Insuring self locking nuts are installed properly!

[Ron Hill]

I was looking at some some posts of pictures (critical updates) with self locking nuts on this Message Board.  To my surprise I found some nuts that although they are of the self locking style were installed and the self locking mechanism was NOT engaged - therefore they are not locked!!!

First of all there are two types of self locking nuts. One has thin vertical serrations which are slightly bent inward (operating like a spring) and the other has a nylon "bushing" embedded in the open end.  The all metal (no nylon) are the expensive type.  Another style, but not a true self locking nut is a nut that has a peen (hammered indentation) to make the threads bind rather than turn easily. 
The reuse of self locking nuts is another discussion all in itself!!

To make any self locking nut LOCK, the standard is to have a portion of one thread showing above the nylon mechanism or open end of the nut.
If you can't have that thread showing you are fooling youself and might better use a thin nut with a lock washer.  There are thinner self locking nuts available, but they are usually special order items.

"Check your Nuts!!"   A few thoughts

[mainesail]

Good point Ron. I'll add one more. The use of Nyloc nuts on HOT items, such as engines, gives little benefit as the nylon softens with heat and looses its "locking" grip.

[Stu Jackson]

I AM THE CULPRIT!  

By a clever process of elimination, like the ONLY picture on that entire two page thread is MINE (!), points well taken, gentlemen.

All I can say, not to be too defensive, is that those nuts have held on there since 1998.  Maybe the nylon melted onto the studs???  

Next time I have the opportunity (chance? need?), I'll do it right.  

Thanks for the heads up.

[Ron Hill]

I didn't mean to pick on Stu, but I just wanted to point out the correct use of a self locking nut.  Most lock nuts are (by design) "thicker" and that's why I mentioned that a thin nut and a lock washer may be better is some applications.
 
You always want to see some thread on the other side of a nut.  If you can't use a self locking nut or even a lock washer, a small dot of fingenail polish on the bolt thread on to the nut will let you know that the nut is backing off - if the dot is broken.

Surprisingly the nylon portion is pretty tough and does stand up to some heat.  I've used the nylon self locking nuts on my duel outputs (bolted on leads) of my Balmar alternator since 1992.  Those bolt output leads get hot, but I wouldn't use those nylon self locking nuts on the exhaust flange.  They are reliable, but like any item it takes a periodic inspection just to make sure all is OK.   A few thoughts