The depths of the Depression was a difficult time for Clessie Cummins to get his fledgling diesel engine business going. But in 1933, he finally convinced a major truck manufacturer—Kenworth—to build standard production diesel trucks. Kenworth chief engineer John Holmstrom added his own idea—a vertical exhaust pipe behind the truck’s cab, to direct the inevitably smoky exhaust away from pedestrians. Thus was born the iconic big American diesel truck.
Cummins had started his company in 1919, a few years after Rudolf Diesel’s patents in the US expired. Initially his focus for the large, heavy and low-output motors was for marine use, but in 1929 he installed one of his new Model U engines in a used 1925 Packard 7-passenger limousine, undoubtedly chosen for its ability to take the 1200 lb diesel engine, both in size and weight. That front tire looks to be oversized for that reason.
Cummins increased its output from 40hp to 50hp @1000rpm, and drove it from Indianapolis, IN to New York, a distance of 792 miles. With an average speed of 31.7 mph on the roads of the time, the 6,000 lb diesel Packard yielded 31.4 mpg, using very cheap (4 cents/gal) fuel oil.
The Packard was to be shown at the New York Auto Show, but it attracted more attention from the marine industry exhibitors across the street than the automotive exhibitors.
Cummins went on a publicity blitz in the next couple of years that included several cross-country trips in custom-converted trucks and buses like this Indiana as well as numerous high-speed and Indy car racers (we covered the Indy 500 racers here).
Except for a few one-off custom installations, no truck makers took the bait. It was in the depths of the Depression, and there was no interest in making the investment to adapt the very slow selling trucks of the time. Cummins’ financial backer William Irwin had a majority interest in California-based Purity Stores, and agreed to convert the small fleet of White trucks to the new Model H diesel.
In 1932, West Coast truck builder Kenworth decided the time was right to commit to the nascent diesel market, and began offering the Cummins HA-4 as a standard factory model. Kenworth’s first diesel-powered production model was built for California-based Valley Motor Express, which requested the truck be shipped down the West Coast from Seattle most of the way by water so it would arrive truly new.
The HA-4 had a 4.875″ bore and 6″ stroke for 448 cubic inches. Fed by Cummins’ own disc fuel injection pump and pushrod-actuated injectors, it made 100 hp @1800 rpm. The larger six cylinder version had 672 cubic inches.
Doesn’t sound like much power, but 100hp was actually a pretty healthy amount for the times, when typical truck speeds on the level was 35-45 mph. Fuel economy was considerably greater compared to a comparable gas engine, and overall fuel costs were even much lower yet, thanks to very cheap diesel fuel at the time. The diesel revolution was on.
By the mid-late ’30s, Cummins-powered Kenworths—and other truck brands—were becoming increasingly common, especially as the distances they covered became greater.
Those greater distances were facilitated by another Kenworth innovation: the first factory integrated sleeper cab, also in 1933. The combination of the two were key factors in the growth of long-haul trucking.
By the 1940s, the classic Kenworth look was already well established.
Along with Peterbilt, the two big West Coast truck makers became the icons of the big American diesel truck.