Looking at 1979 SR650 disc swap

Hello,

I recently purchased a '77 650B and I love it, however I'm wanting to make some upgrades and am thinking of purchasing a '79 SR650 for the disc brakes. I currently have wire wheels with a single disc up front and a drum in the rear. I was wondering if the swap to the aluminum wheels with dual disc up front and single disc in the rear is fairly straight forward? As in mostly a bolt on situation without fabrication? I'm pretty sure I'll have to swap the swing arms. Any advise would be great, thanks.

I think it would be, except for the mounting of the rear brake master cylinder which bolts to a couple of mounting tabs welded to the frame downtube at the right rear of the engine so some fab work may be in order.

Another minor issue that you'll encounter along with the rear master cylinder mounting bracket that Nate mentioned is, your 650B rear wheel is 18" and narrow (2.25" ), the rear wheel on the 650D (SR) model is 16" and wider (about 3.25" IIRC).

If using the swingarm from a D (SR) model along with it's rear wheel, the width won't be a prob. However, the wheel being smaller in height will likely change the way your bike handles and feels in particular situations like cornering and at higher speeds.

Your best bet IMHO would be to swap both cast wheels, front and rear brake systems, swingarm and brake torque rod/link from a KZ650C (Custom), since it is an almost fabrication-free swap.
The only real item you'll need to address is a mounting bracket for the rear master cylinder.

I did this swap several years ago on my '78 KZ650B, and was fortunate to have the entire KZ650C model to scavenge the parts from.
I took measurements where the rear master cylinder bracket is welded to the frame, then cut it off with an angle grinder (yes, it trashed the donor bikes frame in that spot). Then using my measurements, I had a very competent welder buddy of mine weld it to the frame.
I asked him to make sure the weld was done like OEM (thick and lumpy looking), and I challenge anyone to distinguish it from an OEM weld.

Long story short, it now looks like a C model (cast wheels, dual front & single rear disc brakes), and I don't have to deal with rusting spoked wheels anymore! :woohoo: :laugh:

I did this swap this winter. The lower fork lugs are located in different spots. Use the SR fork bottoms and discs. The swingarms are the same width, however the weldments are different, use the SR swingarm. The rear master is exactly as described above, carefully measure then cut off donor bracket (or just fab your own) and weld on. It is a simple conversion.

BTW, my swap was opposite. I have a SR and tossed the mags and put B series spokes on it with discs all around. My wheels are being trued this weekend.

When I converted my B1 to rear disc I didn´t want to break the powdercoat to weld on a mount for the rear mc, so I came up with this bracket that bolts on to the upper rear engine mounts (obviously using longer bolts there). It took a couple of tries to get it right but it wasn´t too hard.

Ooops, wrong pic, here we go:

That sure beats the heck out of trying to weld. Good job on that idea.

So its possible for me to keep the spokes and still put the discs on? How does that work? Thanks

you can keep the front wire wheel just bolt on another rotor and caliper;)

As far as just another caliper, do I use an opposite side one or the same just inverted? Rotor wise the same just inverted? Can use the same reservoir with a splitter of some sort?

Do you think this would work for me as far as front brake setup?
cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll...=STRK:MEWA:IT&ih=018

i just bought these from dave. 2 rotors, splitter w/ hose, 2 calipers l/r,
2 forks.