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MG Midget and Sprite Technical - Damaged Thread on axle casing
|I recently started one of those jobs which got worse and worse! The crux of the matter is that when I tightened up the 1_7/8" nut which locks the hub bearing onto its seat on the axle casing, the thread failed.|
The recommendation is that a torque of 140 ft lbs should be applied to the nut. That's quite a hefty torque and to my mind it's important to stop bearing creep of the inner race around the axle seating. The nut wasn't very tight when I undid it and on re-fitting and tightening up I felt it going at about, guessing, 20 ft lbs.
I have temporarily salvaged it by fitting a new nut and toquing it up to 60 ft lbs with loctite applied. It "felt" as though that was about as tight as I should go with it. However, I have a replacement casing on its way and bearing in mind we have threads that are 40 years old with unknown history, I am wondering what to do about tightening torques.
One possibility is using a bearing lock to stop the bearing creeping and then work at a reduced torque on the nut. Perhaps a bit of loctite with the nut to augment the lock-washer?
Does "everyone" go for the full monty or is that a ftlb or two too many?
At least not having a RWA means the wheel can't fall off!
|LocTite on the nut will keep the nut on, but might let the bearing move. But, "bearing creep" is not really the issue, as some systems are designed to have that. Here, the problem is the loose bearing wearing the axle stub. Use the right LocTite on the axle and bearing and you won't need a nut at all. To be a bit more conservative, use a lesser grade and tighten the nut to 60 or whatever. You WILL need a torch and puller to pull the hub next time, which ought to be past your own sell-by.|
|Graeme, where did the recommendation of 140 ft/lbs come from. That does seem excessive for a fine pitched thread of that size.|
I agree with Guy. 140 is way too high. I believe that's the torque setting for the pinnion drive on the diff.
The rear hub nut doesn't have a quoted setting. If you've done it to 140, that's def' why it stripped.
The outer of the bearing is pressed into the hub -- tightly, and the inner is free to rotate. The inner is clamped to the axle by the big nut, but unless the bearing seizes, I can't see anyway in which the inner could creep around the axle. Also the nut is done up in the direction of wheel rotation, so self locking to an extent.
Just do it up tight enough. I've never used a torque wrench on it, and in fact just use an adjustable wrench. And I wouldn't use any kind of thread sealer on there either.
If you've got 60lbs on it, even that's way too high, and more than adequate.
I's also likely that the nut is knackered rather than the axle thread.
|There are threads in the archives where respected posters quote WSM torque figures of 140lbs/ft.|
I've never found a torque figure but have always done them up FT with a two foot bar on my socket wrench.
On the racer, I used to dispense with the lockwasher and use Loctite, on the recommendation of a respected race car builder. The theory being that under extreme loading, the tab washers actually compress, allowing the nut to work loose and wrecking the thread on the axle casing.
With regard to the thread, you have a very large diameter - I don't have one in front of me, but approx 1.5" diameter - and with a full width nut, the torque figure would be in excess of 1000lbs/ft.
|Here's one reference:|
I also found previously other references which I am checking for again in case I misread them. I know in one of them there was a reference (by Lawrence!) to using stilsons on the nut but can't find that at the moment.
|Well if you're racing that's a different matter, I guess you've got to be sure.|
But in 35 years of doing it up as you say Graeme, with a pair of stilson, and having driven well in excess of 300K miles in my sprite, mine has never come lose. I still have the original nuts, and the very nurled original lock washers on both sides too.
Frankly, and though many people won't agree with me, I think there's too much worry in some of the tech articles. I've never torqued my wheel nuts, and they've never come lose either.
If the nuts and axle thread can stand 900lbs, then i can't see how it ever stripped.
|Dave O'Neill2: thanks for that... I now feel less of a d*ckhead!!|
Opinions seem very polarised on this one. I did find a reference a while back which explained that the bearings needed that level of clamping and other references to two fitters hanging onto long bars trying to undo the factory-tightened nuts! Lets avoid the left hand thread comments :-)
Experience now suggests that FT is too tight for an aged axle casing. But does that have any downsides other than the wheel falling off?
|for reference, here is another article citing a 100+ ft lbs torque, along with the calculations that show it is not anywhere near the limit of the threads and material used:|
Granted, he is talking about MGA/MGB rear axle assembly, but our little A30 housing is not that much different (actually, the nut is the same size, I think).
If the nut has been left loose for years though, and the driving on it like that has allowed it to chafe and erode the threads, then it could possibly get to the point where the threads will no longer hold a torque. That is a theory of what happened to OP.
Whatever the reason why it failed, 20 ft-lbs is so low that definitely something was very wrong with those parts, so he is smart to be replacing the housing.
|Its a big nut and therefore needs a big torque. 140 is not that excessive - although I'd be surpised if anything other that the crankshaft nut would be anything more than 100.|
Just remember, torque wrenches are for the guidance of wise men and the reliance of fools.
|C L Carter|
|I found a table which indicates that that a 1 7/8" af nut UNF thread can be torqued to about 680 ft lbs (this assumes the lowest grade steel). The nut isn't full thickness so assuming 1/2 thickness it ought to be good for around 340 so 140 doesn't seem to be unreasonable. But that assumes thread in good condition of course.|
I think in fact that (as someone else suggested) the nut took the bulk of the failure. Replacing the nut helped me get it all reasonably tight again although there was some rounding off of the tops on the axle threads.
|Here's the thread title you asked about Graeme.|
It's in the 2012 Technical Archive. Last post 06 June 2012 "Axle oil seal gasket - totally confused" .
|No Lawrence, that wasn't the one. Only 30 posts! Hardly worth reading :-)|
It did feature your stilsons, Alan pointing out that stilsons were "not ideal", and someone who used a toolmakers clamp to grip the nut.
Think it was probably a few years old!
|Ah well then, |
--- open the Sprite technical archive, enter 'rear hub' into the search box for all years, and then choose 'this phrase' as the filter.
When the page open, scroll down to the 'Rear ---- ' and you can spend a few mins/hours finding the thread you want. :)
|I don't think it's the size of the nut that determines the torque figure but rather the grade of the material (steel). For example it's obvious that a brass nut on the exhaust manifold stud will strip at a lower torque setting than a steel one. The lowest grade steel referred to is this higher or lower than back axle casing steel and does it assume new rather than used several times over 30+ years|
In my own record of torque settings I have 25, 46 and 80lb listed for the axle nut. I forget what setting I used, probably 75 being anxious of the foot note in brackets that states Toby stripped his nut at 80.
|If you were to "unwind" the contact surface of the thread between the axle and the nut, then the fact that it is a large diameter obviously gives a long contact length.So a high contact area capable of carrying a high load. However it is only a thin nut which means less contact than if it were a full width nut. The fine pitch thread also gives a low "gradient" to the thread which means that for a given torque, a relatively high axial thrust is produced (i.e. compression) to hold the hub on. However the large nut size clearly is a consequence of the design which needs space through the middle for the halfshaft, it isn't necessarily that size in order to give a high clamping capability.|
It seems to me that there is no great benefit in having a high compression load on the hub (bearing). Its not like the clamping load required on something like a cylinder head. All that is needed is sufficient compression to avoid any relative movement that would then result in wear. What is important is that the nut doesn't work loose - hence the importance of the lock tab washer, and that it doesn't strip the threads - hence I think it wrong and unnecessary to overtighten.
What is "overtightened" ? I don't know as I have never used a torque wrench on that nut. But I use an 18" bar and apply reasonable "grunt" which is probably around 90 ft lbs.
It also seems to me that if this were critical, then the manufacturer would have published a figure, at the very least for guidance of their dealer network mechanics. Although I have seen the 140 figure quoted, I think this has always been a matter of (possible experienced) opinion and not from BMC. Not a primary source, to use an historical research analogy.
