renewing unusual swing arm bushes on 61 super rocket - what to do?

[mikeb]

Question: how do I recover from this one?

Looks like someone has already inserted bronze bushes into my swingarm. If you look at the pics there’s a bronze-looking bush in each side. Outside of that a small metal spacer that sits inside a large fibre washer. The spacers/washers are about 2.5mm thick. On one side the bush sits flush with the swingarm but on the other its recessed a few mm. Its unclear what was contacting the swingarm on that side (tho obviously the washer). Inside the swing arm there’s something loose between the two bushes (I can’t see it or get to it yet). There’s no grease nipple fitted.

Also the spindle securing plate has broken off so it was only the seized spindle (in the bush) that held against the timing side nut. Makes me wonder what was turning – the spindle in the bush or spindle in the frame plates or half each? The hole in the timing side frame plate has worn oval.

A rough measure of the gap between the swingarm and frame plates in about 4.5mm – about right I guess if silent bloc inners are supposed to protrude a couple of mm each side. ie I don’t think the swing arm has been narrowed, tho I don’t know what width they should be.

All this looks like a fairly well made modification, albeit one bush is recessed and one washer/spacer is separated. Does anyone recognize this set-up?

And what to do? Drive it all out and fit some new silent blocs? Somehow remedy the current bushes?

Thanks for any suggestions you can offer.

Mike

[edboy]

well , i would grease it all up , replace and think yourself very lucky.
what do you want.
a medal

[coater87]

 OK,

 Someone went to a lot of trouble there.

 they probably knew replacing the silent blocs is a pain, and its not like they were that great anyway.

 I would be checking out fits, putting things together, etc.  Figure out what the P.O.'s plan was, see how badly what you have is worn, and if it still works before taking it apart. If he was onto a good idea, and its usable I would keep it going.

 If its worn out, obviously its gotta come apart. Then you can get good measures and decide if you want to duplicate what the P.O. did with custom unworn bushings, or (if its still possible) go with silent blocs. Or possibly have to repair/ replace your swing arm.

 Lee

[muskrat]

G'day Mike.
I did that modification on my 1957 A7SS Cafe 26 years ago. Not exactly like yours, the bushes I made were top hat type. Is there a distance pipe between the spindle and bush to stop the frame from clamping it all tight?
Do as Lee suggests.
Cheers

[mikeb]

Musky - by distance pipe do you mean the small metal spacers inside those fibre washer that sits between the bush and frame plate? (it is visible on the pics) or am i misunderstanding that? if so then i guess those small spacers need to be exactly the right width to allow just enough movement without binding the swingarm...?

Also Musky in one thread you said you fitted a grease nipple to your set up - do you mean through the centre of the swing arm into the space between the 2 bushes?

I guess what happened is the spindle froze in the bush and the swingarm movement broke the spindle from its securing plate. hence movement and frame wear

[muskrat]

G'day Mike.
There should be a tube that goes all the way through that the frame clamps on when the spindle nut is tightened. The bush and swing arm rotates on this (like the inner of the original silentbloc).
Yes that's where the grease nipple goes.
I'd say what happened is the clamping force of the nut locked it all up and the twisting force broke the spindle locking tab.
Cheers.
Bugga late for work!

[chaterlea25]

Hi All,
Attached is a link to a thread on Britbike forum on alternative swing arm bearings and a link to a PDF drawing
of a needle roller conversion.

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=622841&Searchpage=1&Main=66918&Words=%2Bbearing&Search=true#Post622841

https://www.dropbox.com/s/ffxgy54qcp1z262/BSA%20swing%20arm%20bearings.pdf?dl=0

Phosphor bronze bearings would need regular greasing where the silentbloc bushes last more or less forever

John

[Worty]

If it ain't broke, don't fix it.  Otherwise, smack the whole lot out and press new Silentblocs in (will probably outlast you and the bike).  Getting my old Silentblocs out was the biggest b*****d ever.  Took an acetylene torch, three hours and lots of sweat and burns - well done BSA.

[KiwiGF]

If it ain't broke, don't fix it.  Otherwise, smack the whole lot out and press new Silentblocs in (will probably outlast you and the bike).  Getting my old Silentblocs out was the biggest b*****d ever.  Took an acetylene torch, three hours and lots of sweat and burns - well done BSA.

I agree with the above. It would probably be the easier option if you need to fix up what you have

I toyed with idea of converting to bronze bushes but decided I did not have the necessary lathe skills and after a failed attempt to fit over size blocs (incorrectly made, and hence returned to britishspares) I got some good blocs from c+d and went the silent bloc route.

The bronze bushes designs need to address end float (side to side movement) of the arm, you need to understand how your design does that (top hat shaped bushes is one way), and you also need to be 100% sure the bearing you have is working correctly, I can’t remember if the bushes should rotate in the arm or against the spindle, Musky can confirm that? I noticed the swing arm holes on my bike were not very round, which makes getting a close fitting (or interference fitting) bronze bush tricky.

