Northern Pacific 4-8-4 "Northern" Locomotives in the USA

By the 1920s the Northern Pacific Railroad needed bigger passenger locomotives. The NP had its motive power department work with the American Locomotive Company's design engineers to develop a new locomotive. They designed a new locomotive with a massive firebox that had a 115 square foot grate area supported by a four wheel trailing truck. It was the first locomotive with a 4-8-4 wheel arrangement.

ALCO delivered the first of 12 of these new locomotives in December of 1926, with the balance arriving early in 1927. Designated Class A, and assigned road numbers 2600 through 2611, they had 73" drivers, 28 x 30 cylinders, a boiler pressure of 210 psi, a tractive effort of 57,500 lbs and weighed 426,000 pounds. Later, the boiler pressure was raised to 240 psi which increased the tractive effort to 65,700 pounds. These were the first of this new wheel arrangement and thus were to be the namesake, with the name "Northern Pacific" selected which was very quickly shortened to just "Northern".

In 1930, the Timken demonstrator came to the NP. While being tested, it suffered crown sheet damage. The NP bought it, repaired it and put it on the roster as number 2626.

Ten Class A-2s (road numbers 2650 through 2659) came from the Baldwin Locomotive Works in 1934. These heavy "Northerns" had 77" drivers, 28 x 31 cylinders, a boiler pressure of 260 psi, a tractive effort of 69,800 lbs and a weight of 489,400 pounds.

In 1938, eight Class A-3s (road numbers 2660 through 2667) were delivered from Baldwin. The specifications for these locomotives were identical to the Class A-2s except that each weighed 2,400 pounds more.

The eight Class A-4s (road numbers 2670 through 2677) were delivered by Baldwin in 1941, and had the same basic specifications as the A-3s, but were different in appearance, with 14 wheel centipede tenders and vestibule cabs, and they were 1000 pounds heavier.

The last of the 4-8-4s purchased by the NP were the Class A-5s, which were built by Baldwin in 1943. This group of 10 (road numbers 2680 through 2689) were built to the same specifications as the Class A-4s, but turned out to be 16,200 lbs heavier. They were among the heaviest of all the Northern type locomotives ever built, at 508,500 pounds only the Santa Fe Class 2900s weighed more.

There are no surviving Northern Pacific Northerns.


ClassRoad NumbersYr. BuiltBuilderLocomotive Wt.
A2600-26111926ALCO426,000 lbs
A-12626 (ex Timken 1111)1930ALCO477,500 lbs
A-2s2650-26591934Baldwin489,400 lbs
A-3s2660-26671938Baldwin491,800 lbs
A-4s2670-26771941Baldwin492,800 lbs
A-5s2680-26891943Baldwin508,500 lbs

Class Details by Steve Llanso of Sweat House Media

Class A (Locobase 272)

Data from [] (7 Feb 2004) . (Thanks to Chris Hohl for correcting the valve gear ID and to Bill Todd for his 25 October 2017 email pointing out a state ID mixup for both Glendive and Jamestown .) Works numbers was 67010 in December 1926, and 67011-67021 in January 1927. The NP assigned even road numbers to the first six (2600-2610), and odd road numbers (2601-2611) to the last six.

Valve motion had limited cutoff. These were the very first 4-8-4s to be bought and go into service, that event occurring in 1926. One significant factor in the development of the big-firebox version of the 4-8-2 Mountain was the predominance of low-calorie "Rosebud" coal in the NP's region.

According to Richard Drury (1993), tests on trains while trailing a dynamometer car revealed two main truths: "The engines produced more horsepower when they were worked hard, and they were slightly under-boilered." Drury also notes notes one unusual design feature - the outside cradle frame carrying the trailing truck, a feature shared with the Canadian National and the Chicago & North Western Hs (Locobase 252).

