Split lock washers worthless? - Defender Source
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  #1  
Old August 19th, 2010, 10:51 AM
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Split lock washers worthless?

On one of my other forums I follow there is a lot of discussion regarding the relative worthlessnes of the beloved split locking washer.
In several studies, for the aerospace industry in particular, the split lock washer was found to have virtually no effective locking capability. Other types of locking washers, such as the toothed washer were also found to have no effective locking capability. Indeed they can cause failure when the teeth dig into the surface and cause cracks. The general consensus is that lock washers of any kind do little or nothing to prevent loosening of fasteners. Far better is either a flat washer ( as long as it is of sufficient hardness to neither distort compress or otherwise smush ) or nothing. The best s the use of a thread locking adhesive such as Locktite.
For through bolting, again the thread adhesive is best followed by a locking type of nut. The secret is to somehow reduce the gap between the bolt and the threads of the fastener. Nylon insert, distortion and split gap nuts which tightly grab threads work well. Of course, castle nuts with cotter pins, roll pins or other means of stopping the nut from rotating are very effective. Safety wire as well.
It is very important in every case to tighten the bolt or nut to it's proper torque which pulls the threads together just to the point at which the bolt begins to stretch. This effectively locks the threads together reducing the interface gap to absolute minimum.

All this was quite a shock to me as I had always put a split washer under every bolt head.
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  #2  
Old August 19th, 2010, 10:57 AM
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Old August 19th, 2010, 11:54 AM
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Stress cracks?...well maybe in "flight critical" components...for the everyday auto, don't think so...
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  #4  
Old August 19th, 2010, 11:55 AM
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Here are a couple of places that show the test results
http://www.boltscience.com/pages/hel...ingwashers.htm

http://gltrs.grc.nasa.gov/reports/1990/RP-1228.pdf

The lock washer info begins on p9
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Old August 19th, 2010, 01:26 PM
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All depends on what's causing it I guess, but from all my pinball work I can tell you that lockwashers DO work.
I've had a number of screws without washers that have backed out over time, but I can't think of any that vibrated loose when I had a star washer under it. Particularly flippers, where you get a lot of high frequency and high energy vibration.

Same with my computer stuff, where you get the screws that have the wide heads with the knurled undersides.

In that forum, did they mention what kind of un-threading they were talking about? Thermal expansion/contraction? vibration? rotating parts?

-Hans
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Old August 19th, 2010, 04:12 PM
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They have their place but engine and driveline are not two of them. Anywhere else should be fine. Better yet use a locking nut, but not a nylock nut in areas that get hot such as a cheap shock absorber.
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Old August 19th, 2010, 05:38 PM
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Quote:
Originally Posted by o2batsea View Post
Here are a couple of places that show the test results
http://www.boltscience.com/pages/hel...ingwashers.htm

http://gltrs.grc.nasa.gov/reports/1990/RP-1228.pdf

The lock washer info begins on p9
I seriously think some engineering talent is being lost in this country - particularly at NASA. Anyone who has worked with a helical split washer, of proper hardness installed properly, will have exxperienced it dig into both the metal surface of the bolted part and the underside of the head of the bolt upon removal - the only way it comes loose is to shave metal off of either. Tell me that is un-effective?

How many times have you seen a split washer installed on top of a flat washer? THEN it does nothing, because when it tries to bite between the washer and the bolt head, the flat washer spins against the base part - and no holding torque is created.

Also, if the base and bolt material are too hard, the washer can't bite - again rendering it ineffective. But to me - that is just improper use. To be sure, in a high tech application like an airframe, you don't want your lock washer removing flesh everytime you pull the bolt. But they work great for steel structures.

