Torquing lock nuts with nylon inserts - FAIL?

[440beep]

Rob at Mancini said that the same Buffalo, NY manufacturer makes both the Mancini and MP shackles. The ones I got, part#MRE139P.

45 ft-lbs of torque on any nut is the same, the type of nut makes no difference.
The box did say GM on it.
I used these, no problems:
View attachment 686428

 

[dadsbee]

The box did say GM on it.
I used these, no problems:

I was waiting for someone to point that out.. same part number for '69 era Dodge and GM leaf shackles. Guess AC Delco only likes to cross reference their part number to GM on their labels. Yours may have been better made, or I hope so at $44.99 US. I paid about 25 bucks Cdn each for mine and yep got what I paid for. The OP however probably paid a LOT more through Mancini (for probably the same part!).

 

[JB400]

It takes more torque to physically screw on a nylon lock nut. The threads aren't cut in the nylon. You are cutting the threads in the nylon which is what locks the nut in place. Nonreuseable as a lock nut after it's been used once.

If I remember correctly, you're not supposed to use a nylon lock nut in an application that has to have a spec torque

 

[Don Frelier]

It takes more torque to physically screw on a nylon lock nut. The threads aren't cut in the nylon. You are cutting the threads in the nylon which is what locks the nut in place. Nonreuseable as a lock nut after it's been used once.

Agreed, it's possible that it required way more than 45 ft*lbs just to thread the nut on all the way. Possibly before even picking up the torque wrench - then SNAP.

 

[440beep]

Yes, like I originally stated, I thought I was being smart but in the end was stupid. What I was working on was smarter than me. Needless to say I will NOT be using nylon lock nuts on the new replacement shackle. But still interesting that Dadsbee was using the nuts that came with the shackle and he still broke one of his.

Think this time around I will just get the lock nut snug on the shackle and not torque it.

 

[dadsbee]

Nytrol lock nuts are reusable, over and over again, until you can turn them in by hand and then they go in the big can. Done everyday in Aviation.

If the torque spec is 45 ft lbs and that's what you're shooting for, or haven't even reached yet and the bolt breaks then the bolt is NFG. The nut could be welded solid onto the bolt end and the bolt should still take 45 ft lbs of torsion without breaking!

 

[4spEd]

It may cost a little more but Hotchkis uses grade 8 bolts.
https://www.hotchkis.net/product/he...t-suspension/?searchby=part&partnoval=shackle

 

[BSB67]

45 ft lbs is 45 ft lb, the nylon has nothing to do with it. The bolt only see the torque that is applied by the wrench. And I doubt that the nylon insert take more that a couple of ft lb.

 

[JB400]

45 ft lbs is 45 ft lb, the nylon has nothing to do with it. The bolt only see the torque that is applied by the wrench. And I doubt that the nylon insert take more that a couple of ft lb.

https://airresearch.com/Toolbox/NylockNut.doc


https://nylok.com/fastener-glossary

 

[JB400]

Page 5 is the summary.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a024893.pdf

Page 10 gets into the details

 

[BSB67]

https://airresearch.com/Toolbox/NylockNut.doc


https://nylok.com/fastener-glossary

Thank. This supports my point nicely.

 

[Shorthorse]

Shackles usually come with Stover locknuts. That's what to use. Stovers are usually good for only one tightening.

 

[miller]

Stovers are usually good for only one tightening.

So, Stovers is their name. Sort of in line with nylocks, if it cannot be threaded on by hand, it's good to re-use. That's what we used as a guide...common sense!
Those Stovers are a lot tougher nut, re-usable, over nylocks. Disagree? Send ME any you want to toss.

 

[Fran Blacker]

In earlier post mentioned socket shoulder bolts. Well can't find any with 9/16" dia. shoulder, only 5/8. They are $10.55 each!

 

[Shorthorse]

So, Stovers is their name. Sort of in line with nylocks, if it cannot be threaded on by hand, it's good to re-use. That's what we used as a guide...common sense!
Those Stovers are a lot tougher nut, re-usable, over nylocks. Disagree? Send ME any you want to toss.

You're right, they can be used again, I've done it many times but if you look closely at a new Stover nut you can see that it is actually slightly oval in shape. Part of its ability to "lock" is buy its re-shaping to round during tightening. Once tightened, it has lost some if even just a tiny bit of its original integrity. I guess if a person is overly concerned about something staying in place, new Stovers would probably be in order. Unfortunately, I subscribe to the theory that if it's worth doing, it's worth over-doing.

 

[miller]

Unfortunately, I subscribe to the theory that if it's worth doing, it's worth over-doing.

Along the same lines as one of my theories...why would anyone jump out of a perfectly good airplane?
Yeah, I know...I'm warped.

If it does what it does, it's all good.

 

[440beep]

Got the replacement shackle from Mancini, swapped it out today with the nuts that came with it and no 45 ftlbs of torque, and the Bee is back together fine. Now for the other winter upgrade projects. Thanks for all the insights.

 

[67Charger]

A bunch of guys beat me to part of it, but for education purposes: Interference-type locking nuts, like Stovers (yours), nylocks, etc. will have a prevailing torque (torque required just to turn the nut) prior to the torque required to stretch the bolt which is where it actually gets its holding power. If a lock nut is used INSTEAD of a free-running nut, you must add the prevailing torque to the spec to get the same clamping pressure. Stovers have a notoriously high prevailing torque, and would likely have a relatively high required torque spec from the factory compared to a standard nut. This is simply to achieve the same clamping pressure between the 2. Poly vs. Rubber makes no difference. Poly would simply take fewer turns after the slack was removed to reach torque spec.