The ALCO 251 is a 4-stroke

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

that was developed by the

American Locomotive Company The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer that operated from 1901 to 1969, initially specializing in the production of locomotives but later diversifying and fabricating at various time ...

to replace its

244 __NOTOC__ Year 244 ( CCXLIV) was a leap year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Armenius and Aemilianus (or, less frequently, year 997 ''Ab urbe condita''). The denomination 2 ...

and

539 Year 539 ( DXXXIX) was a common year starting on Saturday 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 ''Ab urbe condita''). The denomination 5 ...

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 () 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 infinite ...

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

) of , and a

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

of . Its designation combines

Alco The American Locomotive Company (often shortened to ALCO, ALCo or Alco) was an American manufacturer that operated from 1901 to 1969, initially specializing in the production of locomotives but later diversifying and fabricating at various time ...

'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 Mo ...

for the

turbocharger In an internal combustion engine, a turbocharger (also known as a turbo or a turbosupercharger) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into th ...

, 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 A 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 balanc ...

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 o ...

engines and the

ALCO RS-1 The ALCO RS-1 is a 4-axle diesel-electric transmission, 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 R ...

road switcher A road switcher locomotive is a type of railroad locomotive designed to both haul railroad car, railcars in mainline service and Shunting (rail), shunt them in railroad yards. Both type and term are North American in origin, although similar t ...

. 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, the ...

. In August 1951, Alco built the ALCO DL420 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, a demonstrator and six units for the

Boston and Maine Boston is the capital and most populous city in the Commonwealth of Massachusetts in the United States. The city serves as the cultural and financial center of New England, a region of the Northeastern United States. It has an area of and a ...

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 rail ...

with the 251 engines. In mid-1954 the

Lehigh Valley Railroad The Lehigh Valley Railroad was a railroad in the Northeastern United States built predominantly to haul anthracite, anthracite coal from the Coal Region in Northeastern Pennsylvania to major consumer markets in Philadelphia, New York City, and ...

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 (New York), city in Schenectady County, New York, United States, of which it is the county seat. As of the United States Census 2020, 2020 census, the city's population of 67,047 made it the state's ninth-most populo ...

, replacing the 244. Engine manufacturing at Schenectady was terminated in 1962, after which all non-Canadian production was moved to Auburn. Engines for

A. E. Goodwin AE Goodwin was an Australian heavy engineering firm, which produced railway locomotives and rolling stock, as well as roadmaking machinery at its factory in Auburn, New South Wales, Auburn. History Founded in December 1935 by Arthur Elliott ...

, Alco's Australian licensee, were built at Auburn or Schenectady; engines for

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

were, until 1961, assembled by MLW using parts supplied by Auburn and Schenectady. After that date, they were built under licence in Canada by the

Dominion Engineering Works Dominion Engineering Works was a company with headquarters in Montreal, Quebec Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in C ...

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

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

Crawler Transporter The crawler-transporters, formally known as the Missile Crawler Transporter Facilities, are a pair of tracked vehicles used to transport launch vehicles from NASA's Vehicle Assembly Building (VAB) along the Crawlerway to Launch Complex 39. The ...

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) in Florida, designed to assemble large pre-manufactured space vehicle components, such as the massive Satu ...

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, Florida, Merritt Island in Florida, United States. The site and its collection of facilities were originally built as the Apollo program's ...

. 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 Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. As of November 2023,

Fairbanks Morse Fairbanks, Morse and Company was an American manufacturing company in the late 19th and early 20th century. Founded in 1823 as a manufacturer of weighing scales, it later diversified into pumps, engines, windmills, coffee grinders, radios, far ...

still lists the 251 on its website for power generation.

North American locomotive uses

Marine Uses

*s built in 1985-1986, 3 × V16-251F per ship, 8,847 hp *

CCGS Hudson CCGS ''Hudson'' was an offshore oceanographic and hydrographic survey vessel operated by the Canadian Coast Guard. The ship entered service in 1963 with the Canadian Oceanographic Service, stationed at the Bedford Institute of Oceanography, cal ...

research vessel A research vessel (RV or R/V) is a ship or boat designed, modified, or equipped to carry out research at sea. Research vessels carry out a number of roles. Some of these roles can be combined into a single vessel but others require a dedicated ...

built 1963, 4 x V16-251B, 8,675 hp (Note, cited link misidentifies engines as ALCO 251D) *

United States Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and Admiralty law, law enforcement military branch, service branch of the armed forces of the United States. It is one of the country's eight Uniformed services ...

Famous-class

medium endurance cutter The Medium Endurance Cutter or WMEC is a type of United States Coast Guard Cutter mainly consisting of the Famous- and ''Reliance''-class cutters. These larger cutters are under control of Area Commands (Atlantic Area or Pacific Area). These cut ...

s, launched 1980-1988, 2 x 18V-251E per ship, 7,200 bhp *

''Reliance''-class

s, launched 1964-1969, 2 x 251B per ship, 5,000 bhp

References

* * * {{ALCO engines Diesel engines Diesel locomotive engines Marine diesel engines

251 __NOTOC__ Year 251 (Roman numerals, CCLI) was a common year starting on Wednesday of the Julian calendar. At the time, in the Roman Empire, it was known as the Year of the Consulship of Traianus and Etruscus (or, less frequently, year 1004 ''A ...