A First Timer’s Guide To Building A Minibike

Laura was depressed. “I write these press releases about cars, and I don’t know what the words I’m writing mean.”

“Yeah, but you’re a PR person,” I answered. “Nobody really expects you to know how an engine works.”

She glared at me. “I expect me to know.”

“You just need to take something apart and put it back together,” Tom said. “I suggest a minibike.”

The above is an exact recreation of a conversation I had with best friend, Laura Conrad, and my husband, Tom Yeager, last summer. Laura told me to make her seem taller in the retelling, and Tom wanted me to refer to him as “El Jefe,” but I refused. This is science. We are all about facts, and the facts are this: Tom’s suggestion to learn by building something made sense. A small motorcycle takes a lot less money and space than a project car, and although it’s not as complex as a modern automobile, the basic parts and principles are the same. Also, we had nothing better to do.

The first step was acquiring a small motorcycle. Honda offers the street-legal Grom, but at $3,000, it would be a shame to tear it apart just for fun. Craigslist is full of Chinese-made mini motos, and although they are cheap and amusing, most use modern electronics, making them less easily rebuildable than the points and pull-start bikes of the 1960s. Besides, Tom wanted Laura to have the old-school experience of working on a vintage machine. After searching the classifieds, I found what I was looking for right in the ROADKILL offices when our publisher, “Minibike” Joe Sebergandio, offered me a late ’60s bike for $400. After checking it carefully for spiders, Laura picked up a wrench and started learning. Initially, the learning included which end of the wrench did what, but over a couple of weekends, Laura got a feel for the tools and some mechanical know-how.

“It didn’t really sink in that I was learning anything until I walked past an engineer’s desk at work and asked him what the piston on his desk was out of,” Laura told me a few weeks after the project. “He looked at me in shock. I don’t think he expected me to know what a piston looked like. I surprised myself, like, ‘Hey, I know things!’ I don’t think I’d tackle a car build on my own or anything, but I’d help someone else. I did get a lot more confident about using tools from the project. I went home and built a coffee table!”

Our rebuild was pretty basic, nothing you couldn’t do on your own or with a kid or friend in your life who wants to learn what a piston looks like. So hey, if you have nothing better to do, why not build a minibike? Here’s how.

The history of minibikes

The history of minibikes parallels that of go-karts, dune buggies, and hot rods. The first ones were made completely from scratch out of leftover parts in garages. Lawnmower engines, sheetmetal, and scrap tubing were welded and bolted together to make zippy little scooters for carving around in race pits and culs-de-sac. In the ’60s, prebuilt and kit bikes started showing up, first in enthusiast magazine ads sold by go-kart companies with names such as Taco and Bonanza, later in big stores such as Sears & Roebuck and J.C. Penny. In the late ’60s, even the Japanese motorcycle companies got in the minibike game with the introduction of the Honda Mini Trail—a far more sophisticated bike than the early machines. Our minibike was a copy of a Taco-style bike from around 1968  called a Torpedo.

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We spent more money at the start to get a complete machine, but if you don’t mind running down parts and pieces, you can find frames for $100 to $200. There are even new kits available from places such as Northern Tool or the revived Taco Mini Bikes brand.

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The first lesson for any would-be mechanic is tool vocab and usage. Our tools were pliers, sockets, a ratchet, combination wrenches, flat- and Phillips-head screwdrivers, and hammers. The claw hammer was there as an example of a tool not for mechanic work.

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“I was worried that I wouldn’t be capable of learning it, like I wouldn’t be wired right.”-Laura Conrad

Diving into a project can be intimidating, but you just take it one piece at a time and start with something easy. In our case, that meant removing the seat.

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Minibikes can be powered by just about any small engine, but the most common are Briggs & Stratton and Tecumseh. Ours was a less common four-stroke Clinton with about 3.5 horsepower. That trio-and-a-half of ponies goes to the rear wheel via a centrifugal clutch and chain. A centrifugal clutch is a simple automatic that engages more as the engine rpm increases.

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Our easy start turned hard when Laura ran into a common mechanical happening—damaged components. The old seat had rotted, and the threaded inserts in the wood were spinning. It took some muscle to remove the fasteners, which we later replaced with combination wood screw/machine screws, but it was a good lesson in problem solving. Also, working upside down gave Laura a chance to practice “righty tighty, lefty loosey.”

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One’s first engine removal is a day to remember.

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Another important lesson: Always keep your small parts with the component they came off of.

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Although we purchased new gaskets, it’s good practice to try to remove old ones without damaging them. It’s common for replacement kits to have different and occasionally incorrect gaskets for your project. It never hurts to have a spare.

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Remember to drain fluids before disassembling an engine and to refill them before starting it.

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Gaining total mastery of the tools. Well, maybe not total.

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“I keep mixing up cam and crank,” Laura complained,  so I told her the bigger word went with the bigger part.
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There are some tasks where it really helps to have a friend, such as when you’re removing a 50-year-old minibike flywheel. Tom held it from spinning with a screwdriver while Laura broke the bolt loose. The flywheel on the Clinton also acts as a cooling element, and it houses the points ignition.

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Finally getting the engine apart was when a lot of the theory started making sense to Laura. “Seeing the parts move, that made it way easier to visualize what you guys had been talking about with the four-stroke cycle and valves and timing.”

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For some of the more complex tasks,  Tom asked Laura to disassemble, reassemble, and disassemble again. Often the first time you go through an action, you aren’t really absorbing it, just trying to not screw it up. “The first time I did the keepers on the valves, it took me 40 minutes,” Laura said. “I was wondering if either of you were ever going to step in and do it for me, but you didn’t, and the second time it literally took less than a minute.”

Something that new mechanics are often surprised by is the importance of cleanliness. “You see parts covered in oil, so you feel like dirt doesn’t matter,” Laura said. “I hadn’t given any thought to cleaning all the parts. I never knew how thorough to be.” Tom’s rule: “If you think it’s clean enough, do it one more time.”

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Someone is getting tired of cleaning. Cylinder walls shouldn’t be scrubbed with harsh abrasives. A soft, oiled cloth will pick up the minuscule metal fragments from inside the bore.

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Test the rings to make sure the size is right. You don’t want to see the ring ends butt up against each other because there won’t be room for expansion when the running engine heats up.

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Fun with tiny tools.  We ordered a small ring compressor, but you could probably make one with a soda can and some hose clamps.

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At the beginning of our build we had to decide if we were going to paint the bike or leave the original finish. It had such cool decals on the engine and frame, so we decided to go with the patina.

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“I feel like this gave me just enough confidence to be dangerous.” – Laura Conrad

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Putting things back together always takes twice as long as taking things apart.

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Back together!  It looks the same as when we started, but it does run better.

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We borrowed a Chrysler Pacifica to take our bikes out for a test drive. One of the benefits of a minibike is that you don’t need a toy hauler or even a truck to move it around. A minivan full of minibikes is a super sleeper load of fun.

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“I was really excited  the first time it ran,” Laura said. “I made that happen!”

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