fastener questions, split lock washer, nylock

[zakthor]

Reading Carroll Smiths book "nuts, bolts, fasteners and plumbing handbook" and have a few questions.

First, apparently split lock washers are useless. I also looked on the internet and there is a nasa fastener guide that agrees they are the same as flat washers once tightened. I suppose there is an assumption about application (sufficiently ridgid joint?) I dunno. I'm asking because my Yakima bike rack bolts to my hitch, the bolt kept loosening which made the rack sway and rattle. No amount of tightening would prevent it. I added a split lock washer under the existing washer and its not loosened for more than a year. Question is when is a lock washer useful? It seemed to save my bacon. I'm assuming the joint design is bad in some way that means the normal rules aren't valid (slight motion? Rack steel too soft?)

Second, nylocks for 911 valve covers are allegedly single use. These go on with very little torque. I can see the plastic on used nuts has been cut by the thread. Carroll smith says they are good because they can be reused "many times" Why can't valve cover nuts be reused? Supposedly good to 250f, is the 911 motor application too hot?

Thanks!

[wdfifteen]

I don't think split washers are the same as flat washers. They continue to put pressure on the nut so it won't turn even if the joint is mildly unloaded. A properly installed bolt is tightened until it begins to stretch, which keeps it tight even if the joint is unloaded In aerospace applications bolts are carefully tightened to a specified level of strain and a lock washer wouldn't do any good (the bolt itself takes up the slack in an unloaded joint). But on backyard stuff that is just tightened "tight enough" a lock washer can keep a joint from coming apart when it doesn't need to.

[billybek]

If nylock nuts won't lock as well the second time around.

Certain applications I used Nord-lock ramp style lock washers. They replaced split lock washers.

[Eric 951]

Nylocks are 1-time use if you want them to do what was intended. We use them in construction and any time work has to come back apart for whatever reason(inspection/repair) new nylocks are used.

[1990C4S]

Lock washers have been replace by chemicals in my world. Loctite is cheap. And one size fits (almost) all.

[1990C4S]

Vibration Loosening of Bolts and Threaded Fasteners

From above:

As a result, a rationalisation of the variety of locking devices used by such major companies has occurred. For example, conventional spring lock washers are no longer specified, because it has been shown that they actually aid self loosening rather than prevent it. There are a multitude of thread locking devices available. Through the efforts of the American National Standards Subcommittee B18:20 on locking fasteners, three basic locking fastener categories have been established. They are: free spinning, friction locking, and chemical locking.

[sammyg2]

Lots of non-engineering types offering their "opinions" in them thar books and articles.

Lock washers are not useless. In the right application they do the job they are intended to do. They do nothing until the nut loosened enough to provide a gap for the split lock washers to expand, and then the knife-edges grab to keep the nut from falling off. But htey can "give" and move enuogh ot prevent proper torquing which causes more problems.

Nylock nuts on 911 valve covers can be re-used many times.
But they are a band-aid for a mis-application.

Bolts (and screws and studs etc) stretch like springs when tightened.
That spring tension should provide enough friction to keep the nut from loosening up.
If it doesn't then chances are the stud is inncorrectly sized or improperly torqued.

If under-torqued there is little or no stretch (as in a 911 valve cover) so a self-locking nut is used to make up for that lack of friction.


Most of the time a lock washer or self-locking nut is used as a compromise.

Example: in order to obtain say 35% of yield on a 911 valve cover without over-squeezing the gasket and warping the cover, the stud would have to be tiny. Really tiny. Like 1/16" diameter tiny. Like, snap off really easy tiny.
compromise.

Note that there is ALWAYS an exception.
Always.

PS how many of us have earned a paycheck with a pair of these band-aid application tools?

[jyl]

Little tube of Locktite Blue (the removable sort) will make most of this moot.

Nylock nuts are re-usable for common, non-critical applications. Even after being re-used, they still have enough resistance to rotation that they won't easily vibrate loose. But for anything where it really matters, I would not re-use them.

[cashflyer]

I use nylocs one time, with a spring washer under them, and a little dab of loctite. Then I secure the nut with safety wire and put a cotter pin through the end of the bolt.

[Tobra]

I used to lay a piece of fishing line across the threads as a ghetto locktite if I did not have the right fastener.

[aston@ultrasw.c]

Deformed thread lock nuts are the way to go.

[wdfifteen]

Originally Posted by cashflyer

I use nylocs one time, with a spring washer under them, and a little dab of loctite. Then I secure the nut with safety wire and put a cotter pin through the end of the bolt.

You're courting disaster of you don't double-nut it and peen the end of the bolt over, too.

[wdfifteen]

I can't believe I'm saying this, but Sammy is right on.
Spring washers, nylon inserts, locktite, and the other securing strategies have appropriate uses. There is no single solution that fits every situation.

[porsche4life]

I can't believe I'm saying this, but Sammy is right on.

Spring washers, nylon inserts, locktite, and the other securing strategies have appropriate uses. There is no single solution that fits every situation.

I think we've finally found a topic he is actually an expert on!

[sammyg2]

Originally Posted by cashflyer

I use nylocs one time, with a spring washer under them, and a little dab of loctite. Then I secure the nut with safety wire and put a cotter pin through the end of the bolt.

Don't forget the tack-weld.

[sammyg2]

Originally Posted by porsche4life

I think we've finally found a topic he is actually an expert on!

... maybe ....

I like my fastener bins.
Cad plated on left, 300 series stainless on the right.

[GH85Carrera]

Originally Posted by sammyg2

... maybe ....

I like my fastener bins.
Cad plated on left, 300 series stainless on the right.

Oh, man. I want that rack in my garage. Right next to the new 918.

I am always scrounging for a bolt or washer and I have a few bis of good new stuff. That has to be several grand worth of goodies.

[URY914]

I use Crazy Glue.

[cashflyer]

Originally Posted by wdfifteen

You're courting disaster of you don't double-nut it and peen the end of the bolt over, too.

Originally Posted by sammyg2

Don't forget the tack-weld.

See.... THIS is why my fasteners keep backing out; I'm doing it wrong!

[Hugh R]

My Brother works at JPL, he builds stuff they send out of the solar system (literally). they are not allowed to use the Red locktite.If they have to take something apart, apparently the loosening damages the nut/bolt threads too much.