A side view of the Jumbo shows a sleek and modern tractor, at least by 1965 standards. The tractor began drawing a crowd almost immediately. “Right away, people came from Brazil, Puerto Rico, the West Coast of the U.S. and many other places, to take pictures of the Jumbo,” builder Alan Adams says. Photo by Nikki Rajala.
Alan Adams already had more natural talent with machinery by age 30 than many men amass in a lifetime. So when he decided to build a tractor designed to tackle specific problems on his Minnesota farm, it didn’t seem like an insurmountable undertaking to him.
“Some of the machinery was getting too small for my farm,” Alan says, “so in 1963, I decided to build a four-wheel drive tractor.”
He’d been using Caterpillars and other tracked tractors before that, and he figured a four-wheel drive could go through anything he could see or work with on the Wendell, Minnesota, farm where he raised wheat, corn, barley, corn, soybeans and sugar beets.
The only limiting factor was the engine in his possession: a 401-cubic-inch V-6 GMC engine. With 180hp on tap, the gasoline-fueled engine meant the tractor had to be big – which it would be. When completed, his creation – which he christened the Jumbo – weighed in at 14,500 pounds.
A close-up of the Jumbo’s articulated construction. Photo by Bill Vossler.
Parts sourced from junkyards
Alan used 1/4-inch steel plate for the framing and housings. Side plates for the engine weighed in at 420 pounds each. He started building the tractor from there, using parts scrounged from junk piles and used machinery lots all over Minnesota.
He learned as he went, and not everything worked like he wanted it to. “Originally I bought two McCormick-Deering WD-9 tractors from a tractor salvage yard to use for the rear ends for this tractor,” he says. “I had to take out all the gears, and then use an outside source of power. But it didn’t work. I used a gearbox from an Adam’s Road Grader, but that didn’t hold, either.”
Then he had special gears made to specification in Minneapolis, and even went so far as to have them electro-hardened. “But they got too hard, and the teeth busted out,” Alan says. “So I went to my local machine shop and had a gearbox made from scratch with no gears and a triple, 80 roller chain of 1/2-inch steel on it, made along with bearings and an eccentric.”
Alan’s home-built Jumbo tractor will pull seven 16-inch plows using 8 gallons of fuel per hour. The tractor has a 140-gallon fuel tank. The radiator holds 10 gallons of coolant. Photo by Bill Vossler.
Finally: a solution, albeit one that involved a lot of holes around the outside to use in tightening the chain – which he attempted to do after using the tractor to plow several thousand acres of cornstalks. But it wouldn’t budge. “The chain was as tight as the day it was put it in,” he says. “It hadn’t worn out.”
The chain had only one downside. “If you’re going to drive it down the road at 20mph or up to its highest speed of 35.8mph, the chain will get hot because there isn’t any lubricant in it,” Alan says. “But if you’re running it in the field at 7 or 8mph, it will run all day.” Its lowest speed is .8mph. Since Alan only used the Jumbo in fields no more than 2-1/2 miles apart, speed wasn’t a problem.
An evolving design
Alan sold parts of the pair of WD-9 tractors to pay for parts he still needed for his Jumbo. He sourced replacement parts from Federal, Ford and International Trucks. The hydraulic system is Gresen, and the power steering, identical to that used on heavy earth-moving equipment, is a Char-Lynn.
A rear view of the home-built Jumbo gives an indication of the tractor’s large footprint. Photo by Bill Vossler.
The tractor’s original transmission was a combination of two transmissions from Clark and White trucks, a 4-speed in front of a 5-speed, which translated into 26 forward gears and 10 reverse gears. “I soon found out that when you shifted the 4-speed down, it tore the 5-speed to pieces,” Alan says, “so I took them both out and put in a Road Ranger 10-speed from a 4x4 truck. So now I don’t have all those gears.”
Another change involved the Jumbo’s tires. “At first I used those WD-9 tires, which were 14 inches high, but too narrow for what we were pulling,” Alan says. “So I split the rims in the middle and added 4 inches in each rim, widening them out, so now I’ve got 23.1x30 tires on it, which is better because of less soil compaction and greater traction.”
