KTM RFS/SXF Hybrid

Discussion in 'Thumpers' started by jar944, Feb 23, 2011.

  1. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    The "easy" way is to cut the cradle out of the 400 and weld it into the sxf frame. Same as I did with my 250sxf chassis in this thread. After that everything is a bolt on deal.

    Any competent welder should be able to do it in a couple hours


    Unfortunately I have to many projects of my own. Not sure how I became the expert, I just like building things :D
    #61
  2. dieselcruiserhead

    dieselcruiserhead Long timer

    Joined:
    Jul 25, 2008
    Oddometer:
    1,464
    Location:
    Park City, Utah
    thank you for this thread, really captivating and definitely has me thinking.

    I found a second completely built '02 RFS that is bored out to 540 for very cheap. I like the earlier pipes because I like the additional torque as well. And then some cheaper '08 250 SX-F.

    I like the idea of being into less than a '08+ EXC would cost as well...
    #62
  3. LukasM

    LukasM Long timer

    Joined:
    Nov 15, 2006
    Oddometer:
    5,445
    Location:
    On a RTW ride - next stop USA!
    If you can do the fabrication and you enjoy projects like this, go for it man. You will be able to make most (all?) of your money back if you take your time selling the rest of the parts.

    Whoever is thinking about a hybrid, Navin is offering a smoking deal in the Flea Market, $99 for a SX-F frame.
    #63
  4. Navin

    Navin Long timer

    Joined:
    Sep 22, 2009
    Oddometer:
    8,475

    Thanks for the mention Lukas! I've got a subframe, a couple tanks too. Man, the used market is tough these days!
    #64
  5. dieselcruiserhead

    dieselcruiserhead Long timer

    Joined:
    Jul 25, 2008
    Oddometer:
    1,464
    Location:
    Park City, Utah
    Definitely can do the fabrication and definitely enjoy stuff like this.

    The issue is I'd want to just get the $$ out of my dialed '02 that I want some components off of, so I'd have to buy a second RFS bike to make it work. I found some cheap ones locally that will do great but they're also older style '02ish.

    I might consider sending the engine over to DJH to get checked over and possible a 540 kit and the stainless valves. Not sure if the '02 means much in terms of weaknesses. The only one I see if that the '02s don't have a Rekluse that can be used. Which I may or may not ever use, my frineds on the Rekluse love them and say I should get one but I've never really used one.

    I have a 41mm carb already so I'd also get the head bored out I figure as well.

    So I'm definitely definitely intrigued. I'd be about $4G into a 250 SX-F and a '02 520 EXC before selling anything...
    #65
  6. cross-country

    cross-country .

    Joined:
    Aug 2, 2005
    Oddometer:
    1,720
    Location:
    Grand Junction, CO
    If you used a 450sx(RFS 04-07) motor, you would not need to chop the frame. You would only need to move (cut off and reweld) the rear motor mounts and find a yz400/426 carb bell. If you find an SMR it would already have a 6 speed in it. There is one on KTMtalk for sale.
    #66
  7. LukasM

    LukasM Long timer

    Joined:
    Nov 15, 2006
    Oddometer:
    5,445
    Location:
    On a RTW ride - next stop USA!
    It's actually the bottom mounts that you need to move/reweld, and you also have to modify the front mounts, either by milling down the cases on each side or by bending the mounts out, IIRC it's 1mm per side.

    But you probably knew this seeing how you built one. :evil
    #67
  8. cross-country

    cross-country .

    Joined:
    Aug 2, 2005
    Oddometer:
    1,720
    Location:
    Grand Junction, CO
    Haha, yeah but I built a 540. Dirttricks did the fab. I think the short stroke is the way to go to fully take advantage of the improved handling, but that is just a theory since I never tried it. I really wanted a 450sx with and exc tranny and flywheel. I think that would have been a great bike, at least where I live/ride.
    #68
  9. Rot Box

    Rot Box Been here awhile

    Joined:
    Oct 31, 2010
    Oddometer:
    253
    Location:
    Northern Utah
    Awesome! :evil
    #69
  10. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    I was close to doing a 450/488, but decided my 505/477 was too close to the same thing. The fact that I don't have any short stroke parts didn't help.

    My 555 is getting a piston/cam/trans swap, and the other is growing to a 637 to try and out power my cr5 conversion.
    #70
  11. cross-country

    cross-country .

    Joined:
    Aug 2, 2005
    Oddometer:
    1,720
    Location:
    Grand Junction, CO
    I was thinking that the short crank was the key to the handling. Again, that is just a thought, I never tried it.

    What tranny combo's are you using?

    This thread needs more pics! The CR is very cool!

