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Circa-1920 Aermotor 2-1/2 hp General Purpose Engine

Dierre and Becky Smith rescue an Aermotor General Purpose engine from a nearby estate sale.

| August/September 2018

  • Dierre and Becky Smith's circa-1920 2-1/2 hp General Purpose Aermotor. Complete and original, it was found at a Texas estate sale.
    Photo by Glenn Thompson
  • The timing gear is just visible behind the flywheel at left. The governor weight (visible at 2 o'clock) is easily adjusted by changing its position on the shaft to alter the engine's cut-out speed.
    Photo by Glenn Thompson
  • Aermotor used its own alphanumeric serial number system, this engine showing serial number 1117.K.
    Photo by Glenn Thompson
  • The original battery box came with the engine.
    Photo by Glenn Thompson
  • The gas tank on the Smiths' Aermotor was most likely fabricated to suit the cart.
    Photo by Glenn Thompson
  • Dierre Smith holds the engine's starting handle, which was still with the engine when he purchased it.
    Photo by Glenn Thompson
  • The Aermotor's mixer features a choke to aid starting. Raising the rod and pushing it sideways keeps the choke closed.
    Photo by Glenn Thompson
  • A close-up view of the flywheel weight for the governor to control engine speed.
    Photo by Glenn Thompson
  • A close-up view of the flywheel weight for the governor to control engine speed.
    Photo by Glenn Thompson
  • A closer view of the cylinder head showing the rocker arm for the exhaust valve and the atmospheric intake.
    Photo by Glenn Thompson
  • The grease cup for the connecting rod at the crankshaft (right). It may be greasy, but the Aermotor runs well.
    Photo by Glenn Thompson
  • Proud owner Dierre Smith with his all original circa-1920 2-1/2 hp Aermotor. Note the original battery box on the ground.
    Photo by Glenn Thompson

Circa-1920 Aermotor 2-1/2 hp General Purpose Engine

Manufacturer: Aermotor Co., Chicago, Ill.
Year: Circa 1920
Serial Number: 1117.K
Horsepower: 2-1/2 @ 400rpm
Bore & stroke: 4-1/8in x 6in
Flywheels: 24in
Pulley: 8in x 6-1/2in
Ignition: Igniter w/battery and coil
Governing: Hit-and-miss
Cooling: Water w/fluted hopper
Weight : 600lb (approx.)
Price: $115 (1920)

Rural residents of the Texas Hill Country often get their weekly paper a day later than their neighbors living in town, so when Dierre Smith and his wife, Becky, looked at the paper that they just pulled out of the mailbox, they were dismayed to read that an estate sale was already underway to liquidate the worldly possessions of a couple who had lived on a nearby ranch. Dierre and Becky went to the sale as soon as they could, but many of the items had already been snapped up by eager buyers — especially the antique tools and implements that Dierre and Becky found most interesting.

Becky is especially interested in old boxes, and she was able to acquire a few wooden ones that appealed to her. When the Smiths inspected their new acquisitions after they arrived home, they found a cylindrical object in one of the boxes. At first glance, Dierre thought that it was a dry-cell battery that had been used in one of the old wall-mounted telephones. After closer inspection, however, he realized that it was actually the ignition coil from an old engine. Operating under the assumption that “Where there’s smoke, there’s fire,” Dierre and Becky hastily returned to the estate sale and inquired if there were any old engines for sale.

Lost and found

The woman in charge of the sale was the daughter of the previous owners, and she didn’t remember that there were any engines sitting around. But she did recall that there was “an old pump or something” sitting in one corner of the chicken coop and she invited the Smiths to take a look at it. As an afterthought, she mentioned that she thought her husband was interested in keeping whatever it was. When Dierre spotted the “old pump” his heart skipped a beat, because he instantly recognized the fluted hopper as the water hopper of an old Aermotor engine.

Becky and Dierre had for years been friends of the couple having the sale. Dierre knew where the husband worked, and he immediately drove there and offered as much for the engine as he felt that he could afford — plus a little more. The man indicated that he had been planning on restoring the engine, but just hadn’t gotten around to it. He said that he would think about Dierre’s offer for a few days.

Dierre counted down the hours and the minutes during the next few days and then contacted the owner of the engine. The man said that although he was interested in the engine, realistically he probably would never get around to restoring it, so he agreed to sell it. Without further hesitation, money changed hands and the deal was completed.


The Aermotor is well known as the company that has made windmills since 1888 (they’re still in business:, but fewer people remember that from the early 1900s into the 1940s the company also made gasoline engines. These included general purpose engines, such as the one Dierre acquired, and both small and large engines specifically designed to pump water. The engines were based on a design by La Verne W. Noyes, the founder of Aermotor Co., Chicago, Illinois.


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