Topic: cb650 cam in the 550

[sixthwisconsin]

So I searched this topic and found some great info about having to clearance the head (maybe if the lobes don't clear). What I would like to nail down is what I need to make the 550 tach work properly. Looks like the 650 tach drive gear is drop in as well but is that all I need? Do I need the tach cable and tach from the 650 to? I spent some time and effort refacing and cleaning my tach and want to keep it.

Looks like all 650 cams are the same? I have seen conflicting info here. If not, what year should I be looking for?

Thanks in advance for the help.

[onepieceatatime]

550 tach is a different ratio than a 650 tach. I do not think you can make the 550 tach work with it.
I have read that the tach cable is the same also.
'79-'82 were the SOHC 650s any of these years should work for the parts. I do not know if any of the DOHC tachs will work.

[RAFster122s]

Don't think the 650 DOHC tachs are compatible. The 550 tach can't work with the 650 cam...sorry!  The ratios are different. The 650 has something like 6 turns to the 5 turns of the 550 gear...so the pitch of the drive gear is different and that changes the shaft speed. It costs too much to have a speedometer shop try and recalibrate it if that could be done. Dont know if the faces are the same size. Might be able to change the face but then you have calibration issues as I think the 650 face is larger and the marks are in different places...

 Sell it on ebay with good pictures or sell it on this forum to another member.

[cb650]

The later 550's had the same size tack so some do swap and look mostly the same.
The the dohc tacks are electric and in a whole pod assembly with the speedo.
Although not electric the 82 nitehawk tack is in a assembly also.

[Greggo]

Sixth, I have done this mod to my '71 500, and I can tell you what you need.  Unfortunately your 550 tachometer won't work with the 650 cam and tach drive.  The ratios are different as mentioned, and it will wind your nicely restored tachometer into oblivion.  If you're a tinkerer, you may be able to swap the drive gear from inside a 650 or 750 tachometer into your 550's gauge, but that's a pretty invasive project.  If you can find a nice SOHC CB750 tachometer, or entire gauge set that's probably best.  Those parts look the same as the 550 gauges, and the tachometer has the correct ratio to work with the cam.  Any 550 tachometer cable will work, the 650's may work as well, but I never had one to try.  The earlier years of the SOHC4 CB650 cam, in all markets except Germany are supposedly the best.  Just make sure you're not buying parts from a DOHC bike...they won't work.  My cam is out of a '79 650, and it gave my bike a nice bump in overall performance.

Good luck with the hunt, and the installation.