Author Topic: B40 swing silentbloc  (Read 303 times)

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Mike40M

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B40 swing silentbloc
« on: 15 January, 2020, 15:33:22 »
I'm new to this forum. Recently I bought a probably ex Danish military bike, in civilized trim.
It works well but there is a significant play, both axially and radially in the swing arm.
After disassembly. silentblocs rubber seems to be in decent shape.
Shaft diameter is 20.35 mm and the inner diameter of the silentblocs are 20.8 and 20.85. Seems the play of almost .5 mm ( .020" ) is what I felt wiggling the swing. It also is has an axial play of .7 mm ( .030" ). I believe that BSA's intention was that tightening the spindle nut should squeeze the silentblocks tight into the frame. If I put a shim between the silentbloc and the frame, I believe it will make it easier to thighten the nut as the frame don't have to flex as much. Still the radial play would remain.
Anybody knows spindle and silentbloc diameters?
Any suggestions on how to fix it?

Mike40M

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Re: B40 swing silentbloc
« Reply #1 on: 31 January, 2020, 16:32:24 »
Finally got parts for it. Luckily the new silentblocs the same i.d as the old ones. No need to replace them. The new axle is a tight fit in the silentblocs. But one interesting part remains. Find or make a shim.

Set up the swingarm in the hydraulic press to check that the silentblocs were tight to each other. Test fitted it on the bike. Now axial play was 1.05 mm (.040"). My guess is that a PO didn,t manage to get them together tightening the axle nut. After some miles, it started to rotate between axle and silentblocs. Less life than the previous design with bronze bushes and a grease cup.