c. 1910s to 1920s Associated 4 HP Engine

 This engine (serial #413204) was made by the Associated Manufacturers Company in Waterloo, Iowa. Initially called the "Farm Hand," the Associated 4 HP engine became the "Four Mule Team" portable engine in 1915. Weighing about 1,000 pounds, this engine was rated at 400 RPM. It cost $130 with the magneto. You can see a video of a "Four Mule Team" being started and run, including lots of close-ups of several moving parts, by clicking or touching here.
 The Associated Manufacturers Company was incorporated in 1910 when Iowa Dairy Separator Company merged with other Waterloo area firms. Initially organized in 1896 to make hand-operated cream separators, the Iowa Dairy Separator company began developing engines by 1909. In 1913, the Associated line of engines was in full production. In 1946, the company was sold to Hamilton Engineering Company.

Notes

C. H. Wendel. American Gasoline Engines Since 1872. Edited by George H. Dammann. Sarasota, FL: Crestline Publishing Co., 1983, p. 35.