The trucks and driveline of Shay locomotives were one of the keys to its success, and their most unique feature. All Shay wheels were drive wheels, driven by a series line shafts, square shafts and sleeve shafts with bevel gears on the line shafts turning the rim gears on the wheels.
Each Shay truck consisted of two wheel sets with rim gears attached directly to the right outside of each wheel. From the left side, these trucks looked almost like a common freight car truck.
On the right side of each truck was added a line shaft with a bevel gear over each wheel rim gear.
These line shafts were attached to square shafts through couplings. The square shafts slid into sleeve shafts, which were attached to the crankshaft through another set of couplings. The square shaft sliding freely in the sleeve shaft allowed the locomotive to take sharp curves. As the truck pivoted to follow the track curve, the distance between the crankshaft and the truck increased or decreased and the square shaft slid in or out while still rotating, delivering power to the truck from the pistons.
The reason Ephraim Shay invented his unique
engine was to haul lumber out of the woods all year. Before the Shay
locomotive, lumber was taken out mostly in winter on animal powered snow sleds.
When trains were put to use, track work was often temporary and at times steel rail was not even used. Logs were laid end to end in place of rails and special wheels were used on the shay trucks to accommodate the timber rails.
These wheels varied with larger flanges and extra wide tread surface. Some even had flanges on the inside and outside of the wheel so the wheel straddled the logs or timbers.
Another version of the Shay truck was built by Mr. Shay himself and not produced at the Lima shops.
Trucks from Lima came in a wide variety of wheel diameters track gauge and gearing ratios. The 1921 Lima Repair Parts Catalog lists five different trucks as standard for shays in production at that time. Note that the left side view [left picture]. This view shows how close the truck looks to a regular freight car trucks.
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Last Updated on 10/10/2014
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