Gear Drive Steam Locomotives
Climax, Heisler, and Shay
Geared steam locomotives have two principal features that especially suited them for logging and other industrial applications, before the day of heavy haul trucks, when such transport was necessarily by rail. Gear drive delivers smoother torque to the drive wheels than the four pulses per revolution of conventional rod engines, and it allows driving all wheels, so that the entire weight of the locomotive and tender contributes to tractive effort. Their smooth torque allows these locomotives to be run continuously at partial slip or at the limit of traction, where a rod engine would spin and burn the rails.
Heisler locomotives have two cylinders, sloped at 45 degrees in a 90 degree-V from opposite sides to a longitudinal crankshaft under the boiler. Shafts, extend fore and aft from the crankshaft, that lies just above the wheel axles, that are driven through double universal joints that angle bevel gears down to the axle centerline on the far side of each truck, the other axle of the truck being driven by side rods.
Climax locomotives have two cylinders, positioned similarly to those of conventional rod engines, except that they are angled upward to the front (to clear the swing of the forward truck) and drive a transverse crankshaft beneath the boiler. The crankshaft, by way of bevel gears, drives an longitudinal drive shaft with straight toothed skewed bevel gears (a design of Bilgram Machine Works) that have non intersecting axes similar to modern hypoid gears.
Shay locomotives originally had one, then two, and finally tree cylinders, although nearly all of today's Shays have three vertical cylinders on the right side, located just ahead of the cab to drive a longitudinal crankshaft. Drive shafts extend fore and aft, past the axles of each (two or three) trucks, with each axle driven by a bevel gear. The boiler is off center to make room for the cylinders, and is therefore smaller than would otherwise be possible for a rod engine of comparable size. The offset boiler also gives lateral balance for the "motor", shafts, and gears.
The Willamette, a derivative of the Shay, can be identified because on all three cylinders the Walschaert's valve gear chambers face outward in contrast to the Shay's Stevenson type valve gear of which two face fore and one aft. In all 34 Willamettes were built near the end of the steam era.
Drive gears of Shay engines are exposed, and require regular manual lubrication. For this purpose many Shays have a permanent five gallon gear oil bucket on the front of the sideboard. All three types of gear drive engines use universal joints in their drive shafts with bronze sleeved slip-joints to compensate for length changes during truck rotation. On the Shay, the crankshaft is lubricated by grease cups and some of these engines were equipped with water jets for cooling the rod ends.
Although the Shay, built by Lima, had the largest share of the market, it also had a serious flaw that, as far as I can detect, was never recognized or corrected. Because the drive shaft runs along the outside of the truck instead of into its center, truck rotation caused substantial length change in the driveline, unlike the other two types with central drive shafts.
Shay literature has many photographs depicting wrecks where the locomotive, entering or leaving an uphill curve, failed to respond to the change in curvature, and ran off the track for no apparent reason. Some texts refer to these locomotives as "rail spreaders" and "flange hounds", both characteristics that support the concept that the trucks could not rotate freely when the drive shafts were under heavy torque.
Shays often derailed in this manner, and I believe, for this design error, that could have been avoided by using roller splines for the slip-joints instead of bronze bushings. That not all engineers suffered this fate may be due to their playing the throttle more variably on curves. Although this problem was not resolved in the original design, the possibility of a retrofit still exists. I first experienced this problem in the auto industry, where independent wheel suspension locked up while accelerating from curves, so that the car remained leaning after a curve until the power was let up.
A roller spline uses bearing balls or crossed rollers running in lengthwise grooves in both the shaft and enclosing housing so that the rolling elements transmit torque while allowing free shaft extension. Currently, a square shaft in a square bronze bushing is used, that although sliding freely under no load, locks up under high torque.
Other than that, the Shay, and its derivative, the Willamette, is a great locomotive, that driven with care, by letting up on the throttle when track curvature changes, lives up to ones expectations.