I also use both locktight on the nut, and bearing grade locktight to ensure that the bearing doesn't rotate in the hub as this most certainly would cause wear.
|Entirely logical that Guy, and I agree with you completely. It just doesn't need to be that tight.|
It's quite common to have the outer race in a situation such as the rear hub just a slight clearance fit as the bearing resistance is less than the drag of the outer race in the hub. The many fit conditions are covered in places like the SKF design guides and it does depend on the application.
I can see the logic of having some clearance fit so as to avoid the possibility of being unable to install a bearing if you were unlucky in mis-matched sizing. But I think it sensible, given that bearing fit locktight is now available, to use that anyway.
|I agree that it "doesn't need to be that tight"|
Just thought I'd add though, that the thickness of the nut is largely immaterial (except for the fact that it itself may yeild if too thin). The bulk of the load on a threaded fastner is actually held by 1 or 2 threads at the end of the nut. If I dig through my old uni notes I could show you the maths =)
|C L Carter|
|Guy, I don't see the need for anykind of bearing glue on the bearing, since the fit is way more than an interference fit, ---- if using the original spec, and the hub isn't knackered. Of course, if your hub/bearing combination is loose, then it might/probably be/is worth using something.|
Have there been many, if any, instances of people reporting loose fit rear wheel bearings?
Hi Christian, same question really. Have there been many, if any, instances of people reporting that the rear hub nut is too thin?
It must have been designed to cope with the clamping load expected of it. Whilst obviously, I haven't spoken to everybody that has ever worked on a spridget or other similarly axled austin, until Graeme mentioned it, I'd never heard of anyone striping one of these threads. I'm sure it must have happened, but I don't think it's a common occurence, in fact I'd say it's the opposite. very uncommon.
|re 140 lb-ft: While the Midget BMC manual doesn't state a torque for the bearing nut (at least not in the edition I have) the MGB manual does list for the banjo axle wheel bearing a tightening torque of 135-140 lb-ft.|
|Lawrence, l hadn't heard of one stripped as such, but they are very easy to cross thread and if one were to persist that would certainly chew the thread off !|
|Yup I agree Guy, but you'd have to persist, as it would be pretty clear that it was crossed, and offer quite a bit of resistance. Having said that, there are plenty people out there I suppose that would just force it on no doubt.|
|Yep - crossed would do it... or corroded... - I have heard of someone tempering a nut before which hardened it so they stripped it that way... they didn't mean to temper it - but they heated it to break it free and then quenched it to handle it - hence they hardened it - Silly really.|
|C L Carter|
|Just adding my six pennyworth to this interesting debate, I remember the 140lb ft figure when I last had the rear axle in bits on my 1275 RWA. I was using a tubular spanner so couldn't use a torque wrench, but applied the maximum I could with a long bar and tube extension and limited by bending the bar. Say 50lb x 2ft = 100lb ft max and it's still OK.|
As I remember not having the official Workshop Manual at the time, I must have referred to my old Haynes manual and, Hey Presto, there's the figure on page 151!
|Well I assume then that there are different versions of the same thing printed by Haynes.|
Mine is a 1977 edition, and has an outline of an RWA Midget on the cover. Chapter 8 page 147, covers the rear hubs as well as the axle. Picture below shows the only torque settings mentioned. 140lbs is the diff pinion nut. Item 35 on page 148 Fig 8.1. Item 3 is the hub bearing retaining nut, no torque figure is given for this.
|Peter: P151 refers to the pinion drive flange nut, which is not the same one. No-one seems to quote the hub bearing torque. Perhaps it's handed down from father to son?|
"Now son, there's something you need to know now you've got a beard and a new torque wrench. It's about.... girls!"
"Oh no dad"
"Listen son, girls know nowt about torquing up hub nuts. Remember this.... it's 140 ft lbs to undo if you turn it the right way, 250 ft lbs if you turn it t'other way"
"I'll write that down dad"
"NO.. never write it down! It must remain a secret from all them new fangled bulletin boards"
"And finally son, ONE of them is a left handed b*gg**"
"Which one dad?"
"The one needing 250 ft lbs to undo son"
(apologies to any ladies out there who do know the secret of happiness when it comes to dealing with hub nuts).
Lawrence: the bearing I had was a "slide" fit on the axle. No play as such but didn't need a puller to remove. That's what I would expect as the nut is intended to secure it. I bet if I took measurements that the length of the step that the bearing sits on is slightly less than the width of the bearing race so it can be clamped by the nut.
|How about this then:|
|I used to teach my gf's all about nuts, otherwise I found them being overtightened on occasions, which I have to confess did make my eyes water. :)|
Yup a slide fit on the axle, but a very tight fit in the hub. I still don't buy that it needs 140lbs of torque to secure it.
|OK I read all that from MGA Guru, and have 5 things to say.|
1) whats a DPM?
2) Why doesn't the front wheel bearing setup need 180lbs then?
3)Is there ANY official reference, to the torque of a SPRIDGET rear hub nut?
4)I confess to having used a chisel and cross pein hammer to remove and tighten my hub nuts, before I discovered I could do it with a pair of stilsons. My hubs have NEVER come loose, and don't have any wear marks as a consequence either.
5) If anyone doesn't believe me, they are very welcome to come to my house, and I'll pull the hubs and show them.
I think 140lbs is a self perpetuating myth, like so much stuff that gets posted.
|MGA guru says.|
"150 ft-lbs is not a lot more, and is only about twice what you would apply to a 1/2" wheel lug nut."
Anybody here doing their wheel nuts up to 75lbs?
|1. Damp proof membrane|
2. 'cos it's a different design with 2 bearings facing each other
4. what's a cross pein hammer, I know what a ball pein hammer is
5. I believe you
|One of these. I only described it, to contrast it with a BFH. You don't need a BFH.|
Ah yeah but Dave, they are a pair of bearings that effectively act as one, and are clamped to the stub axle. Why not 180 lbs to clamp them? They are a slide fit on the axle, so why not 180lbs to prevent them from moving around?
|Actually 140 ft lbs is not that much anyway. I said earlier that I had never used a torque wrench on a rear hub nut, but just use an 18" bar and "grunt" tight. I guessed this to be around 90 ft lbs, but thinking about it I suspect it was a good deal more. Maybe even 140! |
Put a socket and bar on it in the horizontal position. Stand on it.Don't jump up and down or bounce on it. Just full static weight. If the bar is 12" long, chances are that for the majority (if not all) of the people here that will well exceed 140 ft lbs.
Like Lawrence, I just don't think that an actual torque figure is critical. Else it would be in the original manuals. Any time-served mechanic ( a concept, sadly long gone) would understand that it needs to be tight to stop the wheel coming off. And would understand what "tight" felt like without needing to look up a torque figure.
|I should add though, that I don't mind at all if peeps wish to do their rear hubs nuts up to 900lbs. If it makes them feel secure, and the nuts can take it, they should do them up to as much as they can. Waste of extra effort though, IMVHO.:)|
|Exactement Guy. as I recently told someone, I first started playing with cars under the guidance of Rolls Royce, and a Jaguar mechanics (my older brothers best mates ). When I first bought my Sprite, I used to go the Rolls or Jag garage and get their knowledge for free. The first time I changed my rear hub bearings or the oil seal, I was told by them just to do it up good and tight, and it didn't need any great long extensions on the socket bar to do it. which is just as well, as I didn't have the socket anyway. I may well have borrowed one back then but as this was 30+ years ago, I can't remember. They wouldn't have sanctioned the hammer and chisel though, that was my idea. :)|
|that's a Warrington pattern hammer Lawrence, used by carpenters, has no place in an engineer's toolbox !|
|I'm not a qualified engineer, so that gives me free licence lol.|
Ah didn't know there were alternative names for the cross peen hammer, more likely used by Electricians I would have thought. But actually I also have ball and claw hammers too. All very useful, along with a few panel hammers, on the Spridget or any car, depending on what you're doing to it.
|O/T (but related)|
does your 1977 Haynes cover my 1973 car properly because my 1974 and 1980 versions don't
the point - facts are hard to pin down and a lot of misinformation is perputuated some in printed manuals
|Haha Lawrence, I liked your one about 75 lb-ft on the wheel nuts. 1/2" B ones, yes, but 3/8 Midget nuts don't survive that sort of treatment. Good for sales of wheelnuts though :-)|
|I've lost two wheel studs by others overtightening the wheel nuts on my Spridgets|
luckily there's a (Driver's Hand) book that tells you about correct torque for this
did you see what I done there, two in one :)
|Bearing in mind (sorry!) that the same axle give or take an inch or two of casing length was used on Spridgets, Morris Minors, Wolseley/Riley 1.5s, A30/35/40 and gawd knows what else, there are lots of manuals where a torque setting might have been mentioned but I'vs checked a few of the above and can't find a reference anywhere.|
How tight are your nuts? ;o)
BTW cross-pein hammers are very useful for 'stretching' metal, forming curves.
|OK. Being the owner and user of the real Churchill tools since 1965. The correct tool 18G152 is a double ended socket, piloted in the axle casing so it DOES NOT slip off the nut, with an 18 inch effective length Tommy bar, or 16in effective if it is set all to one side. |
One end fits A series and the other B series axles.
