Aermotor Engine

The Aermotor Company began manufacturing windmills in 1888 in Chicago, Illinois. The windmills were well built and the company prospered.

The Aermotor Company produced gasoline engines for pumping water from 1906 into the 1940's. The engines were based on a design by the company founder, LaVerne W. Noyes. One of their distinctive features was that they had open, galvanized-steel water hoppers which were fluted to provide large radiating surfaces to dissipate heat rapidly. The engines were available in two sizes--2 1/2 HP and 5 HP. They were typical of other early engines in that they incorporated a hit-or-miss design. The exhaust valve was mechanically operated by a valve-rocker lever and was held open or released by the governor to regulate the speed. Only the exhaust valve was activated by a cam; the intake valve (atmospheric valve) was sucked open by the vacuum produced by the piston descending within the cylinder and this allowed ambient air to rush in. Beginning in 1908, the governor ran off of the camshaft; this was discontinued in 1910.

An Aermotor engine did not have a spark plug; instead, it had make-and-break points within the combustion chamber. The points were closed during the time that a charge was building in a coil; at ignition, the points would separate and a spark would flash from one contact to the other. The linkage which operated the exhaust valve also tripped the ignitor at the appropriate time--which was slightly before top dead-center of the combustion stroke. Electricity for ignition was provided by either a magneto or a battery.

Aermotor EngineMost Aermotor engines were substantial; the 2 1/2 HP and 5 HP engines weighed 600 pounds and 1,000 pounds, respectively. The 2 1/2 HP engine had a 3 1/2 inch bore and operated at 400 RPM. The 5 HP engine had a 5 inch bore and a 7 1/2 inch stroke; it's twin 30 inch flywheels each weighted 150 pounds. Early engines had magnetos; later engines were available with either magneto or battery ignition systems. In 1920, the 2 1/2 HP engine sold for $115 and the 5 HP engine sold for $165. An engine equipped with battery ignition was slightly cheaper; for example, the price of a 5 HP engine with battery ignition was $155 instead of $165.

The main bearings were lubricated with grease cups. Other areas requiring lubrication had oil-wick slots or pipes containing wicking soaked with oil. During the production history of the engine, colors included dark green, burgundy, universal gray and bright red.

Aermotor engines were unique in that they were 8-cycle; they fired once every four revolutions.The cycles included intake, compression, fire, exhaust, breathe, exhaust, breath, exhaust--plus additional breathe and exhaust strokes as needed to govern the speed. Gasoline was taken in during the intake stroke, but only if the exhaust valve was closed. During the extra strokes, the engines would breathe through the muffler and the open exhaust valve. Because of the 8-cycle design, the engines ran cool and did not need cooling fans. Optional camshafts were available to convert the engines to 4-cyle operation, if desired. Later large pumping engines were cooled with well water.

Another unique feature of  Aermotor engines was that they had small fuel tanks mounted directly on their carburators.  This allowed a farmer or a rancher to add only the amount of gasoline necessary to run an engine long enough to fill a water tank. The operator could start the engine and walk away and the engine would run unattended until the water tank was full and then shut itself off.

A small pumping engine sold during the early 1900's was unique in that the engine was an integral part of a mechanism which incorporated gears to dramatically increase the torque to the point where the small engine was able to move a long and heavy sucker rod up and down in a well and push water up a pipe.  The sucker rod and pipe extended through the base down into the well to a pumping cylinder and foot valve below the water level. The engine and pump with a cast-iron base cost $64 with a magneto and $58 with battery ignition. This engine and pump was especially suited to cold climates and for pumping water long distances. An optional pulley allowed the engine to be used for other purposes. Although this pumping engine was popular and many were sold, they are rare today.  

The Aermotor Windmill Company continues to make and sell windmills; its manufacturing facility is now located in San Angelo, Texas. It is currently the only windmill manufacturer in the United States. Aermotor windmills are found all over the world. Additional information about the Aermotor Windmill Company may be found at