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

Hope that helps.

Cheers

Greg Locock

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.

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

They do nothing.

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

Rod

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

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

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.

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.

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

How about a nylock nut as an alternative.

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

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.

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

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.

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?

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.

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.   

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.

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.

Does anyone know of a definitive study where the helical-split lock washer were compared against, say, prevailing-torque locking methods e.g. Nylok nuts, or perhaps, internal- or external-toothed lock washers?

Tunalover

Those results are in Handbook of Bolts and Bolted Joints.  I am not at work, so I can't give you the exact page number.

Regards,

Cory

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

CoryPad-
When you get a chance, would you please reply with the ISBN for that book?  I'd be obliged.  I'm trying to prove to my boss the worthlessness of the helical split washer (among other things).

Tunalover

tunalover,

The ISBN is 0-8247-9977-1.  The book is available at:

http://www.dekker.com

While you are at it, grab NASA RP1228 at:

http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1990/RP-1228.html

It this NASA Fastener Design Guide, the author states the following regarding helical split washers:

"In summary, a lockwasher of this type is useless for locking."

Regards,

Cory

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

Trying to prove anything to a boss can be difficult and sometimes not worth the trouble. If you are developing a new design you could leave off the lockwashers from the beginning. However, if you have an existing product and want to eliminate them, there are some other considerations.

Besides convincing the boss, you may have to convince his boss, a change review board, and shop personnel.

There might be all kinds of documentation to change. Repair manuals, parts books, etc.

People in the field who know the product might start calling in complaining that the lockwashers were left off.

If anything even unrelated on the part fails and causes an injury, product liability lawyers could point to the elimination of the lockwashers as the cause. Technical explanations could be meaningless to a jury that sees only a greedy management being at fault.

Quote:

If anything even unrelated on the part fails and causes an injury, product liability lawyers could point to the elimination of the lockwashers as the cause. Technical explanations could be meaningless to a jury that sees only a greedy management being at fault.

That pretty much says it all, I am sad to say!

Rod

S9086-CJ-STM-010/CH-075R2

NAVAL SHIPS’ TECHNICAL MANUAL
CHAPTER 075
FASTENERS

075-5.6 LOCKWASHER METHOD
075-5.6.1 GENERAL. Many installations aboard ships, especially older ships, still use lockwashers in diesel
engines and similar equipment to prevent threaded fasteners from loosening. These may be replaced with the
same type of fastener if loosening has not been a problem. If loosening has been a problem, however, replace the
lockwashers with self-locking fasteners. Standard lockwashers are detailed in ASME B18.21.1 (inch) and ASME
B18.21.2M (metric). Lockwashers in common use consist of the helical spring, curved or conical spring, internal
tooth, external tooth, and internal-external tooth type.

Thank you CoryPad!  You're a gentleman and a scholar!

Tunalover

Tuna,

Sorry for the delay in posting this, I have been away from the office, and didn't have access to what I was looking for.

The British Ministry of Defense did a lot of work in this area in the past.

A guy named Light, from British Aerospace published a paper entitled "Vibration loosening of threaded fastenings" that summarized the various MOD studies (along with providing a nice bibliography).  The paper was published in the May 1983 issue of some engineering trade magazine.  My copy has "CME" in the page footer.  I can't recall the actual name of the mag.

Hi All:

We're in the business of restoring classic italian sportscars (mostly pre '55) which includes Maserati, Alfa Romeo, Fiat derivatives, etc.  Our problems deal not only with good fastening systems but also retaining original appearance.

For example, early Fiat (up to ~ '53) used internal star washers over a beveled flat washer when fastening a nut  on a stud to hold an aluminum component.  If it was a steel component, then only the star washer was used.  Early Alfa is different, they used split lock washers over a similiar beveled flat washer.  For rods and mains they used  cotter pinned castle nuts.  Maserati is different again........and of course the French and Germans had their ways. I point this out because in my business hardware originality (in appearance) is important for the history of the car and judging events,  

Having said that, for all critical apps, such as main bearing caps, rods, cylinder heads, flywheels, clutch components, et all, I try to use modern fasterners.  For mains or rods, never a split lock or even a wavy washer as I've seen both break, especially, if re-using a split lock.  So we always use hardened, surface ground parallel washers.   For external non-critical apps and original appearance requirements, we use the orig hardware which usually includes split locks.

Final comment concerns old bolts and studs...........the Italians and other euro countries mostly machined their bolts.  Maserati did their own in-house as did Alfa.  But Alfa engineering was better and knew to have a radius under the head of the bolt.  Maserati machined theirs sharp - often leading to failure.  So check your hardware carefully if you're restoring old cars and re-use bolts (which we often do).

Curious if others have made siimiliar discoveries in the resto field?

Hi all!
From this forum it is clear that split washers are to be avoided as locking systems in most of the engineering applications.
The best device seems to be a self locking nut.
So, in presence of high vibration environment, if the bolt is composed only by the screw (of little dimensions, let say diameter 3 mm), and not the nut, the only way to assure the good locking is the Loctite?
Or exists some other locking system for such an application?
Thanks!

