Old School Equipment: Caterpillar’s J621 Paddle Wheel Scraper
In 2017, I took my father and sons to Casa Grande to examine a 1971 Caterpillar J621 paddle wheel scraper for sale. The machine was used at the Motoland MX Park to build the motocross track, then sat idle for several years. The 621 had three flat tires, dead batteries, and an empty fuel tank. So we put fresh batteries in the scraper, re-primed the fuel system, and brought the old D336 V8 engine back to life. But the machine again went unused for more than a year until I returned to purchase it.
The Caterpillar J621 scraper was the product of a partnership in 1965 between two companies. Caterpillar built the 621 tractor, and Johnson Manufacturing Co. built the J621 paddle wheel bowl. Johnson also manufactured elevating scraper bowls for the J619 and the J621 scrapers. The J621 was equipped with a V8 D336 turbo-charged, 300-horsepower engine, which was also used on Caterpillar 980A wheel loaders. The transmission was an 8-speed, semi-automatic that had a 32.5 mile-an-hour capacity. The elevator was set up with 18 flights that were 6-feet, 6-inches wide and were driven by a 2-speed hydraulic motor to adjust the loading speed depending on the material. The cutting-edge design had the option to add teeth for loading harder materials. The heaped capacity of the machine was 21.5 cubic yards.
The J621 elevating scraper was advertised as a finish machine that was profitable on general earthwork projects. Without the need for a push-cat, the elevating scraper could easily pick up sand and gravel and handle loamy clay-like materials. The elevator turned and mixed the earth as it loaded the bowl, which helped reduce discing and processing material as it was placed in the fill. The machine was an economical way to move earth by reducing the amount of handling the material needed. It also eliminated high-cost equipment needed to push conventional scrapers.
In 1972 Caterpillar bought Johnson Manufacturing and began producing elevating scrapers. The J621 was the predecessor to the 623, which was an update necessary for Cat to stay competitive in the elevating scraper market. However, the J621 was never equipped with a cushion hitch option, even though that feature was available on the Cat 621 open bowl scraper.
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This article originally appeared in the bimonthly Arizona Contractor & Community magazine, Sep/Oct 2021 issue, Vol. 10, No. 5.