ALCO 251

The Alco 251 is a 4-stroke diesel engine that was developed by the American Locomotive Company to replace the 244 and 539 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

Model 251 engine design was initiated in 1949, and like the 244 engine it would have a bore (cylinder diameter) of 9 inches (229 mm), and a stroke of 10.5 inches (267 mm). Its designation combines Alco'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 address 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 for the turbocharger, which minimized temperature differentials but also benefitted performance. Many small improvements were made to the crankshaft, bearings, pistons, injectors and camshafts.