Tractor Trendsetters: International 8-16 & PTO
Written by Larry Gay
With the trend to smaller tractors, IH introduced the 2-plow Mogul 8-16 with a 1-cylinder, horizontal engine in 1914 and the 3-plow Titan 10-20 with a 2-cylinder, horizontal engine in 1915. The Mogul, built at the Tractor Works in Chicago, had one forward speed and an exposed chain final drive. The Titan, built at the Milwaukee Works, provided two forward speeds and used two exposed chains for its final drive. In 1918, International Harvester introduced the International 8-16 and added a power take-off (PTO) attachment the following year. The PTO attachment made the International 8-16 a tractor trendsetter.
The International 8-16 with eight drawbar horsepower and 16 belt horsepower was built at the Tractor Works with a vertical, 4-cylinder engine and a 3-speed transmission. The kerosene-burning engine had a rated speed of 1,000 rpm. The radiator was located in the middle of the tractor, behind the engine, which permitted a sloping hood over the engine. The final drive continued to be two exposed chains. The PTO attachment for the 8-16 is considered to be the first commercially successful PTO in the U.S. There is very little information available about this PTO attachment, but in one photograph the PTO shaft appears to be located under the tractor’s right rear axle and at about the same height as the drawbar. The PTO became a third way for a tractor to transmit power, along with belt power and drawbar power. Harvester later advertised its tractors as "triple power tractors."
Harvesting equipment, such as grain binders, corn binders, and corn pickers, had been powered by a large ground-engaging wheel which was prone to slippage in wet or muddy conditions. The PTO quickly became the preferred way to power these machines and most of the major tractor manufacturers began offering a PTO attachment for their tractors. However by 1926, there were seven sizes of PTO shafts on tractors, located from 32 inches ahead of the drawbar hitch pin to 13 inches behind the hitch pin. The location varied widely as the PTO shaft for the Fordson extended under the tractor’s right rear axle and the PTO shaft for the John Deere D was located above the left rear axle.
The American Society of Agricultural Engineers (ASAE) issued a PTO standard in April 1927 which described the size and type of shaft, the speed and direction of rotation, and a location near the tractor’s centerline above the drawbar and ahead of the drawbar pin hole. Revisions were made in July 1928, March 1931, and August 1941 to improve the standard and eliminate some of the variations. This ASAE standard resulted in a 540-rpm, 1.38-inch diameter shaft with six splines, located on the tractor’s centerline, and 14 inches ahead of the drawbar pin hole.
Larry Gay is the author of four tractor books published by the American Society of Agricultural and Biological Engineers, including Farm Tractors 1975-1995 and Farm Tractors 1995-2005. These books may be obtained from ASABE at 800-695-2723 or asabe.org, click publications and then click book catalog.