Topic: Cb750k1 -72 ”race bike / cafe racer” being rebuilt.

[pinkrimracing]

Hello. I’m starting a thread for my rebuild. I bought an ex-racebike that has been raced in classic racing . It was a bit worn and had a fram color that I did not like. The bike is now street converted, but I will hopefully use it at a trackday some day. Some pictures of how it looked before I painted the frame.











Last picture is of the calipers on the bike. One of them is leaking and I need to rebuild them. Can anyone help me Identify which year they are so that I buy the right rebuild kit?

Best regards,
Per
Sweden

[scottly]

Welcome Per. Measure the caliper piston diameter; if 38mm, they are from a CB550. If 42.8mm, they are from a 750 F0/F1 K7/K8.

[pinkrimracing]

Thank you for help. I don’t think the CB550 ever was sold here in Sweden. It was either Cb500 or 750. Did the K0-K6 all have 42.8mm piston?

[scottly]

No, the K0-K6 had 38mm pistons with finned caliper bodies. The 500/550 calipers were used 275mm rotors, while the 750 used 295mm rotors. Your rotors appear to be the smaller version?

[pinkrimracing]

Engine finally back in frame. Happy days!


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[pinkrimracing]

Welcome Per. Measure the caliper piston diameter; if 38mm, they are from a CB550. If 42.8mm, they are from a 750 F0/F1 K7/K8.

I had time to tear them apart a couple of days ago and the pistons measured 42,8mm so now I just need to find seals and probably pistons since they were a bit pitted. Thank you for input.


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[pinkrimracing]

Some progress.


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[Stev-o]

Hi....I'm along for the "Ride".  nice progress so far....

[scottly]

Welcome Per. Measure the caliper piston diameter; if 38mm, they are from a CB550. If 42.8mm, they are from a 750 F0/F1 K7/K8.

I had time to tear them apart a couple of days ago and the pistons measured 42,8mm so now I just need to find seals and probably pistons since they were a bit pitted. Thank you for input.


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Phenolic pistons are available from member Godffery; they don't corrode, and are significantly lighter than steel pistons.

[SOHC4 Cafe Racer Fan]

I'm not sure if Sweden sells gas with ethanol added.  If so, you will definitely want to line your tank with a liner that will not degrade with exposure to ethanol fuel.

[pinkrimracing]

I'm not sure if Sweden sells gas with ethanol added.  If so, you will definitely want to line your tank with a liner that will not degrade with exposure to ethanol fuel.

Yep we have that nasty stuff here as well. The guy who makes them has been making tanks forever and the resin he uses now withstands ethanol so I’m safe.


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[pinkrimracing]

I’m currently making a new wiring loom since previous owner only needed ignition. I have a question regarding the horn button.

I’m using K7 controls since the K2-switch gear was butchered. According to the K2 schematics, the horn is fed power directly and the horn button grounds it. When taking the K7 switch gear apart, I’m puzzled. It looks like the button is fed through the black wire. When pushing the button straight in, it exits through the light green wire (? - colorblind) and when I push the button to the side (PA), It also feed the blue wire to the high beem. Am I correct in my assumption that the horn is fed 12V via the button and that ground directly to frame?




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[754]

Put a bicycle squeeze horn on it . Lol.. we did it on some customs.

[pinkrimracing]

Haha why not. At least I wont have any problems being colorblind when installing it..