Hi,
The frame of my Dommie 99 shows slight wear marks where the swing arm fits. It’s looks as if the metal tube inside the rubber swing arm bearings has been grinding away at the frame mounting points as the swing arm moves up and down. Should the metal tubes inside the rubber bearings be able to move slightly when the swing arm is clamped into the frame or was my swing arm just too loosely bolted into the frame? The metal tubes are solid inside the rubber bearings and can’t be rotated so the swing arm bearings themselves seem fine.
The wear in the frame takes the form of a circle that is the diameter of the metal tube in the rubber bearing and about 5 thou deep. The end of the tube on one side of the swing arm also has a very slight bur on it - it’s as if the end of the tube has been peened over, but it’s only about 1or 2 thou high. I guess that a result of the tube moving up and down against the mounting point. It seems strange that the ends of the bearing tubes bear directly on the frame mounting points if the metal tubes are designed to move as the swing arm moves.
Any information and advice gratefully accepted.
Thanks.
Regards
Tony
Not a Norton
- Log in to post comments
I suspect that the swinging…
I suspect that the swinging arm nuts have got loose at some time,The spindle can seize in the bush ,but as the inner steel part of the silentblock is not supposed to move this should not matter except that it would be necessary to tighten both sides then to hold things still. Sounds like you may need a shim to take up the clearance , once you have removed the spindle.
- Log in to post comments
Thanks guys. The spindle was…
Thanks guys. The spindle was rusted into the metal sleeves but I have it out now and have bought a new stainless one. I’ll work out what thickness shims I need when I bolt the swing arm back into the frame - but that’s a long time away yet! The nuts on that spindle must have to be done up incredibly tight to prevent the metal sleeves from turning. I would have thought that even a small movement of the swing arm up or down would be likely to cause them to turn, especially when the frame is vibrating during riding over the (now normal) poor road surfaces.
Thanks again for your help.
Regards
Tony
- Log in to post comments
I suppose its possible that…
I suppose its possible that the silentblock rubber has hardened with age and now needs more torque to spring it, Going outside to check mine right away!.
- Log in to post comments
Lesson learnt from a BSA
Took me 3 hours.after getting the shims to get the swing back on the bike. Cleaned the bore with an adjustable reamer. The new spindle was zinkplated. Not a bad idea but a bit (.04mm) too thick plating. Lathe and emery tape. First .5mm shim no problem. On the other side almost impossible to line up without a helper which I don't have. Very tight fit. Finally used a portopower to widen the frame about .010". Guess 500kg force. Then able to get the shim in place and the axle home.
Conclusion: A small axial play makes it much easier to fit the swingarm. A bigger play requires too much torque to tighten the nut thus locking the silentblocks firmly.
- Log in to post comments
On some featherbeds you can…
On some featherbeds you can remove the upper spacer tube which may allow you to spring the frame a little.
- Log in to post comments
The swingarm axle shall be tightened so that the inner sleeves can't rotate. Remember that ideally tightening the axle should be done when the swingarm in a position about where it shall be when a rider sits on the bike But it's fairly common just to fit the rear dampers before tightening the axle. See below what can happen.
Today I'm working on a BSA B40, with a similar problem. Also silentbloc rubber bearings. Axial play 1mm (.040"), radial play .5mm(.020"). Silentblocs inner dia. OK. Alll wear on the axle. Also found that the pair of silentblocs could be pressed together .3mm(1/8"). Remedy is a new axle and buy or make axial shims. As the frame has to flex when tightening the axle, too much axial play will need excessive tightening force.