Standards for lock nuts

jim_geo · Post by **jim_geo** » Thu Aug 10, 2006 7:30 pm

I would have looked this up in my aircraft hardware standards book but haven't been able to find it since returning from Oshkosh. What is the standard for self locking nuts? Are you supposed to have threads beyond the nut or is flush with the lock end of the nut OK?

Wicked Stick · Post by **Wicked Stick** » Thu Aug 10, 2006 7:33 pm

If you refer to the nuts with the nyloc ? plastic ? insert in them, I still would think it wise to at least have a thread or two sticking out past it.

Just be sure NOT to use any of these in the engine compartment.

jim_geo · Post by **jim_geo** » Thu Aug 10, 2006 7:54 pm

Those are the nuts and they are on the main gear brackets (7-A). I am thinking of replacing all the bolts in question with bolts 1/8" longer. I just wish I could find my book

.

captain_john · Post by **captain_john** » Thu Aug 10, 2006 8:33 pm

What does it look like?

Are the threads beyond the nut or is flush with the lock end of the nut?

Like Dave said, they should have at least one or two threads exposed beyond the vinyl.

...or at least, that is what I would do regardless of the callout.

U gotta pic? I would like to see what you are talking about.

CJ

jim_geo · Post by **jim_geo** » Thu Aug 10, 2006 9:36 pm

I'm trying to go easy on the pix these days. Yes they are just flush to the end of the bolt and I'm pretty sure that is not the way it should be. I'll be changing them out just for my own comfort.

Cherokee Driver · Post by **Cherokee Driver** » Thu Aug 10, 2006 11:51 pm

“Standard practice in aircraft industry requires that at least one and not more than three threads extend through the nut. If more than three threads show, a washer should be used under the nut.” Source The Mechanic’s Toolbox CD My standards manual is at the airport so I pulled this source in hopes that it helps. Additionally...

“All bolt installations which involve self locking or plain nuts should have at least one thread of the bolt protruding through the nut.” Source AC 43.131b/2a 7-37

CD

jim_geo · Post by **jim_geo** » Fri Aug 11, 2006 12:58 am

Thanks C.D. I didn't like the way the nuts look and thought I had read something similer to AC 43.131b/2a 7-37 but wasn't positive.

jim_geo · Post by **jim_geo** » Fri Aug 11, 2006 3:06 pm

Turns out I made an error in sorting bolts. AN4-11 in the AN4-12 tray.

captain_john · Post by **captain_john** » Fri Aug 11, 2006 5:14 pm

That'll do it, EVERYTIME!!!

Good catch!

BTW, I like the hat! Thanks again to you and to WS for bringing it back for me from OSH!

I wear it all the time!

CJ

Wicked Stick · Post by **Wicked Stick** » Sun Aug 13, 2006 9:05 pm

Even though I sorted the bolts and placed them in marked trays, I sometimes bring out the bolt (length) gauge and check them to be sure.

prestwich · Post by **prestwich** » Mon Aug 14, 2006 6:01 pm

I heard once, in a non-aviation related conversation, that nylocks should not be re-used, i.e. torque them once only. If the bolt needs to be removed and replaced, use a new nylock nut. Any thoughts or info on that?

Cherokee Driver · Post by **Cherokee Driver** » Mon Aug 14, 2006 6:45 pm

I have a strong opinion on this one...

First of all...Here is what my library references say...Per 43.13 Chapter 7-64 (f)

"Fiber or nylon locknuts are constructed with an
unthreaded fiber or nylon locking insert held securely in
place. The fiber or nylon insert provides the locking
action because it has a smaller diameter than the nut.
Fiber or nylon self-locking nuts are not installed in
areas where temperatures exceed 250 °F. After the nut
has been tightened, make sure the bolt or stud has at
least one thread showing past the nut. DO NOT reuse a
fiber or nylon locknut, if the nut cannot meet the
minimum prevailing torque values. "

Per Standard Aircraft Handbook (5th Edition)

"When fiber self locking nuts are reused, the fiber should be carefully checked to make sure that it has not lost its locking friction or has become brittle. Lock nuts should not be reused if they can be run up to a finger tight position."

Personally, I keep a huge supply of spare hardware in the hanger and I replace hardware pretty routinely. I figure it is very cheap and it leaves no doubt.

I can attest to a self locking nylon nut plate that failed me and cost a landing light and a prop overhaul. Nut plates are not as easy to replace as nylon nuts obviously...however I wish that fastener had been identified as a candidate for replacement. I paid a huge price for a nylon fastener failure.

CD

Wicked Stick · Post by **Wicked Stick** » Mon Aug 14, 2006 8:58 pm

prestwich wrote:I heard once, in a non-aviation related conversation, that nylocks should not be re-used, i.e. torque them once only. If the bolt needs to be removed and replaced, use a new nylock nut. Any thoughts or info on that?

My A&P on the field where I'm based at and whome I trust very much when it comes to common sense and safe aproach says that if you can turn it by hand then it needs to be replaced, But if you need a wrench/socket set to turn it, then the nylon/nyloc nut is still good to re-use.

Everyone has opinions on things like this, so take mine for what it's worth, my opinion only.

JohnR · Post by **JohnR** » Tue Aug 15, 2006 5:13 pm

I was taught pretty much the same thing as WS, if you can turn it at all with your fingers, toss it and replace with a new one. If you have to think twice about it, same thing, repalce it. They are cheap.

When I learned the above I was working on race cars but they were being driven by an A&P who was a crop duster also. I always felt he knew his stuff pretty well and have followed the advice and never had problems on anything. Of course this is my first airpalne so take my opinion FWIW.