Shay engines are steam powered
engines which use vertically aligned pistons on the side, which turn a
crank shaft with gears shafts attached to the wheels. They were
typically used for logging and mining operations where the curves
tended to be tighter, the grades steaper, and the track more
The pistons and crankshaft move, powered by a 9v technic motor.
While not obvious from the picture, the boiler is offset to the
side of the engine, so there is room for the steam cylinders on the
side - which is typical of real shay engines.
Since the engine needs power for the 9v motor, power comes from a tender which doubles as a tool and supply car.
A real shay engine located near Portland, Oregon.