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CB750F Swingarm Upgrade


Chewtoy

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After accumulating parts for a few years, I finally started the upgrade to my CB750F swingarm.

The original arm is made of reinforced tubular steel, and flexes very noticeably when hitting bumps in turns. A popular upgrade in Japan is installing a CB400SF swingarm.

So, I got a CB400SF arm via Rinkya, and a chain guard and rear brake system to boot. Finally got a set of Kawasaki ZXR shocks to mount up, and a set of F2 rims, which I got refinished @ FastForward wheels here in LA - a great wheel shop.

Then I got the swingarm pivot set up to use the stock shaft in the Honda frame, and the rear wheel set to use the CB400SF axle.

First mount shows the wheel is ~ 3/8" off to the right. I'll get some better measuring tools and get some numbers I can get bushings cut from. Might have to cut down the sprocket carrier as well (sigh).

Oh, and the top bushings on the shocks don't fit the pins on the Honda frame. Need some work there as well. Perhaps some delrin or teflon bushings will do the trick.

If anyone has some helpful thoughts, please LMK.

Pics here: https://plus.google.com/u/0/photos/10798003...644367370603601

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Nice.

Are you trying to do it so it can be easily turned back to stock?

Well, it could be turned back, no frame mods, but it's pretty crappy with the tubular swingarm.

Just going for a tasteful mod. Putting Honda F2 forks on the front next, and I have a CB900F motor waiting on the shelf as well.

Going for a similar look as this guy's bike. Have the blue bodywork here as well

BluewF2Wheels.jpg

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OK, I grabbed some copper pipe from the hot water heater replacement last month, and made up some temp spacers for the swingarm pivot. I just spaced the drive side a washer's thickness from the left hand frame side, and took up the rest on the right side with a temp shim of copper pipe.

Lined up the sprockets with the mark 1 eyeball and made a temp shim, Will go to get a el-cheapo laser and make fine adjustments.

The brake side of the axle isn't shimmed yet, but I can see I'll need to extend the tab for the brake backing plate.

Ordering new seals for the rear wheel, and also found new driveline buffers on ebay for cheap, so things are looking good.

Once the seals show up, I'll do the final measurements, and get the shims made up.

One thing, the guy that sold me the shocks sold me two right hand shocks. Wonder where I can find a 'KYB' decal for the left hand shock

Updated the album with the weekend's work.

https://plus.google.com/photos/107980032549...644367370603601

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Well, still waiting for parts, but in the meantime, found a nice CAD program at www.sketchup.com to draw the spacers.

The dimensions in the below are ALL WRONG, this was just a test.

bushing_test.png

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  • 2 weeks later...

Got the laser set, and made some adjustments. Looks aligned. Got the F2 rear wheel seals, check bushing sizes, and finalized the blueprints for the machinist.

The rear brake tab has about 50% engagement, and the disk could stand to be about 1/2" larger. Anyone know what other disks fit the F2 rear hub?

More photos at https://plus.google.com/photos/107980032549...644367370603601

2013-06-23_Laser.JPG

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  • 1 month later...

Finally got my machinist working on the spacers. Also, Honda sells the top shock bushings from the original Honda shocks for only $3 and change each. So I hope to not need to machine up some bushings for that.

Should pick up the bushings on 8/3.

Amazingly, Honda still sells the upper shock bushings so I can pop them into the ZRX shocks to solve the problem of them having the wrong ID for the frame pins.

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  • 3 weeks later...

Got the bushings back from the machinist, and did a test fitment. Axle/wheel end is good. One bushing on the swingarm pivot is too thick and is riding on the end of the swingarm instead of the inner bearing race. Am taking them back for a tweak next week.

bushings.JPG

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  • 4 weeks later...

Got the bushings back after two three tries @ the critical chainside swingarm bushing. My great idea about using Honda top shock bushings failed, went with delrin inserts.

Bolted it all up and it looks gooood.

testfitment.JPG

Now to get a tire and take her for a ride! I have a CB400SF chainguard too :)

More photos at https://plus.google....644367370603601

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Give us a ride report.

It'll be a little bit yet, doing the forks now :)

Might put in that CB900 mill sitting on the shelf as well...

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  • 4 months later...

Finally got the tire on the wheel, and did a full test fitment. Now I need a longer chain (sigh).

It all looks good anyway, though the arm does push the wheel back a couple of inches.

Now to get a larger disk made, hook up a chain, and install the rear brakes.

IMG_7060.JPG

Have to admit, part of me wants to take the arm to a fab shop and pull the wheel forward a couple of inches. Perhaps before the final finish and assembly. For now, will complete the brakes and chain, and get the front end done.

More photos in the album here: https://plus.google.com/photos/107980032549223313420/albums/5884644367370603601

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Before hooking the shocks up, did you run the wheel through its travel to see if the tire would hit the fender?

No, good suggestion, will do that next weekend.

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Oh, can't shorten the swingarm, no clearance between the front of the tire and the swingarm.

Am fairly confident that the wheel will clear the fender, this is a common mod on Japanese F-bikes. But will still check fender clearance.

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  • 2 weeks later...

Not really, just one problem after another to fix. The F bike is my first real motorcycle, so I have sentamental attachment.

And I pulled the shocks and jacked up the tire, it clears the rear fender, but not with a lot of clearance for chain stretch. Other F-biked that have done this mod have gone to a different rear fender. I'll ponder my options, it's not a big deal.

Might pull the old forks off this weekend. New ones are ready to be test fitted.

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  • 3 years later...

It's been some time but I was wondering if you are still working on this project?  I appreciate the detail you posted and wanted to know if you made any other progress with the CB750F?

 

I have a 81' CB900F and just started working on the swing arm. I noticed you have the NC31 version which is longer. I just bought an NC39 which I hear is 52cm +/- 1cm from the pivot to the axle centerline. Maybe this can be an option for you? Also have a CB1000SF (Big1) swing arm but that puppy is long and wide. 

1495073596_20170517_1.jpg

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  • 5 years later...
On 6/1/2013 at 5:36 PM, Chewtoy said:

A popular upgrade in Japan is installing a CB400SF swingarm.

So, I got a CB400SF arm via Rinkya,

....

Then I got the swingarm pivot set up to use the stock shaft in the Honda frame, and the rear wheel set to use the CB400SF axle.

....

Pics here: https://plus.google.com/u/0/photos/10798003...644367370603601

 

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