The Tractor that Brought Diesel Power to Mainstream Farming

When International Harvester debuted its new Raymond Loewy-designed Letter Series tractors in 1939, it was one of their bigger advancements. The improvements came on just about every level, starting with the Lowey styling and ending with solid advancements on the technical side and a bigger big tractor, the Model M, to replace the F-30. Three styled tractors debuted initially, the small A, the midsized H and the burley M, followed shortly after by a Model B, which was mostly an adaptation of the A. These tractors replaced the rather skeletal-looking F-series models and supplanted the W-series fixed tread units, which benefitted from the same level of advancement a year later.

What was missing in the 1939 debut—and what most concerns us soot-heads—is a diesel option. IHC had a diesel option then, one that dated back to 1934. Their 1934-1940 WD-40 was a fixed-tread unit of a type we would later consider a standard tractor, or a Wheatland model. It was for sale through 1940 as the company’s only wheeled diesel farm tractor. For 1941, the Farmall MD (D for diesel) debuted as the company’s first general purpose, adjustable tread diesel farm tractor and a new WD-6 would replace the WD-40 and a more powerful WD-9 would also appear.

The MD diesel was simply a model M, same features and options, but with International’s newly upgraded gas-start diesel. While the MD engine was of a similar design to the WD-40, it had five rather than three main bearings and displaced 248 cubic inches versus 460. They both made approximately the same belt horsepower, which illustrated the improvements in diesel technology. Like the older IH diesel, the MD was two engines in one. For starting and warmup, it operated on gasoline but was then switch over to diesel operation. That was innovative technology in the day, when the few “ag diesels” in use were started by gasoline pony engines or with compressed air.

To start the engine, the driver operated a compression release lever opening a third valve in the cylinder head, called the starting valve, uncovering a separate combustion chamber that both increased the combustion chamber size and exposed the spark plug. With the starting valve open, the engine had a 6.75:1 CR and used a tiny, fixed-orifice carburetor designed only to run the engine at a fast idle. At the same time, the control disengaged the distributor ground, opened a fuel valve in the carb and a butterfly valve that connected the gas cycle combustion chamber to inlet air and closed the diesel intake.

The engine was cranked over using a 12-volt starter and would idle at 6 to 800 rpm. This was enough to warm the engine up as long as needed for diesel combustion to be possible. Though there was a choke, idle speed was not controllable by the driver. After warming the engine up for one to three minutes, the compression release lever was pulled back briskly. That closed the starting valve, shut off the gas to the carb, grounded the distributor (killing the spark), closed the gas intake manifold and enabled the diesel injection pump. The engine then began running on diesel with barely a hiccup. For the shut down, you switched back to gas and shut the engine off with the ignition switch, making it ready for the next start.

This all seems pretty onerous today, but it was one of the more effective ways to start a diesel before batteries and starting systems had enough oomph to spin a diesel over in cool weather, let along cold. Practical glow plug systems were still a decade or more in the future, again limited by battery capacity. The direct start diesels were a big deal when they debuted in the mid 1950s.

The MD was rated in a 1941 Nebraska Tractor Test at 36 belt horsepower, about three less than the gas engine whose block and bore/stroke the diesel shared. Both the gas and diesel had the same rated speed, 1,450 rpm, but the diesel was, of course, more economical. The gas 248-cid four burned 3 GPH at full power while the diesel used 2.4 GPH. The diesel maintained the same lead over the gasser in the in the varying load tests, averaging 1.56 GPH versus the gasser’s 2.16 GPH. With the MD’s 16-gallon fuel tank, a farmer could conceivably do a day’s work on one tank of fuel.

The controls were numerous considering the simplicity of the era, but a number of them were specific to the gas-start diesel. The electrical system was very basic, and the instrumentation was limited to three gauges: the ammeter seen here, an oil pressure gauge and water temperature gauge on the hood.The diesel was backed up by a five-speed transmission and IH advertised the tractor could run a then-impressive 16 mph on the highway. Options included a side-mounted belt PTO, a rear PTO (not live), and swinging rear drawbar. The rear tread width was adjustable from 52 to 88 inches. An optional hydraulic lift, called the Lift-All was optional and worked with most of the available implements built by IH.

The International Harvester MD was a pivotal development that brought diesel power into the farming mainstream. That’s not to say farmers were lining up in throngs to buy the MD, or any other diesel tractor, but one by one they learned the benefits of diesel power. That was despite the learning curve and sometimes-cranky new technology. It was a long time before diesel tractors became as user friendly and familiar as the gas and distillate (kerosene) fueled tractors, but after 1941, the industry got it’s first milepost in the MD. DW

Engine:                                                     Four-cylinder IH
Displacement:                                      247.7 cid
Bore and Stroke:                                 7.88 x 5.25 in.
*Rated Belt Power:                             36.56  hp @ 1,451 rpm
*Rated Drawbar Power:                   33.04 hp @ 1,451 rpm
Compression Ratio:                           16.5:1
Transmission:                                       Five-speed
Weight:                                                  5,300 lbs. (unballasted)
Tires:                                                       Front- 6.50-16/Rear- 12-38
*Fuel Consumption:                         2.404 GPH @ full power
Top Speed:                                             16 mph

*As Rated by  Nebraska Tractor Test 368

FREQUENTLY ASKED QUESTIONS

How did International Harvester influence modern agricultural and transportation industries?

