Monday, January 20, 2014

Rebuilding the Swingarm

A fixture for the swingarm was made for measurement on a surface plate to factory specs. It was bent up about 5/16 of an inch on the chain side.  It was hard to see how this had happened as the tubes were square with the surface plate up to the axle section that is brazed on to them. I heated it cherry red and bent it back to the proper location. This movement closed up the axle slot which had to be worked back out to size on a mill. When all was finished it was within a 1/16 of parallel which I thought was good. The axle slots had also been gouged out significantly. This was partially done when I tried to remove the dummy axle which was severely rusted in place. I heated it up but still pulled all the threads trying to get it out. Previously I had tried nut and bolt breaker with no effect. I TIG welded the gouges and milled everything back to its original state.

Inspecting the swingarm to factory specs. 

I had never replaced the silent bloc swingarm bushings on a BSA and thought I would give it a try as mine were quite a ways off center. I thought I might as well learn everything possible on this bike. Silent blocs are a pretty odd setup. There is not a bushing that pivots in the swingarm, but rubber molded between two pieces of steel that flex and allow radial movement. This turned out to be pretty tough, at least the way I attempted it. I tried the method demonstrated in the workshop manual. Grab and twist. No results at all. I made a mandrel on a lathe slightly smaller than the diameter of the bushing and attempted to press it out. This worked for the center tube only. Bummer. This left the outer steel in the swingarm, which I broke loose with a screwdriver, chisel and heating it with a torch. I’m sure it looked like 3 stooges bike repair attempting the job, but I have the comfort of knowing no one was watching. I even debated discussing it here to be honest but hope I stop someone else from making the mess of their swingarm that I did. I was eventually able to get the bushings out, but I tore up the swingarm. This had to be fixed with an air grinder on the inside and my old friend the TIG welder on the outside. I’m glad I learned how to weld in college. The next time I do this I will rethink my strategy and I do not have a plan at the present time. 

 Bushings removed, the swingarm welded and ground back to its original form. 

Chain side bent back to position, welded and milled to specs. 

Outside of the swingarm welded and benched back to its original form. 

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