The power was evident in several service areas, according to Drury, who cites the substitution of one A for two Pacifics on passenger trains between Glendive, Mont and Jamestown, ND and less-frequent call for helpers on the Livingston-Missoula stretch. They also could run longer without an engine change. Bill Todd added:"I grew up in Bozeman, MT and was quite familiar with most steam hardware running." He then noted the train's reputation in the following: "It was always said that:'You could tell it was

9 PM [in Bozeman], the North Coast Limited was on time!'"

There were break-in glitches, Drury notes, including "...initial difficulties with driver bearings that resulted in broken axles." So big and powerful a locomotive would find its full voice when fitted with roller bearings, as Timken would demonstrate in 1930; see Locobase 930.

Most eventually converted to oil-firing and gave up their booster engines in the late 1940s.

Class A-2 (Locobase 273)

Data from 1930 Locomotive Cyclopedia, "4-8-4 Locomotives on the Northern Pacific," Baldwin Locomotives (1937), pp. 27-28; and NP to 1944 Locomotive Diagrams supplied in May 2004 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for his 16 March 2013 email of Baldwin's 1934 report referred to in detail below.) Works numbers were 61771-61780 in 1934.

Similar to the earlier Alco-built 4-8-4s (Locobases 272 and 930) with the important addition of Timken roller bearings on the axles. The prototype was given the number 1111 and known as the "Four Aces." She was later taken into NP service as the 2626 (Locobase 930). The A-2 was ordered from Baldwin and introduced disc driving wheels. The A-2s had a cast-steel locomotive bed with integral cylinders. 12" (305 mm) piston valves with 8 1/4" (210 mm) travel supplied the cylinders with steam.

Baldwin's report sheds a great deal of detailed light on this class. Like all NP Northerns, the A-2s burned Rosebud coal, a fuel with 22-28% moisture content and 7-9% percent ash. Compared to more typical locomotive coal, which were rated at 11,000-15,000 BTU/pound, Rosebud generated 8,750 BTU. Such low-grade brown stuff was laid by a Standard modified type B stoker on a large grate. The firebox was joined to a very long combustion chamber to extract every last BTU.

Five of the locomotives had a Worthington preheater and the latter five had the Wilson feedwater conditioner. According to his patent filing of 10 October 1929, Lyndon Wilson's conditioner was mounted in the tender instead of on the boiler because it was designed to preheat, treat, and clean the water at the same time. (Patent 1,901,216 was awarded on 14 March 1933.) It used a separate hot-water tank in which the impurities dropped to the bottom and the clean, treated, and preheated water was drawn off the top to supply the boiler. 2655 to 2659 still had the Wilson conditioner in 1944.

Baldwin's report naturally proclaimed that the A-2s were "doing fine work in heavy passenger service." Six of them then operated on the 664 miles (1,069 km) between Jamestown, NDak and Livingston, Mont over the Fargo and Yellowstone Divisions. In summer months, train loads averaged between 12 and 19 cars over ruling grades of 1.1%. Mileage averaged 9,000 (14,490 km) during the summer months and a little less in the winter.

The other four A-2s wrangled trains between Livingston and Missoula, Mont, some 240 miles (386 km). This profile provided a sterner test of 2.2% out of Butte and Helena and 1.8% between Livingston and West End. On the steeper grades, such trains needed a helper.

See Locobases 932 (A-3), 933 (A-4), and 274 (A-5) for later Northern Pacific 4-8-4s.

NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface.

Class A-3 (Locobase 932)

Data from "4-8-4 Locomotives on the Northern Pacific," Baldwin Locomotives (1937), pp. 27-28 and NP to 1944 Locomotive Diagrams supplied in May 2004 by Allen Stanley from his extensive Rail Data Exchange. Works numbers were 62163-62166 in March 1938, 62167-62168. in April and 62169-62170 in May.

As suggested by the 1937 account of the A-2s success on the road (Locobase 272), this class was virtually identical except for slightly larger flues and a few more tubes. 14" (356 mm) piston valve travel was 8 inches (203 mm). The Wilson feedwater conditioner was not installed in the tenders of these engines.

The class was divided between the NP (8) and the Spokane, Portland & Seattle (3).

Class A-4 (Locobase 933)

Data from Northern Pacific Locomotive Cards supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collections. Works numbers 64155-64158 in September 1941, 64159-64161 in October, 64162 in November.

