EMD SD50

General Motors Electro-Motive Division
Industry	Locomotive manufacturing
Founded	January 1, 1922; 104 years ago
Products	Diesel-electric locomotives

The EMD SD50 is a diesel-electric locomotive manufactured by General Motors Electro-Motive Division. Launched in May 1981 as a member of EMD's "50 Series," its production concluded in January 1986, totaling 431 units. The SD50 acted as an intermediary model bridging the dependable Dash 2 series of the 1970s with the microprocessor-controlled SD60 and SD70 locomotives.

History

Designed to compete with GE Transportation's popular Dash 7 locomotives—which combined up to horsepower with contemporary technology and appealing financing and maintenance packages—the SD50 was EMD’s response to market pressure. Despite the enduring reliability of EMD's SD40-2, GE’s innovations compelled EMD to offer price reductions on bulk SD50 purchases.

Earlier GM-EMD models such as the SD45 and SD45-2 were equipped with fuel-intensive and less dependable 20-cylinder engines, resulting in waning demand following the fuel crisis of the 1970s. The SD50 incorporated an enhanced V16 645 engine derived from the SD40-2, increasing power from at 900 rpm to at 950 rpm, and later reaching in November 1984. However, these power boosts contributed to mechanical and electrical complications that negatively impacted EMD's market standing.

In comparison to earlier models, the SD50 was built on a lengthened frame with an extended long hood. The dynamic brake resistors were repositioned from above the prime mover to a cooler section near the engine compartment air intakes, facilitating easier maintenance and better system segregation.

Operators appreciated the SD50 for its improved wheel-slip control and enhanced dynamic braking capacity; one engineer remarked that it offered superior traction compared to an SD40-2.

Technical

The SD50 is equipped with a V16 16-645F3 diesel engine that powers either an EMD AR11A-D14 or AR16A-D18 traction alternator. This alternator supplies electricity to six EMD D87 traction motors, each rated at 1170 amps.

Various traction motor gearing ratios and wheel diameters were available for the SD50, with the most prevalent combination being a 70:17 gearing ratio paired with 40-inch wheels, allowing a maximum speed of 70 mph. Additional gearing options using 40-inch wheels included 69:18 for speeds up to 76 mph, 67:19 for 82 mph, and 66:20 for reaching 88 mph. A configuration with 42-inch wheels was also offered.

Trucking choices consisted of HT-C trucks—distinguished by a hydraulic shock absorber on the center axle—and older Flexicoil trucks. Due to concerns linking HT-C trucks to Amtrak SDP40F derailments, Conrail initially opted for Flexicoil C trucks on their SD40-2 units and their first batch of SD50s, making them the sole customer to do so. Once these concerns were disproven, Conrail transitioned to HT-C trucks for later orders of both SD50 and SD60 locomotives.

SD50S

The SD50S ("short frame") refers to six prototype locomotives constructed in December 1980, which were roughly two feet shorter than standard production units. All six were sold to Norfolk & Western and subsequently Norfolk Southern before being retired in the early 2000s due to their non-standard status. Two units underwent rebuilding in 2008 at Norfolk Southern's Juniata Shops into "SD40E" models alongside several full-length SD50s.

Additionally, the SD50S label was applied to five locomotives assembled by EMD’s Australian licensee Clyde Engineering in Adelaide for Hamersley Iron. These shorter variants featured dual cab roofs designed for insulation against Pilbara’s intense desert heat. Withdrawn in 1995, they were sold to National Railway Equipment Company and exported to the United States in 1999 for leasing purposes. Later acquired by Utah Railway in 2001, units numbered 6063 and 6064 changed hands again in June 2017 when sold to Chicago, Fort Wayne & Eastern Railroad; unit 6064 was subsequently transferred by Genesee & Wyoming to Indiana & Ohio Railway and renumbered as units 5016 and 5017.

SD50F

The SD50F represented a Canadian adaptation of the cowl unit design, incorporating a "Draper taper"—a recessed section behind the cab intended to enhance limited rearward visibility. A total of sixty units were produced for Canadian National Railway, assigned road numbers 5400 through 5459. Initial operational difficulties with the engine necessitated a temporary reduction in power output to . Although these units were later restored to their full power rating of , they continued to experience persistent issues, including failures related to the engine, power assemblies, and crankshafts.

Original owners

Railroad	Quantity	Road numbers	Remarks
SD50
Baltimore & Ohio (Chessie System)	20	8576–8595
Chicago & North Western	35	7000–7034	Unit #7009 preserved at Illinois Railway Museum
Chesapeake & Ohio (Chessie System)	43	8553–8575, 8624–8643
Conrail	135	6700–6834
Denver & Rio Grande Western	17	5501–5517
Kansas City Southern Railway	10	704–713
Missouri Pacific Railroad	60	5000–5059
Seaboard System Railroad	81	8500–8552, 8596–8623
Norfolk Southern	20	6506–6525
Hamersley Iron	5	6060–6064
Norfolk & Western Railway	6	6500–6505	Short-frame SD50S variant
Canadian National	60	5400–5459	Cowl unit configuration

Rebuilds

Numerous SD50 locomotives have undergone rebuilds to match the specifications of the EMD SD40-2. Since the SD50 already incorporates Dash 2 features, this refurbishment primarily entails reducing power from at 950 rpm down to at 900 rpm by modifying the Woodward Inc PGE engine governor.

Preservation

• The Chicago and North Western Railway locomotive #7009 is conserved at the Illinois Railway Museum located in Union, Illinois, recognized as potentially the earliest SD50 preserved.

External links

Lytle, Stan. EMD SD50 list. Accessed 16 February 2005.
TrainWeb.com. The Unofficial EMD homepage. Accessed 7 January 2005. Contains extensive builder records for EMD locomotives.
Union Pacific Railroad Locomotive Department, Locomotive Diagram Book, Union Pacific, 1994.
Electro-Motive Division of General Motors, SD50 Operator's Manual 1st Edition November 1980, Electro-Motive Diesel, 1980.