Topic: Rear wheel compatibility issues.

[JamesM]

Bike: 1978 CB750
Rear wheel: 1973 CB750
Bearings: 1973
Sprocket:1973
Axle: 1978
Drum: Pre 1977

Okay, now when I tighten the axle nut down it locks the drum onto the wheel not letting it turn freely as it supposed to do. I have two different pre 1977 drums and they both do it, (the '78 drum does it as well)

Does the 1973 hub have a year specific drum or something?

This is why I hate bolting stuff together from different years, wish I would have just laced an 18" rim to my 1978 hub now...

Anyways, thanks in advance.

[JamesM]

I made sense of it to myself at least. If I were to put a spacer in between the bearing and the drum to keep the outer lip of the drum off of the hub then it wouldn't lock up on itself.

Is there actually supposed to be a spacer in there?

[70CB750]

Did you match it against cmsnl schema or manual?  There may be a piece missing.

[JamesM]

Yep, I don't appear to be missing anything.

[MCRider]

I made sense of it to myself at least. If I were to put a spacer in between the bearing and the drum to keep the outer lip of the drum off of the hub then it wouldn't lock up on itself.

Is there actually supposed to be a spacer in there?

You have to visualize this. There must be a solid spacer stack, the size of the inner race of a bearing, that travels the entire length of the hub/axle. IF not when you tighten it down you'll put something in a bind. There should be no part of the axle that is unsheathed by this stack. So if internally in the air spaces there is bare axle exposed, you're missing something.

[scottly]

Is the spacer that goes between the bearings in the hub missing?

[MCRider]

Is the spacer that goes between the bearings in the hub missing?

Adding to my and Scottly's post:

The "stack" of spacers/inner races is such that when complete, you can crank down on the axle nut to an obscene amount, and the wheel will turn unimpeded by anything.  There is no amount of torque you can put on the axle nut that will cause anything to rub or bind.

[JamesM]

Yes, the inner spacer between the bearings is there.

It's like the drum goes in to the hub too far? Like I said, I made a spacer to go in between the bearing race and the drum's inner race and tightened it down and it spins freely.

I'd rather not run that if it's not what's supposed to be there, but I am just at a loss here.

[madmtnmotors]

http://forums.sohc4.net/index.php?topic=103860.msg1161713#msg1161713

[Tugboat]

The 1977/78 swing arms are 10mm wider than the earlier ones to account for the offset front sprocket on the K7/K8 motors. Thus, even though you're not "missing" any parts, your spacer stack is too narrow.

[JamesM]

^Thanks. Should I add a 10mm spacer in between the hub and drum to keep the drum off of the hub like I had planned?

[raymond10078]

Is your brake side bearing flush - or set into the housing (past being flush)?

For my 78, the bearing will go about another 1/8" in to the end of the counterbore - but the bearing is meant to be flush only.  This would affect how "deep" the brake sets into the hub . . . .  Just a thought.

[Retro Rocket]

The K8 swingarm is wider and the K8 sprocket carrier is 10mm wider, i think the spacers are different a swell so there's more than one difference, its not a simple drop in...., You would need all the K8 parts {spacers and sprocket carrier} to mate to the K3 hub, the sprocket carrier is important because without it your chain won't line up properly...

[JamesM]

kandrtech- I'll have to check

Rocket- I'm running a '74 motor, with an older front sprocket too.

I'm using all the K8 spacers and axle with the '73 hub, and an earlier drum.

[Retro Rocket]

kandrtech- I'll have to check

Rocket- I'm running a '74 motor, with an older front sprocket too.

I'm using all the K8 spacers and axle with the '73 hub, and an earlier drum.

Ah, ok..   Sometimes its just easier to get the original part...

[JamesM]

I think what I'm going to do is get an earlier axle and spacers, and an earlier swing arm so that I have peace of mind that everything is kosher.

So that leads me to one last question: does an earlier swingarm bolt right in and fit correctly on a '78 frame?

Thanks.

[70CB750]

Yes.  78 swingarm dropped right in 73 frame for me.  It would be odd if it didn't work in reverse 

[JamesM]

Awesome, thanks.

Now to track down a swing-arm and axle, finish my oil bag and wiring harness and get this build done in time for spring!

[Tugboat]

The upper LH rear shock mount on your 78K frame has a 10mm "shoulder" on it that makes the wider swing arm from the 78 line up correctly. Compare it to the RH side and you'll see what I'm talking about. In order to use the older swing arm on your newer frame, you'll need to remove that shoulder. Otherwise, the LH shock would be crooked. \ not |

[JamesM]

^ Thank you for the info. Should that be the only issue I run into? Are they the same length?

[Tugboat]

Not sure. I've got an F bike so that's a whole other ball o' wax.

[70CB750]

^ Thank you for the info. Should that be the only issue I run into? Are they the same length?

If you mean shocks - yes - I mocked up shocks on the K3 frame after welding in new top left shock mount.  Swingarm - I can measure for you when I get home today.

[the technological J]

im kinda confused, i think this swingarm business is just gonna further complicate things
if you have all the parts for your k8 hub assembly you should be able to switch them out no prob.. all the honda wheel specs are identical the assemblies(like the sproket carrier) has changed along with the spacer... i have switched wheels from my ko and k8 in a matter of minutes various times(only had one good tire between the 2 of them)

http://forums.sohc4.net/index.php?topic=103860.msg1161713#msg1161713

if you have these parts for the k8 the 73 rim should be no problem


 if the sprocket isnt gonna line up then i would  get a 10mm off sprocket from cycle x

btw i think the k3 swingarm is shorter

[JamesM]

Update:

So I bought a '72 CB750 and I harvested its swing arm, and rear axle/spacers for my bike. I get the swing arm on, and throw the axle/spacers in my wheel and the drum is still rubbing on the damn hub! So I decide to compare my supposed '73 CB750 hub to the '72 hub I just got. And they're different. The '73 CB750 wheel I got off of ebay has a longer lip on the drum side of the hub. So there's my answer why the drum rubs on it.

My question is this: Aren't '69-'76 hubs all alike? Is my '73 wheel actually from a '73 CB750 or maybe from a different member of the CB family? I'm pretty pissed right now I've spent time and money trying to make that wheel work for weeks now when its been an incorrect hub the whole time



The wheel on the left is the one I got off of ebay. The one on the right from the '72 CB750 I just bought.

Thanks.

[BPellerine]

wheel on left is 79 or later cleaned one up for my bike thinking it would drop in but ran into the same problem with that lip try a complete 78 or earlier wheel assembly and you will see what I mean.the wheels I tried came from known sources.maybe my mistake can help you.