I built a small model steam engine in 1958 – ¾" bore and stroke – mine was a 90 degree V twin double action. That is the steam (I actually used compressed air) supplied power on both the up and down stroke. Because high pressure tended to lift the cylinders off the base plate, it didn’t have much power, but it was mostly self starting and the kids had a lot of fun with it. Like my Allen model gas outboard, one day it just disappeared. . . 🙄
