Shay Locomotive

Last crawled date: 4 years, 3 months ago

When lima locomotive works received the design it was not impressed, until John Carnes influenced the company to utilize the idea, resulting in the classic shay design. Shays had regular fire-tube boilers offset to the left to provide room for 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. these shafts had universal joints and square sliding slip joints to accomodate motion of the swiveling trucks. Each axle was driven by a separate bevel gear, and used no side rods. although the shay was the most common geared steam loco, it had a signifigant flaw that was not corrected. because the drive shaft lies outside the trucks, instead of going along the centerline, truck rotation when following track curvature causes substantial drive line length change, unlike the central drive shafts of the Heisler and Climax locomotives. in modern drive shfts, this effect is accomodated by roller splines instead of bronze slip jointsthat lose their ability to slide under high torque. some photos show Shay locos, before uphill curves where they failed to respond to change in track curvature, thereby running off the track 'for no apparent reason.' some texts refer to the Shay as 'rail spreaders' or 'flange hounds', both characteristics of the trucks that do not steer freely under heavy load. other disadvantages include the noise of gearing, and the rather low top speed. #locomotive #shay #stam_locomotive #steam_engine #train