The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: beezermacc on 15.06. 2020 23:39
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Anybody who has tried to remove a swinging arm which is rusted in will know what a PITA this job is. My first piece of advice would be..... if you don't have to remove it, don't! I've had to do this job quite a few times over the years and I reckon I've perfected a method which works well. It's a bit brutal but recognises the futility of trying to remove the swinging arm spindle when it is rusted in! If you try to remove a spindle that is completely rusted in you will bend the side plates that support the swinging arm. Also covered is silentbloc removal. The link will take you to a word doc with pics that some may find useful. I did this last week and it took me about 40 minutes.
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxwcmlvcnltYWduZXRvc3xneDo1YmY2NzkxODk4YTQ0Njll
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Thanks Beezermacc, Mine is original but OK for now but I will file this away for when I need it.
Col
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Well that brought back unhappy memories from the 3 times in the past I've had to do this ,it must be the worst job to need to do on a A10.
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Later hollow type spindle:
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More pics
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I thought this thread was familiar, and sure enough a series of posts concerning the woes and tribulations of the swinging arm and its bushes was in full flow just over a year ago.
The design relies on the friction between the ends of the bush inner sleeves and the inner cheeks of the frame plates to prevent the inner sleeves of the Silentbloc bush turning. The through spindle is not a pivot as such, just a location and retainer for the inner sleeves. Any wear to the plates reduces the contact area between the inner sleeves and the plates, as both surfaces need to be flat and in full contact for the design to work as intended, the clamp nut pulling the frame and inner sleeves into one solid lump.
In fact, any rust and corrosion on the spindle actually locks the spindle and the inner sleeves together and increases the resistance to turning by transferring some of the turning force to the spindle end plate and its securing bolt, much more than the relatively small area of the ends of the inner sleeves alone.
The rubber of the bushes is thin, and the spindle needs to be tightened with the suspension loaded. Tightening with the arm hanging down will put much more shear stress on the rubber than otherwise when in use.
On the subject of dismantling, the spindle can be considered as sacrificial, in stubborn of cases this is the only way to get it out. As such, here's a thought.
It is one case where rust and corrosion act as a locking compound, giving more support to the inner sleeves to resist rotation, but certainly not in the way the designer intended. But a seized spindle/sleeve means the bushes are better supported and located than just by being clamped between the frame cheeks, as the spindle also has a positive location and security at either end.
You could Loctite the spindle and bushes instead of relying on rust and corrosion, but this would need to be done with the suspension loaded, as mentioned earlier, not an easy trick. Loctite should prevent corrosion, a little bit of heat will soften it, and the spindle will pull out.*
Swarfy.
* All pigs fuelled and ready for take off.........
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I have heard mention of tensioning the swinging arm spindle under load before. This is something which doesn't make sense to me. I'm not aware of any such recommendation in a service sheet or unofficial manual published by Haynes, Clymer or anybody else. I would have thought if this was necessary there would be mention of it somewhere official or semi-official. The A65 has the same bushes and, in the A65 genuine BSA workshop manual, it states specifically that the rubber is under tension 'as soon as the fork moves'. Even when these bikes were in regular use they were only being ridden for a very small proportion of their lives so, tightening up under load would mean that the bushes were strained when the bike was at rest which would accelerate their wear and act as a counterforce to the rear suspension spring, i.e. making the suspension soggy. The purpose of silentbloc bushes is to eliminate wear which used to play havoc with steering and suspension in cars. The fact that the bush contributes to the suspension effect is a fringe benefit and not a design intention. In fact, if you assemble the swinging arm without the suspension units and tighten the spindle you will find that the effect of the silentbloc bush is minimal through the natural range of travel. It is only if you try to move the swinging arm outside its normal travel that the effect of the silentbloc becomes significant and if the silentbloc were subject to this force on a regular basis it wouldn't last very long. BSA used these to eliminate the maintenance of swinging arm bushes and stated in the workshop manual that they were intended to last the life of the machine. I have dismantled quite a few of these over the years, and changed many a pair of rear springs, and I have never come across one which which had been assembled under load.
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BM You appreciate the Silentbloc works by virtue of the relative movement between the inner and outer steel sleeves, mediated by the bonded rubber tube. The rubber is subject to shear forces, and for long life these forces need to be minimised.
One way is to ensure the bush spends most of its time subject to the least stress, and for this reason it is accepted automotive practice to finally tighten any suspension bushes in the position they will spend most of their time, namely with the vehicle on its wheels and with the suspension subject to normal static load.
