The Allis-Chalmers Model G Rear-Engine Tractor
In 1948, Allis-Chalmers introduced an unusual tractor with the engine at the rear. The engine was positioned with the flywheel toward the front and attached directly to the integral transmission/rear axle. A tubular arched frame connected the rear portion of the tractor to the front steering axle with a wheelbase of 68-1/2 inches.
A 4-cylinder, 62-cubic-inch Continental water-cooled engine powered the little tractor. The radiator was located above the flywheel housing, just behind the 5-gallon fuel tank that in turn was just behind the operator’s seat.
Although few if any Model G tractors were sold in that state, Nebraska Tractor Test No. 398 was conducted from July 16 to July 30, 1948, resulting in 10.33 hp on the belt and 9.04 hp at the drawbar while consuming 1.17 gallons of fuel per hour. For comparison, the Nebraska Tractor Test for the Farmall Cub in January 1956 recorded 10.39 hp on the belt and 9.87 hp at the drawbar.
The maximum drawbar pull for the Model G was 1,167 pounds with a 100-pound wheel weight added to each front wheel, giving a total weight of 1,749 pounds with a 185-pound operator. This resulted in 72 percent of the total weight on the rear axle, but was 82 percent without the front wheel weights, which provided excellent traction.
The 4-speed transmission had two first gears: a “special low” good for 1.6 mph and a regular first at 2.25 mph, both at 1,800rpm rated engine speed. Sales literature stated a ground speed of 0.75 mph could be obtained in “special low” by throttling back the engine speed, which would result in a low idle speed of about 845rpm. Maximum travel speed in third gear was 7 mph. Narrow 4.00-12 front tires and 6-30 rear tires let the tractor work in closely spaced rows.
Wide range of implements for the Model G
Allis-Chalmers produced a full range of implements for the G, all of which mounted under the arched frame behind the front axle. More than 30 are shown in one publication, ranging from a 12-inch 1-bottom plow and a two-way plow to a 4-foot field cultivator and a 5-foot sickle bar mower. Of course, there were many variations of planters and cultivators. Wheel treads were adjustable in 4-inch increments from 36 to 64 inches, which accommodated up to six narrow-row planters.
The excellent crop visibility made the G an ideal precision cultivating tractor with rear axle clearance of 17-3/8 inches. Single- and double-bar toolbars were available for mounting all types of attachments at any location, and the implements could be raised either manually (with long levers) or with the optional hydraulic lift. Rear furrowing bars were available to wipe out tire tracks, and with the hydraulic lift could be set for delayed action to the raising and lowering of the main implement.
In addition to Allis-Chalmers implements, other manufacturers also produced implements for use on the Model G. One such product was the Midwest front-end loader built by Maquoketa Co. in Maquoketa, Iowa. The loader wisely attached only to the rear axle and had an advertised lift capacity of 1,500 pounds. This probably was the lift capacity of the hydraulic system, because the small 30- by 40-inch-wide manure bucket with forks could not have held more than a few hundred pounds. The frame was constructed with 3-inch tubing and 44-inch single-acting hydraulic cylinders 2 inches in diameter were used to raise the load. The bucket was tripped manually.
Advertising promoted the Model G as a second tractor on many farms by highlighting the unit’s versatility. It could be used for light drawbar work, and an optional 1,950rpm belt pulley allowed it to drive elevators, saw wood, shell corn and grind feed. Yet even though it had very similar horsepower to the Cub, it was never as popular in the Midwest, possibly because of its configuration. The Model G obviously found its niche in the truck farm and special crop markets.
Inspiring the competition: Hefty and GBT
According to Norm Swinford in Allis-Chalmers Farm Equipment 1914-1985, almost 30,000 Model G tractors were built from 1948 through 1955 at the company’s Gadsden, Alabama, factory. In January 1949, list price was $760 ($7,774 today), but it increased to $900 by February 1951. More than 60 years later, it remains a popular tractor for collectors, and has been the inspiration for several similar tractors.
In the 1970s, one such tractor became available: the Hefty tractor, built by Holtan Axle and Transmission Co., Juneau, Wisconsin. Holtan built several models of small tractors, but the rear-engine version was appropriately called the Model G. It had a water-cooled 4-cylinder Continental R800-46 gas engine rated at 27 hp at the PTO and a 6-speed transmission with a range of travel speeds from 0.84 to 8.07 mph at 3,300rpm rated engine speed. A 3.5 gpm hydraulic pump with 1,500 psi relief pressure was provided.