When we were working on virgin cars = cars that have not been f&^*d with, it was normal to put a very hefty pull on the end to get these nuts loose, commonly my weight was not enough, and I had to pull up, adding leg power. That means the factory torque was in excess of 1.33ft x 155lbs = 206.15lbsfoots. Sometimes it took two guys, and occasionally it required jacking the car up by the Tommy bar. Go figure. (That bar is tough - and still straight!) The point here is that while the torque is not critical, it is "pretty damned tight", 140 is about minimum that a healthy wimp would get with the correct tool.
The factory saw fit to supply, and I still have, a hub puller 18G304 and adaptors 18G304*, and the tools 18G134 and adaptors 18G134*to press the bearings out of the hub. It can therefore be assumed that it was at least normal that everything was in the "light press fit" range. Such is my experience.
Note also that the bearing with any spacers which might be used in a particular hub, MUST be proud of the hub .001-2 or such that tightening the half shaft or outer hub WILL clamp the bearing outer race solid. If a hub is worn beyond this, then replacement or LocTite is essential.
I have taken cars apart that have been run long periods with the nuts loose but locked. or the outer race loose in the hub - it beats things to death and wears out all surfaces - axle, nut and locktab washer - and fills the oil with metallic debris. This has been known to seize bearings, and in race use at least, twist the ends of the axle case off.
The front bearings are solidly locked in place, by the nuts and spacer. The big difference is that the front wheels are not subject to the constant load reversals and hammering of the drivetrain, especially on starts and in the lower gears. When they are so subject, as in a front drive car, the torques again go into the 150-200+ range, or bearing/hub/spindle failures result.
And to drive the point home-
The "pein" is the other end to the flattish hammer face, some hammers having two of those, hence no pein. Ball pein hammers have guess what? Warrington hammers are cross pein, but are hardly representative of real cross pein engineer's hammers, which typically are in the 2 1/2 to 6lb range, but do come bigger (20lb) 'n smaller, down to Jeweler's riveting hammers(2oz). As opposed to straight pein engineer's hammers, which have the "pein" parallel to the handle. Wait until you meet a diagonal pein one, with one end LH and the other RH! A rack of assorted being favoured weapons of metalworkers.
|Thanks FRM, that is useful info about the factory tool.|
Out of general interest, would one need more torque to undo than to do up a nut like that? It always seems so.
|It does seem so, and I've spent a lot of time thinking about why. I think that first the lubricant film squeezes out over time, and secondly there may be some actual cold metal flow, which locks the parts in place. It seems more noticeable on parts which are neither very hard nor very smooth, like these stamped out bits - parts which leave marks in the adjoining faces. Hardened and ground parts do not seem to do this to the same extent. And it does seem to be time dependent - less noticeable after a few minutes than after hours or days.|
|Stiction also has a lot to do with it Guy. |
Yup very interesting FR. Not sure I got the point of all that stuff about cross 'peen'(also spelled pein) and ball peen hammers though. I only mentioned using one, to illustrate that you don't need a BFH to undo a rear hub nut. My 16oz wooden handled stanley did easily, and it had NEVER been removed before, it wasn't 'loose', and hadn't thereby caused all the damage you describe below.
I'm quite sure your right though, that at the factory they would have used the correct tool for assembly. It would be odd if they hadn't. As regards how tight they did the nut up, I'd like to see the proceedures manual. I suppose in the absense of a torque figure, it must have said something like; -- "get the smallest wimp on the assembly line, to lean on the bar with all his F#$#$#ing weight" -- then. :)
Of course when advising those that followed the sale of the car, the factory would stipulate the tools to be used. They wouldn't likely do anything else, esp if the intention was the service and repair in a BMC or approved garage. However, those tools were not always available, and often more expensive than something else that would do the job just as well.
For example you don't need a rear hub puller on a Spridget. Turn the brake drum over, bolt on, and use it as a slide hammer/puller. Works every time.
Bearing removal from the rear hub, unlike the front hubs which have have drift pockets, involves pressing on the centre race, or whacking it with something. Yup if you have a press, it's nice, but if you don't, you can just as easily drift the replacement back in with very little effort using a 16oz stanley hammer and old bearing.
|Whoops, I made a mistake.|
My Stanley cross peen hammer is only 14oz.
|Lawrence, what is your point?|
Geez, we have explained to you by using thread calculations that the nut is capable of far more than 140 ft lbs. That was not "opinion", it is fact, supported by engineering design practice.
We have also had the benefit of a highly experienced British car mechanic agreeing with it.
We have also found MGB manuals which state the same torque value.
Apparently your only point is that if you don't see it written in a manual with your car's name on it, then all other sources of information are of no importance.
The nut needs to be tight, and because it is such a large diameter, "tight" is more than you are used to thinking of, because most of the fasteners are much smaller diameter. It is too bad that BMC didn't write this one down, but we have identified so many sources which support the number of at least 100 ft lbs, and as much as 140 that you really need to stop trying to turn it in to a debate.
|FR Millmore: everything you say is confirmed by my efforts on Google over the passed few weeks. There was even a post here which I found which confirms the idea of two blokes leaning on the socket tool to undo the factory fitted nut. Sadly can't find the post in archives.|
Your comments about bearing fit also ties up with my experience in the paper industry. I have seen 50mm shafts with 1 mm deep grooves worn down by the inner race turning on the shaft so I am very aware of the consequences of that nut not effectively locking the race.
The problem really comes down to this. If 140 is the "design" torque, how probable is the fact that old axle casings would fail prematurely and therefore shouldn't be subject to the same standard. Although I agree that it is all about "feel" when tightening from my recent experience "creep" started at very low torque and by then I started to worry that if the thread was very near to failure whether an overload on the wheel during driving could "burst" the remaing thread out? I think that is it likely that if I can get around the 60 ft lbs I would leave it at that rather than going on the hunt for ANOTHER casing having broken this one. About half the posters regard that as an acceptable torque, but others don't!
On another note, seeing that axle casings are no longer available "new" can one with a damaged thread be economically recovered?
|What's your point Norm?|
Which MG manual says a Spridget rear hub nut should be done up to 140lbs? I don't have an MGB, so can't tell you if the rear hub nut on an MGB is quoted at 140lbs or not. Not relevant is it? A spridget isn't an MGB. If the Spridget hub was meant to be done up to a minimum of 140lbs, I'm quite sure that it would have appeared in the official publications at least once in the production life of the Spridget, or perhaps as a service update afterwards.
Many of the nuts on spridgets, and all manner of cars, are capable of being done up to torques way in excess of those stated in the manuals -- when they are stated. Does that thus mean then, that for the sake of safety and peace of mind, that you should go to the max potential torque with all nuts?
"Apparently your only point is that if you don't see it written in a manual with your car's name on it, then all other sources of information are of no importance"
No that's not my point at all.
