mk1-forum.net

A friendly international forum for people interested in the tuning & modification of classic BMC vehicles
It is currently Fri Nov 24, 2017 9:19 pm

All times are UTC [ DST ]




Post new topic Reply to topic  [ 48 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: Rear radius arms
PostPosted: Wed Oct 25, 2017 3:15 pm 
Offline
User avatar

Joined: Thu Aug 08, 2013 3:16 pm
Posts: 5886
fitting rollers to each end of a mini arm used to be a 'bodge' done on cheap recon radius arms as it removed the cost of the reaming

the problem with fitting a roller to the outside of a mini is that it soon gets sprayed with a mixture of water, salt and fine muck which gets into the rollers and just destroys them in no time

we used to get them back as surcharge units and every time, without fail, the bearings would look like rat turds and the shaft would have a huge ridge in it.

_________________
should you wish, you can contact me on rich@minispares.com

'long beard boss'


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Wed Oct 25, 2017 5:47 pm 
Offline
User avatar

Joined: Sat Jul 15, 2017 5:35 pm
Posts: 513
Location: Abingdon Oxfordshire
I fully see the point that you're making Smithy. The motorcycle comparison is mixing apples and pears for several reasons and we all chatted about this (I'm a Commando owner) at the weekend. As does the comparison with the principal of UJ's. It's all about loads AND lubrication.

To be honest, the lubrication of the inner end of the shaft is almost pure fantasy no matter how hard we try to excuse BMC futility! The only real way to get lube into - or rather BETWEEN the bush and the shaft - is by getting it there under pressure DIRECTLY. Because grease, like all liquids, will always take the line of least resistance. If that means that it is shoved further up the shaft towards the needle roller where there is an easy escape route, that's where it'll go. But it will not get between the bush and shaft while there's an out!

One of the drawbacks of a small project like this is that while we're engineers/metallurgist/chemist, we're not car experts so we/I'm having to rely on you for good feedback and comments. Also while it'd be all very nice to bush and line bore/ream both ends* testing such a modification would be impossible...... but I digress. But that is why the VERY simple idea of modifying the shaft will be put forwards - thanks to feedback here! All feedback is welcome and taken on board.
* a very simple job to make and press in an insert capable of taking an identical outer bush


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Wed Oct 25, 2017 7:38 pm 
Offline
User avatar

Joined: Mon May 07, 2012 6:10 am
Posts: 2462
Location: Big Red, Australia
Peter, sorry, I don't know why I've been missing this thread.

Drilling and fitting 2 x grease nipples. Going back to the early days of bushes both ends, the factory did release a TB recommending to do just this, however, to locate the hole so it is just clear of the bush. There's no reason why it can't be right under the bush, but as has already been raised, when fitting up, you want it indexed away from the load side. You would ideally want to fit them up so the hole was just on the leading side of the load so the grease can form a lube wedge, the only issue here being, the bush rotates both ways. To make the inboard easier to grease, fit remote greases like they have on many machines. You could bring them up to the dashboard if you wanted :mrgreen:

Fitting 2 x bushes / bearings. Our Big Wheel Mokes, like the Metro (that came later) have needles on both ends. This to me has always been quite wrong. The needles of course only transmit the load across about 3 or 4 needles and each do so in a fine line, so the spot loadings are huge. Bushes on the other hand are much better suited to very high loadings at low speed - exactly what we have here. The stock coff coff bushes really are only rubbish. They are a bit of bushing material swept up from the floor, sprayed on to some tin plate and then rolled up in a rollie machine - no wonder they failed. Many many years ago in the wife's Moke I fitted Bronze Bushes both ends, cut a spiral groove through them for the grease. They have done over 200 000 km and still no sign of wear. The other bonus is that while you still need a quality steel for the shafts, they no longer need hardened ends.

Just flicking back the the needle rollers - if the shaft ends aren't hard (>64 Rc) and don't have enough depth of hardness (>0.030") then the shaft will fail in short time. The leverage ratio of the arms put 5 x the weight that's ultimately on the wheel in to these bearings and shafts. It's worse on the inboard end because we have the equally added loading from the rubber cone (via the trumpet and knuckle joint). If the shafts are too soft, it's like running a steam roller over a mattress. If the depth of hardness is not deep enough, it's like running the steam roller over a mattress that has a 3 mm sheet of ply laid on top and so is worse than soft shafts as all the stuff that flakes off ends up in the rollers and grinds them to bits.

