Tractor Trendsetters: John Deere 7020 & 4620
Written by Larry Gay
With the trend to larger farms, farmers began asking for tractors with more power. The tractor engineers responded by designing engines with larger displacements and faster rated speeds. During the 1960s, factory-installed turbochargers became popular. Turbochargers forced more air into the engine cylinders which permitted more fuel to be injected into the cylinders. This resulted in more power without increasing the engine’s displacement or rated speed. The John Deere 7020 and 4620 were introduced for the 1971 model year with turbocharged engines which were also intercooled, making them tractor trendsetters.
The intake manifold intercooler cooled the air after it left the turbocharger, making it more dense and permitting more fuel and air to be taken into the combustion chamber of the engine. The additional fuel resulted in an increase in power. The 7020 was a 4-wheel-drive tractor with an initial rating of 145 PTO horsepower and the 4620 was a 2-wheel-drive tractor with 135 PTO horsepower. Both models were powered by 6-cylinder, 404-cubic-inch John Deere turbocharged and intercooled diesel engines. By comparison, the naturally-aspirated 404-cubic-inch diesel engine in the 4020 tractor delivered 95 PTO horsepower and the turbocharged version in the 4320 produced 115 PTO horsepower.
The 7020 tractor was equipped with an 8-speed Syncro-Range transmission and an optional high-low transmission increased the number of forward speeds to 16. The Roll-Gard Cab with a ROPS frame inside the cab was standard equipment and dual tires were optional. The 4620 offered a choice of the 8-speed Syncro-Range transmission or a Power Shift with eight forward speeds. Optional equipment for the 4620 included a front-wheel assist powered by hydraulic motors, dual rear tires, and the Roll-Gard Cab.
The John Deere 7020 was the first tractor with a turbocharged and intercooled diesel engine to be tested at Nebraska. It produced 146.1 PTO horsepower during its test in April-May 1971. Testing of the 4620 followed in May-June and it developed 135.7 PTO horsepower with the Syncro-Range transmission and a nearly identical 135.6 PTO horsepower with the Power Shift transmission.
The use of an intercooler started a new trend in tractors. Now tractor engineers could use one size of engine to develop a family of three models with three levels of power. The smallest used a naturally-aspirated engine, the middle size had a turbocharged engine, and the largest was powered by a turbocharged and intercooled engine.
Larry Gay is the author of four tractor books and the "Machinery Milestones" articles in Heritage Iron magazine. To learn more about this magazine which focuses on the 1960-1985 era, go to heritageiron.com or call 1-855-old iron.