In 1930, 14 Class S-2s (road numbers 2575 through 2588) came from Baldwin with 80" drivers. With 73" drivers, the S-1s were better suited for dual service, but the S-2s were truly passenger locomotives. The Class S-2s had 29 x 29 cylinders, a 225 psi boiler pressure, a weight of 420,900 lbs and a tractive effort of 58,300 pounds.
There is only one surviving GN "Northern", number 2584 at a depot in Havre, MT.
|Class||Road Numbers||Year Built||Builder|
Heavy dual-service oil-burning engines. GN's signature improved Belpaire firebox was joined to a combustion chamber that contributed 108 sq ft (10.03 sq m) to the firebox heating surface. Unlike many other large superpower engines of the time, this design had no arch tubes or syphons. And the Elesco exhaust steam injector was less common than feed water heaters. It was rated at 10,000 US gallon capacity. Steam admission came through 14" (356 mm) piston valves.
Only six built before design changed to lighter engine with high drivers (Locobase 262). They were nonetheless highly serviceable locomotives that remained in service until 1956 (2553), 1957, and 1958.
The S-2 had high drivers and smaller boilers than the earlier S-1 (Locobase 261) and was more completely dedicated to express passenger service. In fact, Charles Wood noted, these were the first 4-8-4s to have 80" drivers and would be the only such engines until 1937. Turning on friction bearings when delivered, the S-2s would get Timken roller bearings in 1945.
Another change was the squaring of the cylinder dimensions so that diameter equalled stroke. This resulted in slightly more cylinder volume. The boiler was fitted with a Sellers exhaust steam injector that could process 4,500 to 7,350 US gallons (17,033 to 27,820 litres) per hour. Even in mid 1940s, the S-2's adhesion and engine weights were only slightly higher than the specified weight limits in the original order.
To save weight, the GN eschewed their by-then standard Belpaire firebox in favor of a radial-stayed firebox. This large cavity had a combustion chamber (111 sq ft/10.3 sq m) as delivered; 22 sq ft (2.05 sq m) of arch tubes were installed later.
Like their predecessors, the S-2s were oil-fired, but the specs required that the frames were "to be arranged on frame with flat surface for future application of stokers." The class burned oil for most of their 25+-year careers and had the only all-welded tenders on the GN. Some S-2s were converted temporarily in the late 1930s to burn coal and trailed tenders carrying 17,000 US gallons of water and 24 tons of coal.
Wood's assessment of the class was mostly laudatory: "Long winded engines, fast and durable, their only fault was a tendency to be very slippery when starting a heavy train." (p. 96). Engineers developed a starting technique when the S-2 was hitched to a freight train that Wood said "[M]uch to the consternation of the Master mechanic" would set the engine's air, pull the engine's throttle, and release the air. "Th added kick would urge tonnage into motion without wild slipping." There was a big risk, however, in the engine "slipping a driver tire and taking the locomotive out of service." (p. 99).
By 1949 the S-2s had been supplanted in Empire Builder service and relegated to secondary duties.
|Specifications by Steve Llanso of Sweat House Media|
|Railroad||Great Northern (GN)||Great Northern (GN)|
|Number in Class||6||14|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||19 / 5.79||20.75 / 6.32|
|Engine Wheelbase (ft / m)||45.50 / 13.87||47.75 / 14.55|
|Ratio of driving wheelbase to overall engine wheebase||0.42||0.43|
|Overall Wheelbase (engine & tender) (ft / m)||94.90 / 28.93||91.17 / 27.79|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)|
|Weight on Drivers (lbs / kg)||273,700 / 124,148||247,300 / 112,174|
|Engine Weight (lbs / kg)||472,120 / 214,150||420,900 / 190,917|
|Tender Loaded Weight (lbs / kg)||375,780 / 170,451||326,560 / 148,125|
|Total Engine and Tender Weight (lbs / kg)||847,900 / 384,601||747,460 / 339,042|
|Tender Water Capacity (gals / ML)||22,000 / 83.33||17,250 / 65.34|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||5800 / 22||5800 / 22|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||114 / 57||103 / 51.50|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||73 / 1854||80 / 2032|
|Boiler Pressure (psi / kPa)||250 / 17.20||225 / 15.50|
|High Pressure Cylinders (dia x stroke) (in / mm)||28" x 30" / 711x762||29" x 29" / 737x737|
|Tractive Effort (lbs / kg)||68,466 / 31055.69||58,305 / 26446.73|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.00||4.24|
|Firebox Area (sq ft / m2)||401 / 37.25||401 / 37.25|
|Grate Area (sq ft / m2)||102 / 9.48||97.75 / 9.08|
|Evaporative Heating Surface (sq ft / m2)||5405 / 502.14||4781 / 444.17|
|Superheating Surface (sq ft / m2)||2444 / 227.05||2265 / 210.42|
|Combined Heating Surface (sq ft / m2)||7849 / 729.19||7046 / 654.59|
|Evaporative Heating Surface/Cylinder Volume||252.80||215.65|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||25,500||21,994|
|Same as above plus superheater percentage||33,405||29,032|
|Same as above but substitute firebox area for grate area||131,328||119,097|