The Alco 251 is a 4-stroke

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-cal ...

that was developed by the

American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer of locomotives, diesel generators, steel, and tanks that operated from 1901 to 1969. The company was formed by the merger of seven smaller locomo ...

to replace its 244 and

539 Year 539 ( DXXXIX) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Strategius without colleague (or, less frequently, year 1292 ' ...

engines. The 251 was developed to be used in diesel locomotives, as a marine power plant in ships, and as a stationary power generator.

Development

The model 251 engine design was initiated in 1949 and, like the 244 engine, it had a bore (

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an ...

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid f ...

) of , and a

stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...

of . Its designation combines

Alco The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer of locomotives, diesel generators, steel, and tanks that operated from 1901 to 1969. The company was formed by the merger of seven smaller locomo ...

's identifier for that bore and stroke - 2 - with the year its design was approved for laboratory testing - 1951. Chief Engineer of Diesel Engine Design, Paul Vaughan, designed the 251 to improve upon the major weaknesses of the 244. A wet block design was used to overcome severe thermal differences which existed in the dry block 244. The welded block and base was kept, as was the four-point mounting. New in the 251 was an

intercooler An intercooler is a heat exchanger used to cool a gas after compression. Often found in turbocharged engines, intercoolers are also used in air compressors, air conditioners, refrigeration and gas turbines. Internal combustion engines ...

for the

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

, which minimized temperature differentials and also benefited performance. Many small improvements were made to the crankshaft, bearings, pistons, injectors and camshafts. To avoid the problems caused by rushing the 244 into production, the 251 was put through an extensive testing process. The first 251 engines installed in locomotives for testing were

inline-6 The straight-six engine (also referred to as an inline-six engine; abbreviated I6 or L6) is a piston engine with six cylinders arranged in a straight line along the crankshaft. A straight-six engine has perfect primary and secondary engine bala ...

designs of . A simple, safe design, it also offered a direct replacement for the aged 539, which was still used in

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...

engines and the

ALCO RS-1 The ALCO RS-1 was a 4-axle diesel-electric locomotive built by Alco-GE between 1941 and 1953 and the American Locomotive Company from 1953 to 1960. ALCO subsidiary Montreal Locomotive Works built an additional three RS-1s in 1954. This model has ...

road switcher A road switcher is a type of railroad locomotive designed to both haul railcars in mainline service and shunt them in railroad yards. Both type and term are North American in origin, although similar types have been used elsewhere. A road ...

. Like the 539, it was produced in

Auburn, New York Auburn is a city in Cayuga County, New York, United States. Located at the north end of Owasco Lake, one of the Finger Lakes in Central New York, the city had a population of 26,866 at the 2020 census. It is the largest city of Cayuga County, ...

. In August 1951 Alco built the

ALCO DL420 The ALCO DL420 was the prototype ALCO S-5 switcher diesel-electric locomotive. It was built in August, 1951 using an early six-cylinder 251 engine rated at and RS-3 subassemblies in its construction. It rode on two-axle trucks with a B-B whee ...

test unit with a six-cylinder 800-horsepower 251 engine. Ten GE 78-ton units followed in mid-1953 and were exported to the Consolidated Railroads of Cuba. The following year seven

ALCO S-5 The Alco S-5 (DL 421A) was a diesel-electric locomotive of the switcher type rated at , that rode on two-axle trucks, having a B-B wheel arrangement. This was Alco's second attempt to build a replacement 251-engined switcher to replace the 539-e ...

, a demonstrator and six units for the

Boston and Maine The Boston and Maine Railroad was a U.S. Class I railroad in northern New England. Originally chartered in 1835, it became part of what was the Pan Am Railways network in 1983 (most of which was purchased by CSX in 2022). At the end of 1970, ...

were built. Two GE X3341s were built in 1954 for the

White Pass and Yukon Route The White Pass and Yukon Route (WP&Y, WP&YR) is a Canadian and U.S. Class III narrow-gauge railroad linking the port of Skagway, Alaska, with Whitehorse, the capital of Yukon. An isolated system, it has no direct connection to any other rai ...

with the 251 engines. In mid-1954 the

Lehigh Valley Railroad The Lehigh Valley Railroad was a railroad built in the Northeastern United States to haul anthracite coal from the Coal Region in Pennsylvania. The railroad was authorized on April 21, 1846 for freight and transportation of passengers, goods, ...

supplied an FA-2 and FB-2 for installation of test 12-cylinder 251A engines. The Lehigh Valley units were tested for a year. In 1954, the 251 went into production with the

. The next year production of the V-12 followed at

- where the 539 engine was built - and a V-16 version built at

Schenectady, New York Schenectady () is a city in Schenectady County, New York, United States, of which it is the county seat. As of the 2020 census, the city's population of 67,047 made it the state's ninth-largest city by population. The city is in eastern New Yo ...

, replacing the 244.

Power generation

The

designs of version of the 251 engine replaced the 539 engine in 1954 in Alco's low-end line of power generation packages. The 244 engine was still used in higher-end power generation packages until it too was replaced by 251-engined power generation equipment in 1956. A pair of Alco 251C engines is also used for powering the 6,000,000 lb (2,721,000 kg)

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

Crawler Transporter that transport rockets and their platforms from the

Vehicle Assembly Building The Vehicle Assembly Building (originally the Vertical Assembly Building), or VAB, is a large building at NASA's Kennedy Space Center (KSC), designed to assemble large pre-manufactured space vehicle components, such as the massive Saturn V and t ...

to the

Launch Complex 39 Launch Complex 39 (LC-39) is a rocket launch site at the John F. Kennedy Space Center on Merritt Island in Florida, United States. The site and its collection of facilities were originally built as the Apollo program's "Moonport" and later m ...

. Ultimately a refined and successful design, the 251 outlived Alco. For a time it was built in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

Montreal Locomotive Works Montreal Locomotive Works (MLW) was a Canadian railway locomotive manufacturer which existed under several names from 1883 to 1985, producing both steam and diesel locomotives. For a number of years it was a subsidiary of the American Locomot ...

. As of September 2020,

Fairbanks Morse Fairbanks, Morse and Company was an American manufacturing company in the late 19th and early 20th century. Originally a weighing scale manufacturer, it later diversified into pumps, engines, windmills, coffee grinders, radios, farm tractors, fee ...

still lists the 251 on its website for power generation.

North American locomotive uses

References

* * Steinbrenner, Richard T. (2003). The American Locomotive Company - A Centennial Remembrance. Warren, NJ: On Track Publishers, LLC. {{ALCO engines Diesel engines Diesel locomotive engines Marine diesel engines 251