Topic: 1976 CB750F - first bike, first build - mild cafe

[Jerry Rxman Griffin aka MuthaF'er]

post up your CBX sprocket carrier that came with your CBX wheel.

[riffman12]

did your measurement account for the thickness of the sprocket on the 600?

sorry not quite sure what you mean. I'm not using the 600 carrier, I think that's just in the pic for comparison

I'm using the CB450SC carrier. I don't even know if it will fit on my hub to be honest - just that it's one of the few I've seen with 5 studs that's skinnier. I'm winging it a bit here.

If this doesn't work, I'll either be machining down the surface on my current carrier, buying an offset front sprocket, or getting a new wheel (and possibly swingarm) all together

[riffman12]

post up your CBX sprocket carrier that came with your CBX wheel.

Not at home at the moment, but here's a couple pics of it. You can see how thick it is in the 2nd picture.

[riffman12]

well the sprocket carrier arrived today annnnnd it doesn't fit

The way I see it I have 2 paths forward:

1) keep trying to make this mix of parts work. Either mill down the sprocket carrier I have or hope an offset front sprocket fixes my issue. My worry wth this is that the bike will continue to fight me all the way. This is my first motorcycle build and I'm worried than I'm over my head with all this custom stuff.

2) Revert back to all 1976 parts (swingarmm wheel etc.) and possibly a GL1000 front end. I don't have any of the '76 parts so I'd need to do some eBayiing. I'd be throwing away a lot of time and money I've already invested into the '77 and '79 parts, but it would make things a lot easier going forward.


Pretty bummed at the moment as I was really hoping that new sprocket carrier would help me out.


Would anyone like to convince me whether or not a GL1000 front end swap is a good idea?

[timbo750]

Make a decision on what it is you want the bike to be when you finish. Then persevere with it and be patient, the answers will come to you. However if you just want something to ride then do what is the easiest.  I am into my 4th year,  I was in no rush, the bike was a basket case and I wanted to get it right the first time. The next builds will only get easier.

Sent from my GT-I9505 using Tapatalk

[Jerry Rxman Griffin aka MuthaF'er]

Forget the front for now and concentrate on the rear. Fix one thing at a time ;-) 

Keep in mind you use EBay so unload your unused stuff there and it won't hurt so bad.

Persistence and patience are virtues.

[Retro Rocket]

You need an early F model swingarm first off, get that sorted then attack the rear wheel, Jerry went through the F2/3 swingarm problem a few weeks back, its better than trying to change the top shock mounts...  By "hoping" parts fit you are going to end up with more problems, your CBX rear wheel shares its chain line with the Boldor, since we haven't established the difference in chain line between the CBX/Boldor and the early F model, everything is a guess, some very accurate measurements need to be taken before going any further....

[riffman12]

OK well to avoid redoing the WHOLE front and rear end with spokes... this is my current plan:

1) find a '75/'76F swingarm - anyone have one they want to sell? 

2) Find a rear comstar from an F2 bike (77/78) with the 4 stud cush drive

3) get a narrower cush drive from any pre-77 bike, mount it to the F2 comstar


This way I should have the correct width swingarm and a rear comstar with the same spacing and chain line as the factory '76F spoke wheel...right? Or am I missing something?

[Jerry Rxman Griffin aka MuthaF'er]

Swing arm - no problem. Axle, brake stay, adjusters included. $28 OR BEST OFFER. Maybe $28 and free shipping? Blast and paint or let the coater do it for you.

http://www.ebay.com/itm/1976-Honda-CB750-CB750F-CB-750-f-swingarm-swing-arm-/301275380362?hash=item4625697a8a:g:~4AAAOSwEK9T6TCp&vxp=mtr

Wish I could help you with my spares but until both bikes are done and tested I won't start unloading.

[riffman12]

Thanks again, Jerry. I'm in talks with a guy who has a '76 arm thats already PC'd black. If that doesn't work i will head to eBay

Do you think this plan of older cush drive on 77/78 Comstar will work? Are the spoke and comstar cush drive's interchangeable? I've been searching a lot and can't find anyone that's done it, only spoke to spoke cush conversions ('75K cush on a '77K for example)

[Retro Rocket]

Thanks again, Jerry. I'm in talks with a guy who has a '76 arm thats already PC'd black. If that doesn't work i will head to eBay

Do you think this plan of older cush drive on 77/78 Comstar will work? Are the spoke and comstar cush drive's interchangeable? I've been searching a lot and can't find anyone that's done it, only spoke to spoke cush conversions ('75K cush on a '77K for example)

77/78 comstar cush drive is still 10mm too wide, I'd be machining 10mm off the carrier you have if you are determined to keep the CBX/Boldor wheels, you are still going to have to make up axle spacers to make it all fit.

[riffman12]

77/78 comstar cush drive is still 10mm too wide, I'd be machining 10mm off the carrier you have if you are determined to keep the CBX/Boldor wheels, you are still going to have to make up axle spacers to make it all fit.

Yes the plan is a 77/78 Comstar with a '76 or earlier cush drive.

'79 CBX rear wheel is going bye bye.

[Retro Rocket]

77/78 comstar cush drive is still 10mm too wide, I'd be machining 10mm off the carrier you have if you are determined to keep the CBX/Boldor wheels, you are still going to have to make up axle spacers to make it all fit.

