[2005-04-11]

I have had the idea of building a minibike rattling around in my head (like the ball in a spraycan) for a couple years. Of course I wanted to build it from scratch, and scrounge up as many of the parts as possible, since I would not feel right spending good money on a minibike. Last summer I found an engine at The Black Hole, and the project began.

This engine I got was part of a water pump assembly that looked like it has inadvertantly been used as a submersible trash pump. I was able to smash the cast iron pump impeller off of it, and clean it up alittle bit, but of course it would not start right away. I took the head off and saw why - the combustion chamber was about helf full with rust flakes. It looks like this thing had sucked up quite a bit of water in it's day. Not to be easily defeated, I cleaned it up as best I could, rebuilt the carburetor, and finally got it running. I'm sure the compression is terrible, and the carburetor is almost completely shot, but at least it ran.

I got some neat knobby wheelbarrow wheels from Home Depot, and ordered the stuff I couldn't scrounge up from a go kart company. The new parts included a centrifugal cluch, a combination brake and sprocket assebly for the rear wheel, a chain, and a twist throttle. I also found a new Tecumseh carburetor on eBay.

I made a drawing of how I thought we should build the frame and fork, brought the welder and chopsaw over to Brian's house, and we got to work.

We built the frame out of some 7/8" thinwall steel that looks like it was once part of an old tent frame or awning or somehting. It is not the strongest stuff, but it should be just right for this project. I wanted the frame to be a bit longer than most minibikes to accomodate an adult rider, and decided on double top tubes to have a solid platform for the seat. My favorite part of the minibike is the fork. I used 1" thickwall steel and angle iron to build ghetto double-crown fork. Then to join it to the headset, I got 2 wheelbarrow wheel bearings from the hardware store. The bearings sit in the top and bottom of the headtube, and the fork is attached with a long 3/8" bolt that goes through 3/8" holes in the crowns of the fork. It works like a champ! The handlebars are just welded straight to the fork.

Astro (the Great Dane) was our constant companion during the minibike building.

Roofus too. Notice I didn't say "helper", I said "companion". As soon as dogs learn to fetch beers, animal shelters will become completely empty.

Dreaming of how sweet it will be to cruise this thing!

So we got the frame built, installed the engine (or motor as the NASCAR guys like to say), and decided to try to get it running. And I do mean "try". I'm not sure what happened since we first had the engine running, but it sure as hell won't start now. We got it running for about 20 seconds on pure starter fluid, and probably flooded it enough to completely wash away all the oil - and any hope of making compression. We went through about 5 battery charges turning it over with a cordless drill. So we gave up.

Ha! I almost forgot the best part of building this thing! We got it all set up, and ready to roll (if the motor had started) and went to crank it up with a power drill. And the drill spun the starter-side crankshaft bolt off. Hm - that's weird. Holy shit - we put the motor in backwards! This thing turns the other way! The motor is cooled with a little built-in rat cage style fan, and I'll damned if those things don;t look like they should turn the other way. So yeah, we had to take it out and turn it around. Bicycles are right-side drive (I assume because of the freewheel threads?) and motorcycles are left-side drive. I guess roto-tillers are probably left side drive too :)

This is not mirror-imaged - the motor is really installed backwards.

Fortunately my buddy Frank at The Black Hole had a brand new motor that he could be convinced to part with for $75. I love that place. If Ed doesn't have it, Frank probably does. Frank had the motor in his "shop" - a unistrut and stanless sheeting shed built onto the resr of the building and completely filled with tools, fragments of machinery, stuff that might be useful one day, and oil that has leaked out of stuff. He even has a little home made siren alarm system thathe has 30 seconds to disable after opening the door. I don't think he has ever made it in 30 seconds, so remember to plug your ears :) At least now we have a good motor for it. I really would have preferred not to buy a new motor, but oh well. At least it was a killer deal.

The very professional purpose-built shop

Trying to get the mixture right so it will start (man, I really am gonna go bald)

Notice that I am controlling the throttle by figertip. Watch out for the hot exhaust :)

Finally the minibike is fully functional

Hijinks ensue