Installing CM400 18" Comstar Wheel on Front

[Waco750F]

It appears the wheels are identical, save 19" stock and CM400 18". I believe I will also need the Speedo gear for the 18" wheel and that both disks should mount to the 18" wheel.  The plan is to install the smaller wheel with 100/80-18 to get better corner turn-in; it should also improve
 rake/trail.
Anyone else have experience with this swap or comments? How far out in left field am I?
Thanks, and ride safe, always!
Curt

1982 CB750F SS

[TOOLS1]

My only thoughts would be to check the size of the axle, and width of the rotors when mounted onto the wheel. Other then that I cannot think of any reason it would not work.
TOOLS

[Waco750F]

Got the CM400 wheel coming from ebay with the speedometer gear that goes with that 18" wheel. The local Honda parts counter gave me the part numbers for 750 and 400 bearings; same part number but different suffixes (6302U and 6302Z). I'm thinking if the hubs are the same width, the 400 wheel can be assembled using 750 bearings and stackup, enabling me to retain twin disks rather than single disk.

It sounds do-able. Any thoughts or experience doing this wheel swap?

[shinyribs]

Re: the bearing numbers. U= plain, unsealed ballbearing.  Z= metal shielded. Just a fyi. Although, it's very odd to see a Z bearing used in a wheel. Z's metal shields don't provide any dust or water protection at all, they are designed to reduce interference that could come from static electricity created by the spinning bearing. If at all possible, don't spend the extra money for a Z as it is useless in this application. An RS bearing will be dust and water proof.

As far as fitting the rim, you'll just have to get the parts in hand, take some measurements, scratch your head and then smile when you figure out how it fit all up. Good luck. Sounds like a neat project.


*edit: a 6302 sized bearing has a 15mm I.D.. I thought these bikes had a 16mm front axle?

[Waco750F]

Wellll, as I should have expected, the 18" wheel is about 1/2' to 3/4' narrower at the hub. Couple of ideas, please feel free to comment.

1. Ditch the front end entirely and fit another model with twin discs to the front end that have an 18" wheel. (more $$)

2. Find a tire with a shorter profile/side wall height and stay with the 19" wheel. (need a new tire, anyway)

3. Mill a shim for each side of the 18" hub to bring the discs out to the original distance for the calipers. The only issue here is the speedo gear and how to fix it in position. I believe it rides against the fork to prevent rotation with the wheel... and a potential safety issue. (more $$)

[TOOLS1]

Could you space the calipers in instead of spacing the discs out? The speedometer drive is held into position when the axle is tightened, so that is not a problem.
TOOLS

[Waco750F]

Tools1,
The width of the CM400 hub is about 3"; the 750 hub is about 3 1/4" - 3 1/2" or so. I think to move the calipers in is a viable option but the speedo gear has a stop that engages on the lower fork tang.

I can't get an accurate measurement because the 750 wheel is still mounted on the bike but it is wider than the CM hub.

Thanks for the idea!

[TOOLS1]

That tang is just an alignment tang. It just lines the drive up, so that you do not kink the cable while installing the wheel, it does not keep the speedometer drive from turning. The drive is pinched between the axle and nut as a wheel spacer.
TOOLS

[Waco750F]

Tools1,
After this kernel of true knowledge and genius, and I quote shinyribs: " I am beginning to smile."
Looks as if I can shim the calipers inward once the discs are on the new wheel since it is narrower. Just need to watch how close the calipers get to the spokes.

Then fab axle spacers to the axle and axle nut. I seriously doubt if the CM and CB axles are the same length and will need spacers.

[Waco750F]

The wheel swap is complete! Had a couple of axle spacers made (why they are a different width, I don't know). But the wheel bolts up, lines up with the rear wheel, and the rotors are aligned with the rear wheel.  I'm waiting on the seat before I ride it. One funny thing: the CM400C had a single disk rotor. I am able to retain the twin rotors. The right caliper bolted up to the fork; the left caliper needed a 1/4 spacer to bolt up to the fork.  Any ideas or is this just serendipity? I was focused on retaining the original axle bolt length to not skew the forks and experimented with washers to align the wheel but could not make it work with equal washers on both sides. One spacer is about 1/8 in wider than the other (right side).

[TOOLS1]

Sounds good. As long as the wheel is centered, don't worry about the spacers. They are different between sides on the stock setup anyway.
TOOLS

[Waco750F]

I needed to hear that, Tools1!

Thanks!