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MG Midget and Sprite Technical - Washers and such like

Assembling the rear suspension on my Frog project, I thought I would use the illustrations in the Moss catalogue as guidance, in particular for the various bolt fitments. But given the various illustrations on different bolts which show flat washers alone, spring washers alone, both together and none at all I am now wondering what the proper logic is.

I thought that the "tang" ends of a spring washer were designed to grip the underside of a plain nut, and whatever the fastening is tightened against, to stop the nut from working loose. But if this is true, then why in several places does it show a spring and a flat washer. This would seem to lock the nut to the flat washer, but since the latter could still turn then what purpose does this serve?

In other places there is just a flat washer - I presume this is to spread the load or reduce the friction as the nut is tightened?
Whilst others use just a spring washer, presumably locking the nut against the panel or object being fastened.

So, what are the rules or guidelines from an engineer's perspective?

GuyW

Hi Guy - I still need a postal address to send you something. The answer to your question is found here.


Daniel

Good question.

BMC certainly did use the <flat washer-spring washer-nut> sequence on a lot of applications.

I'm not sure what the rules are on this, but I'm sure someone round here will know...
Dave O'Neill 2

Never seen a flat washer on top of a spring washer. But luckily I don't know nuffink.
Nick and Cherry Scoop

Does it depend on the fastening?
This image shows a bolt with nut so is spring washer/flat washer/nut


Jeremy MkIII

...whilst this shows bolt/spring washer/flat washer

I'm like Cherry (no scoop) on this, with a lack of knowledge.


Jeremy MkIII

My instinct is to place the spring washer outermost I.e. component / flat washer / spring washer / nut (bolt sometimes). The flat washer then stops the spring washer biting into or marking the component. The spring washer provides some pre-load presumably. But I'm sure I've placed them the other way round without thinking sometimes!

Bill
W Bretherton

I don't like spring washers because they basically don't work. Once the fastener is torqued they become effectively the same as flat washers.

Don't take my word for it: the link cites just one of many published studies about them

However, what they may do is prevent a fastener backing off beyond a certain point once it has started slackening and allowed the spring washer ends to separate and get a grip of the fastener and component. So although the fastener loses its full clamping force it doesn't just fall off.

So they may be marginally effective where only light installation torque is allowed; for example where screws are installed in soft alloy parts. In that instance there may be some benefit from a flat washer under the spring in preventing the spring washer chewing up the surface of the alloy part, but a chemical lock like RTV or Loctite would probably be more appropriate or even a Nyloc nut, with due deference to their limited temperature tolerances.

There are better ways to mechanically lock high torque fasteners, like serrated (shakeproof) washers, Belleville washers and so on. Spring washers AFAIK are not allowed on aircraft assemblies or milspec equipment. Aircraft gear in particular makes much use of lockwire and Nylocs.

Here's the link:

http://www.boltscience.com/pages/helicalspringwashers.htm
Greybeard

For elevated temperature applications where a nyloc isn't suitable there are plenty of options for all metal locking nuts available.
David Billington

Still about as clear as mud!
The applications I was looking at are not light duty places.
Front 2 spring mounting bolts have just spring washers.
Rear 2 just have flat washers, but the nuts are specials that I think are self locking though not of a sort I have seen anywhere else! I think its called an Aero nut?
Fastenings of damper use a flat washer and a spring, so the nut is "secured" to a flat washer, which presumably could still move.
Check straps bolts have no washers, but use a Nyloc.
GuyW

There's an article here (provided by Henkel, which manufacturers Loctite, so may be somewhat biased) that suggests most forms of thread locking other than chemical threadlockers or saw-toothed flanges are fairly useless after not many load/unload cycles: http://www.machinebuilding.net/ta/t0972.htm (scroll down to the multicoloured graph, copied as the 'Image' in this present posting).

Personally I would use a plain washer to spread the load and avoid marking the mating face, plus Loctite (of the correct grade - there are many to choose from) to prevent loosening. I'd probably lose marks in a concourse competition, but I'd rather that than lose components!