Is it your point, that because someone without any official BMC references, writes an article stating such and such, that we should all fall in line and bow down to the master(s)?
Well Norm, gee whiz old mate, of course the nut needs to be tight. There's a thing. I never would have guessed unless you told me that. Thanks ever so much.
Of course it needs to be tight, tight enough to keep from vibrating off, to keep from allowing the lock washer to rattle around, to keep the hub firmly in place, etc etc etc, ad nauseum. It doesn't take an engineering degree, or an experienced qualified mechanic to work that out for themselves.
And given that these cars have been around for such a long time now, with many if not most people, NOT USING a torque wrench to do up the rear hub to 140lbs - ( and guess what I haven't heard of hubs falling off) -, don't you just think that it might not be that critical, that the hub nut is done up to 140lbs? Esp when that figure was never given by as being necessary, other than since the invention of the bbs and the internet?
But hey, your as welcome to your "opinion" Norm, as I am to mine.
You have a nice day now. :)
|As an observation,in my racing days in the 80's I had my rear axle prepared by Mallock racing. They still exist and use BMC axles! The failure of the rear hub was quite a common problem particularly with worn axle shafts allowing the bearing to 'float'. They just cut off the damaged/ worn hub and welded on a new one on. The casing was checked for alignment using a long steel shaft which was a running fit in the both hub bearings. They always locked the nuts up very tight using the Church Hill tool. Apparently a stripped thread did occasionally occur due to wear on the threads due to a previously loose nut. |
|As I put earlier Bob, "Well if you're racing that's a different matter, I guess you've got to be sure"|
If I were a racer, I'm sure I'd have a very different approach to many Spridget tasks. But this is road use, not track.
|Graeme W - there's no shortage of axle casings (yet) and little demand; I've chucked away several perfectly good ones from breakers because I have enough spares for myself and nowhere to keep them. If through sheer bad luck you need another one, just ask on here and I'm sure it wont be long before one is offered.|
You did not actually say whether it was the nut or the case thread that failed, or both. If the new nut is not too sloppy, it is likely just fine. In my experience, these failures are always due to nuts having been loose at some point, wearing the threads. It used to be common to replace the nuts, but I never had to replace or repair the casings. True that time and miles and ham handed brain dead idiots have had more years to wreak havoc. In any event, if you LocTite the bearing on, and Loctite the nut, you are good to go. An off the wall approach is to find a lathe and make a nut with undersized threads so it fits snugly.
BMC were not a bunch of hicks with an adjustable spanner and a rock; they were a major automotive manufacturer and industrial establishment. While I was admittedly not there, things like this would have been installed with torque limiting power drivers. Such devices have been known and used for more years than you or Lawrence own, but they are subject to considerable variation, especially as tools age. This is NOT a critical torque application "PDT" as defined earlier works fine.
"Which MG manual says a Spridget rear hub nut should be done up to 140lbs? I don't have an MGB, so can't tell you if the rear hub nut on an MGB is quoted at 140lbs or not. Not relevant is it? A spridget isn't an MGB. If the Spridget hub was meant to be done up to a minimum of 140lbs, I'm quite sure that it would have appeared in the official publications at least once in the production life of the Spridget, or perhaps as a service update afterwards"
I deliberately posted and emphasized that IT IS the SAME tool and the SAME experience for BOTH axles. The slight difference in sixes and theoretical torque limits is insignificant.
It has long been accepted, until lawyers and idiots came to control, that a reasonable degree of competence in a field was expected of the practitioners in said field. That is why earlier books have about 6 torque specs while later ones for similar or identical devices sometimes have many pages.
When an opinionated Jackass causes a failure on a road car and kills 9 people, it is at least as important as any racing failure. AND it IS the kind of thing that leads to onerous regulations, such that people in some places and fields CANNOT work on their own stuff, without truckloads of inspections, permits, and certifications. Said Jackass earns his credentials by ignoring the collective experience and knowledge of hoards of people with more than two functioning brain cells. I have taken several thousand of these things apart in 50 years of doing this, sometimes on the same car over many years. And I have the tools and I understand and have studied the theory and science. I KNOW what failures look like, and what causes them.
|LOL. Well bully for you millmor.|
"I have taken several thousand of these things apart in 50 years of doing this, sometimes on the same car over many years." Same car huh? You must be doing it wrong then baby, if they keep coming back with the same problem. :)
Now admitedly, I can't be as old as you, and I was taught to respect my elders. However, since I too have taken a few of these apart, and not had the benefit of the 'correct' tools --- it's only a socket for heavens sake, not a sonic screwdriver --- , and not had one hub fail on me, or ever caused a failure on the road, as you put it, and never killed anybody, I reckon I'll just ignore your over opinionated view of yourself, and carry on in my own sweet way. I'll also keep commenting whenever I feel like doing so.
I also think it kind of strange, given all that experience of yours, that this bbs isn't absolutely full of stories of failed rear hubs, given that so many people aren't full of your wisdom re the 140lbs requirement. Buy hey ho.
Now as a learned man, I know you'll be keen learn something else too. So study this. Up yours :)
With the greatest possible respect, --- of course. ;)
"This is NOT a critical torque application "
So why have you got your frillies in a twist then millmor? lol.
|David: I came to the conclusion that the cost of having a workshop make a new endpiece complete with thread and gbearing housing to set into the end of the axle tube was going to be greater than could be justified.|
In my case I think the thread may be salvageable because a new nut seemed to make the difference and is currecntly torqued up to xx ft lbs (I wont mention the value of xx to avoid relaeasing that cat again) with loctite. I do worry about it bursting off (being a worrier) but more importantly I have "proper" wire wheels and hubs but a steel wheel axle. That plays havoc with the setup on the halfshafts and runs very close to the wheel arch. I have taken the opportunity to get hold of a wire wheel axle casing.
|On one of our axles which had a number of mods to it so representing a fair amount of work, repair seemed a better option than get another exle and modify it.|
We could have welded on a new end as described above, but in the end used a local engineering shop which services a lot of truck axles with the same sort of problem: It's process is to weld/build up the affected area, stress relieve, and re-machine. Worked out well and as the whole rear axle was spun in the lathe to machine the end, the repaired end was sure to be true.
BTW my MGB is onto its 4th axle now, the others have cracked at the change in section between bearing mount and seal area. OK, it's had a hard life as a rally car and some forest roads and riverbeds are not kind to it when taken in a spirited way causing the bump stops to earn their keep, but it does show that in normal use the design has not a lot of spare up its sleeve.
(Of course, the Midget is lighter, but so is the axle)
|Here's an interesting post from way back when.|
"The hub nut is 1&7/8" and according to Restoring Sprites and Midgets by Grahame Bristow should be done up to 45ft/lbs."
I haven't got this august publication, so I can't say if that's printed in there or not, or indeed even if the book is any good. Anybody got it?
I've also been reading about the purpose of torque, as being applied to cause a degree of stretch in the stud or bolt that it's applied to. So in this case, as it's not a bolt or a stud, and it seems pretty unlikely that it was intended to 'stretch' the end of the axle, I would say, as I've said before, torquing this nut isn't needed.
|45lb/ft is the torque setting for the wheel/lug nuts.|
|On the point about more torque seems to be required to undo than do up a nut, I believe that to be a fact. The reason is that when doing a nut up to a certain torque you are already moving the nut and the pressure is steadily increasing, but when removing it you are starting at the highest pressure from a standing start and so more initial torque is required. You can prove it by doing a nut up to a certain figure and then trying to undo it with the same setting. This is the reason manuals always tell you to undo things like head bolts a bit before re-torquing after an overhaul.|
|Woohoo - my axle has arrived! Now getting close to crunch time with the torque settings! Need a few more days in the gym first.|
|I think I'll torque one end at 140 and the other at 45, just to see which wheel falls of first! That would settle it once and for all.|
|That's what I put earler Trevor. Stiction.|
Another point in this tight or high torque question, is that the lock tab, which is keyed, and thus doesn't turn with the nut -- unless the tab is missing -- is made of relatively soft metal, and deforms when the nut is tightened against it. Unlike the front spindle, which is harder and thicker, and not meant to deform or be bent over the nut.