A blanket statement that helical washers are ineffective because they are just a spring and do nothing when tightened flat just tells me the author didn't do their home work. The guy right out of school or something?
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Old August 19th, 2010, 05:51 PM
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Whether a washer is or is not used under a nut or bolt head seems to have very little to do with loosening due to vibration or other causes. The tightness (torque) on the fastener far outweighs any washer's effect on that. That is to say a fastener not properly tightened could still work loose despite a locking washer. If you consider the entirety of the bolt working against the miniscule resistance of a split washer's one "chisel"...particularly when flattened under a tight bolt head, it defies sense that it could actually do anything but assist in loosening. The ability for the spring washer to get a "bite" comes into play after it has a chance to open up somewhat...long after the fastener has come loose.
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Old August 19th, 2010, 06:13 PM
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Whatever dude. I am going to keep using the factory hardware wherever possible, unless I see that it is not working. If you want to loctite and nylock every last nut and bolt, so be it. Have fun with that. 15 years of Land Rovering and I can't think of any instances where bolts have loosened or failed that I would attribute to the lockwasher. BTW the split washer digging into the base material is not how it locks. They dig in as the bolt is tightened, so the ridge created would only prevent further tightening, not loosening. As for not having a place on drivetrain parts, LR put them all over the place and again if they were that ineffective there would be a rash of pats falling off, that has not occured. So yeah, interesting factoid but not something that is going to change my practice.
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  #10  
Old August 19th, 2010, 06:25 PM
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I'm just passing along what's in this other thread on the Tractor forum. These are not necessarily my own views. I do believe however that the tightness if the bolt is more important than having a washer of any kind under the fastener.
As Dave says, whatever dude.
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  #11  
Old August 19th, 2010, 06:49 PM
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Yep, apparently NASA says they are worthless
http://www.jockeyjournal.com/forum/s...ht=nasa+washer

The Nord-Lock washers look pretty cool though.
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Old August 20th, 2010, 07:32 AM
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Cool. I'll keep this in mind for the next time I blast my Rover into orbit.
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  #13  
Old August 20th, 2010, 08:15 AM
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Cool. I'll keep this in mind for the next time I blast my Rover into orbit.

How did it go the first time?
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Old August 21st, 2010, 07:39 AM
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It (and I) have never been the same. I'm pretty sure it had nothing to do with the lock washers. Lost a headlight on re-entry.

Not shitting on your research Bill. All good stuff and very interesting. I'd be on the side of it not really mattering much in the real Rover world, but in the true technical sense I'd have to see a point.
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Old August 21st, 2010, 08:53 AM
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For what ever reason, folks with Detroit lockers in the rear axle sometimes have issues with the rear axle flange bolts becoming loose on a regular basis. Even with loctite they'll work their way loose.

I had this issue for a while, but I was able to correct my problem with a longer bolt (about 1/8" longer), and with a longer, broader, shoulder. These were also the harder L12's. I have not had any issues since, but I'm also now running ARB's....

But another friend still had issues even after switching bolts. I gave him a hand full of Nord washers. You can buy them from McMaster Carr. These washers fixed his issues. So I also have a hard time believing lock washers do nothing...
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Old August 21st, 2010, 09:02 AM
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Split washers are about having some dynamic tension on the threads even if the bolt/nut rotate slightly while still allowing torque to be set and measured accurately. Even when fitted between a flat washer and bolt head/nut they perform this task,
I have even used them with flat nylon washers to protect/isolate materials while still providing some resistance to loosening if the assembly moves.

Castelated nuts work but only when large enough and when exact torque is not required since it nearly always involves overtightening to get the cotter pin to line up correctly.

What does work and has been common practise in all critical component systems is lockwire and drilled nuts. When installed correctly the torque can be set and then a snug lockwire twisted into place that will physically prevent the nut/bolt from loosening. Drilling nuts and bolts to do this is a serious pain on smaller nuts (under say M16) since multiple holes are needed to be able to get proper alignment. If you look at a race vehicle they will have all the big nuts done with lockwire.
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  #17  
Old August 21st, 2010, 09:13 AM
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McMaster Carr has the bolts with the hole drilled in the cap. Don't see nuts with holes so I'm guessing that securing the bolt head is the way to go. That makes sense of course to keep the bolt from rotating rather than the nut.
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Old August 21st, 2010, 09:32 AM
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I think NASA should really concentrate on o-rings and tile adhesive. After they get that straight, lock washers could be addressed.
Personally I have never experienced a failure of a lock washer. I will continue to use them despite NASA findings because they exert a constant pressure on the fastener while the materials being joined expand and contract.
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Old August 30th, 2010, 02:56 PM
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Another publication to check out.
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