Hercules Engine News

Including Economy, Arco, Jaeger & Thermoil

| April/May 1993

  • 1921 Sears catalog

  • 9 HP Hercules Oil Engine

  • Boos Oil Engine

  • 1921 Sears catalog
  • 9 HP Hercules Oil Engine
  • Boos Oil Engine

20601 Old State Road, Haubstadt, Indiana 47639

Beginning with the fall 1921 Sears catalog, slightly modified and re-rated Thermoils were offered. They were the model UA now rated at 7 and 9 HP; however, there were no changes in the bore, stroke or engine speed from previous U models. There were only three noticeable changes. The combination oiler and fuel previously attached to the rear of the water hopper was gone. They now had the common drip oiler down through the water hopper opening. The redesigned fuel pump was now relocated to a position under the head and operated by a valve push rod. The fuel fill was relocated from a tube up the back of the water hopper to a more typical Hercules shaped spout located at the front of the engine base. A cross section of this engine is shown at bottom left.

Other brands similar to the 7 and 9 HP UA Thermoil were the Boos Oil Engine and the Hercules Oil Engine. Their serial numbers fall in line with that of the Thermoils. From serial number data collected so far, it would appear that about 1500 of this model were built. Currently, at least 20 are known to exist.

A February 1, 1929 Hercules wholesale price list shows the 7 and 9 HP Hercules Oil Engine at $237.50 and $332.50 plus shipping. Included was a plain pulley and a 24 hour oiling system. Such an engine is shown (bottom left), along with a portion of the price list (right). They were used primarily in continuous pumping operations. The UA Thermoils were last shown in the Sears catalog in the fall of 1925 with the 24 hour oiling system being an option,. Next, we'll back up to 'The Cummins Connection'.


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