It makes sense to leave the final tightening of the swing arm spindle to when the machine is on its wheels, or at least positioning the swing arm in its approximate operating position. Tightening with it hanging down and moving it up to near horizontal is already putting extra shear stress on the rubber, something to be avoided. I think you mis -understood my meaning of "under load". I meant on its wheels, with the suspension bearing the weight of the machine. Tightening the assembly in this position puts the rubber under the least torsional stress, and a better chance of longer life.
Swarfy.
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One way is to ensure the bush spends most of its time subject to the least stress, and for this reason it is accepted automotive practice to finally tighten any suspension bushes in the position they will spend most of their time, namely with the vehicle on its wheels and with the suspension subject to normal static load.
It makes sense to leave the final tightening of the swing arm spindle to when the machine is on its wheels, or at least positioning the swing arm in its approximate operating position. Tightening with it hanging down and moving it up to near horizontal is already putting extra shear stress on the rubber, something to be avoided. I think you mis -understood my meaning of "under load". I meant on its wheels, with the suspension bearing the weight of the machine. Tightening the assembly in this position puts the rubber under the least torsional stress, and a better chance of longer life.
Swarfy.
Exactly, on the centre stand, no load on the rear suspension units.
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Afraid I have to disagree with some of the comments re best position to tighten the swing arm spindle.
The metalastic bush is extremely thin and so any rotation of outer sleeve v inner is going to give it a hard time. The suggestion that it should be set when the bike is in the position where it spends most of its time appears valid, but less so on closer thought. If, for example, it’s set as BM suggests (on centre stand) then the bush will be quite happy – but what happens to the bush when the suspension bottoms? I’d say that’s probably enough to destroy the bush, given the amount it has to flex on account of its lack of section. Whereas if the spindle is tightened when the arm is at mid point, the most the bush will ever have to flex will be half of that. So I’ll continue setting swing arms up at mid-travel (approximated by bike on ground with seated rider).
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Sorry BM, I tend to agree with Swarfy too on this - as a (retired) automotive engineer, suspensions are best "finalized" when under net weight conditions such that the forces are normalized before any other forced interventions - we do this with the front forks after an assembly process, why wouldn't you do this with the rear "forks".....
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Well, we'll have to agree to disagree. I'm content to continue to fettle my bikes according to personal experience and the official BSA workshop manual in the knowledge that the BSA factory and I have been doing it wrong since 1954! Royal Enfield and Norton also have been doing it wrong to name another two who recommend tightening the swinging arm when the suspension is at rest, or making no reference to tensioning the bushes. Speaking from personal experience of restoring BSA A10's for over thirty years I have never come across a swinging arm bush that has destroyed itself, though I dare say this may have happened, and have never come across a swinging arm bush that has been assembled under tension. I have no wish to get stroppy about this issue and as stated previously we'll have to agree to disagree. If you read Swarfy's post you'll see that he recommends tightening the swinging arm with the bike in the position in which it spends most of its life, which is on the centre stand. Originally Swarfy said it should be tightened under load which I thought meant with a rider and suspension partially loaded. Similarly I think Swarfy and I agreed that, on cars, the suspension should be finally tightened when the car is sitting on the ground with the suspension under normal, at rest, load (i.e no stress on the bushes). The BSA A65 workshop manual states that the bush starts to tension as the fork (swinging arm) moves and that BSA expect the bush to last the life of the bike. The A65 referred to also has a hollow swinging arm spindle so has the thin section rubber in the bushes. I return to my previous comment that, if BSA thought it necessary to tighten the swinging arm spindle in a tensioned state, they would have said so.
One further point, the original post was a well-intentioned attempt to help people remove seized-in swinging arms. It was subsequently hijacked with a reply about tightening swinging arm spindles, a completely different subject. The original post, which in my opinion was quite useful, has probably been forgotten by most members of the forum and obscured by the unnecessary confusion caused by 'advice' which runs counter to official BSA workshop practice!
That's me not getting stroppy by the way! I love you all, really!
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On a pragmatic level, SilentBlocs have been an item on BSAs for decades and for millions of miles now, and while seizing is almost a given, I've yet to hear of "tearing" ever being an issue, even at the lowest point of BSA valued ownership when they were disposable ride-to-work hacks maintained by poverty-stricken apprentices, etc.
I can understand the theory of positioning the bushes correctly before locking them up, but in reality, does it make any difference? Doesn't seem to..
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but in reality, does it make any difference? Doesn't seem to..
