From GEM: This month's engine has a crank case of aluminum which follows a square configuration. All parts are from bar stock. The 3 ounce copper gas tank is in the base, the crankshaft is 5/16th with a 1" stroke, the connecting rod is square brass, the piston is cast iron and ground and lopped to fit the receiver which is of two pieces and made of pressure die steel. The head is of cast iron, the valves are in sleeves pressed into the head. The valves are of stainless. The exhaust muffler is of brass and etched square. The configuration of the carburetor is square and made of brass and contains a check valve. There are two pairs of helical gears to make up the side shaft configuration. Another pair of 2 to 1 gears runs the fly cubed governor by which a catch system holds open the exhaust valve to govern the speed, This is called Hit & Miss. The little fan on the side keeps this engine very very cool. Cecil Heyn was a aerospace tool and die maker.