The earliest cyclemotors made during the last century were steam powered, their popularity however dwindled with the introduction of the internal combustion engine. Some people still argue that with development the steam engine is still a viable alternative to the IC engine. The following article gives one view of the direction this development should take.
The secret behind designing a seccessful steam bicycle motor is in getting a well-designed flash boiler and controls. A high boiler pressure ensures the break up of water droplets and for the same reason, hairpin grids of tubes would be better than round coils. One problem likely to occur is overheating at low speeds. To combat this the use of a two-speed gear would be advisable. Gears are not usually used on a steam engine because its maximum torque is available at zero revs. However, the use of a low gear would ensure a full supply of feed water at low speeds.
The use of a slide valve would also be advisable, although this involves more friction than mushroom valves.
Slide valves are long lasting provided they have a good oil supply, a reasonable stem pressure (say 500psi) and care is taken to avoid excessive superheat.
Such an engine is basically a development of the Pearson-Cox engine used in many early motor cycles. Plans of such an engine can be found in a couple of articles in Model Engineer (21st April 1960 - 5th May 1960) on which this article is based. Those who say it can't be done may like to know that a Canadian produced several hundred steam cyclemotors in the 1970s. These had the engine driving the front wheel by a roller and were apparantly quite successful. Unfortunately I have no details about them - any help would be appreciated.
This article was first published in Buzzing, Volume 4, Number 2 in Summer 1985
