The SD7 is a model of 6-axle diesel locomotive built by General Motors Electro-Motive Division between May 1951 and November 1953. It had an EMD 567B 16-cylinder engine producing 1,500 horsepower (1.12 MW) for its six traction motors. United States railroads bought 188 units.^[1]

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EMD SD7
SP 1518 at the Illinois Railway Museum
Type and origin Power type Diesel-electric Builder General Motors Electro-Motive Division (EMD) Model SD7 Build date May 1951 – November 1953 Total produced 188
Specifications Configuration: ​  • AAR C-C Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Trucks EMD Flexicoil C Wheel diameter 40 in (1,016 mm) Minimum curve 23° (250 ft (76.20 m) radius) Wheelbase 48 ft 7 in (14.81 m) Length 61 ft 2+3⁄4 in (18.66 m) Width 10 ft 8 in (3.25 m) Height 15 ft 4+1⁄2 in (4.69 m) Loco weight 309,000 lb (140,000 kg) Fuel capacity 1,200 US gal (4,500 L; 1,000 imp gal) Prime mover EMD 16-567B RPM range 800 Engine type V16 diesel engine Aspiration Roots-type supercharger Displacement 9,072 cu in (148.66 L) Generator D-12-C Traction motors (6) D-27-B Cylinders 16
Performance figures Power output 1,500 hp (1.12 MW) Tractive effort 77,250 lbf (343,600 N)
Career Locale United States Disposition Some still in service, others preserved

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This was the first model in EMD's SD (Special Duty) series of locomotives, a lengthened B-B GP7 with a C-C truck arrangement. The two extra axles and traction motors are useful in heavy, low-speed freight service. EMD continues to produce SD series locomotives to this day.

Some SD7s both high and short-hood can still be found in service today on shortline railroads and industrial operators, although most Class I roads stopped using these locomotives by the 1970s and 1980s.^[2]

The SD7 was conceived as a modification of the existing EMD GP7 with two additional powered axles, one for each truck. Providing two more axles served two purposes: it gave the locomotive more tractive effort compared to the four-axle GP7, and it distributed the locomotive's weight more evenly.^[3]

EMD produced its first examples of the SD7 in May 1951, using the 567B engine. Starting in August 1953 a total of 26 SD7s were produced which used either the 567BC engine or the 567C engine.

SD7s were originally set up to run long hood forward, usually noted by the letter "F" painted adjacent to the top step of the long hood boarding steps. Many were later changed or upgraded to run short hood forward as is today's Association of American Railroads standard.

EMD ended production in November 1953 and began producing the SD7's successor, the SD9, in January 1954.

• • Burlington Northern #6008 (ex-Great Northern #558) is preserved at the Minnesota Transportation Museum in Saint Paul, Minnesota. #6008 was one of the first 20 SD7s to be built in 1952; it's currently under restoration to its original appearance as Great Northern #558.
  • Southern #197 is preserved at the Virginia Museum of Transportation. It was originally built as Central of Georgia#201.
  • Southern Pacific #1518 (ex-EMD demonstrator #990), is preserved in operational condition at the Illinois Railway Museum. #1518 was the first SD7 (later converted into an SD7R) built by EMD,
  • Portland and Western formerly rostered SD7 #1501 (Ex-SP #5280), being retired on July 19, 2023. While it was originally going to be scrapped by PNWR parent company Genesee and Wyoming Inc. as part of a fine resolution agreement with the EPA,^[7] it was acquired by Dieselmotive Company, Inc. (BUGX) and was shipped for storage on the Blackwell Northern Gateway Railroad. Following the FRA's work stoppage order of the BNGR in February 2024, the fate of #1501 is to be determined.^[8]