MLW "M420" Locomotives: Specs, Roster, History

Published; August 13, 2024

The M420 was produced by the Montreal Locomotive Works (MLW) during the mid-1970s as a continuation of Alco's former C420 line.

The 2,000 horsepower model was a modest success although only 98 were produced between 1973-1977, including a small order of eight cabless "B" units for British Columbia Railway.

The M-420 emerged as a pioneering model in the integration of the wide-nosed Canadian comfort cab, a design innovation spearheaded by Canadian National and shared with units like the GP38-2W, GP40-2W, and GP40-2LW.

By the early 1990s, this cab design had become an industry standard. Locomotives from this era, including General Motors Diesel units, often had a "W" appended to their model names to denote the wide-nose feature, although this was not an official part of the model designation.

Delaware-Lackawanna M420W #2045 an C425 #2457 are tied down at Scranton, Pennsylvania on the morning of September 24, 2020. Doug Kroll photo.

Historical Context and Development

Montreal Locomotive Works had been manufacturing steam locomotives in Canada since 1883 with the Locomotive & Machine Company of Montreal's establishment that year.

Alco acquired the company in 1904 and renamed it as the Montreal Locomotive Works, Ltd. (MLW) in 1908. It began began producing Alco's diesel catalog in the 1940s and continued to do so even after its parent ceased U.S. production at the end of 1968.

Interestingly, for whatever reason Alco's products were better received in Canada than in the States. The M420, developed between 1973-1977, was part of MLW's attempt to modernize their offerings and remain competitive against larger firms like General Electric and EMD.

Technical Specifications

Central to the M420's identity is its ALCO 251C prime mover — a 12-cylinder, turbocharged diesel engine. This powerplant delivers a robust 2,000 horsepower.

The 251C engine was renowned for its rugged durability and performance - a far better design over the earlier 244 in main line service - and was Alco's primary powerplant in its Century series.

Attribute	Details
Engine Builder	Montreal Locomotive Works
Engine	4-cycle Model 251C (V12)
Bore & Stroke	9" X 10 ½"
RPM (Maximum / Minimum)	1050 / 450
Main Generator	GE GTA17
Horsepower	2400
Gear Ratio	74:18
Top Speed	67 mph
Wheel Arrangement	B-B
Weight	272,000 Lbs
Traction Motors	GE 752 (4)
Tractive Effort (Starting)	60,400 Lbs at 25%
Tractive Effort (Continuous)	35,000 - 38,000 Lbs at 8 mph.
Multiple Unit Capability	Yes
Dynamic Braking	Yes
Auxilary Generator	GE 553 GY27
Alternator	GE Exciter GY2P7
Air Brake	Westinghouse (26LUM)
Compressor	Westinghouse (3CDCL)
Exterior Dimensions
Total Length	61' 0" (M420): 61' 0" (M420R): 60' 0" (M420B)
Wheel Diameter	40"
Truck Wheel Base	9' 4"
Height to Top Engine Hood	15' 6"
Height to Top Cab Hood	14' 10"
Cab Width	10' m4"
Top Walkway Width	9' 8"
Walkway Width	5' 1"
Engine Hood Width	10' 3"
Center Bolster	36' 5"
Distance between Truck Centers	47' 5" (M420): 45' 9" (M420R): 45' 9" (M420B)
Minimum Turning Radius	30 degrees
Fuel and Capacities
Fuel Oil	2500 Gallons
Lubricating Oil	216 Gallons
Engine Cooling Water	260 Gallons
Sand Capacity	56 cubic feet
Options
Fully Automatic Transition Hi-Adhesion Trucks Air Signal Lines Seal Beam with TrainLines Control Automatic Locomotive Testing

Design and Innovative Features

The M420 was essentially MLW's version of the C420 with a B-B trucks. The locomotive measures approximately 61 feet in length and weighed, on average, 272,000 pounds.

One of the key innovations of the M420 was the use of a wide cab, often called a “comfort cab.” This Canadian design provided better ergonomics and visibility for the crew, addressing safety and comfort concerns that were becoming increasingly important at the time.

