Topic: Have a 1971 or a 1970 cb750 front wheel - I think

[Hondawggie]

I need a front wheel for my 1976 cb750 project bike -- I bought my '76 k6 a couple days ago and it had the wrong front wheel on it, a comstar wheel, and the k6 came with several other wheels the seller wanted out of his garage. 

So I took measurements of the correct front wheel that's installed on a different '76 cb750k6 at my shop -- I measured the hub width, the hub diameter, the rim width, the rim diameter, and the space between the hub and the rim.

Then I wondered if one of those wheels I got from the k6 seller a couple days ago might be the original front wheel, and sure enough, one of them looks the same as the front wheel on the other k6 in my shop.  And this wheel matched the measurements I took of my other k6 wheel from the known-good k6 in my shop.

However there's one thing that caught my eye on this front wheel that came with the k6 I bought 2 days ago -- the hub.

I found a listing on ebay that has the hub from a cb750 that looks identical to the hub on my spare front wheel.  The key notable thing is -- on the right side, the speedo drive side of the hub, there are two cuts on either side of the inner part of the hub normally covered up by the speedo drive I think.

Here's the photo from the ebay listing


My wheel's speedo drive side looks *exactly* like this ebay photo, with those cuts on the area where the speedo drive goes on.

We all know that ebay listers will disassemble a 750 and list the parts and they look at the gooseneck plate and if the plate says "manufactured in 10/70" they put on their ebay ad "this part came off a 1970 Honda cb750" wnen in fact it was a 1971 k1 bike.   Happens all the time.

Because I checked, and the 1971 through 1976, k1 through k6 bike have the same hub, but the 1970 and 1969 front wheel hubs are different.  So this spare front wheel I got 2 days back might not work on my k6.

So I'm hoping this ebay lister who put in his listing "this hub came from a 1970 cb750" is wrong.

Because it makes *no* sense why this 1976 k6 I bought 2 days ago with a poorly-fitting Comstar front wheel and an extra cb750 front wheel, why that extra cb750 front wheel is not the original take-off front wheel from the k6, but is somehow from a 1970 k0. 

But if the wheel I have is in fact a 1970 wheel, I don't think it will work on my k6 because the hub on the speedo drive side might have changed.

Sorry for the long winded.

Can I use the front wheel I have on my 'new' k6?

[Dream750]

See if this helps ... 

The 750 front hub changes with frame number: CB750-1044650, the early / late hub differences are a bit more than just the hub alone. The following info should sort out the parts that you will need:

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

In addition to the service bulletin, note the other associated part number changes that begin with frame number: CB750-1044650.

These 750 diagrams are dated 12/71, click on images for best view:

[Hondawggie]

Thanks -- it looks like there's a 4mm thickness change in the front wheel hub starting with the 1044650 frame -- which happens to be the starting frame number for the 1971 K1 bike.

Thanks for that technical reference -- what that gives me is a way to find out if the wheel I have has a 4mm thicker 1969-70 hub.   However it doesn't exactly say which part of the hub is 4mm thicker, so I'm going to measure from the outermost surface (the axle area) on one side of the hub to the other, then compare. 

I'll measure my known-good 1976 k6 hub off the k6 in the shop, then compare it to this spare wheel I got.  If I'm lucky, I have thinner hub that was used on the later k1, k2, ..., k6 cb750s.

[bryanj]

All the 750 and 500/550 hubs had the two flats, they were the original drive flats for the first 750 speedo drive which is the one you want for a twin disc settup.

It was fairly late on that Honda decided to save a bit of machining time and money by not milling the flats any more.

The drive plate was changed by the way as the early one moved on the flats and caused needle "Flutter"