Ya know Deacon, there used to be plans for converting a Ford Air Conditioner
compressor to a steam engine available thru Popular Mechanics or the old Mechanics Illustrated. A buddy of mine was a machinist and always wanting to
build a small steam powered boat to go fishing in. I'm guessing it would weigh between 10 and 15 pounds but he was telling me something about having to make a different cylinder head for the compressor out of aluminum. He was telling me it wouldn't be much of a job to do.
Then a boiler would have to be built and I've long looked at those Bevrage Companies Co2 cylinders that go to the scrap yard after so many months of service. If you knew someone that could get you one of those then building the fire box around the bottom, finding a small water tank, and then some gages, valves and controls voila !
I'd say it would be a dream to ride in the winter with some saddle baskets on the rear wheel filled with coal or hard wood chips. But we're only talking a few pounds of low pressure steam here.
Just looing at the Dampffahrrad I'd say that Boiler housing has a copper tubing boiler in it and perhaps a smaller superheater toward the top (like a second stage coil to extract the last bit of heat for the steam making process) built in that Co2 tank. (the bottom would be cut off and the top
opened up for a smoke stack like in the photo)
One thing about steam my buddy told me......it's pure force. So if you are chain driven you're goinna have plenty of torque to drive ya. He was telling me the first Robert Fulton steam ships had copper boilers and tubing in them
so I'm sure the small micro boiler could run a bike with impressive results.
If ya had good luck with this.......ya may want to consider making a charcoal
production kiln in the back yard. This could make the argument for a side car full of charcoal fuel. But when others park their motorbikes for the cold winter months......you'd have your own pleasant climate on that steamer. (not to mention riding by the gas stations and waving to everyone)