Trunnion Engine Bicycle:

by George Hebbert

Butane fired, slide valve, VFT boiler, single double acting engine.
Tom Kimmel with George Hebbert’s steam powered bicycle, homemade.

Engine pivot point is just an inch or two above the head, so it is not a true trunnion engine, but it is an oscillating engine in that it does not have a cross-head or connecting rod or wrist pin. The rod from the piston to the crankshaft, which is the rear wheel axle is very long to minimize the angular deflection. The engine frame is reinforced with four long tubes.

This shows the insulated helical coils that take the steam from the boiler to the steam chest. There is a small amount of flexing of this helical coiled tube, but not enough to cause metal fatigue.

This is the pedal operated water pump with the engine driven one on the other side—both trunnions and with copper helical coils to flex for the output. Clear plastic tubing for the water intake.


Engine driven main water pump on the right side.

Boiler is conventional copper with copper vertical fire tubes and a double pancake coiled economizer on top. Smoke stack is not shown. This is not my recommended steam generator nor my recommended fuel source, but it is a conventional historic design, and thus very functional.
The craftsmanship is excellent, also the packaging of the components. I would prefer a different fuel and a mono-tube steam generator for light weight and safety and different valves than “D” valves. However, the mechanicals—the engine design and the two pumps are excellent and unusual and well worth copying.