Here’s a link to a project by a guy with perhaps too much time on his hands. Far from practical, but certainly interesting.
Very interesting. Practical, probably not, but steam is an interesting technology for a two-wheeled vehicle. Not the least because it doesn’t require a transmission or other means of changing drive ratios.
Anyway, steam is a very powerful technology. If you’ve ever seen video of Jay Leno driving one of his steam cars, you know what I mean. I’m keeping my fingers crossed for a yet-undiscovered fuel that could cause steam power to make a comeback.
Fascinating. Two things intrigue me in particular:
1 - He used the original cylinder, and
2 - the location of the exhaust, which seems to jet out about where a person’s foot would be. Check the photo of his wife on the bike.
I agree with the last poster that steam is an underrated technology. In fact, if you consider that a steam car can run on pretty much anything that will burn, it kinda makes you wonder why gasoline engines, with their (comparatively) specialized fuel caught on. I’m sure there’s some kind of economic or technological explanation. In fact, this almost seems Cecil-worthy.
The location of the exhaust makes sense to me. Normally on a 2stroke engine, the fuel/air mix comes in the crankcase and leaves through the head. On this setup, the steam comes in through the head, so it leaves through the crankcase.
IMHO, gas is more popular than steam because you can go out to your car, start the engine and leave within minutes. If you had a steam car, you’d have to start the boiler and wait to build a head of steam before you could go anywhere.
Why wait for one we haven’t discovered yet; there’s a mountain of hot nuclear waste we could probably use for this purpose.
No need for a comeback: steam plants are much the most efficient way to generate electricity from coal and nuclear fuel.
But it’s quite challenging to make a compact inexpensive lightweight efficient steam engine such as would be suitable for an automobile. One big problem is that efficiency pretty much goes out the window without a condenser. And when (as in a car) heat must be rejected to air, the condenser must be large (which tends to mean heavy and expensive).
One of these days I’m going to build myself a steam powered motorcycle just for the hell of it. In the meantime, here’s an article on a guy who converted his Harley to run on steam. A steam motorcycle built back in the 1930s. This gentleman built a steam powered bicycle and car before he died.
I want a steam-powered moped. I’ll park it next to my jet-propelled Volkswagen. 
So this is yours!
Here is a better looking but less practical steam-assisted bicycle. It’s just a publicity stunt and it says you can barely feel the power from the steam engine.