Stefa78

Stefa78,

It is the opinion of many engineers, myself included, that a properly tensioned bolt will not back out, even under harsh vibration.  That being said, I still use loctite.

Yes, I use Loctite on any critical bolt, but in production it is a method of last resort where a joint has not been properly designed. Either the loads were not well understood, or, the hardware was underspecified and somebody or other won't pay for an upgrade.

You could say the same about Nylocs, but they tend to be used where the joint is safety critical but will function correctly with a loose nut and bolt.

Cheers

Greg Locock

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

Perhaps the guiding principle should be, that in a high stress application where the nut can be properly torqued, the threads will self lock. The male threads stretch, and the female nut compresses slightly. This alone will lock a nut and is the proper way to do it.

But not all applications can be tightened with enough torque to create this natural thread locking phenomena. Electrical terminals come to mind, particularly with brass threads. And as already mentioned, mild steel screws through fiberglass panels, and similar very low force applications. There will always be insufficient clamping force to properly lock the nut, and where there is also vibration the result will be obvious.

Either star or split washers can work pretty darned well for low force threaded fasteners, but should be avoided like the plague in rigid high load applications.

For high shock and vibration applications a Nordlock washer works very well.  I have not experienced them coming loose, ever.  This includes fasteners not being torqued correctly, as in, no torque wrench used.

I agree with you for what concern the good design of the bolts, in terms of proper choose of the torque value and the tightening load, as a way of self-locking.
Nevertheless, i met a situation that seems to put it in discussion.
During a vibration test, in which the equipment was exposed to a random vibration in the range of frequencies of 15-2000 Hz and a level of 50 Grms (!!), the fixing screws (in a tapped hole) having a Metric thread with diameter of 3 mm (M3), torqued at 1.05 Nm, with the placement of a flat washer and a curved washer (DIN 137A) under the head of the screws, unlocked after few minutes... Replacing the flat and curved washers with a split washer, torquing the screws at 1.05 Nm, they remained perfectly locked during all the test.
Saying that i won't to justify the use of the split washers, because i met several applications, with bolts M8 or M10 and torques till 50 Nm, in which they broke after the first assembly.
The fact i don't completely understand is why the screws loosen when torqued at 1.05 Nm, that should be a high value for a diameter of 3mm. So the screw should have been properly tightened, and it shoudn't have loosen even without washers of any kind.
However, in that case i avoided the loose with split washers... that demonstrated a locking function.
I'd like to know your opinion about this.
Regards

Stefa78

The two main manufacturers of recip aircraft engines, Teledyne Continental and Textron Lycoming, have used for many years, and continue to use 'split' lock washers, mostly to secure accessories such as pumps & govenors. Fasteners subject to rotation are usually secured by castllated nuts & cotter pins. Why haven't they gone to self-locking nuts? I would suspect that it would cost too much to re-certify the engines with the FAA. I have actually seen very few problems with them over the years, but they should never be reused.

During my years with one of the above, lock washers were going away and being replaced by locknuts. In some cases the use of a cotter pin was an FAA requirement. Many components were safety wired. For example, small or light housings with gaskets, oil filters, drain plugs. These do not get tightened with a lot of preload.

If someone forgets to tighten a bolt holding the wing on, it's nice to have safety wire to keep the bolt (and wing) from falling off.

Stefa78
Could you describe the test fixture and test article a little more? Any inspection of the nut and bolt seats after loosening ?

Hi Tmoose,
the test article is an electronic module having a thin rectangular base shape (the height is very smaller than the base dimensions). Its weight is 0.5 kg,and it is mounted on the fixture by means of 8 screws having a metric thread, diameter 3mm and length 26mm, AISI 304.
The fixture is composed by an alluminium plate fixed on the slip table of the shaker using 12 screws M8, on which is fixed in vertical position another plate, where the test article is mounted (on heli-coil) when vibrated along its vertical axes. The vertical plate is rigidly fixed on the horizontal one using a structural adhesive, screws M8 and two plates mounted in lateral position and perpendicularly to the vertical plate (in a top view the fixture is similar to an H). The fixture's resonance frequency in the area where the test item is mounted is higher than 2000Hz.
An inspection of the screws M3, the ones that loosen after vibrations, was carried out, and no macroscopic damages were evidenced. Nevertheless a little plastic deformation appeared on the thread, and i suspect that the screws were permanently stretched by the tightening and the dinamic loads too (i measured the length of some screws after the unlocking, and they were longer than the new ones, but the measures were not enough and not enough precise to give the best results).
The curved washers became completely flat after the unlocking of the screws, while the split washers left scratches and digs on the surfaces.
I hope that my description is clear enough...(i am sorry for my english...).
Thanks
Regards
Stefa78
     

http://www.boltscience.com/pages/vibloose.htm

"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. "

Also, a nice picture of why simply keeping the nut and bolt from turning can be of little real value.
http://www.boltscience.com/images/boltf6.jpg