When you grind the nut into this 'soft' locktab -- which you are doing, if you apply too much force, -- and also the tab is hard against the axle groove, thus making it harder still for the locktab to move inwards, your as much trying to overcome the opposition of the lock tab, as trying to put additional compression on the inner of the bearing. You'll soon get to the point when all you may be doing is increasing the torque measurement, without turning the nut at all, because it's locked against the washer which can't turn with it.
Additionally, as Guy remarked earlier, and I think has been overlooked " -- However the large nut size clearly is a consequence of the design which needs space through the middle for the halfshaft, it isn't necessarily that size in order to give a high clamping capability."
Clearly the nut had to be big enough. But to then look up the torque tables for a nut and bolt combo of that size, and conclude that it should be torqued to those figures, makes no sense at all.
|The washer is very soft. I can't imagine that giving much of a fight to the locknut as it tightens. But I still think the main purpose of the nut is to satisfactorilly lock the bearing race onto the axle. If it can "creep" (and that is a technical expression) it will damage the surface on which it sits. As I said before, I've seen that happen on machinery where it mills out a sizable groove. I don't think it's about the nut coming loose, but about the bearing turning.|
The only question is....... dah, dah,dah,daaaaaaaaah!
- what torque is needed to stop the bearing turning?
|" But to then look up the torque tables for a nut and bolt combo of that size, and conclude that it should be torqued to those figures, makes no sense at all."|
Was that the conclusion, or that it could be torqued to that figure without stripping the thread?
|Dunno, but I'm never going to torque mine to 140 or even a ton, just to find out. It doesn't need it.|
I reckon if the nut is loose enough to allow inner race of the bearing to rotate, it would be pretty obvious with an open ended spanner, if you have one that size, or a tool makers clamp/vice, as some people use. :)
Also, if the inner of the bearing is rotating, with the nut reasonably tight, there must be quite a bit of drag from outer, in which case the bearing is shot anyway, so you should replace it.
And I've been searching the archives for "grooved" axles. Haven't found any yet.
|Interesting how this "thread" has vacillated around opinion about how tight the hub nut needs to be. |
In the second message FRM says one could manage with only 60 ft lbs together with the right type of Locktight. But later he describes the Churchill tool and says that although a torque figure isn't critical it should be done up "pretty dammed tight" which he puts at 140 ft lbs minimum but likely as much as 205 ft lbs.
I simply queried whether BMC had ever posted a torque figure (of 140) for the Spridget axle as I had never found a primary BMC source of that figure. I also commented that I do them "grunt tight" which I estimated initially as about 90, but on reflection believed it to be a good deal higher. Pretty Dammed Tight as FRM would say.
That's good enough for me. I believe that BMC didn't specify a torque figure because a specific figure isn't critical, and any experienced engineer would know to do it tight enough by feel, and that is good enough.
Incidentally, calling the higher undoing torque "stiction" just gives it a name, it doesn't explain anything! I suspect that it is due to the "meshing" of microscopic metal mountain ranges and valleys between the two surfaces.
|I thought stiction was a word that contains it's own explanation. It's a portmantaue of static and friction.|
Is it a modern term I wonder?
I thought "stiction" derived from stick and friction as things like journal bearings often have a higher torque to start movement than to maintain it.
|I think it depends where you look. Webster has it as static/friction, first used 1946. |
But I too also remember in physics being told it was, as you say, stick/friction.
|"portmantaue of static and friction"|
Fancy words Lawrence. Copied directly, I see, from Wikipedia, except you have misspelled it. Still doesn't actually explain it.
But Wiki does go on to detail molecular and electrostatic attraction, and molecular adhesion as the primary forces involved.
|Actually no Guy. It may surprise you to know that I do know the word portmanteau, and what it means -- even if I spelled it incorrectly. Typo I assure you. :)|
If I'd copied and pasted it from Wiki, I would have spelled it correctly. Actually, I found it in websters, without the word portmanteau.
|Meeting my expectations, Lawrence. I wouldn't expect a different response from you!|
|Nor me from you Guy!|
|"I believe that BMC didn't specify a torque figure because a specific figure isn't critical, and any experienced engineer would know to do it tight enough by feel,"|
However, back then, when many more people used to work on their cars, -- since they were far lower tech than today -- , the average bloke working on his Morris Minor or A40, wouldn't likely have been an engineer. When I was young, and so much younger than today, hey, I never --- knew anyone who had the money to pay a garage to work on their old or newish car, so they did it themselves. Milkmen, postmen, accountants (maybe not them), butchers bakers and candlestick makers et al. I reckon BMC and other car makers would have known that too, and if a torque figure was important, it would have been quoted. In the absence of that, they also knew that most blokes were pretty mechanically interested back then, if not minded and able.
Most people faced with the rear hub nut back then, would realise that it had to be tight enough, even if they'd never even heard of a torque wrench. I used to meet loads of them down Stockwell motors at all hours, and 'esp on Saturdays. As has been said many times, these are simple cars. Easy to work on, because you can see how they tick. Not many mysteries to people who grew up, out of necessity having to fix things themselves. Something Nigel has reminded me of before now I seem to recall.
So whatís changed in the last 15/20 years then?
These days, everyone's hand is held. Not of necessity I think, but of a pre-occupation with safety. Be careful there, donít take that risk, watch that step. Make sure you follow this and that rule. Do a risk assessment, and make sure your shoe laces are extra tight. You can't be too careful. Better over tight just to be on the safe side. And now it infects every aspect of life. Even on bbs.
Exactly as you said Guy, BMC didn't specify a torque figure because a specific figure isn't critical.
|That's a long message Lawrence - well fuelled I presume? ;-)|
I agree with you though. There's too much cotton wool these days!
The Graham Bristow book mentioned earlier is quite good - lots of detailed photos and step by step instructions on restoring/ renovating Spridget components; good for a not very confident "first timer". Its really an illustrated tale of one man's restoration project, easy read and quite lighthearted. He just quotes this 45 ft lbs figure in the text on assembling a back axle (not in the more comprehensive torque tables) and it isn't clear where he gets it from.
Checking my facsimile copy of the Sprite Mark 1 manual it just says to use a new tab washer and to "tighten the nut on". It makes no point about how tight; no adjectives like "firmly" or "securely" or "f*%$*ng tight". It doesn't even say to use the Churchill tool to tighten it on with, although it is listed and illustrated. Howerver it does says to drift the bearing on using a special service tool which implies that this is how close bearing seating is ensured, - rather than by pulling it up tight with the nut?
I very much suspect that this 140 ft lbs figure has come about by someone somewhere mixing it up with the figure for the diff flange nut (which is a critical torque). And the power of the internet has long since spread this error as gospel.
In the 1950's in the UK at least, I believe that home-owned torque wrenches were pretty rare. As even were socket sets - certainly of that sort of size. For nuts like that the old box spanner ruled which itself would limit how tight it could be done up! And not just for DIY users either. Lots of smaller garages would be equipped with only basic equipment by today's DIY standards!
|Guy, good point about who owned a torque wrench way back and also that many village garages only had basic tools as many had progressed from blacksmiths into garages over the years. Although I have had a torque wrench for years I think back then I only really used it for head bolts. It didn't really get used frequently until I had an ally engine.|
Lawrence, I agree with you about pre-occupation with safety and building in higher limits than necessary (perhaps we need a new generation of Colin Chapmans).
Interestingly on the point of how tight things should be, I remember my uncle telling me that when he was an aircraft fitter in the Fleet Air Arm in the 50's and 60's they were not allowed to use ring spanners to do anything up. The explanation was that the correct size open ender was made to tighten the nut or bolt tight ehough and ring spanners exerted too much force resulting in failures etc.
|ha ha. Fuelled with a late night bowl of cornflakes and glass of coco Guy. I was feeling peckish.|
Yup, that's what I meant earlier, about self perpetuating myths. Once they appear, on the internet especially, you can't get rid of them, and they become the gospel of "don't be foolish, everyone know this or that".
