The Mainstreeter of Winter 1999 had a long interview with long-time engineer Warren McGee-- (preserved online at http://pw2.netcom.com/~whstlpnk/wrmcgee.html, accessed most recently on 30 Jan 2006) -- in which he commented on the hunger and thirst of such a large locomotive. Speaking of the Rosebud coal the railroad used, he said: " It was a coal that on the ...Z-6s, you had about an hour and 50 minutes wide open, or two hours and 20, it depended on the firing capabilities of the fireman, and the steaming qualities of the engine."
Firebox had eight circulators, a grate length of 192 in.
Fitted with roller bearings on all axles. Used for heavy freights over steep grades. Note the size of the grate that burned low-calorie "Rosebud coal." ; Z-7 and Z-8 classes were delivered in 1943.
The firebox heating surface included 136 sq ft in eight circulators. With roller bearings on all axles and immense grates measuring 192", these engines served heavy freights.
The Mainstreeter of Winter 1999 had a long interview with long-time engineer Warren McGee, (preserved online at http://pw2.netcom.com/~whstlpnk/wrmcgee.html, accessed most recently on 30 Jan 2006), in which he noted that on the run between Bozeman and Townsend, "I've swept the tank with the broom to get every last drop of coal out of that tender ...Townsend to Bozeman was 27 tons of coal every time, run through that engine."
McGee explained that the grades had something to do with it: "It's all climbing. You'd never shut off, Logan to Bozeman. Townsend to Logan [the other direction], why you had to shut off and avoid going around those curves too fast, so you didn't work full throttle all the way through there. You had to conserve all the coal you could if you didn't want to stop at Logan."
| Specifications | |||
|---|---|---|---|
| Class | Z-6 | Z-7 | Z-8 |
| Locobase ID | 927 | 340 | 928 |
| Railroad | Northern Pacific (NP) | Northern Pacific (NP) | Northern Pacific (NP) |
| Whyte | 4-6-6-4 | 4-6-6-4 | 4-6-6-4 |
| Road Numbers | 5100-5121 | 5121-5126 | 5130-5149 |
| Gauge | Std | Std | Std |
| Builder | Alco-Schenectady | Alco | Alco |
| Year | 1936 | 1936 | 1943 |
| Valve Gear | Walschaert | Walschaert | Walschaert |
| Locomotive Length and Weight | |||
| Driver Wheelbase | 12.17' | 12.33' | 12.33' |
| Engine Wheelbase | 61.83' | 62.17' | 62.17' |
| Ratio of driving wheelbase to overall engine wheebase | 0.20 | 0.20 | 0.20 |
| Overall Wheelbase (engine & tender) | |||
| Axle Loading (Maximum Weight per Axle) | 72650 lbs | 74000 lbs | 74000 lbs |
| Weight on Drivers | 435000 lbs | 444000 lbs | 444000 lbs |
| Engine Weight | 624500 lbs | 643000 lbs | 644000 lbs |
| Tender Light Weight | 398400 lbs | 438000 lbs | 437000 lbs |
| Total Engine and Tender Weight | 1022900 lbs | 1081000 lbs | 1081000 lbs |
| Tender Water Capacity | 20000 gals | 25000 gals | 25000 gals |
| Tender Fuel Capacity (oil/coal) | 27 tons | 27 tons | 27 tons |
| Minimum weight per yard of rail on which locomotive could run | 120.83 lb rail | 123.33 lb rail | 123.33 lb rail |
| Geometry Relating to Tractive Effort | |||
| Driver Diameter | 69" | 70" | 70" |
| Boiler Pressure | 250 psi | 260 psi | 260 psi |
| Cylinders (dia x stroke) | 23" x 32" (4) | 23" x 32" (4) | 23" x 32" (4) |
| Tractive Effort | 104267 lbs | 106888 lbs | 106888 lbs |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 4.17 | 4.15 | 4.15 |
| Heating Ability | |||
| Firebox Area | 756 sq. ft | 756 sq. ft | 756 sq. ft |
| Grate Area | 152 sq. ft | 152.30 sq. ft | 152 sq. ft |
| Evaporative Heating Surface | 5832 | 5749 | 5749 |
| Superheating Surface | 2114 | 2105 | 2105 |
| Combined Heating Surface | 7946 | 7854 | 7854 |
| Evaporative Heating Surface/Cylinder Volume | 189.50 | 186.80 | 186.80 |
| Computations Relating to Power Output (More Information) | |||
| Robert LeMassena's Power Computation | 38000 | 39598 | 39520 |
| Same as above plus superheater percentage | 48109.74 | 50210.91 | 50112.00 |
| Same as above but substitute firebox area for grate area | 239282.66 | 249241.28 | 249241.28 |
| Power L1 | 26752.77 | 28064.47 | 28064.47 |
| Power MT | 813.51 | 836.10 | 836.10 |
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