Topic: Differences between early and later front hubs CB750

[kenhan]

Hi, Im into rebuilding  a K0 1970, Frame 103xxxx. It was not delivered with front wheel (hub) but I have the early front fork with smaller sealings and so on.

I have tried to search on this forum and I have learned that there is a wider wheel hub on the older and it became narrower on K1 (4 mm).
Anyone who knows the differences between the wider/narrower front hubs? Can I use the narrower (I have one) and use something the covers up for the difference?  And what is really the difference, 2mm on each side or is it on one side. I have to know that in order to line up the disc rotor. By the way, this site is really something for cb-nerds like me!
/Ken

[mycb750k6]

"The stock front wheel on all the die cast K0 through K6 were the same. The front hub on the early sandcasts was 4mm narrower on one side. It was also dead center of the rim. The die cast K0 and later had the 4mm offset wider for a second disk rotor so that Honda could sell as stock the same configuration as raced in Daytona in 1970" - Hondaman. Get the book and read the entire story...

[kenhan]

Thanks for the information! The Hondamans book seems to be what I need for my rebuild. I have to inform my wife for Christmas gift
/Ken

[Clutch Cargo]

This hub issue is covered in CB750 service bulletin #26 - 12/23/70.  I think that there are copies of CB750 service bulletins lurking at this site.

[kenhan]

Hi again, thanks, I will check the service bulletin if I can find it.

But I had a second thought after reading Hondamans text over again. What he are telling, is the opposite of what I have read earlier in other posts. As I can understand, he means that the early sandcast hub is narrower and the later is wider. I have checked the Honda 750 parts list and the through-hub bolts for the disc are 106 mm from the beginning to frame-number 1044650, and the bolts are 102 mm after that number. And wouldnt it be more logical to have a narrower hub if you want to add a second disc?  To me that points to an wider early hub? Please help me out on this, have I missed something that I dont understand?
/Ken

[Hinomaru]

Here's the CB750 hub service bulletin #26 dated 12/23/70.

It should help clear things up:

http://data.sohc4.net/SB750/750_26.pdf

[kenhan]

I found the bulletin # 26

Anyone interested here is the link: http://data.sohc4.net/SB750/750_26.pdf
It seems like the hub became narrower from frame number 1044650, so Hondamans text still makes me puzzled.

Thanks for help!!
/Ken

[754]

Anyone know the widths, have one here that looks like 86mm(used a ruler).
 Pretty sure I have a KO one somewhere, would like to keep it.