99.99% of silentblocs were originally tightened in the factory in the position I suggest. If they'd all been tightened so that they are stressed when at rest maybe they would all have destroyed themselves by now! I'm not disagreeing with you, Rex, just suggesting that we don't know what effect tightening the bushes under stress would have, as BSA never did that!
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Well that certainly puts me firmly on the naughty step! My recommendation as to when to tighten that spindle was from my own experience and that of others more knowledgeable than me.
I will agree with BM, as stated in the opening chapter, namely don't do it unless you have to! My additional post was to offer some insight into the design and its problematic shortcomings, not an attempt to take it in a completely different direction.
I would say as an owner you have the choice of accepting established practice or more modern thought. If the machine spends most of its time on the stand.....or time on the road, take your choice.
RD's analysis of the mid way position would be the best compromise for a longer life.
If the design was supposed to last the life of the machine you have to ask why the bushes need replacing in the first place. My first S/A bike, a 1960 model, had a spindle and inner sleeves that almost fell out of the swinging arm, after the usual sacrificial surgery, leaving the rubber and outer sleeves firmly in place. Entirely expected, as the naked suspension had massive sideways slop. Untouched, by all accounts, since it left Small Heath. I maintain the factory method was detrimental to the life of the bushes, but an unintended but fortunate way of increasing demand for replacements.
Just how rare is it these days to find a well used machine still with original bushes and not requiring remedial attention? Somewhat, if mine was typical.
Swarfy.
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Regardless, I think the arrangement sucks.
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To state the bleedin obvious, BSA did not expect, (or want?) their machines to last a human lifetime. I fancy that by comparing the plunger, (and earlier machines) to the SA models you can see the introduction of built-in obsolescence that has become standard practice.
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In the past, when original bushes were available, I replaced them in the RGS and SR just because of some cracks seen on the outer. In hindsight I don't think it was necessary as prodding around before destruction revealed they were only really on the surface, wondering what might be further in, decided to change them for peace of mind. But once the destruction began, it looked like they were pretty solid throughout. I just replaced the bushes during restoration of my BSA WD B40 only because the pin could not be removed and the end of the block gets damaged cutting it away from the frame gusset. Maybe they could be tested in the frame before replacing them (with nothing attached - as in stripped down for restoration), attaching known weight to give a certain deflection?
All the best
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Just some random observations from personal experience and further thought.... I don't think the silentbloc bushes are deliberate designed obsolescence; it's such a bitch of a job to replace them the vast majority of owners would resent having to do the job or pay the money to farm it out so it would be counterproductive. The cost of the bushes, being fairly cheap, would not warrant the hassle. The whole point of designed obsolescence is to make it easy for owners to spend money on a regular basis. There may be other examples of designed obsolescence on the A10 but I can't think of any (apart from the whole bike - BSA went bust for a reason! The Japanese made the A10 / A65 obsolete). Even when these bikes were being used as daily commuting bikes they would probably be on the road for an hour or two on a weekday, the rest of the time they would be on the centre stand. Consider the maths... 10,000 miles (200 miles a week, 40 miles a workday) at an average speed of 30 m.p.h. = less than one hour per day in a 7 day week on the road and 23 hours on the centre stand so, fitting the bushes in anything other than their centre stand position seems to be putting the bushes under unnecessary strain for 95% of their lives. I've fitted plenty of bronze bushes in my time as well and that's not a lot of fun either! Even though silentbloc bushes allow for a bit of instability I think they are an improvement on traditional bronze bushes. The only time I or anybody else in my sphere of friends have needed to change the silentbloc bushes is when it has been desirable to remove the swinging arm for cosmetic treatment (no, not botox!). I've never come across any which were actually worn out, but I've come across plenty of bronze bushes which were worn out. Silentbloc bushes don't need lubricating of course. The best A10 I've ever had was my 1954 plunger, no silentblocs in sight! However my swinging arm A10's handle better, but the plunger was just such a lovely bike to ride. A friend of mine used to work for a firm called Monroe (shock absorbers) and he says the silentbloc bushes are incredible, the twisting force they will withstand has to be seen to be believed and he reminded me that car suspension bottoms out maybe dozens of times every trip and the movement on a wishbone is greater than the swinging arm travel on an A10. For those people who insist on compressing their suspension whilst tightening their swinging arm spindle remember this.... As soon as you take the weight off your bike that skinny bit of rubber is straining and stretching and trying to release itself from its metal casing and it'll be doing it all the time, like a persistent irritating itch which won't give up until it bleeds, every hour of every day whilst you're not riding your bike, whilst you're asleep at night, whilst you're on holiday, whilst the garage door is closed it's out of sight stretching and straining until it starts to release like that first piece of peeling wallpaper that just gets more irritating and worse and worse until it falls off the wall completely... and as soon as the rubber starts to separate from the casing there's less rubber gripping on the casing so it gets easier for the rest of the rubber to creep away like water rotting through cardboard in a nightmare that at first you can hold back but in the end it just overwhelms you and suffocates you in a torrent of soggy papier-mâché, then the ghosts of the BSA design engineers crowd round you and shake their fists and their fingers look like silentbloc bushes and they twist them until their knuckles crack to demonstrate just how resilient the silentbloc bushes are, and you'll scream and beg forgiveness for not paying attention to section D12 of the BSA A65 workshop manual which retrospectively addresses the urban myth that silentbloc bushes are the work of the devil and should therefore live their lives under permanent stress. I promise not to contribute to this thread ever again - really regret starting it - should know better at my age! Good Night!