This octet continued the basic Northern Pacific Northern line with a slight adjustment in heating surface area due to an increase in the number of tubes and and a reduction of the flue count because of the 1/4" (6.3 mm) greater diameter. Firebox heating surface included 99.5 sq ft (9.25 sq m) in six circulators. 14" (356 mm) piston valve travel was 8 inches (203 mm).

Like the others, this set had Timken roller bearings. Unlike the earlier engines, though, the A-4s (and A-5s; see Locobase 274) had vestibule cabs that offered more protection against Northern Tier winters.

Class A-5 (Locobase 274)

Data from Northern Pacific Locomotive Cards supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collections. See also tables and diagrams in 1947 Locomotive Cyclopedia. Works numbers were 64667-64676.

The A-5s essentially repeated the A-4 design (Locobase 933), but weighed slightly more, most likely because certain components could use the high-strength and lighter steel that had been diverted to other wartime use.

Firebox heating surface included that of the combustion chamber and 99.7 sq ft (9.25 sq m) in six circulators. Heavier engines with larger cylinders and higher drivers.Steam entered the cylinders through 14" (356 mm) piston valves. These engines had a very high adhesive weight, which rode on Boxpok cast steel drivers. All wheels (drivers, trucks, and tender) turned in Timken roller bearings.

The low-calorie "Rosebud" coal must have streamed through the stoker at a prodigious rate, considering that the grate demand factor is nearly as high as other engines burning higher-grade coal. Installing a Worthington 6 1/2 SA feed water heater suggests a similarly unquenchable thirst for water. Only big articulated locomotives like the NP's Z class engines carried as much coal and water as did these A-5s trailing a Vanderbilt tender with rectangular water bottom.

This class was booked to run 999 miles without an engine change, a record for a coal-burning locomotive.

Class Four Aces/A-1 (Locobase 930)

Data originally from the Timken Roller Bearing Company's builder's card, supplied in June 2012 by Chris Hohl, an email correspondent who contacted Wes Barris's and later conducted a correspondence with Locobase. Hohl's 6 March 2018 email included a new Timken card dated April 1930 with data changes. See also the detailed account in Allen Merta, Wig-Wag (published by Eastern Iowa Division Mid-Continent Region / NMRA), Vol 3, No 9 (September 2007), pp. 3-11 at; Northern Pacific Locomotive Card 2656, supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. Works number was 68056 in April 1930.

This engine demonstrated Timken's roller bearings while bearing the number 1111. (Its nickname was "The Four Aces.") Timken's builder's card shows a different distribution of weights among the axles for the 235-psi (16.21 bar) boiler and for the 250-psi vessel. Locobase uses the latter in its specifications. Differences in steam pressure accounted for a small difference in the trailing truck booster's tractive effort, which increased from 12,000 lb (5,443 kg or 49.2 kN) at 235 psi to 12,800 lb (5,806 kg or 52.29 kN) at 250 psi.

Allen Merta summarizes some of the specifics of the roller-bearing installation: "The roller bearings on all driving axles surrounded the axle a full 360 degrees. This took up the piston thrust in all directions. Driver pounding was reduced to a minimum. Bearing overheating was eliminated. The roller bearings were completely immersed in oil on all wheels. The oil needed to be changed only 2 to 4 times per year."

Other than the roller bearings on all axles (a big exception), the locomotive was a typical big Alco. In addition to the Walschaert valve gear, 12" (305 mm) piston valves, and Type E superheater, the 1111 was fitted with a Worthington 3-unit, 10,000 US gallon (37,850 litre) capacity, feed water heater, a tender-mounted stoker, a Franklin booster, American multiple front-end throttle, and a ALCO Type G power reverse gear. Firebox heating surface area included 105 sq ft (9.75 sq m) in syphons and 18 sq ft (1.67 sq m) in arch tubes.

Alexander (American Locomotives, 1950, p. 178) describes its tour of 88,992 miles (143,277 km) on fourteen railroads including turns on elite passenger varnish such as the New Haven's Merchants Limited and the C&O's Sportsman. "On the Pennsylvania it handled twelve passenger cars up the Allegheny mountain grade without a helper and even saved three minutes on the standard schedule."

