Cb750f swingarm upgrade to cb400sf

Hi, I recently purchased a new project that being a Honda CB750f2. It has a fully fitted cb954rr front end including brake system and wheel.
The rear swingarm I have to mirror the front end is from a CB400SF.. This is where I’m struggling. The S/A at pivot point is narrower than the stock so will need spacing accordingly. What considerations do I need to think about when having bushings/spacers made up. The rear wheel is the CB400SF wheel so no lateral movement available when considering sprocket alignment, this will have to be done by modifying sprocket carrier at the rear and offset sprocket at the front if required?

Any help or advice would be very welcomed please
Thanks

Alan

Don’t all throw suggestions in at once!

Primary concern is having wheels inline with each other along with sprocket alignment a close second. You could fab shock mounts to compensate for any offset in the swingarm once mounted.

Thanks for that.. I’ve started working on locating the true centre of the rear wheel and making sure it’s central to the bike and the front wheel.

Does anyone know what I need to consider when getting the bushings made up? Like materials and contact surfaces?

Thanks
Alan

Remember that the chain must clear the wheel and the tire, which is usually wider.

Fwiw, your wheel doesn’t have to be 100% inline with the front wheel. I understand aesthetics are what they are, but sprocket alignments very important to eliminate chain and sprocket wear. So get it close on centering but closer on the sprocket alignment. A friend from another forum is building a show bike, it’s a Bmw. He used to race motorcycles and built a lot of them over the years. That is where I’m getting this information. He just had a similar problem, he was 14mm off and He got it down to 3mm off center but 100% on sprocket alignment. Hope this helps.

As for the spacer, machined aluminum would prob work best.




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I second what dwysywd said regarding wheel alignment. Perfectly aligned wheels and perfectly aligned sprockets are your goal, but if you have to compromise that goal, you must keep the sprockets aligned, no question.
Your front and rear wheels are different widths, so as soon as you start to lean they effectively go out of alignment anyway. If they are grossly out of alignment, (15-20mm?) then you may notice a different feeling when turning right compared to left. But less than 5-6mm, it's unlikely you would feel a difference.
There are aftermarket front sprockets available that space the chain outboard about 1 chain width, that may help.
All the OEM spacers that I have ever seen are steel, although I don't know why that is. Lost of times the spacers are mating up to aluminum parts, so I can't think of any reason why they couldn't be aluminum. If I made them from aluminum I'd check the axle tension regularly to make sure the spacers aren't compressing under the tension of the tightened axle.
I personally use 416 Stainless for axle spacers. It machines easier than the more common 300 series stainless, and once the part is done you don't have to worry about finishing it.

Now you have the wheels correctly aligned, measure teh gap on each side. You may be able to find suitable needle roller thrust bearings, but if not I would look at bronze or stainless. Aluminum is not well suited to that application.

If you have to use a different spindle or bearings to match the swingarm to the frame, you could make suitable bushes with end spacers built in like old bikes had.

https://www.motionindustries.com/taxonomy/Bearings/Thrust%20Bearings/Roller%20Thrust%20Bearings/Needle%20Roller%20Thrust%20Bearings/browse/en

https://www.nationalprecision.com/needle-bearings/thrust.php

https://www.google.com/search?q=needle+roller+thrust+bearing&tbm=isch&source=univ&client=firefox-b-1-d&sa=X&ved=2ahUKEwj0zbn9k8PgAhWLxIMKHQMsCDcQsAR6BAgCEAE&biw=1522&bih=773

Okay.. I’ve successfully lined up the rear wheel, the sprockets are not a million miles off so if anything I might have to space the rear sprocket out a little.
I was think about having a spacer made that includes a bush to go inside the pivot bolt holes in the frame.
The previous owner has had the stock pivot bolt machined down to fit the swingarm which means it’s slack in the frame.

Any thoughts??

Also I am unsure how the new swingarm would mount to its original frame so I’m guessing a bit??

Well, you can't have a sloppy swingarm pivot bolt fitting into the frame. Incorporating bushings to take up the radial space, and spacers to take up the axial space makes sense. You don't say what the dimensional difference is. If the difference in diameter between the pivot bolt and the frame holes is only 1 or 2 mm, you might have to open up the frame holes to allow for a bit more wall thickness on the bushes. It's not impossible to machine the bushings with 0.5 or 1mm wall thickness, but it is harder than with a thicker wall.