While the diesel engine has been falling out of favor in passenger vehicles, they remain reliable and powerful workhorses keeping the gears of industry spinning. The diesel engine has been the prime mover of agricultural vehicles for a century. However, the diesel powerplants of a century ago suffered from a major headache, one that International Harvester solved by building engines that started on gasoline first before switching over to diesel fuel.
According to Farmers Weekly, the diesel engine found its way onto farmsteads beginning in the late 1920s. The first diesel tractor is sometimes credited to the 1927 creation of Italian engineer Franceso Cassani, the founder of Società Accomandita Motori Endotermici (Same) tractors. But the Americans weren’t too far behind. In October 1931, Caterpillar introduced its Diesel Sixty Tractor. McCormick-Deering later introduced its own diesel tractor with the WD-40 in 1935. John Deere spent so much time trying to perfect its diesel engine design that it was a late entry that came out in 1949.
While these companies were able to get diesel engines chugging in tractors, early diesel engines suffered from a problem that had a number of potential solutions.
The Problem
One of the problems facing diesel engines even today is being able to start up in cold weather.
Diesel engines work on compression ignition rather than spark ignition like gasoline engines. Diesel fuel is a reliable source of power and if you’ve played with the stuff before you’ve probably noticed it’s usually harder to start on fire than gasoline.
However, one of the downsides of diesel fuel is how it “gels” up in cold weather. As diesel is subjected to weather usually at or below freezing, the paraffin wax in the fuel begins to crystallize. The further this happens, the harder it is to pump the fuel through an engine’s fuel system. In a worst-case scenario, your diesel engine may stall out, if it even starts to begin with. The exact temperatures diesel begins this process varies based on the quality and type of fuel. For example, biodiesel may begin gelling at higher temperatures than conventional diesel.
The diesel engine has been around more than long enough that there are plenty of ways to combat this, as well as the general slog of starting a giant diesel in the cold, too.
Your first line of defense is an anti-gelling additive, something I use in my diesels during the winter. Your modern diesel engine also has glow plugs. These devices sound similar to spark plugs, but they’re used just to get your diesel engine going. A glow plug has a heating element that gets glowing hot, heating up the incoming fuel and air during the starting process to encourage combustion. Bosch says its first glow plug was invented in 1922 while Denso had its own glow plugs in 1929.
Of course, there’s also the engine block heater, which helps you get going by making sure the whole engine isn’t a giant block of frozen to begin with.
The diesel engines of nearly a century ago were old-school. Farmers had to start rather sizable engines by hand cranking, but even starters sometimes weren’t enough to wake up these early diesels from a wintry slumber. To give you an example of this, the Cat 60/65 crawler had a 1,090 cubic inch engine while the IH TD-40 was still a huge 460.7 cubic inches. Both engines technically used hand cranking to start but needed help from gasoline to get going.
Cold weather cranking issues sent manufacturers scrambling for a solution, and the results were very different.
The Engine That Runs On Two Fuels
We’ll start with the way many fans of tractors may know about.
Manufacturers like Caterpillar and John Deere employed what is called a “pony motor.” The pony motor is a much smaller engine attached to the side of a monster tractor engine. These gasoline engines would fire up, rev to 4,000 RPM or above, help pre-heat the diesel fuel, and then is clutched into the main diesel engine, spinning it over until it started.
Many early pony engines were small twin-cylinder mills while others were slightly bigger V4s. Check out this video below to see a pony engine on a John Deere:
Apparently, pony engines lived hard lives. They were started up, run hard, and then shut down. Farmers would often forget to maintain these units and they would suffer from carbon build-up before eventually dying. Those pony engines would then end up replaced with a 12V starter or some other solution, so seeing an old tractor with an original working pony engine is a treat.
As Successful Farming writes, John Deere spent over 14 years developing the Model R and in that time, its engineers considered making an engine that started on gasoline before settling on the design with a pony engine starter.
International Harvester? Well, it went forward with a multi-fuel design.
As Diesel World writes, International Harvester began experimenting with diesel power in 1916. The company’s first engines were of its own design, but in 1927 IH began picking four-cylinder Dorner engines from Germany to study. At the time, those Dorner engines were smaller and lighter than their American counterparts with advancements not seen on this side of the pond. Over time, IH’s engineers would take what they learned from the German engines to create something of their own design.
