2002 Sevenfifty goes modern/retro Cafe

[JohnK]

I have done several projects in my Life this far, I have done everything from race cars to big wheel drift trikes
So the interest has turned to bikes, wanted a 70.s CB750 but couldnt find anything that I liked, then I found and got a killer deal on a decent 2002 Sevenfifty, sure it is not very retro but I am sure I can turn it into one

Here is the main object:

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Had some issues finding a tank, so I tried a chinese made repro from ebay, it was cheap and looked pretty nice but it was according to me too small for my 750
Here is just a test fit, if I wanted to use it I would modify it to go further down over the frame.

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Sourced a USD fork from a Ducati 1100 Hypermotard

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Problem being the fork was too long, I needed to lower it, so I removed the cartridge only to find out it wasnt possible to open the plunger assembly

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Problems are meant to be solved, I cut the shock assy open, inserted my aluminum spacer and rewelded it again.

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Here are some of the stuff soon to be fitted, mono swing and shock from Ducati as well as a Marchesini Wheel

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Also found a CB750 F1 SuperSport tank in Germany and I just had to have it, I won the listing and got it the other day, badly repainted and rusted insides.
Am currently working with acid to remove the last of the rust.

To be continued .


Also found a ne

 

[JohnK]

Got some steering head bearings, now I just have to figure out how to fit a 55mm bearing in a 47mm hole

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My supersport fuel tank after hours and hours of cleaning and rust solving using hydrochloric acid and then baking soda as a neutralizing agent
The tank was full of rust, rust flakes and really old fuel muck, the stench was pretty tough.
Repainted from red, but almost entirely free from dents, also managed to find a fresh flap from the UK, happy days.

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The tank after treatment, unfortunately no Before Pictures, but it wasnt a pretty sight.

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Trying to figure out how to restore the tank flap lock, thinking about fitting a machined aluminium external handle instead, or maybe a simple Dzus fitting.

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[papercutout]

This looks promising! Good work

 

[treitz]

Fun. I'll tag along.

 

[JohnK]

Some progress.

Spent some time stripping the bike from the wiring harness and all the cables, havnt decided if I am going to keep and modify the stock harness or build a new one.

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After a good grinding I managed to fit the tank over the much bulkier top frame tube, need to figure out how to fasten it using rubber grommets or if I need to make a rigid mount, the rear mount should be a breeze to fabricate.

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So here she sits right now, I cut away some scrap on the subframe just to see the overall picture better, now I need to fit the tank with proper mounts, and when the tank is fitted I know where and how to fit the new subframe and at what angle.
Also need to find some 1" steel tubing and a bending tool.

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[JohnK]

Was thinking about subframe materials, I am going for 1", 25mm tubing, but what wall thickness using "regular" black steel should I go for?, 1.5 or 2mm?

Also considering Chromoly but I have heard that it is hard to weld as the material requires pre and post treatment to avoid cracking.

 

[RR100]

Was thinking about subframe materials, I am going for 1", 25mm tubing, but what wall thickness using "regular" black steel should I go for?, 1.5 or 2mm?

Also considering Chromoly but I have heard that it is hard to weld as the material requires pre and post treatment to avoid cracking.

The material thickness will depend upon the subframe design. Are you cantilevering the seat for example? If you post a design I can calculate the stresses and bending moments with consequent deflections for your presumed loads. Regarding the cr-mo tubing, you can safely weld it without "treatment" for this kind of application.

 

[JohnK]

The material thickness will depend upon the subframe design. Are you cantilevering the seat for example? If you post a design I can calculate the stresses and bending moments with consequent deflections for your presumed loads. Regarding the cr-mo tubing, you can safely weld it without "treatment" for this kind of application.

Unfortunately I dont have the dimensions, but here I have sketched the general idea, I will skrap the entire stock subframe and replace it with the red parts
There will also be a significant reinforcement in the mid part just behind the main part of the fram where the top mount for the mono shock will be fabricated, this mount will most likely be joined with the cantilever brace as well as the upper part of the subframe.


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[RR100]

Can you straighten out the "kink" in your diagonal element? If so, the majority of the forces will be in compression on that piece rather than bending, and increase rigidity of the entire subframe.

 

[JohnK]

It is not decided yet, but most likely I will fit the shock mount in the kink as well and then later in the thicker main frame, this would reinforce it considerably.

I have found Cold drawn tubing in 25x2 and 25x1.5mm now

 

[geemann]

Wow JohnK! This looks like a great build! Definitely sticking around to see this one.

I just sent you a PM, let me know.

cheers,
-g

 

[Pod70]

Don't know if this helps but the CBX750 (RC17)and some nighthawks were fitted with a monoshock from the factory - might be worth looking for a frame from one of them. Otherwise the frames and much of the running gear is interchangeable. The CBX750 comes with a hydraulic clutch as standard too which you may want to look into...

Note that the engines have a different firing order so not that easy to swap

 

[tbagginz]

How's the build coming along. Any progress?