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Old 05-04-2012, 08:14 PM   #1
booger weldz OP
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Making a ktm620 into a f450 style bike?

I hope this is the right forum?

Has anyone taken the formula 450 concept and made a streetbike? I have a motarded (17" wheels and sticky tires w a bigger rotor and caliper spacer) 1997 street legal ktm 620. Im looking into building it into a thumper 'crotch rocket'. The formula 450 concept is perfect but i dont have a street legal( or any) honda or yamaha, etc 450 dirtbikes. I dont really know where to begin and i especially dont know how to lower the bike and change the suspension from the ten inches or so of travel to a tight streetbike type suspension without severely screwing up the rake and trail up front and/ or making the rear squat under acceleration, etc, etc.

Would buying a set of , cbr, gsxr, zx or r6/1(or any of those bikes) forks and triple clamps along w the brakes and wheel be a better direction than having the current WP stuff cut down and revalved? Same question for the rear? The body work is easy as i can simply weld mounting tabs on the frame and build a new subframe(im a welder/fabricator by trade). But the suspension, etc has me lost in a plethora of elementary questions and reeks of newbie sorry...

Any help, ideas or build threads of similar projects would be very much appreciated. I love the racey looking bikes, the tight suspension and handling (i previously covered a hawk 650 gt in rvf750 bodywork w gsxr forks and a cbr900 rear shock) But i dont like the inline 4 motors power band (high rev/ no torque or low-mid range) and have only owned twins and thumpers. I currently have a ducati hypermotard i turned into a stripped down, bare bones monster and the ktmwhich besides the motard stuff, has a big gun exhaust and 41 fcr flat slide carb...

I would love an rs250 w a 620cc single powering it!!! It would be for track days but also a daily driver w headlights, turn signals, horn...i just read an article in an old issue of cycle world where a guy put a crf450 motor in a little caguiva mito... It got the gears turning and the light bulbs blinkin in my head...
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Old 05-05-2012, 06:40 AM   #2
sailah
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I don't have any specific advise about the bike itself.

If I were you, I would not cut down the WP forks, you could sell them for more than a nice set of R6 forks or something. You might consider dropping in the entire front end from an 600 class bike and get the forks, wheel and brakes, triples all in one package that way you's just need to either fabricate a custom stem or make bearing cups as the KTM & japanese stuff don't cross over easily for steering bearings.

As to the geometry, and remember I don't design bikes for a living, what I did, on the advice of my suspension tuner, is this. Basically...

1 Get the front end in there just the way you want it, wheels tires etc.
2 Use a magnetic angle finder on the fork legs to set the rake to whatever you want. Just look up the various sportbikes and find out what they are using or even better, specific to the forks you are using to hopefully get the rake and trail pretty darn close. I used a floor jack to lift or lower the ass end of the bike until I was spot on.

3 Hopefully your rear suspension is already set to roll. Burn in the top shock mount, accounting for the fact that when you drop the bike on the rear suspension it will squat under the weight of the bike. It took a few tries before I had it perfect F&R under the bikes weight.

I think I set my rake at 27 degrees and was basically trying to duplicate a Super Enduro geometry.

I will say I got it pretty damn good. My bike flat out rips around the corners with no bad behavior at any speeds. I did the same thing on my CBR off roader and I expect it to perform equally as well.

If you have decided to just dedicate this bike to fairings etc, maybe it might make sense to chop up your forks. Or swap in some Duke forks??
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Old 05-05-2012, 02:09 PM   #3
booger weldz OP
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Okay, thats a chunk of excellent info! So essentially u assebled the front w desired forks and wheel assembly installed and fine tuned the geomotry by setting rear ride height with the shock mounting bracket height? Sounds easy enough, thanks!!




Quote:
Originally Posted by sailah View Post
I don't have any specific advise about the bike itself.

If I were you, I would not cut down the WP forks, you could sell them for more than a nice set of R6 forks or something. You might consider dropping in the entire front end from an 600 class bike and get the forks, wheel and brakes, triples all in one package that way you's just need to either fabricate a custom stem or make bearing cups as the KTM & japanese stuff don't cross over easily for steering bearings.

As to the geometry, and remember I don't design bikes for a living, what I did, on the advice of my suspension tuner, is this. Basically...

1 Get the front end in there just the way you want it, wheels tires etc.
2 Use a magnetic angle finder on the fork legs to set the rake to whatever you want. Just look up the various sportbikes and find out what they are using or even better, specific to the forks you are using to hopefully get the rake and trail pretty darn close. I used a floor jack to lift or lower the ass end of the bike until I was spot on.

3 Hopefully your rear suspension is already set to roll. Burn in the top shock mount, accounting for the fact that when you drop the bike on the rear suspension it will squat under the weight of the bike. It took a few tries before I had it perfect F&R under the bikes weight.

