Featherbed swinging arm torque

Trying fitting a thin washer under each nut. It may be that the swinging arm bolt does not have enough thread cut on it and the nuts are becoming thread-locked. It may also be possible that the swinging arm has rotated in the past and actually cut a grove on the inside of the gusset plate. A temporary fix here would be a thin washer each side of the arm pending some weld filling and grinding.

On my B44 with silentbloc swing arm bushes once the axle is torqued up the movement is all in the rubber in the bush, this normally fails by going soft and then disintegrating. As long as the stiffness is normal you look to be ok, wait for confirmation.

How was the frame repainted?

... the spacer tube part H12-2/1090. This should stop the silentblocs moving inwards which sounds as though it's the problem you have.

The outer edges of the inner bush of the silentlocs on the B44 are proud of the OD of both the rest of the silentloc and the swingarm so only the inner bush touches the gusset. On the BSA the swingarm is bored with 2 diameters so there is no need for a central spacer as there are lips on the ID to stop the silentlocs moving inwards. If your swingarm has a single ID with no lips then you need a central spacer to keep the 2 silentlocs a set distance apart or they will move and allow other parts to touch the gusset.

I would add washers to effectively bring the outer edges of the inner bush ID outwards on both sides, once torqued then the interfering part currently touching and causing the higher friction should have a larger clearance from the gusset and take the effort to more the swingarm to just deflection of the rubber. If the effort stays the same there are other issues at play.

The reason I suggested the missing spacer was that the gusset plates would then be pulled inwards to foul on the swinging arm itself. It's a bit like the QD rear wheel which needs the spacer to locate the bearings properly. In fact the proper layout should prevent the swinging arm touching the gusset plates at all hence would prevent the wear you mention.

I don't know how you can be so sure that the spacer is in there Richard, as you have not had it apart. Clearly something is amiss, and I would not proceed with the rebuild without correcting it. That means removing the spindle and bushes and replacing them, and repairing whatever has happened on the inside of the gusset plates. It is tightening up with that torque because you are in effect bending the plates/frame, which clearly should not happen.

If you had the frame/swinging arm assembly powder-coated, the heat involved would have destroyed the bushes. If it was wet-sprayed and oven cured, the same applies.

A cautionary tale for other restorers......

I’ve never had a problem powder coating swinging arms with the metalastic bushes in situ, Maybe I’ve been lucky? 

Dan 

Well, that is my understanding, Dan. Notwithstanding that, there is clearly an issue here which needs resolving before the rebuild continues.

Like Dan, I have had several swinging arms powder coated with the silentbloc bushes in situ without any problems. My powdercoater confirmed that the  rubber would not be affected during the cure. It depends on the cure schedule for the process and the resin system of the powder coat. 

As with all we do with our restorations, check with the experts you are planning to use first and get their advice  before starting. 

Richard,

I had this problem with my Slimline swinging arm.  The spindle iss seized inside the silentblock bushes, so the only way for the swinging arm to move is to rotate the spindle in the frame gussets.  This has then caused the gussets to wear on the inside, so that now when you tighten everything up it all locks together.

Really you need a new remove the seized spindle, which may mean cutting it out, which is not an easy job.  When I did this I ended up having to replace the silentblock bushes as well.  Unfortunately your paintwork is likely to suffer, but you've got to resolve the problem otherwise you'll cause even more damage to your frame.

Philip.

Richard - it sounds like you have sorted it.  It doesn't matter if the spindle is seized in the bush since it is not supposed to move relative to the centre bush anyway.  It is supposed to be as you have assembled it - the spindle locked tight to the frame plates, and the plates gripping the centre bush.  The arm should ideally be somewhere in the middle of its travel when the spindle is finally tightened so the Silenbloc rubbers are relaxed when the bike is in use, and then the swing arm movement all takes place by twisting the rubbers.  Just like those rubber suspension units often found in trailers.  The centre bush stays fixed relative to the frame, and the outer bush stays fixed relative to the swing arm.

Drawing the frame tubes inwards should not matter - it's a bit like a part way stage in 'cold setting' a frame.  The tubes already have high locked-in static stresses from manufacture, so I wouldn't concern myself with the bending stress since it does not vary constantly in use - so it won't lead to fatigue damage.

I've recently pressed out the two Clayflex bushes. No spacer. The bushes are 79mm long on the inner, I make it that a spacer would have to be around 55mm long. However, they took almost the full 10 tons to press out so the pivot pin end nuts could not have pulled the side plates in enough to squeeze the bushes in further. Without a spacer, and 'soft'  fit bushes , the sides could easily pull in. There was about 4mm of inner bush showing when fitted, if that's normal (everyone ?) then you could inspect yours and see if there has been some pull-through.