"Custom" Conversion Swingarm

typ181r90 · Jul 7, 2014

According to Chris Bynum's site on conversions, a custom swingarm can be used to use a /5+ tranmission with the corresponding final drive and the LWB /6 drive shaft. It appears in the picture that all that was done was cutting the /2 flange off, and then welding the LWB flange and bell housing onto the /2 swingarm, boring out (or welding in a /6) hole for the axle to 17mm, and then making a plate to relocate the rear shock bolt.

Am I correct in assuming these are the changes that have to be made, anyone tried this before? I can take my own measurements for the cutting and welding, but does anyone who's done this before know the measurements offhand (mainly the length from the front of the swingarm to the new flange in the rear?

I was just rebuilding the front forks + regreasing the steering stem bearings on my 75 R90/6 when I noticed some frame damage at the frame neck. Since I'll have to take everything apart to get that frame fixed, and since I'm still a long ways from getting the various parts for a complete R60 together, I'm thinking of taking the conversion route so I can at least keep riding in the years it'll take me to get the other stuff sorted.

69zeff65 · Jul 9, 2014

I don't think you have to cut or weld anything

A friend of mine did his R 75/5 into a /2 frame about two years ago and I believe all he did was use a LWB or /6 drive shaft and coupling in the /2 swing arm. He turned the coupling down on a lath so it would fit inside the /2 housing, he only cut a little bit away and it fit as though it was supposed to.

typ181r90 · Jul 9, 2014

69zeff65 said:
A friend of mine did his R 75/5 into a /2 frame about two years ago and I believe all he did was use a LWB or /6 drive shaft and coupling in the /2 swing arm. He turned the coupling down on a lath so it would fit inside the /2 housing, he only cut a little bit away and it fit as though it was supposed to.

That method can be used if you are going to use the /2 final drive. Unfortunately I have 1 /5 final drive, and 2 /6 final drives, but no /2. If the later final drive is retained, the flange needs to be moved and modified.

69zeff65 · Jul 9, 2014

It might be worthwhile to buy a /2 FD

This is just my opinion but you might be better off looking for and buying a decent used /2 final drive instead of cutting up and re-welding the swing arm to make the later FD work.

Its more than just cutting and welding it back together, you have to line up all that stuff real close or at best you will eat bearings and seals and worse case you won't be able to get it together for the build. I'm sure any decent machinist/welder can do the job correctly but at what cost?

Will a /2 wheel fit onto the /5 /6 FD? If I get a chance today before work I'll check this out for myself.

Those conversion bikes are neat and very practical when done right but here are some things to consider.

Early (pre-/2) R 50, R 60 & R 69 frames are less solid than the later /2 frames, over the years the frames were modified, gussets were added and center stand mounts were changed so the better frame to use for a conversion are the later /2 frames unless you add the gussets to the frame during the build.

You can usually find a good used frame on line (IBMW) for your R 90 for around $100 + shipping and get that bike back up and running a lot faster than it would take to build your conversion bike and you can continue to search for the R 60 parts. If you go the replacement frame for your R 90 route you should consider a /7 or later dual shock frame as they stronger and have better bracing and gussets added from the factory.

You have to change out the electrics to accommodate the 12 volt R 90 motor, /5 headlight assembly and handlebar switches are almost a bolt on items but cost big $$$ for them in good shape.

There are a few more things to consider that escape me at the moment but hopefully this helps you out a little in figuring out what direction to take.

typ181r90 · Jul 9, 2014

69zeff65 said:
This is just my opinion but you might be better off looking for and buying a decent used /2 final drive instead of cutting up and re-welding the swing arm to make the later FD work.

Its more than just cutting and welding it back together, you have to line up all that stuff real close or at best you will eat bearings and seals and worse case you won't be able to get it together for the build. I'm sure any decent machinist/welder can do the job correctly but at what cost?

Will a /2 wheel fit onto the /5 /6 FD? If I get a chance today before work I'll check this out for myself.

Those conversion bikes are neat and very practical when done right but here are some things to consider.

Early (pre-/2) R 50, R 60 & R 69 frames are less solid than the later /2 frames, over the years the frames were modified, gussets were added and center stand mounts were changed so the better frame to use for a conversion are the later /2 frames unless you add the gussets to the frame during the build.

You can usually find a good used frame on line (IBMW) for your R 90 for around $100 + shipping and get that bike back up and running a lot faster than it would take to build your conversion bike and you can continue to search for the R 60 parts. If you go the replacement frame for your R 90 route you should consider a /7 or later dual shock frame as they stronger and have better bracing and gussets added from the factory.

You have to change out the electrics to accommodate the 12 volt R 90 motor, /5 headlight assembly and handlebar switches are almost a bolt on items but cost big $$$ for them in good shape.

There are a few more things to consider that escape me at the moment but hopefully this helps you out a little in figuring out what direction to take.

Yeah, I was aware of the /2 frame changes, I had planned on adding the gussets and actually making my own centerstand mounts as one is broken on the current frame.

As far as the wheel goes, /2 wheels need to be modified (from what I understand) to work with later fds, but along with my slew of final drives, I also have /5 alloy wheels and hubs. My R60 frame is literally just that, a bare frame. I'd automatically be switching over the electrics as I'd be doing large parts swaps, complete with converting to telescopic forks

Concerning the R90/6, I had someone look at the frame and the neck damage is about 2-3 degrees off center. I have never dropped the bike or gotten in an accident, so the frame has likely always been like that in my 6 or so years of ownership, just noticing it now. I was able to take the bike up to 110+mph without any problems tracking, take my hands off the bars doing 50mph without any wobbles, but now I know the damage is there and it'll drive me nuts. The guy told me to button everything back up and keep using it, but I'm still on the fence. I know all about the ebay frames with titles for 100-150$, but who knows that another used one I buy won't be warped somewhere.

I'm going to be thinking pretty hard about this this week. I still have the Aermacchi I built to ride around while I ponder options, unfortunately a bike that tops out at 65mph isn't practical for highway commuting duties, or driving in NJ in general

69zeff65 · Jul 10, 2014

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