building a custom trailbike: Honda CRF chassis + XR250R engine

Discussion in 'Some Assembly Required' started by jesusgatos, Mar 30, 2011.

  1. Rot Box

    Rot Box Been here awhile

    Joined:
    Oct 31, 2010
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    355
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    Northernmost Utah
    Cool build! I like your Alaskan camper--I have one too lots of fun :)
    #21
  2. jesusgatos

    jesusgatos fishing with dynamite

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    Sadly, the Alaskan Camper is long gone. Gave it to a friend when I started building this. Those Alaskan Campers are great though. Super well-built.
    #22
  3. jesusgatos

    jesusgatos fishing with dynamite

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    Sold my KTM to raise some money for GatosBros and the XRamblers aren't finished yet, and I've got almost all the parts I need to finish this bike, so I started working on it again. Just a few hours here and there, in between other projects.

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    Ended up having to remove quite a bit of material from the frame in order to get the engine to sit in the right place. The 'right' place being determined primarily by the height of the countershaft sprocket (trying to mimic the location of the stock CRF engine).

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    After finishing the rough fit, had to modify the XR's swingarm engine-mount bushings to locate the engine a little more accurately.

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    Tried turning them on a lathe. No way. Had to anneal them first.

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    Then I went to go see my buddy Mark at MDR and he bored them out to 17mm for me.

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    Then I used some old calipers and other tools that I inherited to measure the width of the frame and all the swingarm components in order to figure out what kind of bushings I'll need to make to locate the engine side-to-side.

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    Was curious about the capacity of the downtube, so flipped the frame over and filled it up with water. Anybody want to guess how much it holds? If you get it right I'll... send you some GatosBros stickers?

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    Also took some measurements from the stock engine cradle tubes, purchased some 1x1" x .120-wall 6061 tubing and had some new engine cradle tubes mandrel-bent. Those are done and they turned out really nice, but I didn't taken any pictures because I haven't fit them to the chassis yet.

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    #23
  4. jesusgatos

    jesusgatos fishing with dynamite

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    #24
  5. yzmaico

    yzmaico Slacker

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    Oh man! I'm diggin' this thread! Loved my old XR's.

    The inmate that was selling his XR400 for $2,700, just shows how many true trail riders miss the XR line-up. Such is life in the wacky U.S. market place.
    #25
  6. jesusgatos

    jesusgatos fishing with dynamite

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    Haven't had a chance to start fitting the engine-cradles yet, but this is what they look like. Went ahead and had them mandrel-bent because if bending square tubing with a rotary-draw bender distorts the fuck out of the inside and outside walls. These on the other hand, turned out berry niiiiice.

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    #26
  7. jesusgatos

    jesusgatos fishing with dynamite

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    Been busy with other projects and before I got back to building this bike, my brother dumped another one in my lap. We'd bought a couple DMC CR80 conversion frames a few years ago. An XR100 and an XR200 version. There were a few problems with the XR100 that I had to fix, but the XR200 frame was a disaster. Engine-mounts didn't line-up, header flange didn't clear the frame, couldn't use the kickstarter, footpeg mounts were bent, etc. The modifications required to stuff an XR200 engine into a CR80 frame are extensive, and the quality of this conversion was so poor we never even bothered to build it up. But that little XR100 conversion sure was a lot of fun...

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    ...and we already had all the parts, so I decided to take a few days and bust it out. If nothing else, finishing it would make more space for other projects, which I desperately need.

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    Chopped-up an old CHM exhaust system that came off the bike we pulled the CRF150F engine out of. Picked up a Miller Multimatic 200 portable ARC/MIG/TIG welder a while ago, but haven't had time to practice TIG-welding, so I asked my buddy John to weld-up the exhaust for me. He was pretty impressed with the quality of that little machine, and it turned out pretty well considering that he was on welding dirty old exhaust tubing.

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    CR80 footpeg mounts have a tendency to bend, especially when big kids are having too much fun on them. This is a stock CR80 frame.

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    Was a little bit pissed that the footpeg mounts were bent when we got this frame from DMC, and beyond that, the right side footpeg mount interfered with the kickstarter. So I decided to cut the footpeg mounts off and use a footpeg mount from an XR250 on the right side. Have some reservations about bolt-on footpeg mounts after one fell off my XR650, but it seemed like the best (only) option.

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    Had these little threaded bungs machined and welded them into the frame.

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    Wish I had a plasma torch, but had to hand-cut all these little brackets and gussets.

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    Pretty happy with how it turned out though. Tied into the swingarm pivot and looks to be pretty bomb-proof.

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    Took the opportunity to move the footpegs further back, so had to cut off the left side footpeg mount too. This is how I made sure they were symmetrical. Aligned with the swingarm pivot bolt.

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    Similar gussets on this side, but the footpeg mount is welded to a short piece of tubing that pierces through the frame.

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    Decided to chop-up the kickstarter in order to optimize the footpeg placement. Haven't finished smoothing that out, but it's functional. Good enough for now.

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    There was a small notch in the downtube for header clearance, but it wasn't the right size/shape so I had to cut that out and replace it.

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    Had a problem with the steering stops shearing-off on the lower tripleclamps on the CR80/XR100 conversion, and solved that problem by adding a little more material to the steering stops.

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    The leading edge of this skidplate where it ran into the frame was another abortion. Cut it apart and smoothed it out.

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    Moved the CDI to a little more protected location too. Wiring harness is tucked tight into the frame now.

