M Williams’ 
SHAY LOCOMOTIVE 
IN 7.25” GAUGE

This impressive 7.25” gauge Shay locomotive was shown by M Williams at the 2016 Midlands Model Engineering Exhibition. Modelling Shays was popularised by Kozo Hiraoka with his design in 3.5” gauge of which many examples have been built round the world.

In the 1860s Ephraim Shay became a logger and wanted a better way to move logs than on snow sleds in winter. He built a tramway in 1875, on 2’ 2” gauge track on wooden ties. Greater effficiency was the result as he could log all year round.

Two years later he invented the Shay Locomotive and developed the idea of having an engine sit on a flat car with a boiler, gears, and trucks that could pivot. The first Shay had two cylinders and the front truck was mounted normally while the rear truck was fixed to the frame and could not swivel, like normal drivers on a locomotive.  Shay experimented first with a chain drive from the engine through the floor to the truck axle but the chain drive was not practical and he changed to a belt drive. It soon became popular. Shay patented the basic idea in 1881 and an improved geared truck in 1901.

Shay locomotives had normal fire-tube boilers offset to the left to provide space for, and counterbalance the weight of, a two or three cylinder motor mounted vertically on the right with longitudinal drive shafts extending fore and aft from the crankshaft at wheel axle height. The shafts had universal joints and square sliding prismatic joints to accommodate the swiveling trucks. Each axle was driven by a separate bevel gear.

The advantage of these engines was that all wheels, including in some engines those under the tender, are driven. A high ratio of piston strokes to wheel revolutions allowed them to run with partial slip.

Shay locomotives were often known as sidewinders or stemwinders . Most were built for use in the United States, but many were exported, either by the manufacturer, Lima, or after they became redundant in the US. More than 100 survive today.

PHOTOGRAPHY BY JOHN ARROWSMITH.