The Heisler locomotive was the last variant of the three major types of geared steam locomotive, Charles L. Heisler receiving a patent for the design in 1892 following the construction of a prototype in 1891.[1] Somewhat similar to a Climax locomotive, Heisler's design featured two cylinders canted inwards at a 45-degree angle to form a 'vee-twin' arrangement. Power then went to a longitudinal drive shaft in the center of the frame that drove the outboard axle on each powered truck through bevel gears in an enclosed gearcase riding on the axle between the truck frames. The inboard axle on each truck was then driven from the outboard one by external side (connecting) rods.
In 1897, Heisler received a patent on a three-truck locomotive.[2] As with Class C Shay locomotives, the tender rode on the third truck. Unlike the Shay, Heisler's design did not have a continuous string of line shafting running the length of the engine. Instead, the tender truck was driven by a line shaft above the shaft driving the main engine trucks, connected to it through spur gears. This patent also covered use of a 4-cylinder 'vee four' cylinder configuration.
The Heisler was the fastest of the geared steam locomotive designs, and yet was still claimed by its manufacturer to have the same low speed hauling ability.
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The first Heislers were built by the Dunkirk Engineering Company of Dunkirk, New York, at the time producer of their own design of geared locomotive (called the dunkirk), of which the Heisler could be considered an improvement. They did not adopt the Heisler design, but in 1894 the Stearns Manufacturing Company of Erie, Pennsylvania started to produce Heislers, and did so until 1904. Reorganised as the Heisler Locomotive Works in 1907, it produced locomotives of the Heisler design until 1941.
Heislers were produced mostly in two and three truck variants in sizes ranging from 17 tons to 95 tons. There was one single truck, narrow gauge Heisler built, Lake Shore Stone Products Co. #7.
Roughly 625 Heislers were produced, of which some 35 still exist. Approximately eight of these survivors are currently operational. A 75 ton 1918 Heisler locomotive is on static display at the Travel Town open air museum in Los Angeles. Ex-Curtiss Lumber Company loco number 2 operates on the Oregon Coast Scenic Railroad during the tourist season. And the 3-truck 90 ton West Fork Logging Co #91 operates on the Mt. Rainier Scenic Railroad in Elbe Washington, who also have a 78 ton 3 truck on static display. Cass Scenic Railroad State Park in Cass, West Virginia operates a 90 ton, 3 truck Heisler built in 1929. Another Heisler two truck locomotive can be found on static display next to the headquarter's building of the former Pacific Lumber Co. in Scotia California. Heisler serial number 1260 built in 1912 (2 truck) is currently running on the Silver Creek and Stephenson historical railroad in Freeport, IL.
The Heisler locomotive's gearing was inside the frame and thus protected, unlike that of a Shay locomotive. However, the Heisler's drive shaft, which was located in the center of the frame, limited firebox space.