Topic: Converting a 750K to dual disc

[Brooklyn Bob]

I have a 1977 CB750K and I am not very satisfied with the front brake.  I have all new parts from the master to the caliper and am using EBC HH brake pads with an EBC rotor.  I came into possession of a reportedly front wheel from a 1977 CB750SS\F (seen below) with twin rotors.  There is also a pic of the axle that came with it.  Anyone know if there is a reasonable chance of using this wheel with a second 750K caliper?  The 750SS\F calipers don't appear to be able to be mounted to the K forks.  TIA

Bob

[bryanj]

You will need the 78 F front end to use that wheel and discs, you can fit a second disc, caliper etc to your original but has to be same as you have

[Bankerdanny]

You won't mount F2/3 calipers on your K fork. They mount to the back of the lower using a bracket. The K forks use a completely different caliper and caliper mounting system.

I was able to go the other route, adapt a wire wheel to work with a twin disk F2/3 front end, without too much trouble.

The Comstar hub is narrower and the rotor center has a deeper dish to make up for that, but I don't know if the F2/3 rotor is the same distance away from the centerline of the hub as the rotor on a wire wheel setup.

I would say pull your existing wheel and see if the Comstar and rotor slide into place correctly.

[Brooklyn Bob]

 

"I would say pull your existing wheel and see if the Comstar and rotor slide into place correctly."
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That's a great idea.  Thanks.

Bob
[/quote]

[Brooklyn Bob]

"you can fit a second disc, caliper etc to your original but has to be same as you have"
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That was the plan.  I could see from the parts fiche that the F\SS calipers are not compatible with the K forks.  I figure having double the swept area of the stock K bike can't hurt and might help significantly.  The question is, are the wheel and rotors compatible with the K forks.

Bob

[Brooklyn Bob]

Oooops ..................

Neglected to say thank you to Bankerdanny and BryanJ

Bob

[scottly]

The question is, are the wheel and rotors compatible with the K forks.

Bob

The Comstar wheel with it's axle and spacers will bolt up to the K forks, but the rotors are smaller than the 750K rotors, and are spaced further apart. The 550 used the same 275mm size rotors, so you could use 550 calipers, but since the calipers mount to the inside of the fork leg, they can't be moved outward to accommodate the wider rotor spacing.
Thousands of K bikes have had the dual disc conversion done with the stock spoke wheel, and yes, it is a significant upgrade. The F0,F1, K7 and K8 used a 42.8mm caliper, all the K models and the early Fs used the same 295mm rotor, and the stock 14mm master cylinder works fine.

[Bankerdanny]

The question is, are the wheel and rotors compatible with the K forks.

Bob

The Comstar wheel with it's axle and spacers will bolt up to the K forks, but the rotors are smaller than the 750K rotors, and are spaced further apart. The 550 used the same 275mm size rotors, so you could use 550 calipers, but since the calipers mount to the inside of the fork leg, they can't be moved outward to accommodate the wider rotor spacing.
Thousands of K bikes have had the dual disc conversion done with the stock spoke wheel, and yes, it is a significant upgrade. The F0,F1, K7 and K8 used a 42.8mm caliper, all the K models and the early Fs used the same 295mm rotor, and the stock 14mm master cylinder works fine.

The Comstar rotor spacing is deceptive. The dish is deeper, but the hub is thinner. My Lester front with 550 rotors works great with the F3 caliper with minimal spacers, which suggests to me that you might be able to make a Comstar work with K style caliper/bracket