I did make shafts for a while, from EN36A and then had the ends where the needle rollers run induction hardened to 0.040", then ground them back to size. It's important that the core material isn't hard, or they'll just end up brittle and bust the threaded stub ends off.


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Wed Oct 25, 2017 7:50 pm 
Offline
User avatar

Joined: Sat Jul 15, 2017 5:35 pm
Posts: 513
Location: Abingdon Oxfordshire
Thanks again Spider, I knew you'd pop up sooner or later to help the Pete the Pom out! We've overcome the bush lubricating querie by boring the new lube hole right through the shaft, directly central to the bush and needle roller. At the same time blocking the original grease/lube exit hole that was 4" or so from the outer end. The grease now MUST exit centrally under the bush and the needle roller, where by definition it should be!


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Wed Oct 25, 2017 10:55 pm 
Offline
User avatar

Joined: Thu Feb 05, 2015 9:40 am
Posts: 1025
Peter Laidler wrote:
I fully see the point that you're making Smithy. The motorcycle comparison is mixing apples and pears for several reasons and we all chatted about this (I'm a Commando owner) at the weekend. As does the comparison with the principal of UJ's. It's all about loads AND lubrication.

Peter in my note I left out the discussion of loads because without going away and calculating them I cannot say whether either the bush or the needle roller bearing where designed correctly.

I do not see why the motorcycle swing arm is any different to one Mini radius arm to be honest. They both do exactly the same job. You may say that the side loads are higher on the Mini due to cornering forces but in reality they are not due to the lean angles used by motorcycles in cornering.

Again the loads in a UJ are much higher on smaller diameter bearings in propshaft UJ's than in the Mini rear suspension with both being cageless rollers. The only thing that makes them live is the angular displacement. This causes the internal rollers to rotate (it requires more than 2 degrees of angularity in the shaft planes to make it happen) spreading the wear and the load points as it does so.

I propose the failure of the Mini inner bearing has two primary root causes.
1: The quality control of the shafts in hardening and assembly causes issues with the roller bearing and the bush.
2: The inability to reliably lubricate the bush end (through maintenance or poor design) causes angular displacement between the shaft and the needle roller which prevents the rollers moving around the diameter of the shaft. This leads to brinelling of the shaft and locks the roller to one spot which accelerates failure. This is exacerbated by the poor hardening of many of the shafts.

Fingers can be pointed at both the design team (for not making it robust to poor quality control) or the manufacturing team (for allowing the poor quality to be built in the first place) but either way I propose that a properly designed, manufactured and assembled double needle roller bearing would be more robust than a double bush.

A common misconception about bushes is that they will support greater loads than needle rollers. This is incorrect. A bronze (leaded tin which is the strongest composition avaliable) bush has a maximum load bearing capability of 100 N/mm2. A typical needle roller will support around 4000 N/mm2, over an order of magnitude higher.


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Thu Oct 26, 2017 1:15 am 
Offline
User avatar

Joined: Mon May 07, 2012 6:10 am
Posts: 2462
Location: Big Red, Australia
smithyrc30 wrote:
A common misconception about bushes is that they will support greater loads than needle rollers. This is incorrect. A bronze (leaded tin which is the strongest composition avaliable) bush has a maximum load bearing capability of 100 N/mm2. A typical needle roller will support around 4000 N/mm2, over an order of magnitude higher.


Smithy, considering the Needle Roller on it's own, yes.

However, when applied in this application and that (as you have also referred to) they only run on shafts of variable quality then as I've found, they are not up to the job, but not through a failing of the bearing, but the shaft. Also, Bearings really only support higher loads when there is some moderate speeds involved, not the extreme low speeds of the trailing arm arc movement.

They had similar issues on the Crawler that's used to move the Apollo Rockets, they initially fitted bearings to the crawler tracks and I think it only went a few hundred yards on it's first try out before the bearings spewed out over the gravel. I think it was Timken who were called in to sort it and they came back with bushes, which I understand are the same ones from back then that are still in there to this day.

