The Walter Minor is a family of four- and six-cylinder inverted inline air-cooled engines, developed under auspices of ing. Šimůnek and used on light aircraft. First produced in 1929, the Minor engines' family has an advanced design for the period and sports steel cylinders, aluminum heads and overhead valves, with identical bore and stroke of 105mm and 115mm, respectively. Typical power ratings varied from .[1]
After Walter concentrated on the turbine powerplants only, the production of piston engines has been transferred to the Avia company that further developed the family, bringing fuel injection, as the Avia M-137 and M-337. Nowadays the smallest of the family, the four-cylinder carburetted Minor, is produced by a small company in the Czech Republic, while the M337 was available from the LOM Prague.
Data from: Oldengine.org [2]