Merta comments on the assiduity of most of the trial railroads: "Twelve of the 14 railroads seriously tested the Four Aces. In freight service, the locomotive made 328 freight runs pulling an average of 83+ cars per trip, an average speed 29.8 mph. On the Chesapeake & Ohio, Four Aces started and pulled a 132 car coal train weighing 9,864 tons. In passenger service, Four Aces made 227 runs with an average of almost 11 cars per trip at an average speed of 41.2 mph."

Most often remembered from this tour were the publicity shots in which a few men (or fetchingly clad young women) pulled the 1111 along a track to demonstrate the silky smooth, low-friction qualities of the roller-bearing installation.

Former employee Daniel Simon forwarded a photo of the 4 Aces and wrote at [] (last accessed 9 June 2012) and quotes the Wikipedia entry for the 1111 as saying, "A total of 52 different parts manufacturers agreed to supply their parts for the locomotive 'on account' until the locomotive operated over 100,000 miles (161,000 km).

The NP's number for this engine was 2626. Ironically, Drury (1993) reports, the Northern Pacific wasn't particularly persuaded by the tests because the 1111's firebox wasn't designed to burn the railroad's low-grade coal. It stayed on the NP largely because it had suffered crown sheet damage while on the railroad (the last of the 14 to trial it) and Timken didn't want it back.

Merta reports: "The [crown sheet] damage occurred when locomotive crews allowed it to run low on water near Auburn, Washington." He also contends that the NP set up a adversely biased comparison between its A-class 2607, which run only 3,465 miles since fitted with new driving boxes, and the 1111, which had seen little maintenance in the previous 91,780 miles.

The NP purchased the engine on 8 February 1933.

After repairs, the NP found 1111/2626 "durable and inexpensive to operate." A later Northern Pacific diagram shows slightly different distribution for the boiler's evaporative and superheater heating surface areas. EHS is given as 5,061 sq ft (470.18 sq m) while the superheater is credited with 2,157 sq ft (200.39 sq m) most likely due a difference in how one handled Type E superheater areas from the Timken calculations.)

The A-1 pulled Trains 1 and 2 between Seattle and Yakima, Wash at first. Despite a less than enthusiastic reception, the NP could only agree that Timken's claims had been borne out, says Merta: "When the first complete general shopping of 2626 was done in 1934, the driving boxes were disassembled. The roller bearings were in excellent condition and could have returned to service, but the decision was made to replace them because the locomotive had 280,000 miles on it."

By 1935, the 2626 ran the 656-mile (1,056-km) stretch between Seattle and Missoula, Mont. Throughout its career, the 2626 trailed the same tender, which Timken's T.V. Buckwalter conceded was too small. In November 1946, the NP fitted the 2626 with an oil burner. The NP removed the 2626's trailing-truck booster in October 1947 and the Worthington feed water heater in July 1951.

