The Original Cummins Diesels

Thermoil engine

Aden L. Hawbaker, 85S6 Talhem Road, Chambersburg, PA 17201, with his Thermoil engine made by Cummins for Sears, about 1920; 2 HP.

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40646, Cummins Engine Company, Inc., 1000 Fifth Street, Columbus, Indiana 47201.

This article is reprinted from Cummins Clippings, magazine of Cummins Engine Company, Inc., Columbus, Indiana. Permission to reprint has been given by Ken Davidson, Editor. The article was brought in by Aden L. Hawbaker, 8586 Talhelm Road, Chambersburg, PA 17201, owner of a restored Thermoil engine.

The first Cummins diesels were known as Hvid type oil engines. They were built under a license granted by a Robert M. Hvid who owned the U.S. patents for the fuel and combustion system. During the years 1919 through 1922, Cummins built 1?, 3, 6 and 8 horsepower Hvid engines. All were single, horizontal-cylinder type.

Except for size, these engines were of the same design. The details are shown on the cross section that appears with this article.

The Cummins Hvid engines were compression ignition engines. We call them 'diesels' today. They had a precombustion chamber into which fuel was fed by gravity through metering valves controlled by the governor. The fuel was fed into the cup during the intake stroke. During compression, the fuel would heat up and partially vaporize. Then, when it reached ignition temperature, the vapor would explode and drive the main fuel charge with the cylinder.

Cummins never was able to resolve several problems with this fuel system. First, the ignition timing varied with fuel quality, air temperature, and other factors. Clessie Cummins' first diesel invention was a means to mechanically time the ignition. By lengthening the fuel valve, he sealed off the orifices between the cup and the cylinder until the proper time for ignition. This invention enabled Cummins to get six horsepower from an engine that was originally designed for five horsepower.

A second problem was rapid car-boning inside the pre-ignition chamber cup because of the precombustion of the fuel. After a few hours, the engine would lose power and the cup had to be cleaned. While this was easy to do, most people who bought the engines had neither the mechanical ability nor the inclination to clean the cups.

A third problem was that people had trouble starting the engines because they did not understand compression ignition. They tried to crank against compression, the same way they started gasoline engines then. Carl Hertel, Cummins Shop Superintendent, spent many weekends in the field teaching people how to use the compression release. One Saturday he went down to the Ohio River because they'd had a complaint.

'What the guy was doing,' he said, 'was cranking against compression. You know how they worked? You threw up the lever and pushed the valve in and you would get it spinning and then just take the crank off and throw the lever down and it would start. He just let the engine run. I went in there and shut it off. He said, 'Oh, you will never get it started. There is only one man on this river strong enough to start it.' I said, 'It's easy if you know how,' and went in and started it.'

The worst problem, at least the most dramatic, was that the fuel valves leaked, resulting in overflowing and overspeeding. Hertel told about going to Chicago to start one:

'This I will never forget because I went up there and started it for him. We were in there talking and left it running. We got over against a horse stall and the flywheel cut through the boards.'

These engines were among the smallest ever built and Cummins did not have manufacturing equipment capable of the necessary precision. The Hvid system worked pretty well on larger engines with bigger valves. Actually, Hvid engines-when properly adjusted-ran on a true diesel cycle. The Cummins engine operated best on kerosene, but advertising said that they could be run on old butter, fish oil, crude oil, and just about anything else that would flow and burn.

Cummins built and sold only 22 engines, all six horsepower, during 1919. Then they got into a real fiasco.

While Cummins was developing and going into production of the six horsepower engine, Sears Roebuck was having Hercules Engine Company of Evansville design a line of Hvid engines of 1? to 9 horsepower for sale to farmers through their mail-order catalog. When Hercules found that they could not produce all of the engines Sears wanted, they suggested that Sears contact Clessie Cummins. As a result, Cummins agreed to produce 4,500 of the 1? and 3 horsepower models-engines that hadn't yet been built and tested. Hercules built the larger sizes listed in the 1920 through 1923 catalogs.

Sectional view of Cummins oil engine.

Sears apparently was impressed with Clessie Cummins' ignition timing device because part of the deal was for Cummins to supply injectors for the six horsepower engines built for Sears by Hercules. We sold over $10,000 worth of six-horsepower injectors to Hercules in 1920.

Sears sold the engines as 'Thermoil' kerosene engines on terms of '$5 down-thirty days trial-ten months to pay.' The farmers took advantage of these terms. They bought the engines, used them for thirty days, returned them, and got their down payment returned. Sears then returned these engines to Cummins. Although most of the returns were runnable, they were all scrapped.

An original (1919) Hvid engine; 3 HP, 1 cylinder, 600 rpm.

Cummins' sales reached a peak of $25,000 in December, 1920, and then collapsed to less than $5,000 in February, 1921. Engines were returned faster than they were shipped. Returns actually amounted to more than 20% of sales. For the next four years, Cummins had little to sell. In some months sales were less than $100, mostly for contract machining jobs that came in.

Cummins really benefited from , this sad experience because they decided to develop a new fuel system independently of what other companies were doing. Hans L. Knudsen was hired as Chief Engineer, and it was largely through his work that a successful fuel system was ultimately developed.