    Add a hydro clutch and leaky CS and no one would ever know it's Japanese heritage.:lol3
    #71
  12. dieselcruiserhead

    dieselcruiserhead Long timer

    Joined:
    Jul 25, 2008
    Oddometer:
    1,464
    Location:
    Park City, Utah
    How is the '08ish 250 SX-F suspension? I know it's pretty good compared to older models. I'd be looking for more of a trail friendly push ride for a heavy guy/gear (I weight 230 before gear). I think the 250 suspension is the same as a 450, and with the SX it just has more adjustment controls over the EXCs, right?
    #72
  13. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    As for the cr5 It has a magura clutch already. No leaky cs though. looks more euro with a RFS kicker on it:
    [​IMG]

    Not sure if you saw my thread on the cr5 conversion:http://advrider.com/forums/showthread.php?t=757835

    as for the RFS hybrids, The transmissions are still up in the air. I have a few exc trans and one mxc sitting in boxes. I'll likely go with close 1-4 and wide 5-6 on the 555 and all close on the 637. I agree on the handling being related to the stroke. The 72mm's don't feel the same as the 60mm
    #73
  14. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    The 250sxf forks are closed chamber like the 450 but the 250 has softer springs and softer valving. Neither the 450 or 250sxf has good trail suspension. To not beat yourself up you would need to revalve front and rear.

    The exc has open chamber forks.
    #74
  15. dentvet

    dentvet Long timer

    Joined:
    Aug 4, 2008
    Oddometer:
    1,376
    Location:
    hunt country virginia
    Hey Jar, Is it feasible to do a reversible hybrid? I have an 08 christini 300 and would love to put my 520 into it for a trip out west.
    #75
  16. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    Not with a 520 for sure. The 250/300 frames don't lend themselves to having that large of a motor without cutting.

    I heard you picked up a christini. It's too bad you didn't get a chance to climb the glen burn.
    #76
  17. Semtexsam

    Semtexsam n00b

    Joined:
    Dec 29, 2012
    Oddometer:
    2
    Hi,
    Hi,

    ThIs is my first post in this forum, been visiting for a couple of years and to be honest I thought I was registered but now sorted. I have been through most of the forums reading about this project and will have some questions to ask from thime to time, may as well ask before making a mistake.


    Now that Christmas is over it it time to start my winter project. Happy New Year everyone hope you all had a great time. January and Febuary are two if the darkest,coldest and possibly some snow so not much riding.

    The swing arm has already been machined and all fits well at the back when placed with the engine. Took some measurements of the front of the frame and engine and wondering what others have done. The engine is 118.5 mm wide and the frame is 100.5 mm, I am assuming that the engine has to be narrowed. Is it as simple as shaving nine mil of each side ?.

    Have not removed the lower mounts but planning to reuse them after the front has been sorted, is this possible or do I buy new ones from the likes of Dirt Tricks.

    Any help will be appreciated especially if pictures are included.

    Alan.
    #77
  18. overlander

    overlander Gravel Travel Tours

    Joined:
    Apr 25, 2003
    Oddometer:
    406
    Location:
    Wicheetaw, KS but longing for Texas
    What a great assimilation of info about frame geometry and some excellent craftsmanship to boot! Keep up the good mod work!:clap
    #78
  19. dieselcruiserhead

    dieselcruiserhead Long timer

    Joined:
    Jul 25, 2008
    Oddometer:
    1,464
    Location:
    Park City, Utah
    An interesting thing about the XC4 engine is there are some guys making them pretty solid with merging of the cases and new pistons and once they do that they are pretty solid. The RFS are great engines but I feel like they are really tall and the new chassis is pretty killer. I love how jar944 is modifying them using a merging of the new and old frames.

    Once thought that crossed my mind was to use a 400 RFS and change the volume to 450 or larger, similar to the stroke of the later 450 XC4s, and then merge it in. Then you get the RFS with the performance of the later 450s. The 530s are the same stroke and bore as the old RFS 450cc and 510cc engines, so I feel like that would be pretty killer?
    #79
  20. jar944

    jar944 Been here awhile

    Joined:
    Aug 2, 2010
    Oddometer:
    769
    Location:
    Chantilly VA
    a 450 frame should be around 1-2mm narrower than the front mount, are you using a 250 frame? The mounts are easy enough to reuse if you are careful. I don't believe DT is selling any hybrid parts anymore, so you would have to make your own if you were unable to re-use them.

    True there is less reason to do these now (unless you already have a RFS sitting) the 09+ RF4 and the 10+ xc4 motors seem to have all the bugs worked out.

    As for the 400 into a 450 Thumper has a custom 95mm piston to make it a 453 with a stock 525 cylinder. Everyone that has one seems to love it...
    #80