Spring Fever Amazon Diesel Powered Mini Bike Pt 1

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Spring Fever. I’m not sure how it hits in less desolate parts of the world, but around here it gets our brains churning with ideas. After six months of snow and rain, the itch sets in for all the ill-advised marketplace transactions, wild pet projects and trips we’d like to take. With summer and hope on the horizon, we scoured the shop for something entertaining to do after hours—something just for fun—and the perfect project was in the corner gathering dust.

Sipping and Swiping I can trace the genesis of this idea back to a particular Whiskey Wednesday in June of 2023. Somehow, Jeff had stumbled upon a small air-cooled diesel engine on Amazon selling for a measly $179.99. Essentially the redneck cousin of Harbor Freight’s Predator 212, the Amazon diesel displaces 196 cc and is rated at 3 hp and (wait for it) 35 Nm [26 lb-ft]. I trust that figure as much as anything else on Amazon, but there was no doubt that we had to get our hands on one of these engines.
It arrived in Amazon Prime fashion just several days later in a ridiculous wooden crate, and we had it billowing black smoke several minutes later with the hokey wing-nut silencer removed. Boys will be boys, I guess. The little diesel is one hell of a buy if you ask us. It starts and runs great, and the build quality is far better than expected for the price of admission. Where things get a little silly is the language barrier.
‘Fill diesel, can’t fill other diesel,’ the sticker on the fuel tank instructs. The stock muffler supplied similar insight, as its label warns ‘High temperature papt, dont touchit.’ And it’s a good thing we’re well-rounded small engine mechanics, because the instruction manual included with the engine is actually for a water pump.
With the power to move something on our hands, we needed a vehicle that could be revived with the stump-pulling power of the Amazon diesel engine, and we arrived at the most logical solution possible—a mini bike.

Facebook Marketplace brought numerous possibilities to the table, and we settled on a stripped-out, rather homely-looking Sears-Allstate Roper mini bike, probably built in the 1970s. It’s neither conventional nor stylish compared to its peers, and upon closer inspection, it wasn’t in all that good of shape either. The suspension was seized, the fenders, seat and grab bar were long gone, and it was wearing a partial shade-tree restoration. But something told us this was our machine, and greatness lay in store for it.

Unholy Combination Unfortunately, that’s about as far as it went for the better part of two years, a classic case of perfection being the enemy of progress. That is, until we gave ourselves a deadline to piece this thing together with whatever we had lying around. We still needed a few important pieces, including a torque converter and some tires, and you can guess where those came from.

For $55, we were pleasantly surprised with the quality of the Vevor 30-series torque converter, and it’s a super adjustable setup for haribrained projects like this one. However, we had a slight size mismatch between the engine’s output shaft and the drive clutch of the torque converter, a situation we rectified by running the engine on the table with a file on the output shaft. (Insert joke about the lathe we have at home.)
Having proven on the bench that our 3-hp engine would bring the CVT to full shift, we got to work fitting it in the chassis. And that’s where our issues started. The CVT’s driven clutch interfered with the back of the frame and the valve cover was all over the front legs of the frame. Sounds bad, but the solution was quite simple.
The Roper frame is comprised of three sections: the front fork, the main tubular section and the rear section that serves as the swingarm and engine mounting plate. There’s a pivot point on the bottom of the chassis that allows the swing arm to move, and by relocating that point further back and shifting our engine to the rider’s left, everything came together.

The Scrap Bin Provides With our Shinko 421 3.50 x 10 Golden Boy tires mocked up on the crusty three-piece wheels, we had a roller (of sorts) and continued piecing it together with whatever junk we had lying around. The diesel’s stock silencer wouldn’t do, and while numerous parties involved wanted to see a stack and tractor flapper, I shot ’em all down in favor of a more conventional upswept exhaust.
Straight from the scrap bin, the header is made from 1-inch mild steel and the muffler is 1-1/2-inch stainless with the tapers and bends made from pie cuts. While testing the ergonomics, we decided a heat shield was a worthwhile addition, made from sections of the same 1-1/2-inch stainless. We later added a homebrewed silencer insert in the tailpipe to bring decibels back to livable levels.
Our new hot rod was starting to take shape, but we were missing a critical piece to keep this thing propped up when we’re through terrorizing the neighborhood. If the Roper ever had a kickstand, there was no evidence of it, so we went back to the scrap bin to look for options.
If you’ve been following our Honda CB550 street tracker build, you’ll recall that we ditched the bulky center stand in our latest update. While it seemed obnoxious on the Honda, it fit the mini bike like a glove, and we fit it on the swingarm’s pivot point with minor trimming. We then hacked a couple inches off the legs to suit the mini bike’s diminutive stature and welded on some feet for sure footing.
We were starting to see our perverse vision of a crude-oil-burning pit machine come to life, but a few things still weren’t hitting the mark. The fuel tank was a big one, as the mini bike’s triangular frame ruled out conventional motorcycle tanks, and the engine’s original tank looked like an afterthought when moved up top. The only logical solution was something completely custom, and we fabricated a rad diesel tank out of aluminum. You’ll have to tune in to the next installment for that.
But I will leave you with this tidbit, and it’s a prized item from my personal stash that I hope you’ll appreciate. The Roper’s frame comes to a wide and abrupt end out back, and with the OE rear fender long gone, the side profile was missing something. We mocked up several options, but an old dirt bike fender I’d grabbed while combing a bone yard put all the others to shame.
It had that skinny shape and goofy curves of the 1970s, but the selling feature was a faded yellow ‘Udder Mudder’ fender extension. I shuddered to give up this prized piece of junk, but the bike had spoken, and it installed easily with a quick bracket we fabbed up.

Tiny Bike Mini-Series What you’ve just read brings us to a point where our diesel mini bike rolls around and has all its big working components in place—or so we thought. I promise you, there are hiccups, creative workarounds and real tech coming in the next installment before the big reveal.
I think back to some feedback I received on an article not long ago, where a reader was miffed that I thought something was worthy of being featured on the pages of Bike EXIF. To that we say, why not? While you won’t find a site on the web that’s more dedicated to the art of building real motorcycles, you’re missing out on a whole lotta fun if that’s your sole focus.

The whole idea of this series is to build something off-the-wall—a hairbrained idea brought to fruition by sheer will and the wealth of cheap parts available on the web. And since this bike’s already seen some test passes in the parking lot, I’ll reveal that it’s put a sh*t-eating grin on the face of everyone who’s twisted the throttle. And that’s what it’s all about, right?


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