This is a salesman's sample demonstration sleeve valve engine model. The engine is made from a heavy lead type metal, it has a turning knob on the back to rotate the piston through it's working steps. The sleeves at the top of the piston move up & down with the piston to allow intake, compression, explode & exhaust. The action is described on a rotating dial at the lower left. This is a very complex model and only 4 1/4" high, but weighs over 1 1/4 lbs!