The wide cab also featured a short nose, improving the engineer's line of sight - they began to make an appearance in the States in the latter 1980s and have since became the industry standard for their added safety features.

Another significant feature was the Hi-Ad (High Adhesion) truck - sometimes referred to as the "Zero Weight-Transfer" truck - which were engineered to maximize traction through weight distribution and improved suspension systems, reducing wheel slippage during operation. This was particularly advantageous in North America’s varied and often challenging terrain.

West Tennessee Railroad M420W #3560 (ex CN #2560), along with B23-7s #3172 and #4070, are at Jackson, Tennessee on September 22, 2007. Doug Kroll photo.

Operational Impact

MLW produced 88 units of the M420, which were primarily sold in Canada; Canadian National was one of the largest operators.

The M420 demonstrated remarkable versatility. On freight duties, the locomotive showcased its ability to haul considerable loads over long distances efficiently. The power generated by the 251C engine, coupled with the Hi-Ad truck design, provided exceptional tractive effort, minimizing the need for multiple units.

Variants and Derivatives

The M-420 family included several notable variants:

- The M-420R, with five units built between 1974 and 1975 for the newly independent Providence & Worcester Railroad (P&W). These used trade-in parts and AAR Type B trucks.

- The M-424, an uprated version of the M-420, featured dynamic brakes and increased power output to 2,400 horsepower, tailored for service in Mexico.

- The M-420TR and its sub-variant, the M-420TR-2, served as switcher locomotives. The M-420TR units were sold to Roberval & Saguenay, while fifteen M-420TR-2 units went to Ferrocarril del Pacífico.

Both variations diverged significantly from the standard M-420 design, featuring a lowered hood, shorter frame, and end-cab configuration, making them uniquely suited to their specific operational roles.

Production Roster (M420 Series)

Original Owner	Road Numbers	Quantity	Serial Number(s)	Completion Dates
MLW M420W
British Columbia Railway	640-647	8	M6068-01 thru M6068-08	9/1973-10/1973
Canadian National	2500-2529	30	M6071-01 thru M6071-30	5/1973-10/1973
Canadian National	2530-2559	30	M6081-01 thru M6081-30	3/1974-7/1974
Canadian National	2560-2579	20	M6092-01 thru M6092-20	9/1976-12/1976
F.C. de Venezuela	M001-M002	2	M6097-01 and M6097-02	8/1976
M420B
British Columbia Railway	681-688	8	M6088-01 thru M6088-08	6/1975-7/1975
M420R
Providence & Worcester	2001-2002	2	M6075-01 and M6075-02	2/1974
Providence & Worcester	2003-2005	3	M6086-01 thru M6086-03	4/1975-5/1975
M420TR
Ferrocaril del Pacifico	522-536	15	M6089-01 thru M6089-15	7/1975-9/1975
Roberval & Saguenay	26-27	2	M6051-01 and M6051-02	4/1972
M424W
Ferrocaril del Pacifico	560-566	7	M6114-01 thru M6114-07	7/1980
Ferrocaril del Pacifico	567-575	9	M6114-61 thru M6114-69	5/1981
Ferrocaril Unidos del Sureste	525-527	3	M6114-70 thru M6114-72	8/1981
National de Mexico	9500-9551	52	M6114-09 thru M6114-60	9/1980
National de Mexico	9552	1	M6114-08	7/1980

Minnesota Commercial M420W #35 is outside the shops at St. Paul, Minnesota on August 29, 2015. This unit is the ex-CN #3574. Doug Kroll photo.

Legacy

The M420 series holds a distinct place in railway history due to its embodiment of mid-20th century diesel-electric locomotive advances and its role in the evolution of ergonomic and performance standards.

Some M420 units continue to be operational, including within the U.S. as former Canadian examples have made their way south, serving as a testament to MLW’s engineering prowess and the locomotive’s practical design.

They offer a tangible connection to the pragmatic innovation that characterized much of the mid-to-late 20th century rail industry. Locations where they can still be found in service in the States include Minnesota Commercial and Genesee Valley Transportation's family of shortlines