I'm often too lazy to get my torque wrench of the hook on the garage wall, and like you Trevor, I mainly use it on the head, or the crank big end bolts, but can't always be bothered elsewhere. And you're dead right about Blacksmiths. There are two old garages near me, both used to be blacksmiths, and one still looks like it is. I wouldn't be surprised if they still serviced horses. :)
|"it does says to drift the bearing on using a special service tool which implies that this is how close bearing seating is ensured, - rather than by pulling it up tight with the nut?"|
That's particularly interesting Guy. I recently changed the oil seal on my offside rear hub. I used the reversed brake drum, slide hammer fashion, to get the hub off, and found that I had to push the hub back on again with more than a little effort. --- Not having the correct service tool, I used the nut when I had a decent amount of it threaded on the axle.
So that confirms your finding. Even after 45 years, my rear bearing/axle is still a tight interferance fit. Not much chance of the inner race rotating at all I wouldn't think.
|The "special tool" is a drift. One for the oil seal and one for the bearing. I had wondered if the bit that the bearing goes onto is maybe slightly tapered.|
Another interesting bit is that it says very clearly that the outer bearing has to fit flush or slightly below the hub face so that when the halfshaft is tightened on, it properly seals the rubber ring and paper gasket. I had (wrongly) thought the bearing had to stand fractionally proud so the the halfshaft would clamp against it to stop it moving around. I saw that FRM stated this also earlier on as well, but it is the opposite of the factory manual advice. I used bearing locktight there anyway.
|I've got a spare pair of freshly assembled rear hubs. I bought them cheap earler this year. I'll take a look and post a pic or two Guy.|
Otherwise, there it is, isn't it? The answer is that the design is for the bearing to be a tight interference fit on the axle casing. It can't rotate because of that. So assuming you haven't got a damaged axle, AND you have a quality original specification bearing, why would there be a problem, or a need to tighten the retaining nut to extreme torques?
"quality original specification bearing" I wonder if there's an issue here after all, with aftermarket non RHP or whatever make original bearings? Might there be non original spec bearings out there, that fit the hubs correctly, but are a 'loose' fit on the axle?
Maybe that's the root of the stories about bearings spinning on the axle? -- At least on the road, not on the track, where the cars are subject to far greater stresses.
Going back to the origins of this thread, I don't see that there was a bearing/axle clearance/rotating issue anyway. It was a knackered thread issue.
Not ignoring your reference to the paper milling industry Graeme, how does the original axle look anyway, re the suface where the bearing seats?
|"He just quotes this 45 ft lbs figure in the text on assembling a back axle (not in the more comprehensive torque tables) and it isn't clear where he gets it from."|
How about this Guy? The author knows that today, people - his target audience -- are aware of torque wrenches and have access to them. He also knows that using a rather vauge term to described how tight to go, might leave his "first timers" in some doubt. So using his own experience, he puts a reasonable figure on it. Not too much, not too little. Just perfect porridge.
|I've been away for a day or two so only just saw Lawrence's comment about the figure in the Haynes manual and of course he is correct. That torque figure does relate to the pinion drive flange nut, not the hub nut. (Mine's a later 1990 edition.) Sorry for any confusion.|
|Here's the pics of one of my spare hubs. I gave the outer race of the bearings a good whack, to test if the bearing was fully seated. You know when it still has further to travel by the sound and the feel of it, and on both of my spare hubs the bearings are definately fully seated in the hubs.|
They do sit proud of the hub face, by about 0.008"/0.02mm. I tried a 9thou, and that was too tight. The half shaft is clamped without the paper gasket or rubber oil ring, and with the nuts just a little over finger tight, so as not to distort the flange.
Btw, the bearings are R&M, but then you already knew that.
|Spot the typo. "0.008"/0.02mm"|
That is exactly as I would expect it to be, and that is how mine were last time I assembled. Seems logical that the bearing should stand just sufficiently proud so that the outer race is clamped up by the half shaft flange.
But the WSM says that it is essential that the paper gasket is compressed before the shaft flange pulls up against the bearing. As it then goes on to say that a DIY made gasket should be 0.010" it seems that yours is just OK as a 10 thou gasket would have 2 thou of compression before the bearing is contacted. It makes no warning of what happens if there is no compression onto the bearing though but I suppose that wouldn't happen so long as the bearing itself was as specified.
|Makes you realise though, that its the rubber ring that keeps the oil in, not the gasket.|
|Good on ya Lawrence. Sometimes I feel that some of the posters here like to scare munger with their superior knowledge, when what is needed is usually reassurance or just some good advice. You know who I mean ;).|
|If you remember I used a toolmakers clamp to remove and re-tighten the hub nut. The wheel has not come of on it's own yet.|
|I did a bit of research on the correct installation of bearings. Under conditions as we have in our rear hubs we have a stationary inner and rotating outer race. The load direction is fixed. Under these circumstances several bearing manufacturer sources suggest that the outer ring should be an interference fit and the inner can be a slide fit. Creeping ie the bearing rotating in its housing is a risk for the outer, not inner race. The load causes minute local stretching of the race ring and as this cycles round, the race can move or "creep" this leads to wear.|
If I have interpreted this correctly - and I would be happy to hear from someone who has proper experience here - it means that the inner race does not need hefty clamping by the nut! But the outer race does!
In my installation I thought the outer race was the one which was a tight fit and needed pulling, not the inner. Is is probable that the half shaft flange or the w/wheel hub extension is intended to clamp the outer race in the housing? After all if the race protrudes slightly it would do just that. Perhaps that's why they say there is a max thickness for the gasket? As the bearing could hold the hub off a gnats, the rubber O ring fills the gap!
And now...... do four wheel nuts torqued to say 40 ft lbs and clamping the outer race have the same effect as 140 on the inner race?
|Pete, Likewise, I also use a toolmakers' clamp as it opens wide enough is fully adjustable and neat enough to fit in between the wheel studs.|
Not sure if its an error in the manual, but in the Sprite (Mk1) manual it doesn't include the rubber O ring in the exploded diagram of the hub. In the later manual (Sprites 11 to 1V) it includes it on the exploded back axle drawing. Text instruction about compressing the paper gasket before the bearing is the same.
PS Graeme, I think the 140 as a specified figure is a fictional one
The rubber O ring was a modification to the hubs to improve oil sealing - same on early Morry minors - not sure when it came in.
|The Mk 1 manual has an exploded drawing of the hub, in which the rubber ring is absent.|
And over the page is an exploded drawing of the whole back axle, which does show the ring!
The text makes no mention of it!
My A35 Haynes manual shows the back axle illustration with the O ring.
I wonder when it came in? I need to check the rear hubs on my Frog!
|Graeme, you said you had a ww hub on a disc wheel axle. Since (at least on the MGA) the disc axle case is 2" wider, you probably don't have full engagement of the shaft splines at the diff. Have you checked?|
To add to the discussion a new twist (pun intended) - the point is not to tighten up the nut as tight as it will take, but in this case to apply sufficient pressure to stop the bearing inner race turning. Now we can calculate approximately what force that is using the screw formula and an assumed friction factor - it comes out very high, in the 000's of lbs. So how could the bearing possibly turn? I think the answer is that it takes very little motion to torque to say 40 or 100 ft lbs because the system is very stiff and has no stretch in it to hold the tension, unlike tightening a very long bolt or stud. So, things like temperature changes can tighten or relive the force very easily.
|Art - you are right, my axle is (was) the standard steel wheel variety. THat's how all this started because I needed to replace a worn ww hub extension and found to my horror that I had about 1/4" of half shaft engaged in the diff. I had the shaft only partially inserted in the hub inorder to make sure the diff end (which is where they fail) was fully engaged. However things took a turn for the worse when I screwed up (literally) the hub nut when replacing bearings. I now have the correct casing!|
(not yet fitted).
|Graeme, you may also need a different handbrake cable with the new casing. On my MGA the DPO had done the same thing - fortunately he hadn't driven it like that. I had to swap casings too.|
As my previous post and quote from early Haynes manual - 1972 print - 'Very early cars may not have the O ring seal'.
|"Graeme, you may also need a different handbrake cable with the new casing"|
That would depend on the age of the car.