How International Harvester Shaped Modern Agriculture and Transportation

The story of International Harvester is a fascinating journey from the age of the horse-drawn reaper to the era of advanced diesel engines. The company’s influence is far-reaching, impacting both agriculture and transportation sectors significantly.

Pioneering Agricultural Machinery

International Harvester traces its roots back to Cyrus McCormick, who patented a horse-drawn reaper in 1834. This innovation began a revolution in agricultural practices as McCormick’s machines became instrumental in America’s westward expansion. In 1902, a merger formed International Harvester, which dominated 90% of the grain binder market.

The company’s foray into tractors began in 1905, but it was the introduction of the Farmall tractor in the 1920s that truly transformed farming. The Farmall’s design, featuring high ground clearance and a unique configuration, set the standard for modern tractors. These machines allowed farmers to replace horse teams, significantly reducing operational costs and improving efficiency.

Expanding and Innovating Tractor Models

Throughout the years, International Harvester continued to innovate, releasing various successful tractor lines. The introduction of the F-Series and the sleeker letter series in the 1930s and 1940s broadened their impact. Models like the Farmall Regular, followed by the more powerful F-Series and letter series like A, B, H, and M, became iconic. These tractors were known not only for their utility but also for their durability, ensuring they remained beloved by agricultural enthusiasts.

With the Hundred Series, starting in 1955, International Harvester prioritized power and versatility, cementing its role as a staple in farm equipment.

Influence in Transportation

International Harvester’s footprint extended beyond agriculture into the automotive and transport industries. Starting light truck production in 1907, the company later focused on heavy-duty industrial trucks. Though it ceased making light trucks in 1975, their endeavors in transportation technology continued to influence the industry.

The diversification into home appliances like refrigerators and air conditioners demonstrated their adaptability, although this division was eventually sold to Whirlpool in 1955. The adaptation to changing markets was a hallmark of their strategy.

Corporate Transitions and Legacy

After selling its farm equipment division to Case, leading to the formation of Case IH in 1985, the company rebranded as Navistar International Corporation. As Navistar, they produced varied diesel engines, notably for Fordpickups, and expanded into manufacturing school buses and military vehicles.

The legacy of International Harvester is one of innovation and transformation. Through its development of durable, efficient machinery and vehicles, the company not only shaped agricultural practices but also left an indelible mark on the transportation industry. In doing so, it set a standard for modern industrial practices that continue to influence these sectors today.

When did International Harvester manufacture its first tractor?

International Harvester entered the tractor manufacturing scene in 1905, marking their initial production of these agricultural machines.

How did International Harvester’s Farmall line evolve over time?

When International Harvester debuted its new Raymond Loewy-designed Letter Series tractors in 1939, it marked a significant leap in agricultural machinery. These advancements spanned from the innovative Loewy styling to substantial technical improvements, culminating in the robust Model M, which replaced the F-30. Initially, three styled tractors were introduced: the small A, the midsized H, and the burly M. These were soon followed by Model B, an adaptation of the A. This new lineup replaced the skeletal-looking F-Series and overtook the W-Series fixed tread units, which saw similar advancements a year later.

The journey of Farmall began much earlier. Originally, it was a single model designed to replace horse-drawn equipment, offering farmers a versatile, cost-effective alternative. The Farmall line quickly evolved, introducing the F-Series designations like F-20 and F-12, reflecting both technological improvements and a shift in agricultural needs. By 1936, these tractors adopted the striking Harvester Red No. 50, a color that became iconic.

What was missing in the 1939 debut—and what most concerns us soot-heads—is a diesel option. IHC had a diesel option then, one that dated back to 1934. Their 1934-1940 WD-40 was a fixed-tread unit of a type we would later consider a standard tractor, or a Wheatland model. It was for sale through 1940 as the company’s only wheeled diesel farm tractor. For 1941, the Farmall MD (D for diesel) debuted as the company’s first general purpose, adjustable tread diesel farm tractor and a new WD-6 would replace the WD-40 and a more powerful WD-9 would also appear.

The introduction of the Letter Series marked a pivotal moment in the Farmall line’s evolution. Each letter denoted a specific model, from the smallest A to the powerful M, with the MD introducing a diesel engine. This innovation was a game-changer, despite the initial learning curve. Farmers gradually embraced the benefits of diesel, paving the way for future advancements.

The MD diesel was simply a model M, same features and options, but with International’s newly upgraded gas-start diesel. While the MD engine was of a similar design to the WD-40, it had five rather than three main bearings and displaced 248 cubic inches versus 460. They both made approximately the same belt horsepower, which illustrated the improvements in diesel technology. Like the older IH diesel, the MD was two engines in one. For starting and warmup, it operated on gasoline but was then switch over to diesel operation. That was innovative technology in the day, when the few “ag diesels” in use were started by gasoline pony engines or with compressed air.

By the 1950s, the Farmall line continued to evolve, transitioning to the Hundred Series, where numerical designations indicated power levels. Models like the 350 became common sights on farms, underscoring the line’s adaptability and enduring legacy in agricultural machinery.

The International Harvester MD was a pivotal development that brought diesel power into the farming mainstream. That’s not to say farmers were lining up in throngs to buy the MD, or any other diesel tractor, but one by one they learned the benefits of diesel power. That was despite the learning curve and sometimes-cranky new technology. It was a long time before diesel tractors became as user friendly and familiar as the gas and distillate (kerosene) fueled tractors, but after 1941, the industry got it’s first milepost in the MD.

The Farmall story is one of continuous innovation and adaptation, reflecting the changing landscape of agriculture and the relentless pursuit of efficiency and power.