Duryea Power Co. built a small engine with two horizontally-opposed cylinders giving only 2 hp at 1,200 rpm, under the direction of Canadian pioneer Rupert Turnbull around 1905.

-Shortly afterwards the 16 hp Duryea-Turnbull was built. This wasw a 4-stroke, liquid-cooled engine with simple ignition by small batteries.

-The intake valve opened automatically while the exhaust valve was driven.

-It had no crankcase or exhaust ducts.

-As Duryea, there appears an axial type engine (barrel?) from 1937, at the USNA, number 3307-452.8.

From Appendix 6: An open-crankcase engine was constructed by Duryea Power Co. This engine gave 16 hp  at 1000 rpm, and was designed by Turnbull. That is why it is sometimes known as Duryea - Turnbull.

-Now we have an image of this engine. At the time, it was the lightest in the world. This was in 1905.

“16 hp twincylinder” (PiP = pm)

-Because of the design it was possible to increase the number of cylinders by coupling sets of two opposed cylinders, so the 45 hp, 6-cylinder engine came out.

“The 6-cylinder Duryea” (PiP = pm)