2626's last run came on 4 August 1957 when it hauled a train from Seattle to Cle Elum, Wash (about 80 miles away) and returned.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID272 273 932 933 274
RailroadNorthern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)Northern Pacific (NP)
Number in Class12108810
Road Numbers2600-26112650-26592660-26672670-26772680-2689
Number Built12108810
Valve GearBakerWalschaertWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)20.25 / 6.1720.66 / 6.3020.66 / 6.3020.67 / 6.3020.66 / 6.30
Engine Wheelbase (ft / m)47.17 / 14.3848.42 / 14.7648.58 / 14.8145.58 / 13.8948.58 / 14.81
Ratio of driving wheelbase to overall engine wheebase 0.43 0.43 0.43 0.45 0.43
Overall Wheelbase (engine & tender) (ft / m)90 / 27.4396.25 / 29.3496.2596.75 / 29.4997.50 / 29.72
Axle Loading (Maximum Weight per Axle) (lbs / kg)63,000 / 28,57673,800 / 33,47574,00074,000 / 33,566
Weight on Drivers (lbs / kg)251,000 / 113,852294,000 / 133,356294,000 / 133,356294,000 / 133,356295,000 / 133,810
Engine Weight (lbs / kg)418,000 / 189,602489,400 / 221,988491,800 / 223,077502,500 / 227,930508,500 / 230,652
Tender Loaded Weight (lbs / kg)313,000 / 141,975387,600 / 175,813386,050 / 175,110443,300 / 201,078443,500 / 201,168
Total Engine and Tender Weight (lbs / kg)731,000 / 331,577877,000 / 397,801877,850 / 398,187945,800 / 429,008952,000 / 431,820
Tender Water Capacity (gals / ML)15,000 / 56.8220,00020,000 / 75.7625,000 / 94.7025,000 / 94.70
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)24 / 21.802727 / 24.5027 / 24.5027 / 24.50
Minimum weight of rail (calculated) (lb/yd / kg/m)105 / 52.50123 / 61.50123 / 61.50123 / 61.50123 / 61.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 185477 / 195677 / 195677 / 195677 / 1956
Boiler Pressure (psi / kPa)210 / 14.50250 / 17.20260 / 17.90260 / 17.90260 / 17.90
High Pressure Cylinders (dia x stroke) (in / mm)28" x 30" / 711x76228" x 31" / 711x78728" x 31" / 711x78728" x 31" / 711x78728" x 31" / 711x787
Tractive Effort (lbs / kg)57,511 / 26086.5867,073 / 30423.8469,756 / 31640.8369,756 / 31640.8369,756 / 31640.83
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.36 4.38 4.21 4.21 4.23
Heating Ability
Firebox Area (sq ft / m2)485 / 45.07512 / 47.57490 / 45.54589.70 / 54.78589.70 / 54.78
Grate Area (sq ft / m2)115 / 10.69115 / 10.68115 / 10.69115 / 10.68115 / 10.68
Evaporative Heating Surface (sq ft / m2)4884 / 453.904964 / 461.174703 / 437.084673 / 434.134672 / 434.04
Superheating Surface (sq ft / m2)1992 / 185.132174 / 201.972095 / 194.701930 / 179.301930 / 179.30
Combined Heating Surface (sq ft / m2)6876 / 639.037138 / 663.146798 / 631.786603 / 613.436602 / 613.34
Evaporative Heating Surface/Cylinder Volume228.43224.69212.87211.52211.47
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation24,15028,75029,90029,90029,900
Same as above plus superheater percentage31,15437,37539,16938,57138,571
Same as above but substitute firebox area for grate area131,387166,400166,894197,785197,785
Power L130,15939,34039,27937,74437,743
Power MT1059.591180.001178.171132.121128.26

Principal Dimensions by Steve Llanso of Sweat House Media
ClassFour Aces/A-1
Locobase ID930
RailroadNorthern Pacific (NP)
Number in Class1
Road Numbers1111 / 2626
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.25 / 5.87
Engine Wheelbase (ft / m)45.83 / 13.97
Ratio of driving wheelbase to overall engine wheebase 0.42
Overall Wheelbase (engine & tender) (ft / m)89.77 / 27.36
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)264,000 / 119,749
Engine Weight (lbs / kg)417,500 / 189,375
Tender Loaded Weight (lbs / kg)294,000 / 133,356
Total Engine and Tender Weight (lbs / kg)711,500 / 322,731
Tender Water Capacity (gals / ML)14,200 / 53.79
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)21 / 19.10
Minimum weight of rail (calculated) (lb/yd / kg/m)110 / 55
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 1854
Boiler Pressure (psi / kPa)250 / 17.20
High Pressure Cylinders (dia x stroke) (in / mm)27" x 30" / 686x762
Tractive Effort (lbs / kg)63,663 / 28877.09
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.15
Heating Ability
Firebox Area (sq ft / m2)483 / 44.87
Grate Area (sq ft / m2)88.30 / 8.20
Evaporative Heating Surface (sq ft / m2)5120 / 475.66
Superheating Surface (sq ft / m2)2100 / 195.09
Combined Heating Surface (sq ft / m2)7220 / 670.75
Evaporative Heating Surface/Cylinder Volume257.54
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation22,075
Same as above plus superheater percentage28,477
Same as above but substitute firebox area for grate area155,768
Power L140,445
Power MT1351.00

  • 1111 (Timken Roller Bearing/NP Builder's Photo, YesterYearDepot)
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Wes Barris