In 1930 GM had acquired Electro-Motive and in 1938 constructed a new plant for the company in La Grange, Illinois to build and fabricate its own locomotives without the need of subcontracting. During 1936 development on the new model 567 engine began and after two years of rigorous work and research it was ready for production during late 1938. When designing the power plant engineers worked from the 201-A and its failures. These improvements included things like a welded frame, forged castings, the use of cast-iron pistons (which lasted roughly five-times longer than the 201-A's aluminum pistons), reducing crankshaft and bearing stress as much as possible via particular attention to mounting, and most importantly allowing parts to be interchanged among different models whenever and wherever possible.
This last point in particular gave EMD a major advantage over its competitors by offering railroads an additional incentive in reducing operating and maintenance costs; new and various models could be purchased knowing that most parts could be swapped or changed between them. The two-stroke, "V" design was named for the 567 cubic inches of cylinder displacement and it set the stage for how EMD listed all future engine models. Brian Solomon notes from his book Electro-Motive, E Units And F Units that "As originally designed the 567 engine was aspirated using 'uniflow' air scavenging forced by a cam-driven Roots blower running at roughly twice the engine speed." When changing, modifying, and/or improving the same model, which ocurred often with the 567, sublettering was used. The original 567 was used only in the E3, E4, E5, and E6 passenger models built between late 1938 and 1942.
The FT of 1939 utilized the upgraded 567B and the E7 of 1945 featured the 567A. All of EMD's first-generation models sported 567s, which continued through early second-generation models as well like the GP30, GP20, SD35, and GP35. However, that changed in 1966 when the builder unveiled its new model 645 prime mover first appearing on the SD38 and GP38 designs cataloged that year. The 645 offered more horsepower and improvements of the 567 while continuing to provide high quality and relability for which EMD had become known by that time. Today, numerous 567s remain in service across the country powering everything from covered wagons to early second-generation models still in regular freight service. In an ironic twist of fate rival General Electric now offers comparable replacement parts of 567 components. For more information about EMD's later model 645 prime mover please click here.
(Thanks to Brian Solomon's The American Diesel Locomotive and Electro-Motive, E Units And F Units as primary references for this article.)
For more reading on Electro-Motive locomotives and the 567 prime mover consider the book EMD Locomotives from author Brian Solomon. The book highlights the history of EMD from its earliest beginnings in the 1920s, to its phenomenal successes in the mid-20th century, and finally its decline into second spot behind General Electric in the late 20th century and eventual sale by General Motors in 2005. The book features 176 pages of EMD history and is filled with excellent photography and illustrations. I would also highly recommend Mr. Solomon's Electro-Motive E-Units and F-Units: The Illustrated History of North America's Favorite Locomotives, which covers the history of the 567 and its application in the classic covered wagons.