The EMD SD50 was a diesel-electric locomotive built by General Motors Electro-Motive Division. It was introduced in May 1981 as part of EMD's "50 Series", but prototype SD50S locomotives were built from 1980; production ceased in January 1986. The SD50 was in many respects a transitional model between EMD's Dash 2 series which was produced throughout the 1970s and the microprocessor-equipped SD60 and SD70 locomotives.

History

The SD50 was produced in response to increasingly tough competition from GE Transportation Systems, whose Dash 7 line was proving quite successful with railroads. While EMD's SD40-2 was a reliable and trusted product, GE's line included locomotives up to with more modern technology, as well as very competitive finance and maintenance deals.

GM-EMD had previously produced 3,600 hp locomotives, the SD45 and later SD45-2, but these used huge, 20-cylinder engines with high fuel consumption, and demand for them dropped sharply after the 1970s fuel crises. The SD50 used the same V16 645 as the SD40-2, but uprated to 3,500 hp from . This proved to be a step too far; the 50 series models were plagued by engine problems which harmed both sales and the reputation of EMD.

The subsequent SD60 model replaced the overstressed 645 engine with a new engine series, the 710.

The SD50's long hood saw changes from previous EMD models. The overall frame length was increased, and the long hood was made substantially longer. The resistors for the dynamic brake grid were moved from their previous location above the prime mover to a new, cooler location in front of the engine compartment air intakes, where they were more effectively separated from the rest of the locomotives' systems.

Technical

The SD50 is powered by V16 16-645F3 series diesel engine driving either an EMD AR11A-D14 or an EMD AR16A-D18 main alternator. The power generated by the main alternator drove 6 EMD D87 traction motors rated at 1170 amps each.

Depending on customer options, the SD50 was available with a multitude of traction-motor gearing ratio and wheel size options, the most common of which being the 70:17 ratio with 40 inch wheels, this allowed for a top speed of . Other gearing options for the SD50 with 40 inch wheels include 69:18 for , 67:19 for and 66:20 for . 42 inch wheels were also available.

The SD50 could be equipped with fuel tanks sizes from up to , had a lube oil capacity of and a cooling water capacity of .

SD50S

The SD50S ("short frame") were prototype units built in December 1980. They were shorter than production locomotives by approximately 2 feet. All of these prototypes were sold to the Norfolk & Western and passed to the Norfolk Southern; they were withdrawn in the early 2000s as non-standard.

The designation also applies to five locomotives built by EMD Australian licensee Clyde Engineering for Hamersley Iron. These were also shorter than production SD50s, and were equipped with a special double cab roof for insulation against the hot Australian desert sun. When withdrawn from Hamersley Iron service, they were sold to National Railway Equipment Company and exported to the U.S. in February 1999 and used in national lease service. They were subsequently sold to the Utah Railway in June 2001, where they remain.

SD50F

The SD50F was a Canadian cowl unit version equipped with a "Draper taper" (inset section aft of cab for limited rear visibility). 60 were built for the Canadian National Railway as road numbers 5400-5459. Early engine problems resulted in a temporary down-rating to 3,300 horsepower. Eventually the units were re-rated to 3,500 horsepower, however they, like their U.S. cousins, continued to suffer from relatively low reliability, frequently suffering engine, power assembly, and crankshaft failures.

Original Buyers

Owner	Quantity
Baltimore and Ohio Railroad	20
Chicago and North Western Railway	35
Chesapeake and Ohio Railroad	43
Conrail	135
Denver and Rio Grande Western Railroad	17
Kansas City Southern Railroad	10
Missouri Pacific Railroad	60
Norfolk and Western Railway	6
Seaboard System Railroad	81
Southern Railway	20

Current owners

As of 2008, current owners and operators include:

• CN: 31 SD50Fs remain in service (as of September), while 29 have been retired
• CSXT: inherited SD50s from the B&O, C&O, Conrail (split with NS), and Seaboard System; 25 ex-CR units assigned to MofW service; at least 18 units de-rated to 3,000 hp.
• Helm Financial: lease operator owning ex-UP (nee CNW) SD50s; 6 ex-CN SD50Fs have recently been acquired.
• Hudson Bay Railway, which is owned by OmniTRAX: 10 ex-UP (nee-MP) SD50s
• Kansas City Southern: 9 SD50s it originally purchased and 25 ex-NS (nee-CR) & CSXT (nee-CR) SD50s.
• National Railway Equipment: operates 44 ex-NS & CSXT (nee-Conrail) SD50s.
• Norfolk Southern: Retains 4 of 26 SD50s it purchased and 46 ex-Conrail units; the 6 SD50Ss have been retired.
• Reading, Blue Mountain & Northern: 6 units purchased from UP.
• Southwestern Railroad: 2 ex-UP (nee-DRGW) SD50s
• Union Pacific: inherited 60 SD50s from Missouri Pacific, 35 from Chicago & North Western, and 17 from DRGW via Southern Pacific. All retired by 2007.
• Utah Railway: 5 ex-Hamersley Iron SD50Ss
• Watco Companies: 18 ex-UP (nee-CNW) and 2 ex-NS (nee-Conrail) SD50s

References

• Lytle, Stan. EMD SD50 list. Retrieved on February 16, 2005.
• TrainWeb.com. The Unofficial EMD homepage. Retrieved on January 7, 2005. Contains fairly complete builders' records for EMD production.
• Union Pacific Railroad Locomotive Department (1994). Locomotive Diagram Book. Union Pacific Railroad Company.
• Electo-Motive Division of General Motors (1980). SD50 Operator's Manual 1st Edition November 1980. Electo-Motive Division of General Motors.