I think I set my rake at 27 degrees and was basically trying to duplicate a Super Enduro geometry.

I will say I got it pretty damn good. My bike flat out rips around the corners with no bad behavior at any speeds. I did the same thing on my CBR off roader and I expect it to perform equally as well.

If you have decided to just dedicate this bike to fairings etc, maybe it might make sense to chop up your forks. Or swap in some Duke forks??
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Old 05-05-2012, 02:16 PM   #4
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The duke forks are tempting, i had a '96 and did a few trackdays at buttonwillow raceway on it. The brakes are definitely up to the sportbike task! Dont they still have a bit more travel then 'normal' bike suspensions though? That would be the easiest route for sure. I got a little headshake on mine if i was sloppy coming onto the one real straightaway at that track...
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Old 05-05-2012, 06:35 PM   #5
sailah
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Quote:
Originally Posted by booger weldz View Post
Okay, thats a chunk of excellent info! So essentially u assebled the front w desired forks and wheel assembly installed and fine tuned the geomotry by setting rear ride height with the shock mounting bracket height? Sounds easy enough, thanks!!
Pretty much
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Old 05-06-2012, 01:59 AM   #6
MODNROD
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I rekn it's a great idea!
I had a 2006 640 SM, and it went like stink with mid-50's rwhp. I often thought how dynamite the thing would be if it was a few inches lower, as it was with standard height WP front and rear the thing would rip roundabouts quite merrily thanks!
The Showa forks and shocks found on most late-90s early-00s sports stuff works well, and would still have 5" or so travel if you needed it, and would be pretty cheap to get somewhere. I agree with Sailah, the WP stuff you have is worth a good coin (after the 640 SM, I can see why, it's just brilliant), and would easily cover the retrofit. I rekn the 620 would crank out 50+rwhp, with bags of grunt, the 640 was easy to do, pipe, can, FCR, and pocket port.
One thing I found out on my 640 though that you might like to consider, especially if you love the torque of a thumper, is replace the FCR41 with a FCR37 (yep, a 37, off a YZ250). I found on mine compared to the 41 the 37 only lost 2 or 3 rwhp right at the top, but everything under 6000 the 37 stomped all over it, and the throttle response was evil, really, really good grunt.
We need pics when you're done......
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Old 06-26-2012, 11:57 AM   #7
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Quote:
Originally Posted by MODNROD View Post
One thing I found out on my 640 though that you might like to consider, especially if you love the torque of a thumper, is replace the FCR41 with a FCR37 (yep, a 37, off a YZ250). I found on mine compared to the 41 the 37 only lost 2 or 3 rwhp right at the top, but everything under 6000 the 37 stomped all over it, and the throttle response was evil, really, really good grunt.
Hey guys would you be able to point me in the right direction on putting a FCR 37 on a 04, 640.
Ive been looking at thread after thread my brain has turned to mush and my eyes are starting to bleed

Any info or links would be realy useful

Dave
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Old 06-26-2012, 12:28 PM   #8
B.Curvin
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My .02.

When the F450 idea first popped up my immediate thought was, "The swingarm angle will be all wrong. The bike will either squat way too much exiting corners, or the shock will be so stiff (to prevent squat) that it wont hook up worth a darn."

I said as much and was told I was wrong. Everyone I know that built an F450 bike has struggled to get them to hook up and drive off the corner. They also have a tendency to not hook up well mid corner. Unless you can raise the swingarm pivot I wouldn't lower the bike more than a couple inches.

JMHO, YMMV, etc and so forth.
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Old 06-26-2012, 02:59 PM   #9
jdrocks
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there was (or is) a Booger Weldz on Pirate, you the same guy?
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Old 06-27-2012, 05:26 AM   #10
a1fa
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Are you talking about a 450 Super Single?



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Old 07-11-2012, 10:03 PM   #11
ejunker
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Easy Answer

Watch the classifieds and buy a 660 MZ Skorpion. My first round was making a KLX650R into a road rocket. It's great w/52 RWHP at 315 lbs gassed and ready. My MZ's are a bit less brutal, but one's on the way to 60-65 RWHP at 340 curb wt.
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Old 07-12-2012, 08:55 PM   #12
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Are you talking about a 450 Super Single?

Not a single, but super-fun none the less
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Old 07-12-2012, 11:02 PM   #13
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I don't beleive it would be super super hard to get one set up well, 600 front end, stiffer shorter rear shock, just enough to get it into streetbike territory without screwing with the squat too much.

The rest of the lowering can be done with a low slung subframe, you don't absolutely need an extremely low cog on a race bike, it helps to have it a bit higher when you go to more extreme lean angles, but it really does help getting that weight forward as much as possible.
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