The design is by Mr A.Slack who built it to drive
a model tug boat and described it in M.E. 2-11-73.
The picture is of the copy that David built and
he also built a slightly larger version.
The displacer is driven by a curved connecting rod from a disc crank at the top of the near-vertical shaft behind the cylinder. The shaft is driven from the crankshaft by bevel gears.