The larger of the two engine had a cylinder like a steam engine with a rod going through the back end of the cylinder through a packing gland. The rod had a flat thing on it that rode in a slot, the connecting rod was pinned on the end of the round rod. It appeared that the fuel and air mixture was drawn into the rear of cylinder on the compression stroke then transferred to the combustion chamber as the exhaust blow down ocurred, an early form of two stroke.