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    Last thing to do was machine these little bushings that allowed us to run a GatosBros KTM stabilizer mount on these aftermarket upper tripleclamps. John helped me out with that too.

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    Done. Final assembly to verify that everything fit right and get it out of my way. Rob will tear it down and have the frame powdercoated.

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    #27
    shinyribs and Foxed101 like this.
  8. jesusgatos

    jesusgatos fishing with dynamite

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    And now back to our regularly scheduled programming. Think this is about where we left off, and I haven't got much further.

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    Using a right-side XR250 footpeg mount on this bike too. Located the point where I wanted the forward mounting hole to be (lower and further back than stock), and drilled that out, taking care to keep the drill parallel to the swingarm pivot-bolt. Could only drill up to 5/8" because of the way the frame is shaped. Have to use an air grinder to remove the rest of the material so I can slide the 1" bung in there.

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    Trimmed-up an extra engine cradle tube and test-fit it. Going to tuck those tubes up a little tighter, closer to the bottom of the engine, but these are going to work out great.

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    Was going to wait to remove this part of the frame until after I'd welded-up the lower engine cradle, but wasn't able to install/remove the engine so bye-bye. No worries about anything moving. Downtube is SOLID.

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    #28
  9. RFVC600R

    RFVC600R No sand here :'(

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    :lurk

    How did I not see this thread before?:lol3 Prolly because I'm a noob.

    :lurk
    #29
  10. jesusgatos

    jesusgatos fishing with dynamite

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    Borrowed a few high-quality burr-bits from a friend and WOW, what a difference. It's at least 2-3 times faster/easier than working with the shitty bits I was using.

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    Finished fitting the test-piece and then started fitting the real engine cradle tubes. So far so good.

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    Verified that I'm able to remove/install the engine with the engine cradle tubes in place.

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    And made a temporary mount to locate the engine so I can start making the rest of the engine mounts.

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    #30
    shinyribs likes this.
  11. crypto666

    crypto666 Long timer

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    Cool projects, all of them. I really miss my M-35, and I wanted to do the same thing and build it in to a camping rig. Mostly I just used it for running to the store and dragging trees out of the forest. Everyone loves the M-35.
    #31
  12. ls400x

    ls400x Adventurer

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    Love these builds. Great write up and photos. Motivates me to work on my bikes.
    #32
  13. thecanoeguy

    thecanoeguy just a yobbo from oz

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    progress????/
    #33
  14. jesusgatos

    jesusgatos fishing with dynamite

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    None. Been working on the gypsywagon caravan. Making some big strides forward on those projects, but nothing on these bikes or the XRamblers.
    #34
  15. 888bart

    888bart Adventurer

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    This is exactly the project I've just bought all the bits for...2006 CRF250 rolling chassis, everything except the engine and a 96 XR250 engine, ancillaries and wiring loom. So I'm all set to start, thought i'll do some research and I spot your thread.
    In my experience as an engineer........check twice.... cut once !
    I See that you've now cut away the upper horse wish bone and had said that you would have done that in an earlier post..... in your experience will the engine fit without cutting out the bottom cradle tubes, just by cutting away the upper wish bone ? I was considering making engine mounting brackets for the rear mounting instead of using the swing arm bolt. (Using a short shoulder bolt on either side of the swing arm to leave a gap in the middle for new brackets). this in my eyes would mean I could shift the rear mounting to a point where none of the casings would clash at the back of the lower frame where you had been grinding with the die grinder.
    Your thoughts would be very much appreciated.
    #35
  16. 888bart

    888bart Adventurer

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    Now I can see why it's taken you so long..... I had the engine inside the frame last night (scalloped a small piece out of the horse wish bone to get it in). biggest problem is lining up the drive sprocket to get chain to miss frame............... Conclusion...... this is not a viable transplant......to many difficult problems (drive train alignment, kick start clearance, and exhausts clashing with main down tube) without cutting and shutting chassis big time.
    Any-one else thinking of this, don't get me wrong, I think it's a great idea.. plenty of cheap CRF rolling chassis about (to expensive to repair compared to value of bike) plenty of XR 250 engines...... but far to much work needed.
    I'm going to try an XR 200 engine in the same chassis as the engine is much smaller.. post more when I know...
    I'm also going to try the XR 250 engine in an RMZ 450 chassis......... same reason, plenty rolling chassis about as uneconomic to repair when they blow up.
    #36
  17. jagger_snitt

    jagger_snitt Pencil Pushing Dreamer

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    what about the CRF230 without a kickstart would eliminate a variable you just need to put a battery somewhere for the electric start,just a thought.
    #37
  18. 888bart

    888bart Adventurer

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    Jagger, have you tried the CRF 230 engine in a 250 frame ?
    I'm on the look out for an XR200 engine. and have my eye on an RMZ 450 chassis.
    any-one out there got an RMZ 450 and a CRF 250 they can picture side by side for me ? cradle cavity measurements would help immensely.
    #38
  19. Navin

    Navin Long timer

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    This to you guys is easier than maybe adding a throttle limiter to a 250f or doing a top end every two years?

    image.jpeg
    #39
  20. jesusgatos

    jesusgatos fishing with dynamite

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    Don't think engine would fit with stock engine cradle tubes, even with the upper wishbone removed. Maybe if you rotated the engine up/back a little bit, but better to maintain something closer to stock drivetrain geometry. Have everything lined-up, right where it needs to be, including swingarm/engine mounts, kickstarter clearance and footpeg mounts. Just haven't had time to finish putting it all together. Everything fits.
    #40
    Pezz_gs likes this.