questions about nylock nuts?

I'm not very mechanically inclined, so I've come to you experts for a few questions regarding nylock nuts.
My brother owns a boat down in Florida. Before taking it out
recently, he had some work done on the steering system. It appears the mechanics removed the nylock nut, and didn't replace it with a new one. A couple days later, the nut backed out, and the steering system became detached, and we lost control of the boat. We hit some rocks (because we couldn't steer), and it caused a lot of damage. We've been told that you're not suppose to re-use these nylock nuts. Is that true?
Does salt water impact the effectiveness of nylock nuts?
Should nylock nuts be re-used, or replaced?
Are there other, safer nuts that could have been used, to avoid this?
Or, was this just "one of those things"?
Any help or insight would be appreciated. Thanks!!!
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"matt" wrote: (clip) It appears the mechanics removed the nylock nut, and didn't replace it with a new one. (clip) ^^^^^^^^^^^^^^^ I hope the mechanic has good insurance. Whether or not he reused the nut, he's the one who put it on. It's like basketball--the last one who touched it is responsible.
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matt wrote:

You're really asking for legal advise and we're not lawyers. Nonetheless, my advise is to ask the fastener manufacturer and the boat builder for their recommendations.
My gut feeling is that if the nuts were used to retain a non-moving part, they should have held together longer than "a couple of days" even if the nylon bush was worn out, provided they were properly tightened.
If the nut secured a moving part in such a way that the movement tended to unscrew the nut, I'd say that a nylock was a bad application and it should have been safety-wired.
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matt wrote:

No, it's not the water, it's the repeated wear on the locking part that is worn out by re-use. But, if the mechanic replaced a Nylock fastener with a plain nut, they are idiots. If they reused the old Nylock nut, and this is the first time it has been re-used, I'm pretty surprised it got loose in just a couple of days. But, on safety-critical systems, you certainly shouldn't do that, either.

The timing of the failure strongly suggests it was NOT "one of those things", but directly caused by improper maintenance.
Jon
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On Wed, 11 Apr 2007 17:28:22 -0500, Jon Elson

weeeell speaking from aviation practise, where safety might just be paramount, you can reuse a locknut as long as it is tighter than finger tight when you do it up. if the nut runs freely then it should be replaced.
the nylock part of the nut doesnt give the nut structural strength it merely delays it dropping off the stud if it happens to loosen.
Stealth Pilot
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matt wrote:

I've reused them for years on dirt bikes. But having a seat or number plate bolt come loose is a whole different issue than a part of the steering gear.
In critical applications, they are one shot.

There are a variety of metal to metal lock nuts, several species of lock washers, and thread locking compounds such as Loctite or Vibra-tite.
The mechanic sure looks to be responsible, who ends up paying for it though, you folks will have to hash out.
The good news is, apparently nobody was seriously hurt. That could have had a tragic ending...
Jon
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Nylock nuts, particularly in water, should ALWAYS be replaced - and for safety reasons it is good to drill the end of the bolt or stud and install a cotter pin or clevis clip to prevent the nut from falling off if it does come loose.
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You definitely need to make contact with the original manufacturer and make a record of every conversation you have with them. Go from there.
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A nylock nut is like a virgin. After it's been used once, it's all still there, but not in unused condition.
Go get a couple of new nylocks. Twist them on a bolt with a wrench, and feel the resistance. Take it off. Repeat. You will notice that it gets easier each time, and you can get to a point where you can do it with your fingers.
The mechanic made a POOR choice of nuts. He should have used a nut that has a stamp on the outside on three facets that makes it fit really tight. These can be used over and over, but hold MUCH better than nylocks, which are more susceptible to vibration and temperature. Your mechanic did a crappy job, either from not knowing, or not caring. A few new nylocks would have been a couple of bucks. Some of the specialty nuts would not have cost more than half a buck apiece. Even using two generic nuts, and jamming them would have been better. There's Loctite, and all manner of techniques known to mechanics, even down to simple damaging of threads or capnuts to prevent nuts backing off.
I'm telling you things mechanical. I know this about fasteners, and I don't work on boats or cars for a living. A paid professional boat mechanic should know these things. I'm sure you can't prove intent, but there is definitely some question of lack of due diligence. You will not have a problem proving that the work was substandard, but collecting will be another issue.
Good luck.
Steve
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On Wed, 11 Apr 2007 17:29:24 -0700, "Steve B"

Known in the trade as "stover" nuts

The problem with Nylocks in water is Nylon absorbs water and expands, which deforms the nylon itself. Then attempting to re-use they deteriorate faster than those not used in water. The nylon gets "hard".

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Thanks for all the information, guys. I am now a quasi-expert in nylock nuts!!
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And on aircraft use they are "verbotten" in the engine compartment.
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I use them in a lot of high-dollar automation design and builds. I never reuse a nyloc. That $1 for a new one is a whole lot less than the $1000's, or 10's of $1000's it could cost to fix a crash.
--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Nylocks can be reused a limited number of times. The problem is knowing how many times the nylock has been used. So in Aerospace, they generally are not reused. The exception is where you assemble a part with a new nylock, then disassemble it to make an adjustment, and reassemble with the once used nylock.
But use in saltwater may be different.
Dan
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It doesn't matter at all, legally: Mechanic works on steering gear, declares it fixed, gets paid. Few days later, steering gear comes apart while underway, causing a crash. He is expected to know what is and is not acceptable practice. I would not even get into a discussion about locknuts. The Mechanic is responsible.
Joe Gwinn
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