1935 Varcin

70 hp at 1700 rpm

Musée de l'air et de l'espace, Paris, France, Dec 2018

This engine is described as a "rack and pinion engine". The following page found on the Aircraft Engine Historical Society web page illustrates the internal structure of this engine. The two opposing pistons are directly connected. The partical pinion gear, which is attached to the propeller shaft, engages one rack of gear while moving one way, and he other rack while moving in the opposite direction. The partial cam "C" and the four bushing or rollers "G1" to "G4" insure proper alignment for the gear during the change over.

I think this engine has great potential of "junking up" the insides of the case. Can't call it a crankcase, since there is no crank.