Swing Arm Development

In a previous thread here

commando-frame-straigtening-t23185-15.html

I included a picture of a swing arm I'm using in my current MK3 build. There was some interest in the construction details, and I've got it apart now for repacking and new seals, so I thought I'd show the construction. I originally built it somewhere in the '80s for my PR. This is the only shot I have that shows the swing arm, and it doesnt' show much, but this is where it started.



When I quit road racing, I sold the PR to a friend of mine who restored it back to original, but I kept the swing arm and cradle. I later used it for a Norton-powered streamliner that a friend and I ran for a few years at Bonneville. We welded a structure on it so we could use a monoshock design. This is a shot of it as used in the liner.



When I finally got around to rebuilding and modifying my street MK3, I decided to use the swing arm. I removed the monoshock structure to go back to twin shocks.

This is a picture of the arrangement of bearings, spacers, and seals.



The stepped spacer between the bearings is sized to provide a little pre-load on the bearings.

This is a picture of the cradle to show the steel top hat bushings I pressed into the cradle. They are a tight fit on the swing arm pivot bolt. The spacers in the inner seal are sized to give a tight fit between the cradle and swingarm. I have to persuade it on with a mallet. There is no slop at all in the swing arm fit. The cradle is one that Old Brits sells as part of their electric start conversion, which I am using on this build.



Ken

Thanks, Ken - that is most appreciated - it always helps to see how other people have done jobs you're about to do!

Ni ce work. That is one honkin' big monoshock tower!

grandpaul said:

Ni ce work. That is one honkin' big monoshock tower!

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Yeah, for a street bike it would be. But for the streamliner it was a reasonable size. This is how it looked installed. We had Works Performance re-valve the shock and fit a really high rate spring.



Ken

the assembly pic really shows the effort needed to get a set of bearings to replace the factory bushing setup. but will surely eliminate unwanted movement.

so the million dollar question... when are you going into production? or sell the drawing set?

Not planning to get into the swing arm production business. And, unfortunately, the "drawing set" consists of a bunch of grease covered sketches and notes drawn on lined paper in the shop. I tend to do this sort of stuff in a cut and try, and then cut again sort of process. I'm pretty slow at producing CAD drawings, so I pretty much only do them if I need to get a quote from the local CNC shop. When I made the swing arm, I knocked together a crude jig from scrap metal, but it's long gone.

Ken

lcrken said:

Not planning to get into the swing arm production business...............I knocked together a crude jig from scrap metal, but it's long gone.....Ken

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Well damn the bad luck, that's too bad for the rest of us :mrgreen: Thanks for posting the photos of it though, that rear brake caliper looks to be right where it ought to be. I'd like to have one if you change your mind, put me on the list

This is drifting far off subject, but did that steamliner ever find its way to the salt and if so how did you make out?

Always interesting to see others solutions.
Which dimension has the beam on the swing arm (width, hight and thickness) and material quality?

WZ507 said:

This is drifting far off subject, but did that steamliner ever find its way to the salt and if so how did you make out?

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Yes, it did. We ran it at the salt in 2006, 2007, and 2009. Never had much luck. The engine always ran great, right up until 2009 when the Lucas Rita ignition failed (my fault for not using isolator mounts for the box), but we had all sorts of other problems with shifter, chute release, tach, crashes, etc. I gave up on it after that, and went back to running a conventional bike (wideline frame/Commando engine). My partner in the experiment replaced my Norton engine with his Guzzi engine, and we ran it with reasonable results in 2012.

This is how it looked in 2009:



Ken