International Harvester introduced its new Raymond Loewy Letter Series tractor in 1939. It was one of their biggest advancements. Improvements were made on all levels, from the Lowey styling to the solid technical advancements and the larger big tractor (Model M) that replaced the F-30. Initialy, three styles of tractors were introduced: the A small, the H midsize and the Burley M. A Model B that was based on the A followed soon after. These tractors were designed to replace the rather skeletal F-series tractors and replaced the W series fixed tread units that had been in use for a year.
What was missing in the 1939 debut—and what most concerns us soot-heads—is a diesel option. IHC already had a 1934 diesel option. The WD-40 unit from 1934-1940 had a fixed-tread, similar to what we now consider a standard tractor or 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. The MD engine had a similar design as the WD-40 but it was equipped with five main bearings instead of three and displaced 244 cubic inches versus 460. The diesel engines were similar in design, but the MD engine had five main bearings instead of three and a displacement of 248 cubic inches versus 460. MD, like the older IH Diesel, was a dual-engine vehicle. The MD started on gasoline and then switched over to diesel for warmup. That was innovative technology in the day, when the few “ag diesels” in use were started by gasoline pony engines or with compressed air.
The driver would open a third cylinder head valve (called the starting valve) to expose a separate combustion room, increasing the size of the chamber and exposing the spark plug. The engine was fitted with a 6.75 to 1 CR, and a fixed-orifice, tiny carburetor that only allowed the engine to idle at high speeds. The control opened the fuel valve on the carburetor, disengaged the distributor, and also opened the butterfly valve connecting the gas cycle combustion chamber and the inlet air.
The engine would be started with a 12-volt battery and idle between 6 and 800-rpm. The engine was warmed up for as long as it took to allow diesel combustion. The driver could not control the idle speed, even though there was a throttle. After the engine had been warmed up for between one and three minutes, the lever to release the compression was pushed back quickly. The compression release lever was then pulled back quickly. The engine began to run on diesel almost immediately. To shut down the engine, you switch back to the gas and turn off the ignition.
It may seem a bit cumbersome today, but this was one of the most effective ways to turn a diesel on in cold weather before batteries or starting systems could do it. Glow plugs were not practical until a decade later, and again battery capacity was a major factor. Direct start diesels made a huge impact when they were introduced in the mid-1950s.
In a 1941 Nebraska Tractor Test, the MD was rated at 36 belt horsepower. This is about three less than a gas engine that shared the same block and bore/stroke as the diesel. Both engines were rated at 1,450 rpm. However, the diesel was much more fuel-efficient. The gas 248 cid four used 3 GPH of fuel at full power, while the diesel only 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 a lot, especially considering how simple the time was. But some were unique to the gas start diesel. The electrical system and instrumentation were very basic. There was just three gauges – the ammeter, the oil temperature gauge and the water pressure gauge. The tractor was available with a side-mounted PTO belt, a live rear PTO, and a swinging drawbar. The rear tread was adjustable between 52 and 88 inches. The Lift-All, an optional hydraulic lift that worked with many of the implements made by IH, was available.
International Harvester MD is a key development which brought diesel power to the forefront of farming. 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. This was despite a steep learning curve and some clunky 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
[divider]Typical Specifications: 1941 Farmall MD[/divider]
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
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
Explore the Diesel History of International Harvester Tractors on Diesel World