The Aermotor Pumping Engine

When wind was absent, this engine got the job done.

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by Glenn Thompson ED.D.
The Aermotor’s relatively light flywheel and small gas tank limit running time.

The Aermotor Windmill Co. has continuously manufactured windmills since 1888 and its products are a common sight in the U.S. — especially in the Midwest. Although many people are familiar with Aermotor windmills, few are aware that the firm also manufactured gasoline engines from early 1900 into the 1940s. These included general-purpose engines and engines specifically designed to pump water. The original design for the engines is attributed to the founder of the Aermotor Company, LaVerne Noyes.

For over 100 years, Aermotor windmills have been based on a rather simple design. The wheel (fan) is mounted at the top of a tower where it is exposed to strong and consistent wind currents. Steel blades (sails) are set at an angle on the wheel and when the wind catches them, the blades cause the wheel to turn. The hub of the wheel is attached to gears and these cause a long rod, known as the sucker rod, to move up and down. The sucker rod goes down to ground level and continues inside the well casing. Near the bottom of the well, the sucker rod is attached to a plunger that moves up and down inside a cylinder. During an up-stroke, seals on the plunger and a check valve (foot valve) at the bottom of the cylinder trap water inside the cylinder and force it up through a pipe to ground level. If there is no windmill or during periods without wind, a pumping engine can be attached to the sucker rod to bring water to the surface.

LaVerne Noyes patented the engine for the Aermotor pumping engine in 1909. The engine soon became popular and sold well. It was priced at $58 with battery ignition and $64 with a magneto. Although the engine was only rated for 1hp, back-driven gears increased the torque considerably, and the engine was able to remain cool while moving long sucker rods up and down for an extended period. The sucker rod could be attached to the final gear in three different places to produce three different lengths of strokes.

When shopping for an Aermotor pumping engine, customers could choose from three cast-iron bases that were intended be mounted on a substantial platform over a well. An optional auxiliary pulley could be mounted on the engine so the engine could be disconnected from the sucker rod and used as a general-purpose engine.

Engine operation

The Aermotor pumping engine was sold with a small gas tank. This was because many owners put in a limited amount of fuel so the engine would run for a predetermined length of time and shut off automatically. It would then not need any further attention.

The Aermotor pumping engine is an air-cooled hit-and-miss engine with a 3-inch bore and a 3-1/2-inch stroke. Gasoline from the fuel tank goes to a spray nozzle in the mixer where the amount of fuel injected is regulated by a needle and seat. There is no air filter. The intake valve is known as an atmospheric valve because it is spring-loaded to keep it shut until suction caused by the piston moving within the cylinder during the intake stroke causes it to open and admit the air/fuel mixture.

The exhaust valve is operated by a rocker arm and is either held open by the governor to reduce the speed or allowed to close to permit an ignition stroke and increase the speed. The Aermotor engine is unusual because it is based on an 8-cycle design. Piston strokes include intake, compression, ignition, exhaust, breathe, exhaust, breathe, exhaust. Additional breathe and exhaust strokes are added to reduce the speed. Fuel is only taken in during the intake stroke. An optional camshaft was available to convert the engine to 4-cycle operation so that it could handle the heavier load of an unusually long sucker rod in a deep well. The 8-cycle design of the Aermotor allows the cylinder to remain cool without a water hopper or a fan. Unusually large cooling fins on the cylinder assist in cooling the engine.

Coil and battery ignition

Ignition is based on the use of a coil and a battery. The same rocker arm that controls the exhaust valve also controls ignition. There is no spark plug. A pair of “make and break” points inside the combustion chamber close during the compression stroke; this causes a charge to build up in the coil. When the points are released, just before the piston reaches top dead center, a spark is created and this ignites the air/fuel mixture. A Webster magneto was also an option.

Accumulator, not collector

Allen Becker of Boerne, Texas, hails from a family of accumulators. His father filled over a dozen buildings with interesting items during his lifetime, and Allen’s wife was an antique dealer. Allen doesn’t consider himself to be a collector because that implies he has a plan and looks for specific items. Allen simply acquires things when he stumbles across them and thinks they are interesting.
There’s an old saying that “It isn’t what you know, but who you know,” and that is the reason that he wound up with his Aermotor pumping engine. In the early 1970s, he had a friend named Wimberley who enjoyed attending auctions and garage sales. He would purchase things and then sell them later to people who were interested. Mr. Wimberley spotted the Aermotor engine on a farm near San Marcos, Texas, and knowing that Allen had several old engines he contacted him and arranged to meet him at the farm. Allen was able to buy the engine from the owner for $50. According to a standing arrangement that Wimberley had with Allen, his finder’s fee was a hamburger with fries and a tank of gas for his pickup.

Allen believes his Aermotor engine is an early model built some time during the period of 1908 to 1910. This opinion is based on the presence of the “dogbone” governor only found on early models. There is no evidence that the engine ever had a brass tag. The only record of production are the letters NREI stamped into the top of the camshaft housing. The engine is rated at 1 horsepower. The single 1-1/4-inch-by-20-inch diameter flywheel is surprisingly light, confirming that the required torque is achieved through the back-driven gears. A lever extends from the back of the engine to the front to control ignition and to hold the exhaust valve open during exhaust and breathe strokes of the piston. The movement of the lever is controlled by a cam mounted on the camshaft. The “dogbone” governor consists of two opposing weights mounted on the camshaft, which move in and out by centrifugal force and which act on the cam. To increase the speed of the engine, the weights pivot out and allow the exhaust valve to close; to slow down the engine, the weights pivot in and hold the exhaust valve open for additional exhaust and breathe strokes.
Allen’s Aermotor engine is mounted on an aftermarket base made of angle iron and pipe. The engine runs with a homemade coil. The relatively light weight of the engine has made it an appealing choice to take to shows.

Glenn Thompson is a retired university professor. He and his wife live on acreage in the Texas Hill Country where they maintain a wildlife management program. Much to his wife’s chagrin, Glenn has a cherished collection of some three dozen riding lawnmowers, garden tractors, and compact tractors cluttering up the place. He can be reached at 830-997-5738 or

A special thanks to Allen Becker for contributing his knowledge to this article.

Sources: A History We’re Proud Of,; Aermotor Gas Engines, Gas Engine Magazine, November/December 1989; Herd, Tom, July 23, 2015, Aermotor 8-Cycle Engine Questions, Smokstak Antique Engine Forum; How A Windmill Pumps Water,; Matthews, Harry, Aermotor Windmill Engine, Harry’s Old Engine,; Meincke, Mark, The Complete Guide to Stationary Gas Engines, 1996; Windmills on the American Plains, U.S. National Park Service, May 10, 2019; US Patent 936,558, Directory of American Tool and Machinery Patents; Vossler, Bill, An Appreciation for Aermotor, Farm Collector Magazine, August 2020; Wendel, C.H., American Gasoline Engines, 1994.

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