Classy & Powerful Diesel Tractors

The 1950s was the last decade in which the small crawler was a player in the agricultural tillage industry. To that time, crawlers (A.K.A. tracklayers) offered farmers a lot of drawbar power in a small and economical package.

By the 1950s, wheeled tractors had narrowed the drawbar power gap in the smaller tractor markets. Plus, farms were getting bigger, requiring faster travel between fields. To a farmer that only worked his section out back of the house, a 5 mph crawler was fine, but as farms got bigger and fields were separated by road travel, the 15-25 mph road speed of the wheeled tractor became just as important as the being able to pull larger implements with less horsepower.

Tim Haban’s ‘52 TD-6 is a standard track width set up for ag use, but has what appears to be 16-inch track shoes replacing the standard 12-inch parts.

In this installment, we give you the juxtaposition of the same model crawler outfitted two ways; one for agricultural work and the other for construction and earthmoving. They are both essentially the same crawler and share the same ability to mount implements, but each was sold for a different purpose.

The TD-6 was the smallest in an updated line of new International Harvester tractors that debuted in the late 1930s. It debuted in 1940 and joined the big TD-18, the medium TD-9, and several others in a range to counter the Caterpillar juggernaut that had been sucking a lot of the air out of the room in the crawler market. Initially dubbed “TracTracTors,” they were good enough to be a challenge to Cat and they sold pretty well. The TD-6 was equivalent in size and power to the Cat D-2 but was actually in production to 1969 in various forms, much longer than the D2 that ended in 1957.


The big difference between the two crawlers is at the rear. The Ag unit has a swinging drawbar and a 540 rpm PTO. The dozer has the same drawbar but no PTO and a very elaborate hydraulic system to operate the blade.

The TD-6 came in three iterations, the ‘40-55 first series units, the Series 61 from ‘56-60 and the Series 62 from ‘60-69. Though most used a four-cylinder diesel, a gasoline engine was also on the options list for all three series. Variants included an orchard model with narrow tracks, extra tin, and a tail seat. The IH crawler line was quite popular and well regarded in the era of our two feature tractors, with 30,035 TD-6s built from ‘40-56, plus another 8,355 T-6 gassers and a few hundred orchard models. The later 61 and 62 Series weren’t quite so popular, with only 5,349 of them built, combined. As far as we have been able to determine, the Industrial Yellow (Federal Yellow) paint started for the TD-6 with the ‘56 Series 61 units.

The powerplant for the TD-6 was the same as used in several wheeled tractor models, including the model MD, the D248. It started on gasoline via an electric starter. The driver operated a compression release lever opening the third valve in the cylinder head, called the starting valve. It uncovered a separate combustion chamber that both increased the combustion chamber size and exposed the spark plug and a separate intake manifold with a tiny carburetor big enough to run the engine at a fast idle. With the starting valve open, the engine had a 6.75:1 CR. At the same time, the control disengaged a distributor ground to let the magneto go active, 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 Ag TD-6 has a hydraulic system as well, which was optional, but it’s more or less equivalent to what a wheeled tractor of the era would use.

The engine would idle at 6-800 rpm on gas for as long as needed to make enough heat for diesel combustion. Though there was a choke, idle speed was not controllable by the driver. After warming the engine up, 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 shutdown, you switched back to gas and shut the engine off with the ignition switch, making it ready for the next start.

The operating station is virtually identical between the two tractors, though the dozer would have some extra hydraulic controls and the ag unit has a PTO lever. Crawlers were noted for much less ride comfort than wheeled tractors… if the term “comfort” can be applied to any vintage tractor.

By the end of the ‘50s, International had moved their crawler line more into the construction side than the ag side and gave then a more industrial look by painting them yellow. You could still get an ag crawler, but not many did. Internationals crawler line withered through the ‘60s and ‘70s and as the company faced it’s ultimately fatal financial crisis, the entire construction line, including crawlers, was sold to Dresser Industries.


One shot from each crawler shows the two sides of the TD-6 engine. Displacing 247.7 ci from a 3.88 x 5.25-in. bore and stroke, the four-cylinder diesel started on gasoline and was then switched to diesel once warmed up. This was International’s signature diesel system for many years. It avoided the weight and complexity of a pony engine in an era where direct electric start diesels were still just over the horizon. Despite only producing about 40 horses on the belt, the TD-6 could deliver 34 of them to the drawbar in the Nebraska tests. IH underrated them a little from the Nebraska test at 36.23 belt and 29.5 on the drawbar. It was a three-main engine that was dry sleeved.


1949-52 International TD-6 Crawler

ENGINE: D248, gas-start diesel
BORE & STROKE: 3.88×5.25 in.
*RATED BELT POWER: 40.25 hp @ 1450 rpm
*RATED DRAWBAR POWER: 33.78 hp @ 1451 rpm
FLYWHEEL POWER: 39 hp @ 1500 rpm
RATED TORQUE: 155 lbs-ft @ 850 rpm
WEIGHT: 7,235 lbs.

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