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sickboy
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3,544 Posts
Discussion Starter · #1 ·
May as well start a thread for the bike im working on.
Building a cafe racer supersingle

81' gs250 frame but is getting all cut to hell
Modified gs250 tank, going to put some knee recesses in it and such
Using zx7r 52mm forks
cbr250 rear swingarm, possibly flipped upside down
R1 or R6 rear shock (I have both)
CRF250r 21" front wheel (not 100% on this, have to see what it looks like)
RM250 19" rear wheel (not 100% on this, have to see what it looks like)
Cafe tail, 1 off fiberglass going to be built by me. (havent built it yet)
havent decided on rearsets or pegs
Engine is going to be a 450cc+ single somewhere in the 50hp range so probably either a crf450x or a wr450 motor or somthing around there that is kick only with a lighting stator and possibly no battery.
I want to keep this right around 1:4 power/weight ratio so right around 250lb's or so.

Im DW for next few days and hoping to have zx7r front forks on and cbr250 rear end on and chassis rolling so stay tuned for pics if your interested!

Started life as this....



After just a couple hours it turned into this...

 

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Sounds like a fun build I'd like to chop up my wife's cb400 and do this same thing to it
 

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sickboy
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3,544 Posts
Discussion Starter · #3 ·
Thanks, ya should be a fun build.
This bike is my main inspiration for this build.




 

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forks and valves... WTF?
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671 Posts
Sounds like a fun project. Only thing I'd do different is use a CR500 engine... at least that's the engine I'm considering for a similar project. Anyway, I like franken'bike projects. Keep us posted on the progress.
 

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sickboy
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3,544 Posts
Discussion Starter · #5 ·
Sounds like a fun project. Only thing I'd do different is use a CR500 engine... at least that's the engine I'm considering for a similar project. Anyway, I like franken'bike projects. Keep us posted on the progress.
contemplated using a cr500 motor as where i live in tucson we have no emissions on motorcycles but they are also pretty hard to come by.
What is your thoughts on the cr500 vs the kx500 sense the kx500 uses a counter balancer which I would think would make it a little better for street use?
 

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forks and valves... WTF?
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671 Posts
contemplated using a cr500 motor as where i live in tucson we have no emissions on motorcycles but they are also pretty hard to come by.
What is your thoughts on the cr500 vs the kx500 sense the kx500 uses a counter balancer which I would think would make it a little better for street use?
To be honest I don't know much about the KX500s. I do have a custom street bike with a KDX450 engine, but it is a much older generation so not realistic to compare.

Just doing a quick search on Craigslist, there are many more CRs available, but they seam to be more expensive than similar KXs. I do know that there are still alot of OEM and aftermarket parts available for the CRs. To me that is a big advantage.

I know that the KXs have a powervalve which should give more broad power (as if either bike doesn't have enough power anywhere rev range), but I'm not familiar with them having a balancer(?) From what I've read they both vibrate quite a bit.

The big challenge with either engine is going to be vibration and starting. I've been doing research on compression release valves and planning to add one to my CR. Supposedly they make starting MUCH easier and otherwise have no effect on normal performance.

As for vibration, I've read about a lot of people trying to make rubber mounts with minimal positive effects. There is a guy in Australia who did a huge project adding a counter balancer to his CR. In the end it was only marginally successful. He eventually took the CR engine out of the bike and plans to use something different.

My plan is to use an older steel frame (as you are) and use heavy gauge steel plate on all the mounts and let the frame absorb some of the vibration.

In terms of being the best choice with the least amount of problems and best reliability, the CRF would certainly be the most practice so hard to argue with that.
 

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sickboy
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3,544 Posts
Discussion Starter · #8 ·
Ok, so baby progress but I know you guys love pics... got a whole lot more of the frame cut up. Still need to add the seat hoop and 3 braces but its looking like this frame is going to easily be under 20lb's so thats good. Still have to cut the 2 back "stems" off too sense I am going monoshock but I am going to use them to help me center the hoop so they are staying on for now.



Also got the stem onto the zx7 triple, was a task sense they are drastically different sizes but after making a sleeve and getting it to within .001" of dead nuts centered/straight and welding it to the sleeve for good measure I think I should be good to go. Of course I dont have a pipe to press the bottom bearing on the stem so I will not be able to actually bolt up the front end till tomorrow.




Also was able to sweat (freeze and heat) in the new bearing races which made me SUPER happy because as you can see there is damn near no flat spot on top of them so I was very worried that I would damage them trying to press them in.

 

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sickboy
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3,544 Posts
Discussion Starter · #9 ·
Well I got the front end on, and the 21" wheel loosely in place. As well as the cbr250 swingarm and 19" rear loosely in place. I have to say I personally fucking dig the stance of the bike overall. Cant wait to get started on the tail.
What do you guys think of the wheel sizes being 21/19? and obviously im not going to leave dirt knobbies on them but maybe some enduro tires or something.







 

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sickboy
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3,544 Posts
Discussion Starter · #11 ·
Well im waiting on parts (axle and swingarm bolts) but still hoping to get the cafe hoop all welded on this week and maybe start on the tail.
Having trouble deciding what to do for front brakes. I like the look of the 21" front but if I use the crf front wheel I am not sure what to do with all the mounting tabs and ish on the other fork leg. I think it will look odd just having them on there but not used. Any suggestions?
Only thing I can think to do would be to use a 21" dual disk harley front spoke wheel. That way I can run dual calipers yet keep the 21" size and the spokes.
 