I fixed my oval frame hole issue (circa 015” out) with pieces of tin can placed strategically around the spindle, a bodge but it’s still ok 8k miles later. To weld the hole up in the frame up and then /drill machine a new hole with correct alignment would be hard.

[RichardL]

A long time ago now, after a lot of debating about it here on the forum, I conceded (kicking and screaming) to the concept that the frame plates compress against the nub ends of the inner tubes and that the extent of swingarm rotation is all in the rubber. Mikes arrangement would have no possibility of this. The thin rings could not freeze the brass bushings. I believe they are there as part of the gap filling needs and to keep the fiber washers from wearing away. So, this method and the needle bearing method are evidently intended for rotating free on the spindle, while the rubber "blocs" nothing. I'm not saying this is a bad thing necessarily (other than the fiber spacers) because I still have my doubts as to how many silent blocs are actually working  the way that was pounded into me.

Richard L

[mikeb]

Thanks all for helping to figure this out.

I think as Lee says someone did go to a lot of trouble on this so it would be good to make it work. But it does not have a distance tube (like Musky describes). So the bushes rotate around the spindle and the small spacers/rings inside the fibre washers have to be exactly right to stop end float (like what Richard says). So if it’s over tightened (like Musky says) or gets water in it and freezes up then the spindles turns in the frame etc. hence the failure.

So maybe I could get someone capable (not me) to line bore (?) through the current bushes to fit a distance tube. Or drive the bronze bushes out and start again. I’d be reluctant to just refit new spacers/rings tho maybe they could be re-designed and made waterproof.
A side note - C&D unfortunately don’t have silent blocs currently as they say the quality of what’s around is too low.

Its BSA club night tonight so those guys may have some ideas too.
All further thoughts very welcome.

And Ed – when I get this sorted I’d like that medal you mention – thanks.

[duTch]

 Either I'm missing something or it seems to me that there's something missing, and those small sleeves don't seem substantial enough to take any pressure...thinking about it

[KiwiGF]

Thanks all for helping to figure this out.

I think as Lee says someone did go to a lot of trouble on this so it would be good to make it work. But it does not have a distance tube (like Musky describes). So the bushes rotate around the spindle and the small spacers/rings inside the fibre washers have to be exactly right to stop end float (like what Richard says). So if it’s over tightened (like Musky says) or gets water in it and freezes up then the spindles turns in the frame etc. hence the failure.

So maybe I could get someone capable (not me) to line bore (?) through the current bushes to fit a distance tube. Or drive the bronze bushes out and start again. I’d be reluctant to just refit new spacers/rings tho maybe they could be re-designed and made waterproof.
A side note - C&D unfortunately don’t have silent blocs currently as they say the quality of what’s around is too low.

Its BSA club night tonight so those guys may have some ideas too.
All further thoughts very welcome.

And Ed – when I get this sorted I’d like that medal you mention – thanks.

Hi Mike, just realised we’ve met at the Taranaki rally (I think) :-)

Britishspares (for once) took on my complaint on the blocs, and sent them to John Saywell to be machined down in o.d. This was done several years ago on circa 20 sets, but maybe they still have the machinied down blocs in stock?

I’m still not sure if the designer of yr s/a bearings meant the spindle to form half of the bearing, but I agree with Dutch that if he did, then the metal rings inside the fibre washers have too little bearing area, evidence of which can be seen on one bronze bush having a groove cut in it. Maybe the fibre washers were also intended to control end float?

I’m not impressed with the idea of doing the spindle nut up just the right amount to spring the frame and get just a small amount of end float, it might work in practice but does not seem a “technically correct” design

I think I remember a discussion on whether the swing arm does or does not have a “step” in diameter to prevent the blocs pressing in too far, mine does have this step so there is no need for a centre tube, unless the bronze bearings are supposed to be turning in the swing arm.

[mikeb]

yes Kiwi - we met in the 'naki - good rally that was.
and dutch I agree those spacers/rings look too puny for the job. That may explain the groove in the end of one bush (where the fibre washer was mangled)

actually the spindle has a step in it at the RH/threaded end, inside of the RH frame plate! So i guess that's what stops the plates getting bent in (when the locking plate isn't broken off at the left end). So maybe I don't need a distance tube through the bushes??? Just need some better end spacers rather than those tiny rings in the fibre washers? maybe some large washer-like spacers of the right thickness..?? tho not sure how to keep water out, other than grease.

if so this just got easier! comments?

[muskrat]

G'day mike.
Trouble is if you make new end spacers and tighten the spindle the frame crushes on them and the swing arm stopping any swing action of the s/a. The distance tube is like the inner of a silentbloc and is locked between the frame plates when the spindle is done up. The bushes revolve on the tube. You can make new end spacers to go over the tube but allow a few thou end float of the s/a on the tube.
The idea of the spindle nut locking up the tube/silentbloc inner is to give the frame rigidity (year right ). Without it the frame flexes more than usual .
Cheers