Northern Pacific 105

1200-hp Diesel Switcher

Engine 105 is a twelve hundred horse power model SW1200 diesel-electric locomotive designed for switching cars in railroad yards. The Electro-Motive Division of General Motors (EMD) built 1024 between 1/54 and 5/66. 105 was built in July 1957, receiving builder's number 23480. It has a V-12 567C prime mover, m. u. capability, some upgraded electrical components, and has been upgraded to roller-bearing journals. The horn visible in the photo is an ex-Minneapolis, Northfield, & Southern Hancock air chime, which sounds something like a steam locomotive whistle. It also has a normal diesel air horn.

NP 105 was built for the Lake Superior Terminal & Transfer and acquired by MTM in 1987. The LST&T was a terminal switching railroad in Duluth, jointly owned by the Great Northern and the Northern Pacific. Its locomotives were painted in the colors of the Great Northern.

(For all of its working life, 105 wore the same colors as LST&T 101. Though painted now for the Northern Pacific, it was only indirectly owned by the NP and never wore their colors. The NP did own a diesel switcher numbered 105, but it was an earlier NW-2 model.)

105 is called a diesel-electric because it uses a diesel engine (called its "prime mover") and an electric transmission.

Its prime mover is a model 12-567-C. It is a V-12 with 567 cubic inches of compression per cylinder. Unlike most diesel engines, it is a two-cycle design. Most gasoline and diesel engines are "four-cycle" because to create power the piston must travel down to draw in fresh air, then travel back up to compress the air. The diesel fuel is then injected, and in the hot air it explodes, forcing the piston down and creating power. The last step in the cycle is when the piston travels back up to expel the exhaust gasses. A 567 is unusual because it has pumps that force air into the crankcase under the cylinders. When the piston travels all the way down, it uncovers vents to the crankcase. Air from the crankcase rushes in, purging the exhaust gasses and filling the cylinder with fresh air. The piston travels up to compress the air, the diesel fuel is injected and explodes, and the piston is forced back down, uncovering the vents again.

The electric transmission design was borrowed directly from trolley car and electric locomotive technology. A generator bolted directly to the prime mover generates 600-volt DC electricity. This powers electric motors (called traction motors) geared directly to each axle. 105 has four, one per axle. A diesel locomotive like 105 could not use a direct mechanical transmission like a car, because the gears and clutch required to withstand the tremendous power would be far too huge to fit inside 105.

Historians may notice 105 acquired ditch lights in 1998. For public safety, the Federal Railroad Administration has made them mandatory for any locomotive which travel over any public crossing at speeds of 25 mph or higher. Locomotives built before 1950 are exempt for historical reasons, but 105 is not quite that old.

For years, Northern Pacific 105 was the main O&St.CV locomotive. With the arrival of Soo 559, and later BN 6234, it became their backup. Those locomotives, with road trucks, are better suited to running at speed than 105. In 2006 and 2007, 105 has been the primary power for the Jackson Street caboose rides while Andersen Windows 3110 underwent a top-deck overhaul.