This too is why Bushes are used on King Pins in Trucks - High Loads and Low Speeds. It's also in part why we have slipper bearings in our engines too, though the speeds are higher, but thet's dealt with by lubing with a continuous flow of oil.

Coming back to the job at hand, if you look at the 1100 and 1800 series, they used Tapered Rollers on the swing arms to basically get bigger balls in there, for the issues that I raised in my earlier posting regarding the huge spot loadings from needles. You can clearly see this when you remove the old shafts, the bearing end is always buggered and the bush end is OK - provided they were greased.

I'll add too that there does appear to be some concern here about getting grease in to the bush and bearings. I've always made sure that the grease tube between the bearing and bush (or other bearing) is pinched firm by the tube. I don't bother with the plastic ones, I always reuse the steel ones. This will reduce the grease that 'leaks' in to the arm, it won't eliminate it. I also jack the vehicle up and get the rear wheels airborne before greasing. This is to un-load the normally loaded parts of the bearing & bush to get the grease where it's needed. I can't say I've had a lube problem here.


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Thu Oct 26, 2017 5:36 pm 
Offline
User avatar

Joined: Sat Jul 15, 2017 5:35 pm
Posts: 513
Location: Abingdon Oxfordshire
Spider has answered the matter as it stands without getting into mathematical and technical mission creep for the subject in hand I feel. This is because while anyone could covert to the mechanically (unsatisfactory ?) double needle rollers or the more robust and satisfactory double bushes. But we've got to live with what we've got - a mixed bag of a bush and bearing and quality that's best described as '...marginal'. So in this project I'll try and arrive at a simple fix during a rebuild that ensures that BOTH ends are properly lubricated.

Incidentally, anyone that's unhappy with the plastic shaft cover. Help is at hand too. It's a simple matter to fabricate a new metal copy of the old steel one by using old imperial 1" copper pipe and a joiner piece.


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Thu Oct 26, 2017 7:58 pm 
Offline
User avatar

Joined: Mon May 07, 2012 6:10 am
Posts: 2462
Location: Big Red, Australia
Peter Laidler wrote:
Incidentally, anyone that's unhappy with the plastic shaft cover. Help is at hand too. It's a simple matter to fabricate a new metal copy of the old steel one by using old imperial 1" copper pipe and a joiner piece.


Nice idea. I haven't needed to go looking yet, but that's only a matter of time. I did have it in mind to look at some of the steel electrical conduits, but this sounds much nicer to work with. Cheers ;)


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 1:46 pm 
Offline

Joined: Mon May 11, 2015 4:16 pm
Posts: 102
Location: Scotland
It seems that on at least some of the Works cars, owing to problems with fractured radius arm shafts, they substituted a none drilled shaft. The inner needle roller just got the lubrication that came when it was assembled but at the bushed end the radius arm was drilled through the bush and a grease nipple added facing the rear. Thus Direct lubrication of the bushed end and any grease that found its way to the needle roller a bonus.

The very early minis had bushes at both ends.


Top
 Profile  
 
 Post subject: Re: Rear radius arms
PostPosted: Fri Oct 27, 2017 2:24 pm 
Offline
User avatar

Joined: Sat Jul 15, 2017 5:35 pm
Posts: 513
Location: Abingdon Oxfordshire
Thgat's interesting dearg. Quite how on earth they broke - presumably sheared - the almost 1" dia shafts is anyones guess, even if it was mild steel!!!!! Maybe they were just anticipating a breakage or had identified a 'commencement to fracture'* point. Anyway.... But direct lubrication of the bush is exactly what we're going to propose and to get there - and to directly lube the needle roller - is simplicity itself. It'll also cure the problem that Rich spoke of too in that it'll get clean new grease in that will by default, clear the old shite and gunge OUT. But as Spider and Smithy have already alluded to, the centre 75% of the shaft doesn't need to be hardened, it's just a shaft!

(* this is one of those phrases that tech authors used to call 'preventive' expressions. It's either fractured - or it ain't!

Need to contact Rich@ whatever....., how do I get there?


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 48 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: jayare, jbz23, kiwiinwgtn, ranchlands and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Localized by Maël Soucaze © 2010 phpBB.fr