Handbrake cables were the same on both W/W and S/W cars up until 1977 when the design of the handbrake cable changed.
Prior to that, the rods were a different length.
|Dave: thanks, bought that too, although if I have got it right it's actually the rigid rods from the centre pivot to the hubs which need replacing as the distance is 1/2" less each side. Nowadays the Moss type are adjustable I believe but I got a pair of "used" ones.|
There is bound to be one minor item costing 49p plus £4.50 postage which I've forgotten. I also wonder what other "suprises" I'm going to find!
|Talking strictly about road, not race track.|
Going back to this notion of the inner race of the bearing rotating on the axle shaft. How can this happen? I can't find a single entry in the archives of this happening. Nor have I ever known of it happening. It hasn't happened to my '66 sprite after 46 years, and I haven't read or heard of it happening to all the vairients that had this axle setup. If this was a problem it would be known about.
The inner race is more than just an easy slide fit on the axle. It needs a puller or a slide hammer to pull it off. It needs more than just finger tip pressure to put it on. The outer spins so freely on the inner via the balls, that it's difficult to imagine rational forces coming from the outer bearing sufficient to cause the inner to rotate on the axle. If there is suffient drag coming from the outer race, enough to rotate the inner race, then the bearing is toast.
The outer race has to be pressed or hammered in to the hub. You have to press or hammer it out.
If either the inner or the outer are a loose fit on either the axle or the the hub, then something is out of spec. Either damaged axle or hub, or an incorrectly sized bearing.
I don't reckon the nut isn't there for the purpose of preventing the inner turning on the axle, and the halfshaft isn't there to prevent the outer turning in the hub. The nut is there obviously as described, to retain the bearing, against the side forces that would displace it. The halfshaft obviously does the same thing. Of course you need both, but they don't need 140 lbs.
And as you pointed out Graeme, the outer bearing also benefits from the wheel nuts. In fact, the small halfshaft retaining screws aren't doing much at all once the wheel nuts are in place.
I have never done my nut up that tight. My bearings haven't rotated, either on the axle, or in the hub.
|Also, If the outer race was rotating in the hub, there would be very obvious consequential marks on the inside face of the half shaft flange, and on the face of the outer race of the bearing. I've never seen those, has anybody?|
|Lawrence - google "bearing creep"! The rotation of the race has nothing to do directly with the drag from the bearing. The load on the bearing distorts the race a minute amount and since the race relative to the load cycles round, the race can gradually turn. It's just like a hoola-hoop!|
Since the load in our case only moves relative to the outer bearing, that's the one which creeps.
ARe you sure the inner race is a "drive" fit?
|My outer race wasn't a particularly tight fit in the hub. Not so loose that they dropped out of the hub, but certainly no difficulty in removing it by finger pressure. Which is why, when I replaced them, I also used bearing grade locktight.|
|.... but what about the inner race?|
Lawrence has confirmed that the outer race is proud of the face of the hub so the outer component of the hub (the half shaft end flange or the w/wheel hub) will lock it into position and hopefully prevent it creeping.
Yup googled that, very interesting. On the SKF site there are 4 demos. This situation seems to match Demo1, and as you say suggests potential for the outer to creep round.
It then goes on to discuss interference fits. From what Guy says, the fit of his bearing is looser than it should be. Worn hub or wrong spec bearing? R&M bearing or aftermarket?
On mine there's no way I could have pushed the bearing out or into the hub without a press or a hammer. I don't have a press, -- but I do have hammers and drifts :).
As I asked earlier, if the bearing was rotating, by whatever cause, against the force of the inside flange of the halfshaft, wouldn't there be tell tale marks as a result on both surfaces? Are there such marks on yours?
And yep I confirm that the inner race is a "drive" fit as you call it. I can't pull the hub off the axle with just my hands. I had to use the reversed brake drum as a slide hammer, and I couldn't push it back on, I had to use the nut to pull the hub back on.
|SKF also says ---|
Radial location of bearings
"If the load carrying ability of a bearing is to be fully utilized, its rings or washers must be fully supported around their complete circumference and across the entire width of the raceway. The support, which must be firm and even can be provided by a cylindrical or tapered seat or, for thrust bearing washers, by a flat (plane) support surface. This means that bearing seats must be made with adequate accuracy and that their surface should be uninterrupted by grooves, holes or other features. In addition, the bearing rings must be reliably secured to prevent them from turning on or in their seats under load.
Generally speaking, satisfactory radial location and adequate support can only be obtained when the rings are mounted with an appropriate degree of interference. Inadequately or incorrectly secured bearing rings generally cause damage to the bearings and associated components. However, when easy mounting and dismounting are desirable, or when axial displacement is required with a non-locating bearing, an interference fit cannot always be used. In certain cases where a loose fit is employed it is necessary to take special precautions to limit the inevitable wear from creep, as for example, by surface hardening of the bearing seat and abutments, lubrication of the mating surfaces via special lubrication grooves and the removal of wear particles, or slots in the bearing ring side faces to accommodate keys or other holding devices."
My note: There is no mention of using a clamping force to prevent rotation or creep.
|Got one hub off -the side which has been the start of the problem. I can confirm that the inner race of the new (100 mile) bearing (an SKF 6207ZZ) and the inner race of the old bearing are slide fits on the axle journal. I was also supried how easily the nut came undone considering I torqued it to 60 or 70 ftlbs.|
This might be due to wear earlier in its life. Because the brg width is greater than the journal there wouldn't be any form of witness mark.
So why would it wear?
Assume it was tight ie interference fit before any wear took place. It could only wear by turning on the journal. That wear reduced the quality of the fit from the original press fit to a slide fit. Therefore one must conclude that at some stage the original press fit wasn't adequate to stop it turning.
Why was it turning if it has the interference fit? Because the nut wasn't sufficiently tight!
My earlier messages about what is in the workshop manual may be relevant here. It makes it clear that both the oil seal and the bearing should be firmly drifted on before the washer and nut are fitted. Although they list a special tool for drifting them on any suitably sized socket or old bearing race would do it.
The manual makes no mention of torquing the nut or even that it should be done up particularly tight. From this I think that drifting it on is the important bit, to properly seat the bearing rather than relying on the nut to pull it up tight. If last time the bearing was fitted it wasn't seated properly first then that could explain why it now seems slack.
|I presume you mean the nut being slack, Guy? The bearing was a slide fit when I put it on about 100 miles back so something in its history before my time must have caused the looseness. The note in the manual does imply it should be a tight fit on the inner race.|
I see in Grahame Bristow's book he states 45ftlbs for the nut! This is the same as the offial torque for the road wheel nuts and the front hubs. It is in the same sentence stating that the right hand nut has a left hand thread! Mmmmm.
|If Grahame Bristow knows that the torque figure really is 45 lbs/ft, he must have got the information from somewhere. No-one else seems to have found it.|
If he does state that the right-hand nut has a left-hand thread, he is mistaken.
|Sorry to be pedantic here, but the talk is of drifting 'on' - in some passages-- when surely you mean drifting 'in'.|
The oil seal is the first to be drifted into the hub (annoying design feature), followed by the bearing. Both should be a tight fit in the hub.
Then the assembled hub is pressed/drifted/hammered/pulled by the nut (your choice), onto the axle. This should also be an interference fit, not an easy loose sliding fit.
The original bearings were R&M as far as I know, so the SKF bearing you have might not be 'exactly' the correct dimensions, and this might account for it being a looser fit.