Yes the plan is a 77/78 Comstar with a '76 or earlier cush drive.

'79 CBX rear wheel is going bye bye.

There should be someone here that can give you the info on the later 77/78 comstars cush drive, they have a different rear disc bolt pattern and I'm not sure about the cush drive, its possibly different too, I'd ask before buying one though just in case the early cush drive is different, you'll still probably have problems with spacers, nothing is straight forward with these conversions...

[seanbarney41]

I was curious about this very question while recently putting new chain on my F3...but did not really investigate very scientifically.  I can tell you that the exterior of a F3 comstar's sprocket carrier looks identical to exterior of K7/8 sprocket carrier, at least to casual observation.  I did not pull any carriers out of the hub to compare.  We do know that an early sprocket carrier will fit a K7/8 hub and vice versa and that early hub and K7/8 hub are essentially the same, only the sprocket carrier is wider on K7/8.
     I would check to see if F2/3 and K7/8 have the same part number for cush drive rubbers.  If yes, I think you are golden, if no it is not necessarily conclusive given all of Honda's part number funny business.

[riffman12]

I was curious about this very question while recently putting new chain on my F3...but did not really investigate very scientifically.  I can tell you that the exterior of a F3 comstar's sprocket carrier looks identical to exterior of K7/8 sprocket carrier, at least to casual observation.  I did not pull any carriers out of the hub to compare.  We do know that an early sprocket carrier will fit a K7/8 hub and vice versa and that early hub and K7/8 hub are essentially the same, only the sprocket carrier is wider on K7/8.
     I would check to see if F2/3 and K7/8 have the same part number for cush drive rubbers.  If yes, I think you are golden, if no it is not necessarily conclusive given all of Honda's part number funny business.

So i did some poking around in parts fiches

not only do the cush drive rubbers have the same part number, but the whole sprocket carrier itself is the same part on the F2/3 and the K7/8.

So if an early carrier definitely fits a K7/8, then it looks like it should fit the F2/3 wheel 

Now I just hope the F2/3 brake bracket will be the correct width for this setup. I'd rather not use the F1 giant rear brake setup.

[Jerry Rxman Griffin aka MuthaF'er]

Yeah, carriers are the same. 76 and earlier are all the same and 77/78 are all the same. You'll find that the fiches may just be your new best friend. I use Motogrid.com mostly. That and my 2 parts manuals. Remember that the numbers are often superseded and the online fiches can verify that info.

F2/F3 brake bracket?? Which part are you referring to? caliper, link, ??

[riffman12]

F2/F3 brake bracket?? Which part are you referring to? caliper, link, ??

So the F1 has that big dual caliper rear brake caliper. And half of the caliper os integrated into the bracket. This piece specifically:




But I have the rear brake from an F2/3. The rear caliper bracket looks like this:




I'm wondering if the 2 pieces are the same thickness at the axle. ie will I be able to use my F2/3 bracket in my F1 swingarm

[SOHC4 Cafe Racer Fan]

More important than the thickness is the offset of the caliper to the rotor.  Each issue can be addressed with spacers and/or milling off extra material.

[madmtnmotors]

I have an example of each and can do a mock fit up for both and will let you know. Might not be until the weekend though! 

[riffman12]

I have an example of each and can do a mock fit up for both and will let you know. Might not be until the weekend though! 

That would be awesome. Thanks man! 

[Jerry Rxman Griffin aka MuthaF'er]

Consider those 'rear calipers' and not brackets ;-) You tryin to confuse us old guys LOL

[riffman12]

Haha well the 76 unit is a caliper, but the 77/78 is just a bracket that holds the caliper. 

[riffman12]

OK quick update as it's been a while. I've been really busy with wiring, controls, cables etc. as well as waiting for my new rear end parts to arrive. Here's the quick take:

1) It looks like the combination of 77/78F Comstar + earlier sprocket carrier is working PERFECTLY. The chain line between the two sprockets is really straight. Thank you all for helped with that. It even looks like I can use the 77/78F brake caliper holder to avoid using the overpowered '76F rear brake.

2) I finished all my wiring (except for turn signals and tail light as I haven't ordered those yet). Turned the key and all the warning lights, horn, and headlight are functioning properly. Hooray!

3) mounted my freshly re-jetted carbs and airbox with re-oiled K&N filter

4) Last thing before firing the bike was to get the Carpy 4 into 1 exhaust mounted. Perhaps you saw my thread in the Bikes section, but the flanges on the system were not the right size for my 750. See pics:






Here's my factory flanges on top of the new Carpy ones. You can see how the holes are way too close together. They don't fit the studs




I'm talking with Carpy at the moment on how to deal with this. Sounds like he'll replace it.

[riffman12]

update on the exhaust issue: I sent the exhaust back to Carpy and after inspection he admitted fault. He built a new one with new correct-sized flanges, had it coated in less than a week and sent it back to me. He covered shipping, and as I needed turn signals he threw in $60 worth of turn signals to cover the $40 I paid to send the exhaust back to him. Overall a bit of a hang up in the build, but he handled it very professionally and quickly.

I started the bike with the new exhaust and it runs great.


Quick question:

The piece of the wiring harness that comes up into the headlight, do I route that over or under the bottom of my triple clamp? At the moment I have it under and it just looks awkward.

I'll put up more pics soon

[przjohn]

It goes under and has a clamp that holds it up to the lower clamp.