CN 4803 is a GP7 diesel road switcher locomotive built by General Motors Diesel (GMD) of London, Ontario, in August, 1953, originally bearing the road number 7558. In September of 1954 it was renumbered 1703 and repainted in Canadian National’s green, gold & black paint scheme. It was renumbered a third time to 4353 in June 1956, finally becoming 4803 in August 1957. This unit would’ve been repainted into CN’s red, white and black scheme in the early 1960’s. It could have been assigned to virtually all parts of the CN system for most of the year, but every fall most of CN’s GP7 fleet were transferred to branch lines in the prairie provinces for the annual grain rush. In 1984, CN repainted 4803 into its late 1950’s appearance and donated it to the City of Toronto. It was later put on display in Roundhouse Park and remains one our most popular attractions. 4803 was left mechanically complete except for the removal of its traction motors.

History

The GP7 was first developed by General Motors Diesel’s parent company, General Motors’ Electro-Motive Division (EMD) in 1949. The “GP” stood for general purpose; these four-axle units were designed to be applied in virtually any situation. Over 2,000 examples were manufactured for various roads. GP7’s are generally categorized as “first-generation diesels”, meaning they were responsible for directly replacing steam-powered locomotives in revenue service rather than earlier diesels. GMD was responsible for manufacturing these units domestically to meet the unique specifications of Canadian roads, and also for the Canadian divisions of the Chesapeake & Ohio and Wabash railroads. Canadian National were among the last to place orders of GP7 locomotives before the more advanced GP9 entered production, and ultimately only took delivery of 24 units in total. All were equipped with lighter flexicoil trucks, designed to be lightweight to handle the ancient wooden bridges and lighter rail that were still in place on CN’s branch lines at the time. They also mostly came with “barrel” or “drum”-style headlights made by the Pyle-National Company of Chicago, Illinois, which more closely resembled the headlights of steam engines than the diesel locomotives made after the GP7. Like most other roads, CN’s GP7’s were configured to operate “long hood forward”, meaning the seats and control stand faced towards the longer section of the carbody.

CN’s GP7s were powered by a 16-cylinder two cycle diesel engine. Each of the sixteen cylinders displaces 567 cubic inches, or about six times the entire displacement of the engine in a modern Toyota Corolla. This large, slow-turning engine produced 1500 horsepower to turn a 600 volt direct current generator; the generator provided current to four large electric motors mounted in the bogies, each driving one axle of the locomotive. The diesel engine also turned a large air compressor, which supply compressed air for the engine and train braking systems. These locomotives were generally equipped with the capacity to run in sets of up to eight units under the control of single engineer. CN 4803 is also equipped with electrodynamic braking, evidenced by the bulge at the roofline on either side of the long hood. Electrodynamic braking is a process by which the electric motors are turned into generators and the current load produced by the momentum of the train is then dissipated as heat. This system supplemented the friction brakes normally used and greatly reduced wheel wear and wear on the brake shoes.