300 HP Miller, manufactured by the Miller Improved Gas Engine Co., on display at the Coolspring Power Museum.
Manufacturer: Miller Improved Gas Engine Co., Springfield, OH
Serial Number: 1326
Weight: 70,000 lb.
Ignition: Dual spark plug with magneto and battery & coil
This engine is known as a Model 3 Open, which is descriptive of its size and layout. It features a quad-opposed style in the “H” design with one center flywheel. There is a center crankshaft with two cylinders extending forward and two cylinders extending aft, all working on a common crankshaft producing the 4-cylinder effect. “To our knowledge it is the only Miller of this design to have survived, and perhaps the only quad-opposed from any manufacturer to be running in this country,” Paul Harvey says.
There is a cam box located on each end of the engine between the two cylinders. The intake valves are horizontal to the cylinder heads and the exhaust valves are vertical, operated by a pushrod that comes up out of the cam box at an angle and pushes a roller against a ramp, which produces movement that causes the valve stem to rise. “The engine’s equipped with Watts-type balanced exhaust valves, meaning that the force needed to open the valve is constant whether the engine is under light load or full load,” Clark Colby says. “That’s accomplished by having the valve stem pass down through the combustion chamber and seating on the top of the mushroom head of the valve rather than underneath like you would expect.”
Read more about this engine and 38 others in “Coolspring,” published by Gas Engine Magazine.
Contact the Coolspring Power Museum at PO Box 19, Coolspring, PA 15730 • (814) 649-6883 • Coolspring Power Museum website