Tractor Talk: A Pair Of Vintage Cummins Swaps

You’d be forgiven if you think that Cummins swaps are something new and confined to the light truck realm. Not so, diesel heads, and here are a couple of tractors to prove it.


In the 1950s, the era of the diesel tractor was just beginning. Diesel-powered tractors were just a tiny part of a market dominated by gasoline. It might even be safe to say that the propane-powered tractor market share was almost as big as diesels. That was soon to change, but if you were a farmer sold on diesel power in those days, you had slim pickings. Why? Partly, it was the diesel technology of the time, which had only recently evolved into a size practical for tractors with a power output and rpm range that approached gas engine levels. Many farmers were hesitant to jump on the bandwagon and, frankly, the infrastructure wasn’t fully in place to support a large number of diesel tractors on farms.

From the pilot seat, a guy might never know he’s running a Cummins. The controls didn’t change from the 450. These tractors were sold without engines but it isn’t clear if they were configured for gas or diesel engines. The proof meter is showing only 1,714 hours, but it’s very likely this tractor has many thousands more.

Two of a kind! It’s almost a miracle that both of these Cummins-converted tractors have survived. Louis Wehrman (right) and Galen Wilkinson are from different states but bring the two “brothers” together as often as possible. Both of these tractors were operated by Gumz farms for approximately 10 years before being sold or traded off.

On the other side of the manufacturing coin were independent diesel engine builders who promoted the use of modern high-speed diesel engines… their engines, of course… and were looking to place them into as many parts of the motor industry as possible. Among the heavy hitters in this were General Motors and Cummins, who actively pursued tractor diesel conversions.

According to Galen Wilkinson and Louis Wehrman, the owners of the tractors you see here, Cummins invited 28 Indiana farmers to their Indianapolis facility in 1958. The purpose was to float the idea of repowering International Harvester tractors with Cummins engines. Yes, IH was making diesels in those days, but they were anemic things compared to what Cummins was offering.

Gumz farms of North Judson, Indiana, saw the benefits of Cummins-powered IH tractors and stepped up. They ordered two Farmall 450 tractors without engines, one narrow and one wide front. There’s evidence that IH was at least an interested party in this deal, but it isn’t clear how much they were involved. It’s very likely they were “interested” on some level, but little paperwork exists to show the degree of interest. IH was using Cummins J-series six-cylinders in some of their OTR semi-trucks, so the two companies had a little history at least. We also know IH was well on its way to becoming a powerhouse diesel engine manufacturer then and too much business between them would soon have led to market conflicts.

The two faces of the Cummins J4-70. It was a five main, direct-injected engine with two valves per cylinder. Fuel is distributed via a Cummins PT pump and the injectors were the pintle type. These engines were rated for 2,000 rpm, but others revved up to 2,500. We haven’t been able to find a torque rating for this engine but it was likely in the 250-lb/ft range. You may notice the difference in colors between the two engines. It appears this more gold shade is the correct one and matches up to the ’50s era paint. Today, this color is called “Cummins Old Gold” if you can find it. The adaptation looks pretty easy from here, with little more than a steel adaptor plate used to mount to the trans and some mods to the frame rails. Parts for these engines have been getting more difficult to find in recent years.

Other than the engines, they are Farmall 450s… but with a lot of extra juice. The Cummins J4-70 made about 20 hp more than the 280-cid gas-start IH diesel that came stock. Behind the engine, there was a standard 450, including the new IH Fast Hitch and the famous IH mechanical TA (torque amplifier). Louis’ 450 was the one fitted with a wide front as well.

The J-series engines came in four- and six-cylinder configurations with the basic designations J4 (shown) for the fours and J6 for the sixes, both two valves per cylinder. They all shared a basic 4.13 x 5 inch bore and stroke with the J4 making 267 cid and the J6 401 cid about 100 hp @ 1,800, or 110 @ 2,200 for the JS-6. The base J4-70 four made 70 hp at 2,000. The J4-80 made 80 hp at 2,500 with just a little pump tweaking. A JT4 version was rated at 117 hp @ 2,500, the “T” in the designation indicating a turbocharged engine. The JN engines used four valves per cylinder versus two. The naturally aspirated JN-6 made 130 hp @ 2,500. Some two-valve sixes, like the JS-6, came mechanically supercharged (the “S” for supercharged) and made 160 hp @ 2,500. The four-valve sixes came either supercharged (JNS-6, 175 hp @ 2,500) or turbocharged (JT-6, 175 hp @ 2,500). All these ratings came from a 1959 manual. It isn’t clear if any four-valve or supercharged fours were built.

The two Farmall 450 tractors were received by Gumz in December of 1958 and two J4-70 engines from Cummins arrived in March of 1959. The engines and tractors came together shortly thereafter when the engines were installed at Gumz Farms under Cummins supervision. Gumz was, and still is, a major multi-state farming entity, with Indiana being where this German emigrant family first settled in the early 1900s. Gumz used the converted tractors for 10 years before selling them off separately. With new owners, they continued to be viable as farming implements into the 1990s when they began to acquire some collector interest.

Let’s not forget the tractors in all our Cummins excitement. Both the Farmall 450s were standard units, save the few mods necessary to fit the engines. The 450 had debuted in 1956 as an upgrade to the 400 model. The upgrade was mainly an increase in engine displacement. The 450 was at the end of its run in ’58, when Gumz purchased the two without engines. The restyled 460 model would replace it in late ’58. The 460 and its bigger brother, the 560, would be plagued by final drive issues due to their increased power levels being applied to a warmed-over, old generation final drive. Reputedly, the two converted 450s suffered from a touch of this in later years.

While Cummins was actively pursuing the use of their engines in agriculture, this was a marginal market for them until the late ’70s when they collaborated with Case to form the Consolidated Diesel Corporation. The fruits of this collaboration, among other things, would be the B, C and ISL series engines branded both by Cummins and Case. All of those engines would find extensive use in the ag world. Yeah, Cummins conversions are now all the rage, but now you know the rest of the story. DW