The Shay locomotive was the most popular and best-known type of geared locomotive. They were built to the patents of Ephraim Shay, who can be fairly credited with the invention of the concept of a geared steam locomotive. Although Ephraim Shay's early locomotives didn't follow the exact pattern of the later ones, they followed a continual line of development.
The vast majority of Shays were built by the Lima Locomotive Works of Lima, OH, although Shay patent locomotives were also built by the Michigan Machine Works in Cadillac, MI in small numbers.
The vast majority of Shay locomotives featured a regular locomotive boiler mounted conventionally, except for being offset to one side -- generally to the engineer's left. On the other (conventionally, right) side were mounted two or three cylinders, vertically, driving a longitudinal driveshaft mounted at axle height. This connected via universal joints and sliding joints to bevel gears attached to the ends of the axles of swivelling trucks. In the Shay design, every driven axle was driven from the driveshaft, there were no siderods.
Shay locomotives were built in all sizes, from small ten-ton locomotives to almost 200 ton giants. They were divided into four general classes:
- Class A: two cylinders, two trucks. Weights between 10 and 20 tons approx.
- Class B: three cylinders, two trucks. Weights between 24 and 60 tons approx.
- Class C: three cylinders, three trucks. Weights between 70 and 125 tons approx.
- Class D: three cylinders, four trucks. Weights of 150 tons plus.
Few Class D shays were built; they were no more powerful than Class C, just with a greater fuel and water capacity and a better factor of adhesion.
Approximately 2770 Shay locomotives were built; the first production example in 1878, the last for the Western Maryland Railway in 1945. This last built Shay still exists on the Cass Scenic Railroad; one of the largest Shays built, this 162 ton Class C monster had only five years of service when it was retired and placed in the Baltimore & Ohio Museum. In 1981 it was removed from static display, in exchange for a smaller Shay and a Porter locomotive, and placed in service on the Cass Scenic Railroad -- it has now served in tourist and enthusiast service for longer than it did for its original owners. It's still in practically brand new condition.
Shay locomotives were often known as sidewinders or stemwinders on account of their side-mounted driveshafts. Most were built for use in the United States, but examples also ended up in Canada, Mexico, South America and both Australia and New Zealand, among others.
Facts checked on ShayLocomotives.com and at the Geared Steam Locomotive Works at http://www.trainweb.org/gearedsteam/