Jonathan Severn

Grey,
thanks for the info. I remember doing a quick search when this subject came up previously and I couldn't find anything to say spring washers done much.

But of course I always use them (plus an extra flat washer if a nut going on too.

So now I've got to strip the car down to get all those spring washers off and think about all the money I've put into my stocks of various sized spring washers.

You've given me a headache about the money I've wasted and I'll have a sleepless night thinking about the ruined weekend and all the spannering I'll need to do ASAP - fanks fer dat.
Nigel Atkins

The ones I have listed are on the Moss catalogue drawing, which I believe is a copy of the original WSM version. I am sure there are better modern alternatives now, but was wondering what the engineering logic in the original manufacturer's specs was.

The other thing is that the original spring washers - certainly of the larger sizes, are noticeably more robust and harder with a good "cutting end" than any modern ones I have yet seen.
GuyW

I like the idea of letting chemicals do the work, I'm a big fan of spray-and-walk-away type solutions but it always gets so confusing as to what should be used - sealants, bondings, adhesives, glues, etc..

So which colour threadlock would we use on our cars for general nuts and bolts then please?
Nigel Atkins

Guy,
the modern spring washers will bite in sometimes, I can remember seeing the marks on something I've fitted but I can't remember what, I thought at the time it might have meant the spring washer was perhaps turning to bite in(?!!?).
Nigel Atkins

Hijack alert!
GuyW

Yes modern ones do bite in, Nigel. But they are just not as robust as the old original ones. At least the larger sized ones are pretty substantial!
GuyW

Guy,

Some all metal locking nuts I'm aware are Philidas who make a few styles and regarding Aero nuts I wonder if you're thinking of the likes of a Kaynar nut such as http://www.lasaero.com/site/products/article?id=CUB8AQL , they're often used in aircraft for the weight saving aspect and well engineered from a material use aspect as the highest thread loads are at the nut face and reduce away from the face.
David Billington

Hijack - at least I'm on the same subject this time.

I'm with you too with parts books are confusing on washer and nuts use.

I see no reason why you can't find out about spring washer and I threadlock in the same, er, thread.

Washer thickness and OD seems to vary depending on where you buy, I can't think what an original looks like to imagine whether the new thicker ones are anywhere near as robust.

Perhaps you could put up a photo of comparisions.
Nigel Atkins

Hijack only that I thought I had made it very clear that I was seeking an authoritative engineering explanation behind the variety of combinations of flat and spring washers in the original specifications.

Nigel, of course there are modern alternatives which may be of interest, and many of which such as locktight applications could well be better. But switching the conversation to those doesn't shed any light on the logic behind the original applications. That is why I think that is a hijack at this stage.
GuyW

Hijack? I thought it was more a case of thread drift.



I'll get my coat...
Jonathan Severn

Loctite 243 is a medium-strength, oil-tolerant threadlocking adhesive that should be fine for most applications on our cars.
Jonathan Severn

Jonathan ;-) !
GuyW

Do people have much trouble with nuts and bolts coming undone? I've never used Loctite, though I've used Simmonds nuts where specified.

I just assume that the original spec was OK.
Nick and Cherry Scoop

Guy I agree. I'm as confused as you (or even more so) about the use of spring washers, with or without flats. I simply don't understand why they're so ubiquitous. To the best of my understanding they're nearly useless for nearly all applications yet mysteriously the bloody things are everywhere. That's what I was trying to get across.

That's not to say I don't use them at all. I fitted lots only yesterday when I was changing out all 24 injectors in my engine room, but only because CAT specify them and I don't want to run into warranty issues.

For my own purposes though I prefer to bin them and use something better as and when I come across them, which renders the question of whether or not to combine them with flatties redundant to me.

Personally I suspect they're used because at one time there was nothing better and manufacturers simply never got around to moving on. Or maybe there's a cost issue. Perhaps there are significant savings from using ten million spring washers over the same number of shakeproofs.

Yours faithfully;

"Baffled" of Argyll and Bute.
Greybeard

Nick, I agree with you also to a point. Original spec is probably fine. Which is not to say it can't be improved easily and cheaply.

