Rock Island 4-8-2 "Mountain" Locomotives in the USA

The Chicago, Rock Island & Pacific Railroad received two "Mountains" (road numbers 998 and 999) from the American Locomotive Company in 1913, and became the third railroad to take delivery of this wheel arrangement. These two oil burning locomotives had 28 x28 cylinders, 69" drivers, a boiler pressure of 185 psi, a tractive effort of 50,028 lbs and a total weight of 333,100 pounds.

Based on the success of its first two 4-8-2s (renumbered 4000 and 4001) the "Rock Island" ordered ten "Mountains" (road numbers 4002 through 4011) from ALCO in 1920. These Class M50 coal burning locomotives had 28 x 28 cylinders, 74" drivers, a boiler pressure of 200 psi, a tractive effort of 50,430 lbs and weighed 372,850 pounds.

In 1923, thirty more Class M50 locomotives (road numbers 4012 through 4041) were received from ALCO. This time, there was a mix of thirteen oil burners and seventeen coal burners. This batch was identical to the locomotives delivered in 1920 except that the coal burners weighed 367,850 lbs and the oil burners weighed 366,000 pounds.

Three more batches were received: five (road numbers 4042 through 4046) in 1926, ten (road numbers 4047 through 4056) in 1927 and five (road numbers 4057 through 4061) in 1929. These last twenty were built by ALCO and were similar to the others except for an increase in total weight. Four were oil burners and the balance burned coal.

A major rebuild occurred on numbers 4044 through 4061. These eighteen locomotives, designated as Class M50a, were given roller bearings on all axles and light weight running gear. The cylinder bore was reduced from 28" to 26" in a new cast cylinder and forward frame. The boiler pressure was raised to 220 psi, but with the reduced cylinder diameter there was a reduction in tractive effort, which was made up for in greater sustained steaming. These rebuilds were done in the Silvis Shops between 1940 and 1942.

Seven of the CRI&P's "Mountains" (road numbers 4006, 4007, 4015, 4022, 4023, 4028 & 4031) were sold to the St. Louis Southwestern Railroad in 1941. The balance were retired by 1953.


Road NumbersFuelWt. on DriversLocomotive Weight
4012-4041Oil/Coal260,250 lbs366,000/367,850 lbs
4044-4046Coal253,500 lbs378,500 lbs
4047Oil252,900 lbs372,600 lbs
4048-4051Coal258,500 lbs376,500 lbs
4052Coal259,250 lbs375,450 lbs
4053-4054Oil253,450 lbs371,600 lbs
4055Coal257,400 lbs372,900 lbs
4056Oil251,500 lbs369,100 lbs
4057-4061Coal253,500 lbs378,500 lbs
Tender for Coal Burners: 352,400 lbs
Tender for Oil Burners: 355,600 lbs

Class Details by Steve Llanso of Sweat House Media

Class M-50 (Locobase 200)

Data from Railway Age, Vol 70, No 8 (25 Feb 1921); see also "Mountain Type Features New Rock Island Power", Railway Mechanical Engineeer, Vol 95, No 3 (March 1921), pp. 148 and RI 1 - 1942 Locomotive Diagrams supplied in May 2005 by Allen Stanley. (Thanks to Chris Hohl for his correct ID of the valve gear and for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error .) Works numbers were 62142-62151 in November 1920, 64180-64189 in April 1923, 64637-64646 in August 1923, and 65773-65782 in July 1924.

Firebox had three thermic syphons that contributed 116.7 sq ft (10.8 sq m) to the firebox heating surface and represented all of the increase over the 1913 batch. Note the high CHS/GA ratio and the high adhesive factor. Also, these engines used the square cylinder dimensions that were delivered with the two 1914 Rock Island 4-8-2s shown in Locobase 3088. These M-50 rolled on taller drivers and compensated by setting the boiler pressure at 200 psi.

The class was built by Schenectady and Brooks. As delivered, the tenders carried 10,000 US gallons of water (37,850 litres) and 16 tons of coal (14,515 kg); loaded tender weight came to 194,000 lb (87,997 kg).

Some of the later engines were refitted with roller bearings, lightweight main and side rods, and disk-type drivers. See M-50a (Locobase 201). Seven were sold to the Cotton Belt in May 1941. Chris Hohl suggested that a new Locobase entry would more properly reflect all of the changes made in the St Louis-Southwestern shops after they took delivery. That entry is found at Locobase 16176.

Class M-50 (Locobase 3088)

Data from Railway Age (9 January 1914).

Firebox heating surface included 25 sq ft of arch tubes.

These were the first two Mountains on the CRI&P. American Vanadium Facts emphasized that the Rock Island had adopted vanadium cast steel frames in 1912 for all of its heavy road power and that over 100 such locomotives had entered service since then.