Four rear axles were available for the Model G with sliding spline U-joint drives to spur gear boxes at the rear wheels, and that provided easy adjustment of rear axle tread width in four ranges from 40 to 108 inches. To accommodate certain mid-mounted implements, the wheelbase could be increased from 75 to 89 inches by changing the mounting location of the front axle. By 1978 three G models were available with varying crop clearances: the G-18, G-22 and G-27 (the number designated the inches of clearance).
Many options were available for the Hefty G. These included a 2-cylinder water-cooled 27 hp MHI model KE130 diesel engine, a creeper gear that reduced first speed ground speed to 0.20 mph, a rear and a mid 540 or 1-000rpm PTO, and a direct-drive engine speed pulley with electric clutch for a mid-mounted 60-inch rotary mower. Other options were a roll bar, power steering, hydraulic disc brakes and front suitcase weights. In addition to the rotary mower, other implements included a 6- or 7-foot mid-mounted grader blade, front-mounted 90-inch snow plow, rotary tiller, 14-inch 1-bottom plow, transplanter and many other planters and cultivators.
There were also other versions of the Hefty G in 1978. The Lo-G for turf maintenance was just 2 inches lower than the G-18, but only offered the diesel engine and attachments like a 6- or 7-foot flail mower, a 5- or 6-foot sweeper broom and blades. A Hi-G was also available with crop clearances of 36, 40 and 48 inches for use in nurseries and with spraying equipment.
The city of Madison, Wisconsin, was the home for the GBT 2000 rear engine tractor introduced in 1976. It also used the 4-cylinder Continental R800-46 engine in conjunction with a 6-speed forward, one reverse transmission. Although it had nearly the same drive train and hydraulic pump as the Hefty and both were built in Wisconsin, the GBT used flame-cut plate for a frame as opposed to Hefty’s tubular frame.
The GBT’s wheelbase measured 77 inches and the sheet metal was completely different. Ground speeds at 3,300rpm rated engine speed ranged from 0.79 to 9.50 mph and ground clearance was 20 inches. It also had an up-front instrument panel for easy access, which somewhat interfered with the forward view.
The Blue G-1000 and the Russell 3-D
Another rear-engine tractor, the Blue G-1000, was the subject of an excellent article by Sam Moore in the July 2009 issue of Farm Collector. The tractor was built by John Blue Co., Huntsville, Alabama, and used the 60-cubic-inch engine from the Farmall Cub with a 3-speed transmission with a 2-speed rear axle.
Only about 200 tractors were built during 1975 and 1976. A Feb. 1, 1976, price list showed a price of $19,965 without wheels and tires (which ran from $180 to $334, depending on size). They wisely offered a $20 conversion kit so Allis-Chalmers Model G implements could be attached to the Blue tractor. Dealer discounts were 27 percent for the tractor and implements, 10 percent for tires and wheels and 28 percent for parts.
There was even an English rear-engine tractor, the Russell 3-D, built in the early 1980s. It used an arched box beam in the center of the tractor to connect the rear of the tractor to the front axle. That interfered with the view directly in front of the operator, as indicated in a promotional picture showing the operator leaning to the side so he could see down a row. A Deutz 20 hp, 2-cylinder air-cooled diesel engine powered the little tractor in partnership with a hydrostatic transmission.
There was a hydraulic drive in each rear wheel and ground speeds were infinitely variable from 0 to 9 mph. The tractor had 19 inches ground clearance with a long 96-inch wheelbase; the rear tires were a skinny 6.00×36. A May 1, 1980, price list said the tractor sold for “5,200 British pounds” and an optional “weather cab” could be factory-installed for 1,000 pounds.
This article is not intended to be a complete listing of all rear engine tractors, and in fact, the concept of the Allis-Chalmers Model G lives on with production of the Tuff-Bilt tractor which is currently being manufactured in Walthill, Nebraska. FC
Jim Gay was raised on an Iowa farm and received a degree in agricultural engineering at Iowa State University. He is a lifelong collector of farm and construction equipment literature and information. Email him at firstname.lastname@example.org.
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