The Jumbo’s original tires (salvaged from a McCormick-Deering WD-9) were replaced with these larger 23.1x30 tires, which provided greater traction and reduced soil compaction. Photo by Bill Vossler.
Building a bargain
The cab was the biggest challenge Alan says he faced in building the Jumbo. The tractor was assembled inside a barn with a loft that crowded into the work space, leaving no space to put a cab on the tractor. A year later, though, he found a way to add the cab.
The Jumbo’s operator area. Photo by Nikki Rajala.
Almost all of the Jumbo’s operations are hydraulic, including brakes and clutch. Two implements, like diggers or plows, could be used at the same time with a dual remote that Alan set up.
People who see the Jumbo at shows today are amazed. “They crawl around on it and examine it closely,” Alan says, “and try to determine which parts might have come from which different machinery.”
When all was said and done, Alan had a total of $3,200 invested in the home-built piece. “But in performance, the Jumbo compared with other four-wheel drive tractors from major equipment manufacturers that cost over $15,000,” he notes.
Neighbors take notice
After he finished the four-month project, Alan took a neighbor for a ride. “Well, this is going to take two or three farmers to go together to keep it busy,” the man told Alan. “But the next year,” Alan says, “that farmer had three four-wheel drive tractors for himself. Now it’s very common. All the farmers have four-wheel drive tractors, and many have quad tracks.”
The Jumbo was designed to pull two implements at a time.
Though nobody ever offered to buy his Jumbo, Alan says several of his neighbors’ purchases may have been influenced by his homemade tractor. “Those other four-wheel drive brands were coming out then,” he says. “Steigers, Versatiles and so on.”
Progress eventually laid the Jumbo low. “After five years, I realized the new diesel engines had more power than gasoline engines like the one in my tractor,” Alan says. “So we purchased a Steiger Wildcat, but that got too small, and we followed that up with a Cougar. Today we use a 4WD International Harvester and International Harvester Quad Track.”
Now 85, Alan has no regrets. “It was a fun challenge,” he says. “I’m a farmer by vocation, but an engineer by avocation.” FC
Alan Adams: “Always looking for a way to do things easier”
Alan Adams’ mechanical expertise was well known, and not only in his own backyard of Wendell, Minnesota. “People from International Harvester Co. came out to the farm at least four times,” he says. “I showed them things that didn’t work on several IHC tractors, things that should be changed.”
When Alan ordered a new International combine, but didn’t order an unloading auger, International engineers paid another visit. “I told them their 9-inch auger was too slow,” he says. “It took 2-1/2 minutes to unload, but the 13-inch auger I was using took less than 90 seconds. You can get a lot of corn picked during that downtime. Two months later, International had the larger auger in their new combines.”
Alan had no formal training in engineering. “I was always looking for a way to do things easier,” he says. “In the Army, I changed a starter on a 21-ton tank, even though the handbook said you must remove the engine first. I changed the starter without pulling the engine, so they changed the handbook. That’s the most fun, doing something people think can’t be done, and then it works better.”
Once he used a tank retriever to haul a tank that wasn’t operating properly and take it to the shop. When he investigated, he found that when the tank was put into neutral, it went forward, and in forward gear it went backward. Alan reported that the gasket in the shifting mechanism was broken.
His superiors jumped to conclusions. “They asked how I knew the mechanism was broken if I hadn’t torn up the unit,” Alan says. “I said I know that because that’s how it acts. I was told that if I was wrong, I was going to lose my rank.” After the tank was returned from repairs, Alan was vindicated: His assessment had been correct.
Later, sergeants from two different companies sought his help with tank problems that had them stumped. The two then made a friendly wager as to which had the best tank. After maneuvers, Alan got a pat on the back from one of the men – the one who’d won the bet.
– Bill Vossler
For more information: Alan Adams, 29563 310th St., Wendell, MN 56590-9745; (218) 458-2520.
Bill Vossler is a freelance writer and author of several books on antique farm tractors and toys. Contact him at Box 372, 400 Caroline Ln., Rockville, MN 56369; email: email@example.com