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37

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The New Haven men carefully studied the abilities of a particular class of 0-6-0's and another class of 0-8-0s. From these studies evolved a set specifications that were second to none when it came to nitty-gritty details. The proposed diesel had to do anything the 0-6-0 could do and go anywhere it could go. The diesel also would have to equal the dig of the 0-8-0 for certain tasks, couldn't exceed 100 tons, and had to produce at least 600 h.p. from a single power plant. Top speed needed to be only 25 mph, since the units were not to be used for anything but switching, and New Haven switchers were limited by timetable to 20 mph. GE and its two principal engine suppliers, IR and Cooper-Bessemer, discussed the specs at length with the New Haven, then retired to Erie to come up with a locomotive that would satisfy all the fine points.

IR chose to enlarge the existing 6-cylinder 10 x 12-inch engine to 8 cylinders in order to produce the required 600 h.p. With individual injection pumps, this stretching of the engine wasn't particularly difficult. The IR engine had been built along semimodular lines since the beginning, so grafting on two more cylinders involved mainly a new crankcase design. Cooper-Bessemer's offering was its GN-8, which extracted 60 more horsepower from 10 1/2 x 12-inch cylinders at the same 750 rpm as IR's 10 x 12-inch. Both designs were similar in over-all size, so GE proposed a 98-ton hood unit that could take either engine. Finding the GE designed acceptable, but confronted with the choice of engines, NH simply ordered five of each and stipulated that the engines be interchangeable.

This sounded nice to the railroad, but presented some messy problems for GE, IR, and C-B. Each engine builder had to co-ordinate the locations of throttle connections, exhaust pipe, and fuel, cooling-water, and oil lines with those of the other builder and with GE, whose connections on the carbody had to match either engine. An attempt was made to use the same water pump on both engines, but this effort was abandoned. GE had to design a main generator that was suited to the torque-speed curve of either engine and likewise adapt the generator mountings and shaft couplings. The starting winding of the generator had to be capable of cranking either in engine at 32 degrees Fahrenheit.

Aside from the engines, the units had a number of unique features. In view of the low-speed requirements, double reduction gearing was used in order to take advantage of the increased efficiency of a higher traction motor speed. This gave the unit plenty of low-speed dig for kicking cars and starting long cuts -  much more than it could have had if it had been geared for 40 or 50 mph. There was no transition in the control; the motors were permanently hooked up in series, and speed regulation was done by field shunting. No auxiliary generator was used either, so the air compressor and other electrically driven auxiliaries were built with dual-commutator motors that operated on 115 volts at idle and 600 volts at full throttle with equal capacity.
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( Cont. on P38 )