This is our largest and heaviest engine by some margin. It has a Stainless steel hot end, with a brass cold end. Twin flywheels at the rear provide plenty of momentum to smooth out the piston forces. It is a beta style engine with the displacer piston gland stem passing through the power piston. The e.g. the power and displacer piston are on the same axis but with different phases (move out of sync by 90 degrees).