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the witch of a deputy head master at school always had to have her say after the head master had done his rant. she used to say " and just to add!! so here goes ,and just to add silent block bushes should be fully tightened in the resting position. my dad told me and he was a damn good proper engineer. I am not but I always do it on cars *fight* *whistle* I just thought that makes sense if talking about a car on its wheels, so I say bike under it's own weight.
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Andrew, my remark about obsolescence was referring to the whole machine. Nobody thought these motorbikes would be around in the 21st century. What do you reckon was the predicted lifespan; 20 years?
BSA designers were given a brief to keep costs down and at the time these clever bonded rubber bushes became available.
I have fitted lots of these bushes to motor cars of the 50's and 60's.
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Anybody who has tried to remove a swinging arm which is rusted in will know what a PITA this job is. My first piece of advice would be..... if you don't have to remove it, don't! I've had to do this job quite a few times over the years and I reckon I've perfected a method which works well. It's a bit brutal but recognises the futility of trying to remove the swinging arm spindle when it is rusted in! If you try to remove a spindle that is completely rusted in you will bend the side plates that support the swinging arm. Also covered is silentbloc removal. The link will take you to a word doc with pics that some may find useful. I did this last week and it took me about 40 minutes.
https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxwcmlvcnltYWduZXRvc3xneDo1YmY2NzkxODk4YTQ0Njll
Nice work indeed, I love it when someone comes up with a new fix for a nasty problem. Cant remember how I did mine though knowing me it was probably with huge amounts of heat on the SArm...the bike was going to be repainted anyway.
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a beautiful end to a great starting thread BM, love it *clap* *thanks*
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Well, despite my temptation to do so, I'm not chiming in on the under load versus at rest issue. I'm here to say that, when it comes to reading lengthy rants, Andrew's are my favorites.
Richard L.
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The silentbloc was also good enough for Norton to use on the Featherbed frame.
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Indeed. The 2 best handling Brit frames of the era. Far be it from anyone to suggest there's any connection of course, as there be other reasons . . . but all the same . . .
Nonetheless, I am glad not to have had to tackle removal on either my A or a slimline that shares shed space. The only swing arms I've had to 'do' have been heavyweight AMCs, with bronze bushes. Less awkward and no pre-tension issues to worry about there - but even so, they're not a 'just do it before nipping down the pub' sort of job. Luckily, they last well.
By contrast, how much easier are a lot of moderns with taper rollers etc - which is just as well when it comes to replacing endless rear chains without resorting to a soft link. While it took a day or more to repair the last AMC I did, fitting an endless chain and new sprocket kit on my Yam XJR was 'only' a morning's worth of sweat. Pleased, for once, to concede that there had been progress over half a century. (Until I wanted to replace the plugs on the Nipponese beast, that was.)
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If you don't want to use a spring link (which I have no problem with - it's cranked links that fail) why not rivet the chain in situ?
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Could have RD and many owners and some shops do. But they are made, and factory fitted, endless and their riveting is probably better than mine. Lot of power and torque in these things and I just wanted that feeling of confidence, even if being daftly paranoid!
Nothing wrong with split links on our stuff, I do agree - and no practical option really either. Many modern 'boxes have overhung gearbox sprockets, so no need to play with the transmission to replace rear chain, just hoick out s/arm spindle.
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Having ridden thousands of miles on silentblock's
Plain needle rollers
& needle + radial rollers , give me a silentblock any day fo the week.
Almost impossible for one to collapse and have your rear end dancing the Char char every time you open the throttle or back off.