An Engine for Every Engineer

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An inherent problem of the standard Cornish boiler proved to be insufficient grate area when used to burn fuels besides straw or coal. Long grate bars enabled these engines to burn long material (such as slabs), but these boilers lacked the deep firebox needed to burn bulky material, such as wood. On an engine that burned only straw, this would not have been a problem, but Gaar-Scott advertised these engines as being able to burn other materials after changing the fire grates.

To cope with this problem, in 1897 to 1898, Gaar-Scott phased out the Class K and L engines and replaced them with the Class P and Class M engines. These boilers were return-flue but had a deeper firebox more like that of a standard locomotive boiler. Besides retaining the large central fire flue for carrying most of the flue gases, Gaar-Scott used four to six additional 2-1/2-inch diameter flues to carry the initial pass of gases. Several 2-1/2-inch diameter flues were used for the return pass, the number varying with the size of the engine. The Class P was a simple, single-cylinder model, Class M a compound-cylinder model. After building its Class P and Class M engines for only a few years, Gaar-Scott phased these engines out between 1904 and 1905, replacing them with the firm's standard Universal boiler engines with a firebrick arch that could be added for burning straw.

Apparently, no examples of the older Cornish boilers have survived, but at least one complete Class P engine survives: a 22 HP model that sold at the Danny Roen auction in September 2004. The buyer, Robert Holp of Ohio, is currently giving this rare machine the careful restoration it deserves. There are also two incomplete models of return-flue Gaar-Scott engines in a Canadian collection.

Universal Boiler, Single-cylinder Engines

Gaar-Scott introduced its Universal, dry-bottom boilers (Table 3) in the early 1900s. These boilers were designed so a firebrick arch and a straw chute could be mounted to burn straw. The arch and straw chute could be removed and other fuels burned. These engines replaced the earlier return-flue engines as Gaar-Scott's straw burning models. The locomotive-style boiler was simpler to build than a return-flue boiler with an added firebox.

Class S included side-geared, simple-cylinder engines. At first, the Class S engines were built only with standard gearing and cast wheels. As steam plowing became more popular, Gaar-Scott began offering these engines with what were referred to as “Plowing Gear Features.” Plowing-gear engines sported larger diameter (6-foot 4-inch diameter vs. 5-foot 6-inch diameter) rear wheels, made of steel and with riveted cleats that could be replaced when worn. The gearing was made wider and stronger, and constructed of steel and semi-steel. Greater water carrying capacity was an important feature, and, in addition to the standard tank on top of the boiler, an extra tank was added to the operator's platform. Occasionally, engineers deemed this water capacity inadequate, and customers could special order an engine with a tank on the platform, the standard tank between the steam dome and smokestack, and another large tank in front of the smokestack.

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