Abstract: A compact six-cylinder, double-acting hot gas engine having a single central combustion chamber with the cylinders arranged in two groups of three and clustered around the combustion chamber axis at equal angular intervals. The engine has two crank shafts, one per group of three cylinders, rotating in the same direction and synchronized. Each crank shaft has three cranks with adjacent cranks angularly displaced 60 degrees. Each of the cranks of one crank shaft is directed oppositely to a respective one of the cranks of the other crank shaft.

Abstract: Hot gas engine units of the type having four parallel cylinders arranged in two parallel rows of two cylinders per row may be effectively balanced by a minimum of counterweight masses. The engine pistons are connected to two parallel crank shafts and four primary counterweights are positioned on the crankshafts each diametrically opposite a respective crank. The crankshafts engage a common gear wheel rotating opposite to but at the same angular speed as the two crank shafts, and the gear wheel is mounted on a third shaft parallel to the two crank shafts. Secondary counterweights including at least two axially spaced, oppositely directed secondary counterweights positioned on the third shaft are used to cancel the moment about the engine vertical axis produced by the primary counterweights.

Abstract: Hot gas engine units of the type having parallel cylinders in two parallel rows and containing pistons connected to two parallel crank shafts engaging a common third output shaft are juxtaposed into an assemblage of four such units. The output shaft is common to all four units and each of four crank shafts is connected to pistons in cylinders of adjacent rows of neighboring units. In such assemblage the total number of crank shafts in four units is reduced from eight to four and one output shaft will replace four output shafts.