I thought you used the Gingery drawings. Thanks for the offer but I'll stick with my drawings. No sense in getting confused.I did not seal it at all. I used a different set of drawings and the cylinder is made from a solid piece of cast iron which dissipates the heat better. Ray Moye made his using the original Gingery and I don't think that he used any water either. He had his running for several runs of 30 minutes. I can send you my 2d drawings if you want to see what the differences are. Pivot points are different and the arms are quite a bit different.
Interesting engine and a clever use of Plaster of Paris. It reminded me of a job (when I had to work for a living) where we had to hold jet engine turbine blades after worn areas were built up with weld and needed remachining. We used to place them in a temporary holding fixture that located on a couple of critical points. The space around was then filled with Woods Metal, which melts in hot water but is solid at room temperature. When the machining was finished, the whole thing was dunked in hot water which melted the Woods metal that could be reused.Thanks to both of you. I saw the plaster of Paris idea in Home Shop Machinist (or similar). Works really well for CNC type jobs where work holding is a challenge. I use it as the need arises.