Split Washer Placement 9

[wickedmotorhead]

I've seen OE's (and others) put split (lock) washers underneath the head of a bolt or underneath the nut in a mounting configuration. Which one is correct or does it matter? Everywhere I search I get a different answer, I need a educated answer to help make my decision. Thanks.

 

[GregLocock]

They are the invention of the devil and should never be used in a properly designed joint.

Hope that helps.



Cheers

Greg Locock

 

[CoryPad]

Agreed - you van perform a search on this site to verify what others have said on this topic. References like Handbook of Bolts and Bolted Joints or NASA RP 1228 show them to be poor performers.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MintJulep]

I agree with Greg and Cory. The proper place for split-lock washers is in the trash can.

They do nothing.

 

[evelrod]

I, too, agree that the trash is the proper place to store split/lock washers!

Rod

 

[MikeHalloran]

Agreed that no one who understands split lockwashers would use them. However, if you _must_ use them, for political reasons, they only make sense under the nut.

My reasoning is, they have to bite into two surfaces in order to work at all. They can't bite into most bolts. They can bite into most nuts.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[swall]

Anyone have a feel for what the expected failure mode of these things would be?

 

[btrueblood]

The root cause failure mode is that the split washer is specified or installed by somebody who presumes it is an adequate thread locking or anti-rotation device. In its intended use, the split washer cannot prevent nut rotation when the joint is torqued down tight, since the cutting edge is acting parallel to the nut surface. Only after the nut has loosened (which is considered by most good engineers as a failure of the joint) can the edge of the washer "dig in" to the nut and the parent body.

 

[franzh]

One frustrating thing for me is the inside diameter. On a 5/16" bolt, the ID for the split washer and the flat washer is 3/8". I usually wind up using a washer that is undersized (at least according to the marking on the containers). The ID of the washer is a slip fit on the bolt shank allowing full contact of the bolt/nut head with the washer instead of the washer slipping out from 1/3 of the contact area.
On split washers, you will never see them on a critical area, such as internal engine components, transmission internals, etc. Just the tightening process will cause the split to spread open.
Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Hi Franz. I just gotta point out the number of lock washers in "critical" engine components of most of the engines built in the dawn of the industry. Most of the antique engines have lock washers and or cotter keys on all of the main and rod bearing nuts. Even the MGA/MGB engine I rebuilt last year has lock washers on the mains! Don't get me wrong---I still hate the things and in the case of the MGA 1500(my 59 Nash Metropolitan), I substituted hardened washers as spacers eliminating the lock washers.
Also, failure of the lock washer from overtorque , as you point out, results in the piece opening up and, some cases, actually "falling out". If I must use a lock washer I prefer a "star washer" and then only on non torqued applications (infrequent). I tend to overuse lock wire and Locktite red or green---I only use blue on non critical stuff.

Rod

 

[wickedmotorhead]

How about a nylock nut as an alternative.

 

[evelrod]

Well, motorhead (I like that, kinda fits me, too)
Locking nuts of which Nylock is just one brand and type are common alternatives to split/lock washers, but that is not the basic subject under consideration in this thread. The only reasons I can think of at the moment that lock washers are still in use is "cost","availability" and, "convention". Convention, ie, common practice in some industries and the cost factor seem to on the top of the list. Lock washers, even quite large ones, 1/2" to 1 1/4" in size and larger are still in regular use on non torqued connections in the construction industries. Keep in mind that like anything else, the lock washers can be of varrying quality and be made of several different grades of material---some better than others and many just totally useless.

Rod

Rod

 

[swall]

The reason I asked about the failure mode is that BMW used these washers on the four bolts that hold the driveshaft cardan joint flange to the transmission output flange on the R-series bikes. On the first one I took apart for service, I found radial cracks in all of the washers.

 

[evelrod]

Yes, I find lock washers on all sorts of connections, driveshafts, brake calipers, U jounts, CV joints, suspensions bits---the list is endless---I just don't typically re use them when I rebuild or replace such bits and pieces. It's not about cost with me but rather my perception that lock washers are BAD. Maybe I am being paranoid, but I have had too many lock washers fail in normal service over the years not to have developed this perception. I make no reccommendations either way---just pointing out MY opinion.

Rod

 

[Tmoose]

Aircooled Bmw boxer driveshaft u-joint?

There may have been a factory update to get rid of the split washers.

http://pweb.jps.net/~snowbum/torquevalues.htm

"Driveshaft U-joint bolts, non-Paralever models: 29 foot pounds, NO lockwashers, and use Loctite BLUE on clean and
dry threads. I would probably NOT use this high a value on the earliest models with those nasty lockwasher problems,
and HIGHLY recommend getting rid of theose washers and using the shorter bolts, as I have posted elsewhere's on this site. Early models like the /5 were specified at 18 foot-pounds, that was the longer bolts with the split lockwashers. I feel NO bike should have those long bolts and those lockwashers, the 18 foot-pounds is listed here as a courtesy. If one of those lockwashers breaks, or somehow its bolt loosens, the rest soon will, and MAY destroy the back side of the transmission.

 

[swall]

Tmoose--Yes,Airhead.And yes, I am aware of the updates.BTW, have you heard any rumors about the torque value for the 11mm flywheel bolts being upped to 90 ft-lbs from 72?

 

[swall]

Oops, I should have looked at the link first.I see that 90 ft-lb figure mentioned. 90 ft-lbs, oiled should almost get these bolts to the yield point.

 

[Tmoose]

Having been "owned" by a German company for a while, and reading some of the tales of Daimler's managing Chrysler with the previous boss, I narrow-mindedly think that when a German engineer changes her mind it is powerful evidence indeed. For BMW to abandon split washers on the U-joint flange there must suggests that there were significant field failures, and the Chief engineer finally retired.

My Volvos and Corvairs never had split washers on their u-joing flanges.
I might have installed the split washers supplied with my trailer hitch ball, but only because I did not have enough big flat washers to keep the nut from running out of thread.

 

[DaveKillens]

I used to work on aircraft. I can never recall ever seeing a split washer on any component. If a bolt or nut had to be secured against backing out, split pins, or safety wire, or something that mechanically locked the part in place were used. Not just some part that hopefully resisted backing out.
Use a split washer if you don't care if the part fails.

 

[EngJW]

I can think of one application where lockwashers are used and they appear to work. The bracket that clamps a gauge against a panel. You can't tighten it very much without bending it or breaking something. A lockwasher will provide enough friction to keep the lightly tightened nuts from backing out.

A self locking nut, Nylok or distorted threads, would be better of course, but cost may have been a consideration. I agree that lockwashers should not be used in any critical joint.

Lockwashers can be used against soft materials that will not stand a lot of preload.

Internal and external tooth lockwashers are also used with wiring terminals. Sometimes they are not easy to get apart.