Yes I do have trouble with nuts and bolts coming adrift, or trying to. Mostly on single cylinder motorcycles and small diesels (pumps, gensets &c). My experience in general is that spring washers don't much help with them, but there are other things that do.
Greybeard

So the practical solution is to use locktight either instead of or in addition to a spring washer. It still doesn't explain to me the use of a spring washer and a flat washer together, which seems to be a common original combination in many places.

If the spring washer performs in the way I was assuming, with the spring ends digging into the adjacent nut on one side and flat washer on the other, then what exactly does this achieve? All I can see is that if the nut begins to "unwind" with vibration, then it is going to simply turn the flat washer with it. If the flat washer weren't there then the nut would be locked to the surface of whatever the bolt is inserted through, which makes more sense to me. Maybe there is some other magic involved!
GuyW

Surely the spring washer increases the release torque needed for the nut to loosen hence making the fastening "tighter" thank it otherwise would be. The flat washer protects the component being clamped from damage but doesn't reduce the tightness.

Bill
W Bretherton

Guy, my engineering perspective from memory. The ends digging in has no relevance. The clue is in the name as a spring washer is just that, a small spring which when the nut/bolt is tightened is under tension. One of the original design uses was where small amounts of expansion and contraction occur and the washer maintained the tightness of the fixing. The flat washer just spreads the load over a greater area. They were not designed to be used in vibration situations, shakeproof washers being a better solution in that case.

Trev
T Mason

Loctite 243, thanks - so the blue stuff then.

Hey, wot?

I'll get coating ...
Nigel Atkins

Nigel; Loctite publish excellent guidance on product applications, mostly as pdf downloads like this one :

http://www.loctite.co.uk/uke/content_data/95350_Ind._Selector_Inside_en.pdf

One disadvantage of Loctite is the inconvenience of having to thoroughly clean parts that have had it applied before reusing them with more Loctite. Wire brushes, cleaning taps, blah blah.

There are spring washers here and there on my car I confess, but I prefer to replace them with something more effective as and when I come upon them.

(Er - there are books with this stuff in them)!

Sorry about your weekend mate!

Guy - I'm as confused as you. I don't know why they were ever used so ubiquitously, with or without flats. It seems to me that they're nearly useless for most purposes and yet they're everywhere.
Greybeard

With reference to the spring washers not being as robust as the old ones, spring washers come in different, grades and of different cross sectional area,(flat, round, square) another important point is that they also come in metric and imperial sizes, which makes a big difference to the fit, and the same goes for flat washers, in size and thickness,you will struggle to find any imperial size, heavy duty, spring washers in Kendal, Thomas Graham, Westmorland business park LA9 6NS, and Haytons, on sandylands, have the best stock,the only other place is Harry wigins, burneside road
Andy Tilney

OK, here is my "take" on this washer conundrum. Bearing in mind I have never had any engineering instruction. But thinking about the applications:

A flat washer is used either to spread the compression forces of a nut as it is tightened, giving a consistent hard, smooth surface which may also ensure accurate torque readings in some circumstances. (Head studs use a hardened washer)

OR is used where the component being held is of a softer material like alloy that would otherwise be damaged or the fastening would loosen in time as the component surface eroded. (shock absorber mounting bolts)

Then separately for spring washers, as they may be used with or without flat washers, I like Trev's explanation. If the spring is to maintain the compressing force of the nut/bolt rather than to stop the nut turning, then it doesn't matter if it is being used together with a flat washer. If the spring simply maintains that compression where the component might move, even microscopically, or maybe with changing temperature, then that makes a lot of sense. Thinking through the applications on my cars the theory seems to fit pretty well.

Examples:
Alloy thermostat housing? - use a flat washer to protect the alloy together with a spring to maintain pressure on the squishy cork gasket.
Front engine mounting rubbers will move so use a spring washer and a flat is added because the bracket is slotted.
Frogeye rear roadspring mounting bolts use a spring washer to maintain pressure as the spring moves, but no need for a flat steel washer.

