Topic: 1978 cb750f front rotor diameter

[wevans]

By chance, would anyone know the diameter of the front rotors off a 1978 f model ? Im converting my 75 750f to dual disc. I bought forks and calipers off a 78. Got the forks in place and went to mount the calipers and the 75 rotor is too large in diameter and wont allow the caliper mount holes to line up with the mounting holes on the forks. Any help is appreciated! Thanks

[70CB750]

If nobody steps in, I can measure it for you later today.

[madmtnmotors]

You did not get the 78 wheel too? The disks are different (different part numbers between 75F and 78F), and I believe the hubs are different too, to accommodate the extra disk. If you like the spokes, you can get adapters to mount a comstar hub to a spoked rim:

http://motosynthesis.blogspot.com/p/products.html

Not sure about 750 compatibility. The write up on this page is for a CX500.

I don't think the 78 750F calipers are designed to work with 1975 rotors. I think the 78F rotors have a different offset, and I think they might be thinner too. If you got the forks and calipers for the 78F then I would recommend getting the rest of the system:

>Front wheel, with rotors
>Brake lines
>Master cylinder

Edit: In the comments section it is indicated that these work with the SOHC CB750 style Comstars

[wevans]

I believe you are correct. Im kinda stuck here because im building a cr750 replica. I would have bought the 78 rotors but they have more of a mag style spoke pattern to them. My plan was to chuck the 75 rotors on the lathe and trim them down to the correct size. Not sure how to fix the rotor width though but I'll see if i cant make it work. If not, I'll just have to settle for the 78 rotor style for convenience. Thanks a bunch for the help though. Im new to 750 Honda's and this site has helped so much. Thanks again !

[flybox1]

you might be able to find what you need here....He's a member of the forum.
http://www.vinmoto.org/gallery/v/VinMoto-Garage/album03/Godfferys-Garage-123/Parts+and+service/

[scottly]

550 rotors share the same 6 bolt hub as the 750K rotors, but are 276mm diameter instead of 296mm. If the rotors are too thick to fit into the calipers, Godffery can thin them.

[wevans]

I think I'll be ok as far as the offset

[70CB750]

To OP:

http://www.motorcyclespecs.co.za/model/Honda/honda_cb750f_78.htm

276mm