The Gas Engine History of Toro Mfg. Co.

By Staff
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A Toro 'Power Roller'
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Toro Park Junior as shown in a 1935 catalog. Power for both units was Tom's own 2 HP engine. Note the positive crankcase ventilation.
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Jr. garden tractor with the Toro engine, 'Toro/Planet Jr. Engine,' that appeared in the December 1995 issue of Gas Engine Magazine.

My, oh my, how quickly they forget! In the August 2004 issue of Gas Engine Magazine, Doug Oldenburg wrote into “Flywheel Forum” looking for information on an engine he acquired affixed with a Toro nameplate. Doug contacted Toro Co., and was told the company had no record of ever having manufactured its own engine!

Toro did indeed make this gas engine, and Doug’s is the first of the three models manufactured by Toro Mfg. Co. of Minneapolis, Minn., between 1928 and 1955. A reasonable estimate suggests Toro manufactured 30,000 of them.

Toro used this engine on one-reel mowers, three-reel mowers, sickle-bar mowers and lawn rollers. S.L. Allen & Co., Philadelphia, Pa., used this engine on the largest Planet Jr. garden tractor from 1929 until about 1947.

Toro engine production numbers and serial numbers are listed in an engine operator’s and parts manual published by Toro Mfg. Co. in 1949 and reissued in 1954. This covers the late-production 3 and 4 HP engines.

A S.L Allen & Co. publication of 1929 says the Toro engine was being used by June of that year in the Planet Jr. Motor Cultivator, which was also available with the Briggs & Stratton Model PB engine. These units weighed 400 pounds and 380 pounds, respectively. In 1935, Planet Jr. engineered a new, heavier 685-pound tractor to take advantage of the more powerful 3 HP Toro engine introduced that year. The Planet Jr. was a favorite of the truck-garden folks, and the Toro engine was the engine of choice in the company’s growth years of the 1930s and 1940s.

Sorting Engines
From 1929 through 1948, over 90 percent of the air-cooled engines used by Toro in its mowers were Toro engines. The only exception was the 22-inch Park Jr., which, as a cost-cutting measure, used a Briggs & Stratton engine of 1-1/2 HP. The 2 HP Toro was optional. In 1947, Toro built a smaller, lighter-weight mower using a 1 -1 /2 HP engine built by Lauson Co. of New Holstein, Wis. Serious production by Toro seems to have begun in 1929. Initial specifications were for a 2-5/8-inch bore and 3-1/4-inch stroke (17-1/2 cubic inches) engine rated at 1-3/4 HP at 1,600 rpm, but soon raised to 2 HP. Early engines had an American Bosh magneto, but later ones had a WICO. All models of Toro engines had a 6-to-1 gear reduction built into the camshaft. A chain sprocket, belt pulley or power shaft bolted to the camshaft output with three bolts. A compression release was necessary as the engine was normally cranked through the camshaft. All Toro engines were bolted to end brackets set 12 inches apart, just as the 1 HP Briggs & Stratton Model PB engine had been. Indeed, the Toro was designed to be a direct replacement for the PB engine.

In 1935, Toro introduced the Model O. It had a 2-3/4-inch bore and 3-1/4-inch stroke (19.3 cubic inches) and was rated at 3 HP at 2,000 rpm. It had an Eisemann magneto under the flywheel, and in 1936 a flyball governor was placed where the magneto had been located on the first-series engines. The valve springs were enclosed, and a cast aluminum air shroud gave the engine a more streamlined appearance. Further, the engine was equipped with positive crankcase ventilation.

The appearance and displacement of the engine stayed the same until the Model H was introduced in 1938. Initially rated at 4 HP at 2,400 rpm, by 1943 the Model H was rated at 4-1/2 HP.

I don’t have a production record, but I believe the early engine was phased out by 1936. The Model O ended production in 1948, with no. 10174. The Model H reached serial no. 13800 by 1949, but exactly when series production ended is unclear.

Stuart Hall is the undisputed authority of Toro-built engines and Planet Jr. garden tractors built by S.L. Allen & Co. He has some nice information that’s printed below.

Contact engine enthusiast Kenneth Scales at: 2601 Shadynook Way, Oklahoma City, OK 73141; (405)769-4171.

Stuart Hall on Toro engines
In 1928, Toro began manufacturing an engine specifically designed for Toro lawn mowers.

The Toro engine design was similar to the 1 HP Briggs & Stratton Model PB, except the camshaft was a 6-to-1 reduction instead of the PB’s 8-to-1. Rated 1-3/4 HP at 1,600 rpm, the Toro was almost twice as powerful as the Briggs. Factoring in a 20 percent power reserve claimed by Toro, over 2 HP was available.

From 1928 to 1950, Toro built three models and three different variations of its engine. The first model, the 1-3/4 HP/2 HP Model ME, was produced through 1935. The second version, the 3 HP Model MF, was produced from 1935 to 1948. Finally, the 4 HP Model MH was produced from late 1939 until 1955. From 1951 to 1955, these were made and sold as replacement engines only, as Toro had turned to Briggs and Wisconsin engines for their mowers. Between 1953 and 1956, Toro rebuilt 143 engines, affixing them with an ‘RE’ serial code.

The three variations of this engine were a lawn mower engine, an ‘Allen’ engine (made for installation in Planet Jr. garden tractors from 1929 to about 1947) and a ‘stock’ engine for general-purpose use.

Toro history
Toro Motor Co. started in 1914, manufacturing engines for the Bull Tractor Co., Minneapolis, Minn. About 1919, Toro began building a motor cultivator that was eventually developed into the Toro Combination tractor. Toro also built a small, four-wheeled tractor, but all this came to an end in 1927 when, for unknown reasons, Toro sold the patents for its Combination tractor to Advance-Rumely Thresher Co. Advance-Rumely used Toro’s Combination tractor as the basis for the Advance Do All.

Toro lawn mowers were introduced in 1924, beginning with the 30-inch Park Special, the 30-inch Estate Special and possibly the 26-inch Parklawn. These were built until 1930. At the same time, Toro also started building other types of grounds equipment, including a power roller for clay tennis courts.

Early Toro engines were equipped with an American Bosch external magneto. In 1930, Toro switched to Wico magnetos and in 1935 went to Eisemann Model 71-F flywheel magnetos. In late 1939, the firm upgraded to an Eisemann 71-T flywheel magneto, which was used until the end of production.

The very early Toro engines were of the ‘headless’ design, but the valve assemblies (which were attached to the bottom of the cylinder head) could be removed – with seats – from the cylinder head. Early engines had a split fuel tank – the left three-quarters was for gasoline, the right one-quarter for engine oil. The early Toro engines had only two 3/16-inch scraper/compression rings and no oil control ring.

Doug Oldenburg’s engine is definitely a Toro of late 1929 or very early 1930 vintage. His engine has a Tillotson Model MS-19B carburetor and utilizes a Donaldson Sea Moss air filter, also called a ‘Simplex’ air cleaner. Doug’s engine has clearly been turned into a utility engine somewhere along the line.

Stuart Hall, 1701 N.W. 114th St., Vancouver, WA 98685-3741; (360) 576-0740.

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