EMD SD70ACU Diesel-Electric Locomotive
The EMD SD70ACU is a 6-axle 4,300–4,500 hp (3,207–3,356 kW) road switcher diesel-electric locomotive originally built by General Motors Electro-Motive Division, and rebuilt by Norfolk Southern at its shops in Altoona, Pennsylvania. The first locomotive entered the rebuilding process in September 2015, which was the 7299. 60 of these locomotives are now in service as of March 2017. They are currently being rebuilt from the SD90MACs.

All of the SD70ACUs will be rebuilt with the latest EMD cab which meets current FRA crash-worthiness standards. The Siemens electronics will be replaced with Mitsubishi electronics. The rebuild also includes the installation of Ultra Cab II, locomotive speed limiter (LSL), and cab signals. The trucks will be rebuilt only as-needed and traction motors are not being replaced.

In 2018, CP started a similar rebuild with their long dormant SD90MAC fleet. Unlike the NS, the work on these rebuilds will not be done in-house, but by Progress Rail at their Mayfield, Kentucky and Muncie, Indiana facilities.

History
The units that will be rebuilt are all ex-Union Pacific EMD SD90MAC locomotives. The SD90MAC was introduced in 1995 and was designed to use the new 16-cylinder, 6,000-horsepower (4,500 kW) H-engine. However, technical problems with the 265 engine resulted in the locomotives being delivered with the 4,300 hp (3,210 kW) 16-cylinder 710G used in EMD's SD70MAC. UP referred to these locomotives as SD9043MACs, and EMD planned to offer customers the option to upgrade them to the 6,000 hp (4,470 kW) 265 engine at a later date. EMD's upgrade program, however, was never carried out due to unresolved reliability issues with the 265. Over 400 SD90MAC locomotives fitted with the 4,300 hp (3,210 kW) 710 engine were built. 100 units originally ordered by Union Pacific were sold to Norfolk Southern as part of the SD70ACU rebuild program. EMD is responsible for delivering the locomotives, and as of November 2015, all units have been delivered. They are numbered 7229-7328. In July 2016, Norfolk Southern acquired another 10 SD90MAC locomotives from CIT Financial and the Indiana Railroad for the SD70ACU program. They will be numbered 7329-7338.

As of May 3, 2017, units that have received a full engine overhaul meet Tier 1+ emission standards, while units that have not yet received a full engine overhaul meet Tier 0+ emission standards. While all of the rebuilds are being upgraded to 4,500 traction horsepower, the Tier 0+ units generally only make 4,300-4,400 horsepower. Those units that have been overhauled and meet Tier 1+ emission standards are 7233, 7235, 7243, 7250, 7253, 7258, 7293, 7296, 7298, 7305, 7308, and 7319.

As originally built by EMD, the SD90MAC had a fuel tank capacity of 5,700 gallons. While owned by Union Pacific, the units started developing cracks in the frames around the fuel tank mounts. UP worked with EMD to solve the frame cracking problem by adding additional mounting brackets between the frame and fuel tank. In addition, the fuel filler pipes were modified to only allow a maximum of 4,700 gallons of fuel to be added.

As originally built by EMD, the SD90MAC had a maximum weight of 415,000 pounds. After being rebuilt in the SD70ACU program, the maximum weight initially increased to 420,000 pounds due to the additional weight of the new wide nose and cab. Starting with the 35th SD70ACU rebuild, NS began adding additional weight to each end of the units to increase the maximum weight to 432,000 pounds. The first 34 units will also have the additional weight added as shop time permits. Those units that have received the additional weight are 7231, 7232, 7233, 7234, 7236, 7241, 7242, 7243, 7244, 7246, 7247, 7249, 7253, 7254, 7259, 7271, 7272, 7274, 7277, 7278, 7285, 7296, 7302, 7303, 7304, 7306, 7308, 7311, 7312, 7314, 7316, 7317, 7318, 7322, 7326, and 7328.

The original cab and electrical cabinet were replaced with new EMD SD70ACe style isolated cab AAR-style control stand, and electrical cabinet with Mitsubishi electronics.

Units retain their original TA22 main alternator and 1TB2830 traction motors. They are equipped with a CCB II computer controlled braking system and the GE Ultra Cab II Cab Signaling and LSL (Locomotive Speed Limiter).

All units are equipped with NS LEADER/PTC (Positive Train Control) system. They are also equipped for use in DPU (Distributed Power Unit) operation, as well as Automatic Engine Stop/Start.

A new electric parking brake has been added with brake wheel on the left side of the long hood. Ditch lights have also been added to the rear during rebuilding.

Canadian Pacific Rebuilds
In 2018 it was announced that Canadian Pacific had Progress Rail rebuild 30 of CP's SD90MAC fleet into a similar rebuild as what the Norfolk Southern had done. The new CP SD70ACUs will be numbered 7000-7029.

EMD SD70ACU Overview
Type and origin
Power type: Diesel-electric
Builder: General Motors Electro-Motive Division/Norfolk Southern
Model: EMD SD70ACU
Build date: 2015-present
Total produced: 110
Specifications
Configuration:
​ • AAR: C-C
 • UIC: Co′Co′
Gauge: 4 ft 8 1⁄2 in (1,435 mm) standard gauge
Trucks: EMD Radial Steering
Wheel diameter: 42 in (1,067 mm)
Length: 80 ft 2 in (24.43 m)
Width: 10 ft 2 in (3.10 m)
Fuel capacity: 4.700 gallons
Prime mover: EMD 16-710 G3B
Engine type: V16 diesel engine
Aspiration: Turbocharged
Cylinders: 16
Performance figures
Maximum speed: 75 MPH
Power output: 4,300–4,500 hp (3,207–3,356 kW)
Career
Operator: Norfolk Southern
Locale: North America
Current owner: Norfolk Southern
Disposition: Several units currently in rebuild process with 72 completed as of May 21, 2017

See also:

Norfolk Southern

EMD

EMD Diesel-Electric Locomotives

Norfolk Southern SD70ACU No. 7305 pulling train 238.

By Michael Hoskins - https://www.flickr.com/photos/mehoskins21/33926789912/in/photolist-Ud3Yqz-Tb31LR-Ydp2ub-TNvgrc-YUjW2b-Vz6PNQ-UQkW7M-Vz6MXq-TFZTby-TFZEDE-X9FpEd, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=64195474​

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Norfolk Southern SD70ACU No. 7305 pulling train 238.

NS EMD SD9043MAC No. 7325, one of the units that is being rebuilt into an SD70ACU.

By F2Craft Rail - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=43534874

NS EMD SD9043MAC No. 7325, one of the units that is being rebuilt into an SD70ACU.
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