What ever you do, do not use a 12 hp chain saw engine! I did when I was a kid, and it darned near killed me. The bicycle was an old Huffy 26" boys bike. The old McCallough 2 stoke engine first tore out the rear hub and spokes from the rear wheel, then it threw the chain. ( nearly taking my leg with it ) It ripped up the bicycle rear sprocket,stripping off teeth twice.

Finally we used a 18" motorcycle rear wheel set up. [required a lot of wielding and fab work to make it fit.] Once the suicide machine was able to finally to run down the road, the brakes proved to be not up to the job, and I ended up in a ravine about 15 feet deep. Split my lip open too. Replaced the brake linings and fabricated a foot pedal, discarding the hand lever.

Then it burned out the clutch. Replaced that with a new unit. Now it would burn rubber, and take off like a rocket. At high speeds on the street, the front end wobbled and violently shook, making it very hard to control. Changing handle bars didn't help any. The 26" front bicycle wheel and fork weren't up to the speeds or the power transfered from a 12 horse engine pushing it through corners and turns. We tried other wheel and tire sizes, only making the situation worse.

Then I dumped it, ruining the muffler, and banging up the fan shroud. Could not find another muffler. My dad made one out of some old vacuum sweeper chrome wand pipes and a pipe flange. It worked, but was so loud the neighbors complained, and called the cops. The cops came and gave me a ticket. The ticket cost my dad $25.00 for noise ordinance violation. ( he got a stiff warning that the bike was illegal to use on the street ) He rigged up a silencer to thread into the pipe end and it was some quieter, but not much.

Then Later, I spilled gasoline on the hot engine trying to refuel it, and it caught fire.

I kicked it over and ran for the garden hose. But, the gasoline pouring out of the gas tank, set the yard on fire, and finally the whole bike was in flames enough I couldn't get it out. { using water on burning oil and gasoline mixtures is not a good idea } The woman who lived next to us, saw the whole ugly event unfold, and called the fire department. They showed up and extinguished the blackened bike. I got a scolding, and my dad got a bill for $100.00 from the city.

I wanted to try to repair it,but, my dad had enough of it, and took a sledge hammer to the engine case, and cut the frame in half with a torch. The doomed power bike ended up curbside for city trash pick up. My Dad never built another engine powered bicycle again for me. This took place back in 1964. Again, do not use a chain saw engine on a bicycle! It is nothing but trouble!