In article .com,
wrote:

because of the high proce of gas, would putting a motor on a bicycle be
practicle to get to work a few days a week? I live about 18 miles away
it is all highway with a wide berm for bicycles. I have a spare 5 horse
motor from an old tiller. Could I mount a bracket and put it above my
back wheel to drive the back wheel on my 10 speed mountain bike? Would
I be able to pedal it home if the engine failed? How would I rig a
clutch of some sort or would I even need it? Seems like an interesting
project.

How fast could you go with a 5 horse motor?

The setup I saw once was a bicycle that was built for a disc brake in
the rear. Or, rather, the hub was built so. Then he made an adapter
plate to put a large chain wheel (like you see at the crank of the bike,
but bigger) on the disc brake mount, and mounted a chain saw on a
luggage rack above the rear wheel. The chain saw power head came with a
clutch, so revving up would propel the bike, and idling or cutting it
off would disengage automatically. The normal drive line was right
where it always was, so if the engine failed he could pedal normally.
I think he could go about 30mph tops, and the range on one tank
(under a quart) was enough to go however far he went in a day.
The engine spins up to 14,000 RPM, so it was a big reduction from the
engine to the chain ring. The downside is that it's loud and even with
his reduction the engine had to stay below 14,000 RPM most of the time,
which caused carbon buildup. After one engine crapped out he got into
the habit of jacking up the rear wheel (put down kick-stand on concrete
and leaned the bike) and ran the engine at full throttle for a little
bit to help clean it up. Dunno if that even helped, though--I moved.
Personally, I'm working on my legs so I can pedal like hell without
wussing out like I do now. (:

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