Where a nut might come loose on early cars in critical locations it is castellated, with a split pin. And where it is less critical a nyloc type is used (rear check straps)
GuyW

Andy, of those Haytons is still the best as they still have extensive stocks of imperial stuff down in their basement stores and on a good day Tom will let you go and sort through the bins yourself. Butit does tend to be mostly the larger sized stuff for tractors! Thomas Grahams are always helpful, but its all metric these days. Longhorn is another one, though like Harry Wiggans, its more architectural hardware.
GuyW

If Trev is right about the spring washers being there to maintain the tension force on the fitting, then it would make sense to still use a spring washer even when locktight is used to secure the nut against vibrating loose.
GuyW

Guy, on the subject of castellated or nyloc I dont think how critical it is is relevent. I think nyloc superseded castellated in most cases although castellated may still be used in some cases.

Trev
T Mason

Yes I think you are right that Nyloc are now often used in place of castellated (cheaper, quicker to assemble). But they were also contemporary, with the castellated ones still being used on more critical places long after Nyloc were introduced.
GuyW

I don't use any spring washers on my car. I lockwire some bolt heads, use nylock nuts, an occasional castle and split pin, and sometimes use a thread locking glue (Loctite).

If anyone wants to use spring washers that's up to them - I don't see any benefit.
Daniel

Hi Daniel,
clearly there are modern alternatives and ways more secure, but spring washers have been around for a very long time and were used by many manufacturers. With your engineering background what function do you think they had?
GuyW

Hi Guy,

I don't believe I have an engineering background, despite working at specialist Jaguar restoration company from age 11! I'm therefore often reliant on those with a greater knowledge than myself.

The fact that something has been around for a long time and used by a lot of people is simply a fact in its own right and doesn't mean it was a good idea or one that works.

I stopped using them a long time ago and no fastener has worked loose as a consequence of not using them.

I found this:
A ring split at one point and bent into a helical shape. This causes the washer to exert a spring force between the fastener's head and the substrate, which maintains the washer hard against the substrate and the bolt thread hard against the nut or substrate thread, creating more friction and resistance to rotation. Applicable standards are ASME B18.21.1, DIN 127B, and United States Military Standard NASM 35338 (formerly MS 35338 and AN-935).[10]
Spring washers are a left hand helix and allow the thread to be tightened in a right hand direction only, i.e. a clockwise direction. When a left hand turning motion is applied, the raised edge bites into the underside of the bolt or nut and the part that it is bolted to, thus resisting turning. Therefore, spring washers are ineffective on left hand threads and hardened surfaces. Also, they are not to be used in conjunction with a flat washer under the spring washer, as this isolates the spring washer from biting into the component that will resist turning. Where a flat washer is required to span a large hole in a component, a nyloc nut (nylon insert) must be used.

The use and effectiveness of spring lock washers has been in debate of late,[when?] with some publications[11][who?] advising against their use on the grounds that, when tight, the washer is flat against the substrate and gives no more resistance to rotation than a normal washer at the same torque. NASA researchers have gone as far as to say "In summary, a lockwasher of this type is useless for locking."[12][13] However, a spring washer will continue to hold the bolt against the substrate and maintain friction when loosened slightly, whereas a plain washer will not.[b]

The benefit of spring lock washers lies in the trapezoidal shape of the washer. When compressed to loads near the proof strength of the bolt, it will twist and flatten. This reduces the spring rate of the bolted joint which allows it to maintain more force under the same vibration levels. This prevents loosening.[14]

SO the answer to your original question appears to be you don't use a flat washer with a spring washer even if a parts manual suggests you do.

I still need your address..
Daniel

Thanks Daniel, wherever you got those quotes from.
And 11 years with Jaguar, even if you were composing sales brochures, is a lot more engineering than I have. I didn't even get to do metalwork at school!

