The "Fat Hippo" Utility Bike Build

Discussion in 'Some Assembly Required' started by XR4EVER, Jan 19, 2018.

  1. XR4EVER

    XR4EVER 919 excuses to ride!

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    Finally found a proper place to post this build! Howdy everyone.

    I grew up in awe of the mighty Honda Fat Cat. I was 11 when they came out and 12 when production stopped. Resale value never dipped below ridiculous for one worthy of purchase after I was big enough to ride one. So, here I am with more skill, ambition and vision than money, when oportunity just threw a heap of "junk" my way.

    It all started many years ago when I thought, "How hard could it be to build one?" But I could never find enough parts to start with, beginning with an important part: an engine with e-start, auto-clutch and reverse. That's right, if I'm going to do this, it's going to go backwards.

    Well, I finally had luck shine on me late last year. The dad of a friend of my wife is an old farmer who just sort of acquires new junk when his old junk no longer works. His daughter is sick of the mess and brokered a deal for me to get two Honda four wheelers in return for getting another one running for them.

    One of my new acquisitions is an '86 TRX250 utility quad. I got it running after cleaning out the fuel system, but the petcock leaks bad, the timing chain is worn out, and the whole front end is too floppy to drive safely without dumping a ton of money into. This one is going under the knife to turn it into an all terrain, Fat Cat-style utility dirt bike. E-start with kickstart backup, ultra-low gearing, shaft drive and reverse. It will be a blast in the rocks.

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    This will be its build thread. :beer
    #1
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  2. XR4EVER

    XR4EVER 919 excuses to ride!

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    The first big hurtle was figuring out how to utilize this quad's shaft drive to turn a single rear wheel.

    My first plan was to find a junk, shaft drive street bike and use its final drive. That search was fruitless, and wheel widening would have been tough.

    My second plan was to dramatically shorten the driveshaft and have the ring & pinion turn a jackshaft which would in-turn power a chain to the conventional axle. As I started tearing this apart and visualizing it, I realized that would have lengthened the wheelbase too much to be practical.

    "Plan C" was to mix and match parts to make a single-sided swingarm. I was able to use the left side axle tube on the right side of the R&P housing and flip the axle shaft to get the hub in a reasonable location.

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    The only problem with this was how it would limit my tire size. I want some meats! I needed to lengthen the swingarm and driveshaft by 4" to be able to run up to a 25" tire comfortably.

    I started with this:

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    And I am ending up in this ballpark.

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    This swingarm is going to need massive structural improvements to handle the torsional stresses of being single-sided.
    #2
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  3. XR4EVER

    XR4EVER 919 excuses to ride!

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    Another hurdle I had to cross was the rear brakes. I ended up taking one of the front hydraulic drum brakes and cutting out the whole center bearing section with a big enough hole where it would clear the axle tube.

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    A little clearancing with my "mill."

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    I did the same with the backing plate that will get bolted to tabs on the tube. The front hub's studs will go through the rear hub's stud holes and it will all be held together with the lug nuts. More on this later, on how I'll mount the wheel.

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    #3
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  4. XR4EVER

    XR4EVER 919 excuses to ride!

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    When the old farmer was dropping off my two new-to-me fourwheelers and picking up his, he'd just then remembered having an old Suzuki 3-wheeler in one of his sheds. He said I could have that too if I wanted it, but it was missing some parts.

    Still unsure how I was going to make the front end work, I figured I'd be able to pull something off of it. Suzuki was never exactly cutting-edge in their line of 3-wheelers, so I was expecting rigid forks with no front brake...

    I called him the following week to ask more questions about it, and to see if I could come pick it up. He gave me directions to where it was stored, and I met him there that afternoon.

    I was shocked when I pulled up to see an '85 Kawasaki Tecate KXT250 parked there! This was everything I could have ever dreamed!! 9" of suspension travel up front, disc brakes, aluminum wheels...

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    This completely took care of my front-end concerns in one fell swoop. All it's really missing is the handlebars and the seat. I'll be able to morph the front of this frame with the back of the TRX frame fairly easily. Plus I'll have a sweet engine to build something out of later.
    :dllama:

    Even when we were standing there beside it talking about it, he was still calling it a Suzuki. :fpalm
    #4
  5. XR4EVER

    XR4EVER 919 excuses to ride!

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    I was hoping a cool gadget I could use off the Tecate was one of the sweet aluminum rear wheels, but they are just too wide to get one of them to fit. I'm very limited to wheel size and back spacing. Moving it over to the left as far as it can go, it still offsets the center way too far.

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    Oh well.. I'll address that in a little bit. My next goal was to figure out how to keep my semi-float axle from falling out. The original design had it floating between the hub nuts. Since I chopped the shaft in half, I needed to come up with an easy way to keep it in place.

    I decided to drill and tap into the end of the shaft and use a bolt to hold a plate that would retain a spring washer and washer. The hub nut on the other end will hold enough tension on the spring to keep it in place, but not so much that it will destroy the bearings with too much side-load.

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    With that figured out, my last order of business (before I can work on strengthening the swingarm and re-building the subframe) was to build a new wheel. I took the two 10 x 5 1/4" front wheels from the quad and got to cutting. I did all the machine work on my wood lathe by turning a block of wood to accept the ID of the wheel, then using a grinder with a cutoff wheel while it was spinning.

