Swinging arm bearings

The swinging arm does not pivot on a rod on these bikes, the movement is allowed by flexing of the rubber in the silentbloc bushes. I had a lot of trouble removing the old bushes from my 650, but managed it with the aid of a press in the end. I ended up not replacing the bushes, but instead used bronze bushes from a bearing shop and a home made spindle.

These bearings can be replaced with a Manx Norton conversion. I have done this on two of my featherbed frames, and it is a much better than the older rubber bushes. I had to get a blow torch to burn them out of two of my swinging arms, as the press we were using was just not strong enough. There is also a taper roller bearing conversion that is produced by a frame maker and repairer in Pluckley in Kent.

Anthony - Do they often (or ever?) wear out to the extent that they need to be changed - for ordinary road use? Or is this all to improve racing behaviour on the edge? Do they really justify all this work "just to know they are OK"? I bought some new bushes some years ago - but when I stripped the back end I found the old ones were a) impossible to remove and b) had no visible damage and c) obviously had high stiffness in all directions (apart being flexible enough to allow the swing to take place...).

So I left well alone - having more important issues on my bike (and life). The original design is maintenance-free and although more 'proper' bearings might be better on the track, they require mainenance and then wear out anyway. The Commando owners are always discussingthe problems with their arrangements...

p.s. to Don - I understand the spindle nuts should be tightened when the swing arm is in the 'normal' road condition (rider's weight in place) so the rubber load is neutral most of the time in service. So rubber 'fatigue' (caused by huge numbersof extreme load cycles) is minimised.

I have the orriginal bush in my 1960, no sign of it wearing . If its not broke-------.

So, are we all agreed that the swinging arm suspension movement is taken by flexing of the rubber rather than rotation around the spindle?I know this to be the case on Series (ie leaf spring) Land Rovers, but their suspension shackles form a tight 'squeeze' on the inner of the rubber (Metalistik/silentbloc) bushes so that the bolts passing through them are effectively 'locked' to the inner of the bush.I assume that on a Featherbed frame the idea is that the spindle is effectively 'locked' to the inner of both bushes by the bushes being squeezed between the frame webs and the spacer when the spindle nuts are tightened? If so then the spindle needs to be 'locked' to the frame webs (to stop the spindle rotating) - does this just rely on the spindle nuts? Are there supposed to be spring washers under the nuts to achieve this?

Yes, you just do the swinging arm nuts good and tight and it lock it all up. No spring washers. If you want it all to go horribly wrong, get someone to push the old bushes out and neglect to put the centre spacer in when they press the new bushes in. The bushes won't clamp up tight and will move on the spindle. You get side play on the swinging arm and, if you are very lucky, the spindle can snap. At 70 mph on the A1, two up.

Yes, you just do the swinging arm nuts good and tight and it lock it all up. No spring washers. If you want it all to go horribly wrong, get someone to push the old bushes out and neglect to put the centre spacer in when they press the new bushes in. The bushes won't clamp up tight and will move on the spindle. You get side play on the swinging arm and, if you are very lucky, the spindle can snap. At 70 mph on the A1, two up.

I have had several featherbed models and have never worn out a set of those bushes yet even with the added side strain of pulling a sidecar. The bushings just seem to last forever.

On another thread I expressed surprise that the Silentbloc system had the inner bushes 'fixed' to the spindle and that the rubber part flexed to allow rotation of the S/A. Not the normal way of things with cars which often use "Metalastic" bushes. They are normally only for absorbing shocks and making the ride a touch softer. The steel inner bush is normally free to rotate on a shaft or spindle. (As with all my old Jags). Rubber tend to have a lower shearingstrength than when in compression or tension. Still, the S/A bushes seem to last forever. If they aren't sloppy and don't permit lateral movement then they are OK so it's not worth butchering the bike to try and replace them. Having the paintwork stove-enamelled doesn't harm them either. Pretty bomb-proof if you ask me.

Cheers, Lionel

The similar (in principle) bushes at each end of the shock absorbers are not interference fits on their through bolts. The whole idea of the friction between the outside faces of the inner sleeves of the bushes against the frame cheeks being relied on to stop the spindle turning, instead of the rubber just twisting (as the designers intended) is pretty Heath Robinson. I am surprised that oval holes in the frame are not more common.

Anyway - I successfully used a hybrid approach. I cut the swingarm out using a skinny 110mm cutting disk. Then I drilled about 75mm down the centre of the shaft from one end with an 8mm bit. Then I opened that out with a 13mm bit and finally used an 18mm bit to destroy that end of the spindle and the inner sleeve along with it. Next I vapourised the rubber with a blowtorch, then I cut the outer sleeve of the bush with a kind of single-ended hacksaw holder and collapsed it inward. Anybody contemplating this will be please to hear that it is only about 1 1/2"mm thick and quite soft. It appears to be thicker when installed than it actually is.

The last stage was to heat the lot up for 20 mins on the biggest ring on the gas stove to destroy the rubber on the second bush, then get a 150mm long piece of thick-walled tube and knock the spindle and second bush out with a 7lb lump hammer. It came out reasonably easily.

If I had my 'druthers I would have left the little buggers alone and just had the frame blasted and powder coated with the swingarm in-situ.

The new ones are not up for replacement until 2063.

Steve

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