1939 McCormick-Deering WD-40 "cold start" demonstration.

The WD-40 was America's first wheel tractor to feature a diesel engine. The economy of the diesel was well recognized, but until International Harvester introduced the WD-40 in 1934, diesel power had never been applied to American-built wheel-type tractors. The WD-40 was designed for large farms, as evidenced by a maximum of 48.79 belt and 37.21 drawbar horsepower in Nebraska Test No. 246. Production totaled 3,370 units in a run that ended during 1940.

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If the w-40 was a six cylinder engine why was the wd-40 made a six cylinder?