I was fortunate to have acquired a bounty of parts from a mechanic/collector. Basically a 500, a 550 and a 650 bikes worth of parts. No frames. Mostly engine stuff. There are boxes I haven't even looked into until today. Found a good 650 clutch and a 500/550 clutch to compare. I'm super grateful to the guy I got all of this from. He labeled most things. The 1981 650 clutch appears different but in fact measures identical to the 500/550 clutch. Thickness, O.D, I.D. and spline count. The mounting fasteners are different and not oil passages. My 1979 650 primary shaft slides into the early 70's 500/550 clutch nicely. The clutches appear to be interchangeable. The bodies the clutches are attached to look like they have some slight bearing seat differences. I'm not investigating those, so no claims about interchangeability on those. I didn't remove the 500/550 clutch phillips screws since the were chisel struck and would require drilling. So... bottom line, I have a good functioning starter clutch.
All pictures show 1981 cb650 clutch and body on the left and early 70's cb500/550 clutch on the right.