In the long discussion about the front wheel bearings, I was asked by Moss, if the rears had any issues regarding the fit of the rear bearings they supply. I sked here, and nobody reported any. However, since the originals are still easily obtained, that may be why.
It would be interesting to measure the exact dimensions of an SKF against an R&M.
|If the original bearing was a 6207 then the tolerances would be the same. These are so-called "Popular Metric" and are made to a common standard. I don't know when the motor industry went metric. As the bearings are the same for Mk1 Frogs we are harking back to 1958 - would that have been built for metric bearings?|
Driftin "on" not "in" - we are talking about the inner race.
Graham Bristow go his torque information from the "Sprite and Midget Book of Incorrect Facts" I'm an avid reader!
|The drifting in/on comment was with reference to the oil seal, which is in the hub, and precedes the bearing being drifted in. As I said, sorry to be pedantic. :).|
Are you talking about your 'new' axle or the one with the damaged thread?
What was the old bearing, the one you replaced with the 100 mile one you've just removed, also an SKF?
Your axle might already have been worn, or might have had a bearing fitted that was too loose, resulting in the situation you have now. Or as you say, from the nut being too loose. If it is too loose now, even if the correct bearing is in place, then obviously either you need 'glue' or additional clamping force from the nut to compensate.
What if you do it up to 140, and strip another thread?
As nobody disputes, the nut has to be tight enough, but what is that? I still don't see the need for 140lbs.
|"Therefore one must conclude that at some stage the original press fit wasn't adequate to stop it turning."|
How you you know it's been turning, if there are no wear marks? Maybe they all creep, and we weren't aware of it. If so, there don't seem to be any consequencies. So why is it a worry?
|Both the old and the new bearings are loose on the damaged axle.|
"What if you do it up to 140, and strip another thread?"
The language would be unprintable.
I'll know in a wee while how the bearing fits on the new casing.
|Removed the second hub off the old axle. First time I've got to that side. Puts all this thread into perspective - the nut was loose! Not even finger tight! The lock washer was turning with the nut. The washer issue doesn't suprise me as when I reassembled the other side a couple of weeks ago I found that as the nut is tightend it can grip the washer and pull the tab out of the hole into which it fits.|
The inner race on this hub was also a slide fit, not press fit, on the axle. My (old) axle - the one where it is a slide fit - measures 1.377"
The bearing fit is 1.378 +0 -0.003 (from the spec sheets).
|Shouldn't that be -.0003?|
|Whoops! Intended to be -8 micron which is 0.0003|
I introduced this point about "drifting" the bearing ON.(not IN)
The text says that:
"The hub bearing is replaceable in one operation, by pressing into place" - so a press "in" fit to the hub.
It then goes on to say:
"The hub is drifted onto the axle casing using tool 18G 134"
This is the bit I was referring to when I said it was drifted ON. And my point was that they were drifting it on first, and not relying on torquing the hub nut to pull it into place. Not as you put it "pressed/drifted/hammered/pulled by the nut (your choice), onto the axle"
to be pedantic, ;-)the manual is quite specific; only one of those methods is described.
|But is everyone actually saying thet their inner race IS a drive fit on the axle ie TIGHT. After all, the front wheel bearings are loose on the shaft.|
|having dismantled a fair few Midget and Morris 1000 axles recently I've never had a bearing stay on the axle, they always come away complete with the hub, occasionally with hand pull pressure but usually with a small slide hammer|
|Having spent yesterday afternoon rebuilding my back axle I can tell you all that you don't need tool 18g 134 to drift the hub on. A 36mm socket fits over the end of the axle and fits the inner race perfectly so you can then hit it with a hammer (plastic head in my case). The bearings are from Sussex mg and are (i think) firstline. They were a good press fit in the hub and a tight fit on the axle. I'll be doing them up to whatever I consider 'tight enough' once my 1&7/8th socket arrives (incidentally, why does no-one do a 1/2 inch driver socket? everyone seems to just sell 3/4 inch drive).|
|Yes, tight on the axle. I also use the large socket method.|
|Guy, Continuing with my pedantic behaviour, lol ;-) "It makes it clear that both the oil seal and the bearing should be firmly drifted on before the washer and nut are fitted." That's the 'on' I was referring to when I said it should be 'in'. I wasn't sure if you were semi quoting from the book of words there. After that's done, the hub is drifted onto the axle. Yup, I added hammered or pulled on, because I've never even seen that tool, and hammering or pulling has always worked for me. Do you reckon we'd argue, if we ever met in a pub? lol.|
Hi Graeme, "They were a good press fit in the hub and a tight fit on the axle".
So different bearings, different/better fit? That suggests that some bearings on sale as replacements for the original R&M bearings, are not correctly sized.
Also, as I just put in my bearing renovation thread -- The fronts are both a slide fit on the stub axle. They are torqued to only 46lbs, both bearings are a slide fit on the front stub axle, and nobody has ever been concerned about inner bearing race rotation.
As regards the tabbed lock washer rotating when you do up the nut. Which way round are you installing the nut? Does it have a chamfered side? But this bears out what I said earlier. If the nut digs into the lock washer, AND the tab holds, preventing the lock washer from rotating, then a lot of the torque your employing isn't doing anything at all. If the lock washer is turning, maybe the tabs on the new lockwashers aren't much good. I'm still using my old ones, and they don't rotate.
David Smith, "I've never had a bearing stay on the axle, they always come away complete with the hub --". You're talking about the fronts here I assume, as the bearing on the rear hubs can't come out and get left on the axle, because they are drifted in from the front of the hub. Whoops, being pedantic again. :)
|Graeme, apart from the SKF's you mentioned earlier, are any of the other bearings you have marked with a makers stamp? Are any of them R&M?|
|Lawrence "So different bearings, different/better fit?" I'm going to stick my neck out and say 'proper' fit. the old hubs slid off quite easily once I'd given them a tap to break the 'stiction'. The new bearings felt 'right', both going into the hub and onto the axle. |
getting the oil seal fully seated was a nightmare though. what a stupid design.
|Sorry graeme J, I got you mixed up with Graeme W. :)|
I Agree with you about the design of the oil bearing seat. I think I read somewhere the reason for that, but can't remember what it was. Just as well they last for yonks, you wouldn't want to be changing them that often.
graeme Jackson. Were there any makers stamp on the sussex bearings?
|Lawrence what I meant was, they are never a heavy interference fit, usually coming away very easily.|
|Lawrence: the bearing I have removed is a Koyo, marked 6207.|
I was talking to an experience mechanical engineer today who works on Vincent motorbikes and has a largish engineering workshop. He expressed the the view that 140 was going to damage the thread for that thickness nut!
|We could do with a rusted out axle casing to do some destruction testing ;o)|
I did some serious tightening on an A30 hub nut recently and didn't manage to strip it. I was actually trying to undo the nut and was expecting the LH nut to be a LH thread. It wasn't.
I was heaving on it with a big bar and it eventually moved. It wouldn't move any more and I then realised that I had actually been trying to tighten it.
|Hi Graeme W. Do you have any original R&M original bearings to compare it too?|
Is it the bearing that has done 100 miles in service? As it slid out of the hub with little pressure, presumably you're putting it back in?
In the past, when I replaced the oil seal, I reused the bearing. This is in spite of having to drift the bearing out of the hub with a hammer and socket, by hitting the centre race, because there are no drift pockets. I've found in practice it didn't damage the bearing, or rather that I've not noticed any effect -- although I did wonder if I would. However, it doesn't seem to have done, and the bearing is quite a fair few miles old now. Still spins freely smoothly and quietly.
Earlier this year, I also 'rolled my arches' using a steel tube between the tyre and the wheel arch. I wondered if that might damage the wheel bearing, but again doesn't seem to have done. I concluded these rear wheel bearings are made of very tough stuff, seemingly industructable, judging by how long they last.
This thread was discussed between 07/10/2012 and 16/10/2012
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.