Swamp Donkey 2.0 The BW200/XR400 Mashup Build Thread

Discussion in 'Some Assembly Required' started by Hurco550, Oct 28, 2019.

  1. Hurco550

    Hurco550 Keep er' Between the Ditches

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    The first iteration of the fat tire swamp donkey built from a krusty tw200 and bw200 parts went to live out its days as a Gulf Shores Beach cruiser. If anyone wants to catch up on that build, its here:
    http://www.dotheton.com/forum/index.php?topic=75455.0

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    While the original swamp donkey is where it belongs and with who it belongs with, its absence has left a fat- tire-bike shaped hole in my life. I recently found a deal on a 1986 BW200ES close to home for a fair price given the current market on these machines. It was complete and did not appear to be overly abused, coming with a stack of receipts from the original and second owner.

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    Once I got the bike home and fired up for a test ride, a few trips around the parking lot behind my house coaxed a few issues to rear their ugly head. The top end valve train was making some VERY unsavory noises, and there was so much oil puking out of the air box from the crank breather from blow by that you could track the route that I had taken around the parking lot. Long story short, the motor needs a top end overhaul. That is all fine and well, they are simple motors, parts are easy to find etc. The only caveat is that while riding the tw200, which is the same power plant where it counts as the bw200, is that while its power output was adequate to haul my 260 lb self around, adequate doesn't always equal fun. Sure it pulled me up, around and through the Mid Ohio hare scramble course without missing a beat, but it did so much like a lawn mower would. No frills, just chugging. Just like any good red blooded American, I want more. I need EXCESS.

    Enter the Honda XR400R powerplant. This engine has alot going for it, but mostly the 34 H.P. compared to the 15 H.P. of the BW200. The other thing it has going for it is that it fits in the frame of a bw200. I found a this picture on a bw200 facebook page of a guy who put the engine out of a 400ex into a bw200 chassis. The 400ex is a very similar motor to the xr400r, with some differences including electric start vs the kick start only of a XR400. Below is a picture of the 400ex swapped bw200. I like that this picture proves that it fits, but I will not be doing the goofy swingarm stretch or dropping the front end. I still want this machine to be able to eat up the single track.

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    After deciding the route I wanted to go with an XR400R powerplant, I decided that I'd casually keep an eye out on craigslist and facebook market place for the right donor xr400. The universe had other plans. I was meant to find THE PERFECT donor sooner. That day in fact. While cruising along, I found an xr400r Parts bike. It was the frame, carb, ignition, oil cooler and motor. Perfect for an engine swap, and I don't have to feel bad about pulling apart a complete bike in order to complete my goal. Better yet, the whole xr400 pile was $150, which added to the $450 purchase price of the BW200 only puts me at a net total of $600 into this whole project so far. If I play my cards right, ill have a really wicked machine for under $1k. I have not yet decided how I am going to go about working past the oil in frame issue of the xr400, but there may be a bit of frame grafting going on between the xr400 frame and bw200 frame, but I will keep that up to date in this build thread.

    Here is how the xr400r came to me after a 4 hour round trip down by Urbana last night:

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    So, pull up a chair, and follow along with the next hair brained project out of Hurco's Garage. Like all the rest, progress will likely be fast and slow, then rinse and repeat.
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  2. Pezz_gs

    Pezz_gs Cant ride for crap

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    Im in :lurk

    I have a BW200 swingarm as my starting point for my project, which I imported from the USofA.

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    #2
    Hurco550 and sidetrack one like this.
  3. Hurco550

    Hurco550 Keep er' Between the Ditches

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    Per the norm, there has been a bit of a "change of plans".....

    I have stared at the xr400 chassis next to the bw200 long enough to come to the conclusion that I will be better off to use the xr400 frame and build it into a fat tire bike vs putting the engine into the outdated chassis of the bw200. I WAS planning on gutting the bw200 to do just that. Even though I'm far from a purist, I cant let myself cut up a fairly solid old complete survivor. I have decided to sell the bw200 complete and use the proceeds to buy the specific parts I need to complete this project.

    The (current) plan is to now use a tri z three wheeler front wheel/ hub and rotor. The rim itself is identical to the bw200 (same part #) but the hub is cast alloy instead of welded steel on the bw200 and it is disk brake.

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    I plan to mate this to a set of rmz450 usd forks that i've had around for a while. I will make a custom set of triples to offset for the larger front tire and also make them utilize the stock xr400 stem.

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    The next project will be to make a swingarm instead of using a bw200 swingarm. Mine will be mildly based on the honda missle swingarm. The missle kit was available back in the day to convert honda atcs (i believe mostly the 250r) into fat tire dirbikes. In this way i can make it narrower than the bw200, and also get rid of the strange cam/ bushing combo to tension the short chain between the engine and jackshaft.
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    #3
  4. Pezz_gs

    Pezz_gs Cant ride for crap

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    @Hurco550 think that is a smart move. :thumb

    After building a number of contraptions over the years I think 'engine in same frame' is a winner.

    Look forward to your progress
    #4
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  5. Pezz_gs

    Pezz_gs Cant ride for crap

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    Here is my RV125 ‘Reg’ fitted with a PE175 motor among many other mods
    My own mechanical antidive front end with GPZ900R front wheel

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    #5
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  6. Nathan_66

    Nathan_66 Been here awhile

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    Subscribed!! I like your thinking & where the project is now headed. EXCESS, yeah!!!

    Making an extra swingarm or two could help w your project fundage...I'm interested!

