Gnome Motor, with Revolving Cylinders
This illustration shows a Gnome motor with revolving cylinders and its many parts: Spark Plug; Conducting Wire from Collector Ring; Distributor Brush from Magneto; Electric Collector Ring; Fixed, Hollow Crankshaft; Connecting Rod; Piston; Revolving Crankcase; Tappet Cams (male and female); Exhaust Valve Tappet; Exhaust Valve; Intake Valve; Air-Cooled Cylinder. Gnome was the leading type of air cooled motor in the 1920s.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 5) (New York, NY: Thomas Nelson and Sons, 1917)