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forks and valves... WTF?
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671 Posts
Having trouble deciding what to do for front brakes. I like the look of the 21" front but if I use the crf front wheel I am not sure what to do with all the mounting tabs and ish on the other fork leg. I think it will look odd just having them on there but not used. Any suggestions?
Only thing I can think to do would be to use a 21" dual disk harley front spoke wheel. That way I can run dual calipers yet keep the 21" size and the spokes.
Kinda depends on your budget, but you could use a Ducati Sport Classic front hub and have it re-laced with a 21" rim. Another issue to think about is what calipers to use since most wire wheels don't have as much clearance as cast wheels... so if your caliper(s) was designed for use with a cast wheel, it may not clear the spokes on the wire wheel.

Just curious if you are concerned about not have a cush-drive type hub on the rear?

Just my $0.02
 

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Remi's Dad
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17,593 Posts
36 spoke, i think? You could lace up a new used existing hoop. i think the xs has a 36 spoke dual disc? 1972 and newer.

OR..cut the other side off, shave and smooth, put a big rotor and clampy big caliper on the remaining side.
 

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sickboy
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3,544 Posts
Discussion Starter · #14 ·
Kinda depends on your budget, but you could use a Ducati Sport Classic front hub and have it re-laced with a 21" rim. Another issue to think about is what calipers to use since most wire wheels don't have as much clearance as cast wheels... so if your caliper(s) was designed for use with a cast wheel, it may not clear the spokes on the wire wheel.

Just curious if you are concerned about not have a cush-drive type hub on the rear?

Just my $0.02
Havent decided on a caliper yet so we shall see.
Ya I really dont feel like dropping $500 a sport classic wheel, them shits are expensive around here.
And I am not really concerned about using a cush drive as whatever bikes motor (cr, crf wr etc) I am going to use didnt have one on the bikes rear wheel so it should be fine. Have had a couple supermotos and such and never had a problem with it damaging the motor or wearing the chain badly.
Whats your thoughts on it?
 

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sickboy
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3,544 Posts
Discussion Starter · #15 ·
36 spoke, i think? You could lace up a new used existing hoop. i think the xs has a 36 spoke dual disc? 1972 and newer.

OR..cut the other side off, shave and smooth, put a big rotor and clampy big caliper on the remaining side.
Both great ideas, will have to do a lil research on re-lacing to a 21" hoop. And if its a PITA, shave and smooth it is.
 

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sickboy
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3,544 Posts
Discussion Starter · #17 ·
and if i wasnt clear, the upright tubes are getting all cut off. Then braces added and a mono shock. I dont even have PS and suck at paint but maybe this third grade ms paint drawling will get the general idea of my plan across. lol

 

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forks and valves... WTF?
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671 Posts
...whatever bikes motor (cr, crf wr etc) I am going to use didnt have one on the bikes rear wheel so it should be fine. Have had a couple supermotos and such and never had a problem with it damaging the motor or wearing the chain badly.
Whats your thoughts on it?
You certainly don't have to use a cush-drive, but they are nice for smoothing out power delivery which will give you a smoother ride and your hub and sprocket will last longer. I've had solid mounted sprockets on street bikes and they just ride a bit harsh. The bikes you mention are dirt bikes, where there is some natural slip at the tire. So just a consideration. Thats all.

As for the front hub, you could use a XS hub as Ulitimate mentioned... but it will need adapting to fit your modern forks which are set up for a large axle and the hub will need further adapting if you plan to use modern 320mm rotors. All very possible, but takes some effort. The SportClassic hub will be much more expensive as you mentioned, but is already designed for a 25mm axle and big rotors... so time, resources, and skill, vs dollars. Both will get you to the same result but down different paths. I like making stuff as much as the next guy, but if something already exists that will get the job done I'll try to use it, then I can spend more time on the stuff that doesn't exist... but I also understand the need to stay on a budget.

Those are my thoughts.
 

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sickboy
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3,544 Posts
Discussion Starter · #20 ·
You certainly don't have to use a cush-drive, but they are nice for smoothing out power delivery which will give you a smoother ride and your hub and sprocket will last longer. I've had solid mounted sprockets on street bikes and they just ride a bit harsh. The bikes you mention are dirt bikes, where there is some natural slip at the tire. So just a consideration. Thats all.

As for the front hub, you could use a XS hub as Ulitimate mentioned... but it will need adapting to fit your modern forks which are set up for a large axle and the hub will need further adapting if you plan to use modern 320mm rotors. All very possible, but takes some effort. The SportClassic hub will be much more expensive as you mentioned, but is already designed for a 25mm axle and big rotors... so time, resources, and skill, vs dollars. Both will get you to the same result but down different paths. I like making stuff as much as the next guy, but if something already exists that will get the job done I'll try to use it, then I can spend more time on the stuff that doesn't exist... but I also understand the need to stay on a budget.

Those are my thoughts.
Valid point but I can not even find just a used hub, could just buy a complete wheel but still more than I would like to spend. Looks like I am probably going to either use the 21" crf wheel and get a 320mm rotor for it and shave the tabs off the other sides leg or Maybe see what a 19" looks like up front because I can find dual disk 19" spoke wheels all day long for cheap. Would possibly be neat to use a 19" rear on the front so that its nice and fat and then just use 2 rotors rather than a rotor and sprocket. I know some wheels like a harley and some dirtbike rear wheels the sprocket and rotor have the same bolt pattern so could easily just run 2 rotors. hmmmmm much to think about.
 
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