Among their goals was solving the problem of cold weather starting and one day, IH also wanted its own fuel injection system. IH also wanted to produce moderate-cost engines that produced decent power on poor fuel.
Part of why IH didn’t go with a pony engine was because it was believed a pony engine was bulky, expensive, and made engine starting harder than it needed to be. That bit’s a little amusing since IH’s solution looks almost hopelessly complex. IH went through a lot of work to make a diesel engine briefly run on gasoline, from Diesel World:
[T]he essential feature of a gas start diesel was an auxiliary combustion chamber connected to the main diesel chamber by what was called a starting valve. When that was opened, the added volume of the auxiliary chamber dropped the compression ratio from 15:1 to about 5:1 and it contained a spark plug fired by a magneto. The gasoline intake tract was connected to the diesel system via an air valve. A small 3/4-inch bore carburetor supplied enough air and fuel to run the engine at about 400 rpm. A lever connected to various linkages opened or closes valves to the various chambers and disabled either the magneto or the injection pump. It worked better than you might think, especially when viewed in the context of the era when “diesel” and “cold starting” were exclusive terms.
The first generation IH diesels would be manually switched over to gas engine for starting and hand cranked. No, these first engines did not have electric start. The injection pump had a timer that counted the number of engine revolutions (about 700) and it could be used optionally to automatically trigger the system to switch back to diesel operation after approximately two minutes running on gasoline. In most cases, two minutes of running was enough to warm the engine enough to run on diesel but the operator could run the engine on gas as long as needed.
IH was cool enough to explain everything in its brochures, so I’ll pass that down to you.
A spring-loaded rod (1) opens the starting valve (3) which combines the gas and diesel combustion chambers. The lever also moves a poppet valve in the gasoline system from a lower seat (7) to an upper seat (9). A gasoline valve (6) also opens to fill the carburetor (10) and air flows into the intake (8) to the combustion chamber. Another rod (2) levers a valve, which shuts off diesel fuel flow from the injection pump, which isn’t pictured. Releasing this Rube Goldbergian system once the diesel engine is running turns the gas system off.
Yep, that means these were diesel engines with a gasoline carburetor, distributor, and a spark plug for each cylinder.
Diesel World continues that this engine, dubbed the PD-40, was initially based on IH’s existing gas engine architecture. This allowed some existing tooling to be used and thus made development a little cheaper. The engine made its debut in April 1933 and its exact specification varied based on application. This engine in a crawler was a TD-40 while it was called an ID-40 in an industrial tractor, WD-40 in a wheeled tractor, and UD-40 as a stationary generator.
The coolest application of this 461 cubic inch four-cylinder diesel was in the McCormick-Deering TD-40 TracTracTor crawler tractor. I mean, just look at it!
That straight-four was good for 62.5 flywheel HP with a continuous power rating of 50 ponies. The engine was also good for 48 HP at the power take-off.
Oh and don’t worry, you bet I have a starting procedure video for you:
Reliable Workhorses
IH would keep these engines in production for three decades, improving them along the way for better reliability and power. Additional variants included the PD-80 six-cylinder in 1936, the TD-40 and TD-80 second-generation gas-started diesels of 1939, the smaller UD-6, UD-9 and UD-16 engines of the same year, and the massive UD-24 of 1947. How big are we talking about here? The UD-24 was a thick 1,091 cubic inches and made 146 HP.
Observe the sheer girth of this bad boy:
Ultimately, the IH gas-start diesels were complex, but they were proven to be reliable engines. Diesel World notes that these engines often made less power than the competition. However, these engines were able to start reliably when the competition did not. The IH gas-start diesels were smaller and more user-friendly, too. Though, it’s noted that some would prefer the pony motor design since engines with those for starters were arguably better at being bigger, more powerful diesel engines.
IH wasn’t the only producer of this idea. In the late 1940s, Lamborghini used the architecture of a Morris Six engine to create a fuel atomizer that allowed its diesel tractors to start on gasoline, too.
Either way, the pony motor versus gas-start debate was eventually resolved once technology finally caught up. Diesels that could start in any weather made these stop-gap technologies obsolete. But, for about 30 years if you were a farmer, there was a good chance you had a diesel engine that also ran on gasoline.
Hat tip to Oliver!
This is VERY interesting!!!
There were many developments on variable displacement in 2000’s, Saab had an idea with the whole block shifting up and down, but most developments are with very variable valve timing and limiting amount of air going into the cylinders (Fiat Multiair and BMW ValveTronic).