 8 88 inch-pounds

You'll notice that nuts less than 7/16 are not listed on the chart. What does that mean? What's the official word?

One interpretation would be: "those smaller sizes have no prevailing torque listed, thus it's impossible to meet it, thus they must not be reused".

Another interpretation would be: "those smaller sizes are not listed, thus there must be no requirement to be met in order to allow reuse".

So does anyone have an official FAA reference? If you google for fiber nut "unable to tighten" "by hand", you get a lot of hits indicating this is the rule of thumb, but not one of them is an official FAA document.

Inquiring minds want to know.

loctite anyone?

Sorry to take the thread on a tangent, however there is a question that I've had about nylocks for a while.

Is there a good reason not to use a small dab of loctite on threads after nylocks are torqued in place? (There are a few varieties, I'm suggesting the type that's not permanent.)

Thanks muchly! - - Tom in Sacramento

.

It's a Little Like Wearing a Belt and Suspenders

Tom:
There's a couple of good reasons I can think of right off the top.
1. Nylon locking nuts, like all-metal locknuts, are made to specific tolerances for prevailing torque (both on and off). While the actual result changes with reuse, it's still covered by a spec. By adding nylok, those on/off values become meaningless it you're trying to run the nut down to a particular torque - that is, you won't get the clamping force you really want in the joint, unless you removed the old locktite before re-applying the nut.
2. If I were looking to buy someone else's homebuilt and I saw locktite on nyloks, I'd really wonder if the builder followed any good practices or just made up his own. For example, did he also solder all of the crimp joints? Did he overtorque fasteners thinking he'd get a "stronger" joint? I'd probably pass on the plane.
Terry, CFI
RV-9A N323TP

Terry,

I don't use any type of thread lock but I do use yellow torque seal on every nut, and yes I also allow it to contact the threads. I also understand the standard practice is not to put it on the threads but to apply it to the nut and the mating surface. I do both but anytime I remove a nut I knock off the torque seal prior to removing.

It serves a couple of purposes for me. First over the lengthy build time it reminds me that the nut has been torqued. It will also tell you if its backing off and yes at least I believe it will help prevent a nut from backing off but that is just a personal opinion.

Pat

Captain Sacto said:

Sorry to take the thread on a tangent, however there is a question that I've had about nylocks for a while.

Is there a good reason not to use a small dab of loctite on threads after nylocks are torqued in place? (There are a few varieties, I'm suggesting the type that's not permanent.)

Thanks muchly! - - Tom in Sacramento

.

Click to expand...

It's not necessary. Locktite is really best for machine screws and bolts that have no nuts or safety wire hole. Fiber, nylon and mechanical lock nuts have that feature just so the nut doesn't wiggle off if the torque loosens up. IMO if you can not run the nut on by hand, then the lock nut is fine. Otherwise replace it. Although, I usually don't reuse them (there cheap).

I personally prefer the mechanical lock nuts.(http://www.aircraftspruce.com/catalog/hapages/MS21042.php), but have both on my RV.

As far as using Torque Seal, I think that's helpful to spot loosened bolts, but good maintenance practices (proper torquing) really makes it unnecessary.