1925 175 HP Otto

Coolspring Spotlight: A 1925 175 HP Otto engine on display at the Coolspring Power Museum.

1925 175 HP Otto

The 1925 175 HP Otto is likely the largest single-cylinder, conventional two-flywheel gas engine in the known collector’s world. 

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This display consists of a 175 HP Otto engine driving a Triplex 3-cylinder Worthington positive displacement water pump. These pieces of equipment have always been mated together and were installed in 1925 in the Brookville, Pa., water works, only 8 miles north of the Coolspring museum.

This engine includes a sideshaft that drives a governor and over and under exhaust and intake valves. The governor acts upon the stroke of the intake valve rocker arm, so it’s a throttling engine; it throttles by limiting the amount that the intake valve opens. It is air-started with a valve in the center of the cylinder head; a combustion air inlet and gas inlet form the mixer, which is where the engine gets its fuel. The exhaust comes out a water-cooled elbow.

The flywheel on the sideshaft is a normal flywheel, but the flywheel on the offside has a very wide rim, which drove a centrifugal pump that pumped water from a nearby creek into the treatment plant.

Read more about this engine and 38 others in the book, Coolspring, published by Gas Engine Magazine. Order it online at Gas Engine Magazine's store.