I have emailed my address.
GuyW

I think its just down to personal preference in a lot of cases. More modern solutions come along and may be better in some circumstances but not others. I have used Loctite on occasions but am not a great fan of it and I do still use spring washers. Interestingly it made me think when did I last see two nuts used to create a locknut, other than to remove a stud. I cant remember offhand.

This thread also made me think about castle versus nyloc nuts too. While a nyloc may be cheaper to make and quicker to assemble, the castle nut is easier to undo and can be reused several times as opposed to the nylocs once. Funny how so many of the old things are more environmentally friendly than modern alternatives.


Trev
T Mason

In my opinion the bolt diamter would be specifed by an engineer or a senior draftsman with qualifications called a designer.

Like all things in the fifties the class system in many ways was obvious like a doctor advises an injection or a particular bandage but the nurse does that.

No engineer or designer worth their salt would get involved with washers. That was left to a draftsman who did not have his qualifications who would normally copy these details from a previous drawing and if he could not find the previous drawing he would copy it from a drawing that looked similar, therefore I consider the specification of washers was more of "that is the way we always do it" rather than specific design decisions.

Now with regards to parts diagrams, that went even lower and in those times it would be a lady called a "tracer" who would put that together and they were considered someone who did the "non important" work.

Even if they asked what they should put there re washers they would get a flea in their ear from a draftsmen too busy reading his Daily Express than advise the lady as he was not bothered.
Eddie Cairns

The very reason I was after the engineering principles behind their use. If the detail on the drawings was so unreliably selected then an understanding of how they work and how they SHOULD have been selected would be useful.

Not that I am aiming for such originality! As others have pointed out there are better ways of doing things now. Just interested.
GuyW

I can't believe that, Eddie. Surely at the time of the A-Series engine design work, the design engineers would have specified each entire fastening.

A designer who didn't do so wouldn't be worth his salt.
Nick and Cherry Scoop

A nyloc nut can be used more than once and still be effective. There are other nuts that can't be.

I have a vague memory, probably goes back to the Jag restoration company as a kid - where I stripped down lots of XK cylinder heads (mostly 3.4 & 3.8 heads), someone telling me you either use a spring washer or a flat washer but never both. I also think on the Sprite steering column bracket which is aluminium it was/is fastened with a spring washer under the screw head and nothing else.
Daniel

"I have a vague memory, probably goes back to the Jag restoration company as a kid - where I stripped down lots of XK cylinder heads (mostly 3.4 & 3.8 heads), someone telling me you either use a spring washer or a flat washer but never both."

A vague memory?...and did this person know that for a fact?


If it's this column bracket, there appear to be flat and spring washers, both at the clamp and mounting.


Dave O'Neill 2

Lots of applications on a Spridget where an alloy component is fixed with a flat followed by a spring washer. Front shocks, rear shocks,steering rack mounts (early, thermostat housing, carbs.
GuyW

Can anyone be certain that wherever there is a flat washer under a spring washer when the fastener is securing an aluminium component that it was made like that at the factory? Also, if it was made like that at the factory was that the correct engineering practice?
Daniel

The photo above was of my last midget - one family and 43000 from new when I bought it. One of the most original Midgets I have ever seen, so I'm reasonably sure that's how it left the factory.

I have had dozens of BMC/BL cars over the years and it does seem to be the convention, as far as BMC were concerned. Whether it was correct engineering practice or not, I couldn't say...but I would hope so!
Dave O'Neill 2

It's logical. The tang of a hardened spring washer will gouge into an alloy component and apart from that damage, it will also gradually release the tension in the spring washer.
GuyW

Despite all the learned opinions above, my instinct says that a spring washer on top of a flat washer is a workmanlike solution, and I believe the phenomenon of loosening in use is rare in standard or near-standard engines.

Mind you, I have the instincts of a draughtsman.
Nick and Cherry Scoop

In my opinion flat washer under spring washer is good practice but I have no absolute proof of that. It is also worth remembering that when spring washers first came into use many things were over engineered and this practice has changed over the years so what was considered good practice then may not be deemed necessary now.

Trev
T Mason

This thread was discussed between 21/07/2017 and 24/07/2017

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