    By the way, the grateful BW200 Thanks you...
    #6
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  7. Hurco550

    Hurco550 Keep er' Between the Ditches

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    I won the auction on the tri z front hub and wheel and it was delivered today. Now I can start figuring out axles, spacers and caliper mounts to make it work on the rmz450 forks upload_2019-11-11_9-54-18.gif

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    #7
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  8. Hurco550

    Hurco550 Keep er' Between the Ditches

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    DUDE! that thing is awesome. I love it. I like the anti dive fork setup too. Always though those were neat on the Airhead Beamers back in the day
    #8
  9. Hurco550

    Hurco550 Keep er' Between the Ditches

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    Ha I always thing about making extras when I do these projects, BUT I am usually burnt out by the end of a project and never want to build another one again. A couple people wanted me to modify BW200 front hubs for them like i did to put a BW front wheel on the back of a TW200. I just cant find the enjoyment out of making the same thing twice for some reason.
    #9
  10. Hurco550

    Hurco550 Keep er' Between the Ditches

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    I purchased a bw200 front hub, brake and axle. The hub and brake will be modified for use out back and the axle will be used out front. I will have to design and machine a set of triple trees with a wide offset for the tri-z front hub, and it also will utilize the xr400 stem pressed in and holes for the rmz450 forks. You can see in the attached photo the length of the axle vs the stock width of the rmz forks.

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    Also, a bearing swap for the tri z wheel will be necessary to accommodate the bw axle. Good thing, as i dont think the og bearings had more than 2 or 3k miles left in them upload_2019-11-19_9-39-47.gif
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    #10
  11. Jimmy the Heater

    Jimmy the Heater Dirt Farmer

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    Ummm, maybe 2 or 3 inches left in them!
    #11
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  12. greasyfatman

    greasyfatman Long timer

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    Subscribed to the thread. Thought about yz450 fat tire kit for a while. Have fat tire mini bikes.

    Really good use of an xr400.

    Your image isn't showing up for me.

    Attached Files:

    #12
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  13. Hurco550

    Hurco550 Keep er' Between the Ditches

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    Thanks man!

    dont know why the image didn't work, try this one?
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    I am using that kit as a bit of inspiration on how i'm going to do mine. I like to build and fabricate though, and really couldn't much justify the $2600 for the kit, (and that is before wheels and tires)

    It is definitely cool, but way outta my league. I'll hopefully have less than half of that money into this whole project.
    #13
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  14. Hurco550

    Hurco550 Keep er' Between the Ditches

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    These wheel bearings gave me a heck of a fight. The spacer didn't want to move over enough to allow a drift to do the job like normal. I broke the jaws on a set of blind bearing pullers as well. I ended up welding a 1/2" nut to the bearing itself which is the same thread as on the slide hammer. Amazingly even with welding to the greasy carbon steel of the wheel bearing, it was enough to coax the old spinner out.
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    #14
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  15. Hurco550

    Hurco550 Keep er' Between the Ditches

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    I mocked up the front end with the caliper last night. I had to order some oddball wheel bearings to make the tri z hub work with the 17mm bw200 axle. I will also have to turn up some top hat style split bushings to adapt the bw axle to the rmz forks. I had a spare dr650 caliper laying around, which is the same caliper they use on the rmz450 (or so ive read) I think it will play nicely with the triz front wheel. There isn't a bunch of extra space, but as we used to say in the machining world, "clearance is clearance". If, once everything is solid mounted it ends up being to close for comfort, there is plenty of meat on the caliper to grind and shave it down for a bit of extra room. I will also have to make an adapter place to bolt in a 250mm rmz450 front rotor, which should be simple enough since the bolt circle for the tri z rotor is fairly small.

    It is always a game of "one step at a time" to reverse engineer this stuff. I don't tend to draw up or design the whole project from start to finish which gives me a bit of freedom on the build. In this case I have to first set up the axle so that i can get an accurate measurement of fork center to center. Then I can draw up and fabricate the triple trees. Only then can I put the front end on the bike, which will allow me to work out the swingarm design and rear suspension to match the front. All part of the fun.
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    #15
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  16. Hurco550

    Hurco550 Keep er' Between the Ditches

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    Still plugging away. Right now i'm mostly designing parts for the fork conversion and swing arm. Through the facebook tw200 group, I was able to borrow a tw200 swingarm to steal some dimensions from. Also got the 250mm rotor in, so I can make the adapter and finish up the front wheel spacers and bushings.

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    #16
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  17. greasyfatman

    greasyfatman Long timer

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    #17
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  18. Hurco550

    Hurco550 Keep er' Between the Ditches

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    I finally got the oddball front bearings in the mail from China for the swap from the original 15mm TriZ axle size to the 17mm bw200 front axle size. I hope they hold up, because it's the only place I could find the particular o.d. and i.d. I needed.

    Luckily the spacer had enough meat on it to bore out and use with the new axle.


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    Since I'm using the stock caliper mount on the rmz450 forks, I had to go up to a 250mm rotor. I chose an aftermarket KX125 KX250 KLX450R KX250F KX450F rotor for this job, as is uses a 4 bolt pattern as does the tri z hub. I drew up an adapter and had it water jet out of 1/2" 6061.

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    I counter bored the back side to accept the tri z bub.

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    Flipped it around and machined the front step for the rotor and a relief for the mounting bolt.

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    All mounted up, and it spaces the rotor out 1/4" away from the rim, which should help a bit with the clearance issues

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    Here it is against the original tri z rotor

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    #18
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  19. Jimmy the Heater

    Jimmy the Heater Dirt Farmer

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    Might be just me but the pics aren't showing up in the last post.
    #19
  20. Hurco550

    Hurco550 Keep er' Between the Ditches

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    Looks like the links didn't work. I'll try to fix it when I get to a pc instead of my phone.
    #20
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