When they went into service between Phillipsburg, Kan and Limon, Col., reported WJ Tollerton, Chief Mechanical Superintendent, in Railway Age (9 January 1914), their increased power allowed the railroad to consolidate the St Louis and Chicago sections of Colorado trains into one. Over the ruling grade of 1% westbound, the 4-8-2s were expected to haul 16-car, 1,000-ton passenger trains, making 10 stops, at an average speed of 31 mph. Although these were successful locomotives, the Rock Island didn't order more Mountains until 1920, at which time they renumbered these two 4000-4001.

Class M-50 - 1929/M-50a (Locobase 201)

Data from RI 1 - 1942 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error .) Schenectady supplied road numbers 4042-4046 in June 1926, Brooks delivered 4047-4056 in April 1927, and Schenectady finished off the class with 4057-4058 in September 1929, and 4059-4061 in October.

The Rock's 1921 Mountains (shown in Locobase 200) may have had some maintenance issues in the boiler. Given the changes Alco made in these 1926 engines, one suspects that the use of three thermic syphons was a principal culprit as Alco turned out near-duplicates with significant reductions in a couple of areas. Firebox heating surface area was now augmented by two thermic syphons comprising 82 sq ft (7.6 sq m), one less syphon installation than before. The boiler also gave up twelve small tubes in the Schenectady locomotives and fourteen in the Brooks engines and the builder reduced piston valve diameter to 14" (356 mm).

Locobase notes both batches showed an increase in superheater area from the earlier 1923-1924 M-50s. This may have been achieved by using a higher Birmingham wire gauge tube, a difference Locobase has seen in other designs. Schenectady superheaters were credited with a surface area of 1,276 sq ft (118.5 sq m), 46 sq ft less than the later Brooks installation. Both batches used Worthington feed water heaters except for the last two Brooks engines, which were fitted with Coffins.

The 1927 and 1929 locomotives were modernized in 1939-1940 as M-50a with Timken roller bearings on all engine axles, disk-type drivers, and Timken lightweight side and main rods.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassM-50M-50M-50 - 1929/M-50a
Locobase ID200 3088 201
RailroadRock Island (CRI & P)Rock Island (CRI & P)Rock Island (CRI & P)
Number in Class40220
Road Numbers4002-4041998-9994042-4061
Number Built40220
Valve GearBakerBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft / m)19.83 / 6.0418 / 5.4919.83 / 6.04
Engine Wheelbase (ft / m)42.25 / 12.8838.92 / 11.8642.08 / 12.83
Ratio of driving wheelbase to overall engine wheebase 0.47 0.46 0.47
Overall Wheelbase (engine & tender) (ft / m)88.37 / 26.9470.20 / 21.4087.83 / 26.77
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)255,250 / 115,780224,000 / 101,605260,250 / 118,048
Engine Weight (lbs / kg)378,000 / 171,458333,000 / 151,046375,350 / 170,256
Tender Loaded Weight (lbs / kg)352,400 / 159,846160,500 / 72,802352,400 / 159,846
Total Engine and Tender Weight (lbs / kg)730,400 / 331,304493,500 / 223,848727,750 / 330,102
Tender Water Capacity (gals / ML)20,000 / 75.768500 / 32.2020,000 / 75.76
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)20 / 18.2014 / 12.7020 / 18.20
Minimum weight of rail (calculated) (lb/yd / kg/m)106 / 5393 / 46.50108 / 54
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)74 / 188069 / 175374 / 1880
Boiler Pressure (psi / kPa)200 / 13.80188.50 / 13200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)28" x 28" / 711x71128" x 28" / 711x71128" x 28" / 711x711
Tractive Effort (lbs / kg)50,430 / 22874.6950,975 / 23121.9050,430 / 22874.69
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.06 4.39 5.16
Heating Ability
Firebox Area (sq ft / m2)396.70 / 36.85312 / 29368 / 34.19
Grate Area (sq ft / m2)63 / 5.8562.70 / 5.8363 / 5.85
Evaporative Heating Surface (sq ft / m2)4685 / 435.254117 / 382.624563 / 423.91
Superheating Surface (sq ft / m2)1196 / 111.11944 / 87.731338 / 124.30
Combined Heating Surface (sq ft / m2)5881 / 546.365061 / 470.355901 / 548.21
Evaporative Heating Surface/Cylinder Volume234.78206.31228.67
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation12,60011,81912,600
Same as above plus superheater percentage15,12014,06515,498
Same as above but substitute firebox area for grate area95,20869,98690,528
Power L121,54915,39622,800
Power MT744.48606.11772.57

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Wes Barris