Vintage Diesel Engine That Starts On Gas

International Harvester’s Gas Start Diesels

Making diesels user friendly was an uphill struggle in the late 1920s and early ‘30s. The advantages of the compression-ignition engine were generally known but the PITA involved in using one back then often outweighed those benefits. Part of the diesel reluctance was infrastructure related, such supply issues at the user level. Support for diesel powered equipment was few and far between in those days. Day-to-day, especially for hand-started engines, cold weather operation remained a big stumbling block.

The International Harvester Answer

International Harvester (IH) started experimenting with diesels in 1916 with a single cylinder prechamber design concocted in their own shop. Not much came of it but in 1927 the Gas Power Engineering Department bought a 4-cylinder German Dorner diesel to evaluate. The Dorner was impressive enough that in1928, IH engineers made three other experimental test engines and eventually came up with their own design. In 1930, they bought and tested other makes of German-made diesels against their design and found it worthy of production. part of that process was also to design and later build their own fuel injection systems.

Part of the base problem was to solve the starting issue. In large stationary applications, air start was the option. As engines got smaller, some of the smallest (mainly single cylinders) could be hand started but battery technology had not progressed far enough in the ‘30s to make electric start viable in most cases. Caterpillar, and others, used pony engines, a separate gasoline engine that ran long enough to heat the diesel a little and then spin it over. That worked very well but added a lot of bulk, expense and extra steps.

IH developed a system that combined a gas engine with a diesel. We’ll tell you exactly how in a sec, but the engine started on gasoline and then switched over to diesel after it was warmed up. In the long run, the gas start system was probably more user friendly, especially for equipment that had a lot of stop/start cycles, and it made the overall engine package more compact, and IH had the long term goal of adding diesel power to their smaller tractors. The pony-started engines were probably better diesels because they didn’t have to make any tradeoffs on the diesel part of the design. That worked for Cat because the majority of their equipment was bigger. It’s not so much a “which is better” question but more two roads to the same place, each route chosen to better serve the needs of each company.

The Production Engines: PD-40 
and PD-80

The early IH diesels were initially based on IH heavy-duty gas engine architecture. This aided both the development and especially the manufacturing, where at least some of the gas and diesel components could be manufactured on the same tooling. The first production IH diesel was dubbed the PD-40 and debuted in April of 1933. If it was in a crawler, it would be called a TD-40. In a wheeled tractor, the WD-40. A power unit would be a UD-40. If in an Industrial tractor, it was the ID-40. The engine designation was also the tractor designation in this era.

The big innovation was the gas start feature. Look at the nearby illustrations for more detail, but the 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.

A six-cylinder diesel began development in 1933 and was released for production as the PD-80 in February of 1936, debuting in July. It was essentially the PD-40 with two cylinders added. It was a stout seven main engine with wet sleeves. It did have some design evolution over the PD-40, notably an improved combustion chamber. Making 691 cubic inches from the 4.75 x 6.50 bore and stroke, the engine cranked out a maximum of 100 horsepower and 80 continuous horsepower at 1400 rpm. It didn’t find a home in tractors but was offered in a power unit starting in 1937.

The PD-35 engine was a short-lived variant of the PD-40 that only appeared in the ‘37-39 TD-35 crawler. With a bore 1/4-inch smaller than the PD-40, it made four horsepower less, as measured in Nebraska tractor tests. As far as we can see, the PD-35 engine was not offered in anything but the TD-35 crawler, which was marketed as a “budget” TD-40.

TD-14/TD-18

The TD-40 and TD-80 evolved in 1939 with a large number of improvements. The evolution had begun with the 1936 updates mentioned. The original engines were basically sound and reliable, so the main thrust was improving combustion efficiency and increasing output. Major changes occurred to the cylinder head, combustion chambers, fuel injection and the way the gas start system operated. As such, the UD-40 engine became the UD-14 and the UD-80 became the UD-18. The UD-18 found a home in the TD-18 tractor at the end of 1938, making it IH’s most powerful crawler for a time. Initially, the maximum output of the four-cylinder engine increased to 81 horsepower maximum, 68.5 intermittent and 54 horsepower continuous. The six jumped to 119 max, 100 intermittent and 80 continuous. The power increases were not gigantic but efficiency and economy was much improved.

In 1946, another upgrade was released for production, the UD-14A and UD-18A, incorporating more improvements in breathing and combustion chamber design. The result was a maximum of 90.5 horses for the UD-14A and 150 horses for the UD-18A. This series of engines would remain in production into the early ‘60s. The UD-14A is still seen in the 1960 engine catalog but not the UD-18A, which ended in 1958, replaced by more modern six-cylinder designs.

New Kids: UD-6, UD-9 and UD-16

In 1939, two smaller gas-start, four-cylinder diesel engines were released for production, the 248 cubic inch UD-6 (3.88 x 5.25-inch bore and stroke) and the 334 cubic inch UD-9 (4.40 x 5.50-inch bore and stroke). The UD-16 was a six-cylinder variant of the UD-9. Both the fours were available in tractors or as power units. Following previous convention, the UD-6 appeared in the 1940 TD-6 crawler and the  WD-6 wheeled standard tractor and in the 1941 Farmall MD, International’s first rowcrop diesel.

The UD-6 shared a lot of features with the gas and distillate engines that had debuted with the new model M wheeled tractors and the W6 that had debuted for 1939. These new fours were dry sleeved with three main bearings. The new UD-6 delivered a maximum of 45 horsepower at 1500 rpm, though the continuous rating was only 39 horsepower. This series engine used a new IH injection pump that debuted at the same time.

The UD-6, UD-9 and UD-16engines were updated in 1953 with bore increases, the UD-6 to 4 inches and the UD-9/UD-16 to 4.5. This bumped the displacement to 264 and 350/525 cubic inches respectively. With some accompanying tuning and a 100 rpm bump in the redline, the UD-6 delivered a max of 54 horsepower and the UD-9 78.5. These engines saw use in the “Super” versions of the MD, WD-6 and WD-9, as well as with power units. They also appeared in the updated tractor lines like the 400 Farmall from 1954-56 and the W400 standard.

The final evolution of the UD-6 engine line came in 1956, with another bore increase to 4.125 inches. This bumped the displacement to 281 cubic inches. As far as we can determine the TD-9 engine continued on as it was until it was discontinued in 1958.

The Biggest Boy: UD-24

The biggest gas start IH diesel was the UD-24, used in a power unit and the TD-24 crawler starting in 1947. It was a beast, making 1,091 cubic inch from a 5.75 x 7.00 inch bore and stroke. In the big IH TD-24 crawler (built 1949-1959), it made 146 horsepower on the drawbar. Around 1955, IH adopted new terminology and renamed this engine the UD-1091 and it was offered as a stationary unit at least through 1960.

The Final Word

IH got a lot of mileage out of their gas start designs and even late in their 30 year run, when the diesel industry was finally getting a handle on cold starting issues, those so-called “all-weather diesels” still had a strong place in the market. Their design left a few horsepower on the table compared to what came later but even as improved IDI and DI engines came on the market, a lower-power diesel that starts on that cold and snowy day is better than a higher power one that doesn’t.