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Hornet (?) tank looks good but ideally the bottom surface needs to be flat or the back end could be dropped and side panels integrated somehow.

Of the dozens of times I have been through/to Fife it always seemed to rain. Must just have been my bad timing I guess.
 

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What he said^^^

You'll get another 2 inches in wheelbase at least. Might be a good thing, might be a bad thing depending on what you want the bike to do.

Another option is to use the FZR swingarm as a twin shock. Just weld some shock mounts onto the top of the arm near the rear axle. Then (if you're keen / can weld alloy) you could cut out the monoshock section and shorten it to the same length as the CB arm. All depends on how far you want to go.....
 

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The good news is that the FZR600 swingarm is not alloy, it is steel, so it is possible to just shorten it from the axle end to get the same wheelbase as original.
 

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What he said^^^

You'll get another 2 inches in wheelbase at least. Might be a good thing, might be a bad thing depending on what you want the bike to do.

Another option is to use the FZR swingarm as a twin shock. Just weld some shock mounts onto the top of the arm near the rear axle. Then (if you're keen / can weld alloy) you could cut out the monoshock section and shorten it to the same length as the CB arm. All depends on how far you want to go.....
As Hillsy said this can be done, I done it on my alloy swinger and scored 2 inches, i did not go the twin shock route but rather horizontal shock mount, here is the link

http://www.caferacer.net/forum/project-builds/22201-kh400-cafe-racer-modern-vs-retro-2.html

Gavin
 

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just from what I know about cb750 frames and not much else, You would want the upper shock mount to be right where the frame junctions under the fuel tank. Why? it's really strong there.
 

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CB project

Found your project Tay, looks great.
I'm from Falkirk area and run a Facebook page/group called Scotland Cafe Racer.
Have a look and give the page a like, you can then post some photos of your project, the guys would like to see what your doing.
Might even see you out on the road when it's finished. Got a good few guys from up your area on the page.
Cheers
 

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just from what I know about cb750 frames and not much else, You would want the upper shock mount to be right where the frame junctions under the fuel tank. Why? it's really strong there.
Like GT said. Also, the stresses at monoshock upper mounting points could be ten times the shock and force loads of a twin shock upper mounts. Leverage and multiplication factors with shock linkages, etc.

In short you need strong tubes and brackets that feed the stresses directly to where GT said.

Danger, is my business.
 

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"Also, the stresses at monoshock upper mounting points could be ten times the shock and force loads of a twin shock upper mounts."

:/ what did you do, park a car on it.
 

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"Also, the stresses at monoshock upper mounting points could be ten times the shock and force loads of a twin shock upper mounts."

:/ what did you do, park a car on it.
Well get your scientific calculator on the table and work out the variation in leverage ratios and the changing torque loads for a multilink monoshock swingarm setup. Then factor in the shocks loads, the preload and harmonics of the springs and the effects of the dampener.

Yeah, that will take you a week. Draw some graphs or GIF animations.

Danger, is my business.
 

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Stupid teletubby, if there is 10 times the stress why is the bolt and bracket not 10 times stronger ? Because a significant amount of the forces, outside of a little spring loaded gravity that represents mainly the weight of your ass, is being carried on the swingarm bearings.



… slide rule.

What is an average spring rate on a twin-shock?
What is the average spring rate on a lay-down long travel shock?
What is the spring rate on a monoshock? <- it's not 10 times or we'd be up to an 800 pound coil spring.
 

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A teletubby car or truck possibly, a real car or truck, not a chance.

Run out and measure the diameter of the steel rod twisted into coil springs on your lil car.
Then run over to your boyfriends monoshock motorcycle and measure his coils,
then come on back to reality.
 

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lets play this game. progressive recommended rear shock spring rate for CB750 SOHC = 20kg/100lb springs as that is 2 shocks it would roughly equal 40kg/200lb (actual conversion ratio is no 5 but ~5.7... anyways...)
I will use cbr600 rear shock as comparison here, while cbr600 is much ligther bike cbr600 '03 shocks are being used as upgrades for Bandit 1200s - much bigger bike than cbr600. What is the spring rate of cbr600 shock? google gives me 550lb.

thus 5 times is in the right realm if thinking of 1 shock out of two compared to single mono shock. I wouldn't have been surprised if the difference had been bigger - aka closer to the 10 guessed by master genius frame and suspension designer.

The upper mount of dual shocks (where its just a stud and not clevis) is quite a bit weaker structurally than a bolt supported from both sides (as in the example posted earlier). Regardless the force is quite high even if it is not 10x and how the frame absorbs it is important.
 

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I will say having done a similar conversion on my own project (linkage monoshock) that you will have a lot of measuring to do. You won't be able to use the upper section of the frame as a top shock mounting point unless you find a crazy long shock. I think the frame area near the swingarm mount might also be a strong point to figure into your design. I also used the lower frame tube for the linkage mount, but had to carefully position the actual linkage mount plates to get the required geometry, and then play with dogbone lengths.

Cheers,

Earlysport
 
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