    I cut 2 1/4" out of the center of one and fit it into the center of the other and ended with a 7 1/2" wide rim. The backspacing still wasn't perfect, so I had to drill out all of the spot welds and slide the center out another 1/2".

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    Results were well within "spec" for this thing. :rofl

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    This will allow me to run a 24x9-10 tire.
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  6. XR4EVER

    XR4EVER 919 excuses to ride!

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    I started working on the swingarm support system. These tubes will get welded in place and gusseted, and the axle tube will still be removable.

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    With the wheel on:

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    The outside section of the support and shock mount will clamshell the R&P housing by bolting to this plate with welded nuts on the inside.
    #6
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  7. XR4EVER

    XR4EVER 919 excuses to ride!

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    Swingarm beefing at about the halfway mark.

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    #7
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  8. XR4EVER

    XR4EVER 919 excuses to ride!

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    I spent that weekend finishing this swingarm.

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    And I spent time cutting mounts off the frame and expanding the inside of the wheelwell the accept a tire.

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    Next up is the shock mount and frame strengthening to handle the stresses of a single-sided shock.

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    I'll get a rear tire and some longer wheel studs this week to really put this thing into perspective. Seat height should end up right around 32" at its lowest point with a 24" rear tire.
    #8
  9. XR4EVER

    XR4EVER 919 excuses to ride!

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    This is the kind of stuff I wasn't looking forward to in this build. Finding places to put things like the battery, wiring components, exhaust routing...

    4 hours to find a place to put the battery and make mounts for it. :mad: I wanted this done before I start bracing the back end so I don't end up with even less room for it later.

    I found a great place for it under the airbox location, on top of the swingarm pivot. Nice low COG. The airbox will need to be rebuilt at about half its current size, but the element is up in the top half anyway. It shouldn't matter.

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    #9
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  10. XR4EVER

    XR4EVER 919 excuses to ride!

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    I was having a hard time finding longer wheel studs (M10), so I had to come up with something different. I took some measurements and hit my local hardware store. I ended up buying some 2" long 7/16"-20 bolts, lugnuts, a tap, and a die to run the threads deeper on the bolts.

    I drilled the holes in the drum out to 7/16" and tapped the holes in the hub. Now the bolts tighten the hub to the drum, and the remainder of the bolts act as the wheel studs. It should work well.

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    Tire should be here Monday.
    #10
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  11. XR4EVER

    XR4EVER 919 excuses to ride!

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    This tire's dimensions are perfect. I can't wait to ride this thing.

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    I had to cut out those triangulated frame pieces that I previously bent into position. They were just getting in the way, and I have a better plan that involves this sweet upper shock mount.

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    #11
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  12. XR4EVER

    XR4EVER 919 excuses to ride!

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    I won't admit how much time I have into this upper shock mount. Location of this is absolutely critical. Spring rate (angle), travel distance, overall ground clearance, shock adjustability, u-joint clearance and room to add structural support were all factors in this mount's size, shape and location.

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    This tube gives me a nice big area to build from for supporting the torsional forces of an off-center, outboard spring.

    I got the driveshaft welded together and in place to check clearances. The u-joint will rub against the swingarm tube if too much travel is allowed. At the shock's full extension, this is right at the comfortable limit.

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    With half of this supporting its own weight, I'm able to sit on it. Spring rate feels good; a hair on the stiff side, but I'd rather have stiff than wollowy, especially if I'm hauling any loot. The tire will absorb a lot of the small impacts. Seat height should end up at 33" with almost 13" ground clearance. I can sit on it with my feet flat on the ground.

    [​IMG]
    #12
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  13. XR4EVER

    XR4EVER 919 excuses to ride!

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    Squint.

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    After I took this pic, I re-aligned the front end with a more-proper rake, and I measured the wheelbase. It should end up around 55 1/4", which is right around a late model XR250.

    That's where I'm at now. Stay tuned for more, and thanks for reading.
    #13
  14. villageidiot

    villageidiot Long timer Supporter

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    WILDMAN SHIT!!!
    #14
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  15. Tanshanomi

    Tanshanomi Your Favorite Uncle Supporter

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    Impressed with your fab skills and massively interested in how this turns out.
    Subscribed.
    #15
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  16. lesman

    lesman Live easy, Brake Hard

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    55 1/4" wheel base Are you building a road racer? Looks great
    #16
  17. Samtech79

    Samtech79 Two wheeled lunatic

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    Ok.... thats rad. It's as awesome as it is scary looking. Keep it coming!
    #17
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  18. tominboise

    tominboise Long timer

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    Awesome work - amazing what someone with time on their hands and some desire can accomplish.
    #18
  19. r60man

    r60man Long timer

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    This looks like epic fun to ride. I am in!!!
    #19
  20. tinwelp

    tinwelp Professional Idiot

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    Fantastic work... but why a single-sided swing arm? Bearing in mind that "because I can" is a perfectly acceptable answer, I'm just curious why you didn't make it double-sided and avoid a huge amount of fabrication. It's not as if there's enough to be done!!

    I'm in!

    Cheers... Paul
    #20
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