Toro/Planet Jr. Engine

1935-36 Allen engine

1935-36 Allen engine: The new Toro front view, with oversize cotter pin for dipstick.

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The Toro 'air cooled motor' is for a 1935 or 1936 Planet Jr. garden tractor later made reference to by Toro as their 'Allen Engines' made especially for the S. L. Allen & Company, Inc., located at Philadelphia, USA. The Toro air cooled motor was adopted by this company for use on their garden tractors for the 'New Planet Jr. Motor Cultivator' in 1929 because 'The sturdy Toro motor is rated at 1 HP at only 1600 RPM, having a 20% reserve, so that over 2 HP is actually developed. This is twice as much as the motors used on most other tractors of this type will develop.' (Quotes are from a 1929 Planet Jr. pamphlet.)

Toro's first engine, model ME (mower engine) was a substantial increase in horsepower over its counterpart, Briggs models P and PB, which leads me to believe that Toro tried these engines on their mowers and tractors before making their own engine.

The 1929 Planet Jr./Toro engines were the model ME sporting a 2?' bore by a 3 stroke. They had a Tillotson side draft carburetor with no governor, used a Donaldson Sea Moss air cleaner, were fired by an American Bosch magneto. The engine used a vertical mounted ? spark plug ('advertising that it was the same as any motorcycle spark plug and available everywhere'), and bragged about having a camshaft that operated both intake and exhaust valves. 'Both cam operated the only sure way.' No atmospheric intake valve for Toro!

The first Planet Jr. Toro engines were mounted faced in a conventional style as on almost any reel mower. The flywheel side, located to the right of the operator when in handlebar position, turned clockwise. The Toro 6 to 1 reduction unit, driven off of the camshaft on the operator's left hand side, was also turning clockwise from a side view. This was why early Planet Jrs. coupled the number 50 chain to an accessory shaft with a clutch that had what Planet Jr. called 'bull gears' on the ends of the shaft, which mated with the two large ring gears attached to each wheel, thereby driving the wheels in an opposite direction in this case forward rotation.

The pictures are of a second generation Toro air cooled motor, model MF, serial 01865, boasting of a whopping 3 HP at 2,000 RPMs. I believe it to be 1935-1936 model, made when Toro decided to turn the engine around backwards (which I am used to calling forward), so that the camshaft driven 6:1 reduction accessory shaft would now be driven in a clockwise rotation from the right-hand side. This enabled the engine to adapt to current mowing equipment then being manufactured by Toro. The only modification that Planet Jr. had to make to install the new model MF engine on the tractor, was to move the accessory shaft driven sprocket from the left to the right, and replace the bull gears with two #50 chain sprockets, add sprockets to each wheel, which replaced the older ring gears, and now chain drive each wheel to accomplish forward rotation.

The 3' diameter by 3' width flat belt pulley developed by Toro for use on these Allen Engines was now rotating in the opposite direction than on previous models, so you now needed to attach the flat belt to the other side of the accessory when possible, or get a longer belt and point the handlebars towards the accessory or attachment. The insistence of a flat belt pulley by S. L. Allen & Company was to make the Planet Jr. garden tractor more attractive to consumers.

The flat belt pulley can 'run a pump, washing machine, churn, ice cream freezers, cream separator, grindstone, saw, etc.,' and when you use the camshaft power take-off sprocket, you have with the 6:1 reduction of 266-335 RPMs at your availability. 'This we think eliminates any need for also having a stationary engine.' The Planet Jr. should be capable of 'doing it all.'

The new Toro model MF engine incorporated a lot of engineering improvements over the first design ME. The new model now had an Eisemann 71-F flywheel magneto versus the former external mounted American-Bosch magneto. An increased cylinder bore from 2?' to 2', a new piston which boasted of having 2?' compression rings and a new-to-the-industry 3/16' oil control ring. The former 2?' model ME piston only incorporated 23/16' compression scraper rings and was known to use oil and foul spark plugs. The cylinder head was redesigned to incorporate a now canted or slanted spark plug located between the valves for better cooling, and the becoming more modern, 18mm thread size. The Champion 7 spark plug was chosen for Toro's purpose and it was now somewhat shielded from the combustion chamber because Toro had only drilled two 3/16' holes in the head to expose the firing tip to the combustion chamber, hopefully eliminating former spark plug fouling completely. The aluminum alloy connecting rod was made heavier, and no longer used shims between the rod and the rod cap, thereby increasing internal engine reliability. The 3 horse MF engine now had an adjustable 'automotive type carburetor' with a Tillotson model YC-1A updraft filling Toro's needs. Also (I'm quoting from a 1930s Toro brochure), 'built-in automatic flyball governor manually controlled, and new quieter helically cut gear teeth should help ease of operation.' An 'improved' United Oil Bath 6' air cleaner was added, along with a crankcase breather valve plumbed into the air cleaner intake neck.

A 1935 PCV system? Incredible! Also on the model MF were now totally enclosed valve stems and springs in what Toro called the 'valve housing.' In no way was any dirt going to be able to attack this new improved engine, if Toro could help it. The MF also now had a flange mount quieter muffler of a 5' diameter and 5' width. Finally, Toro smoothed the' rough looks of the first ME engine by adding a cast aluminum flywheel housing and cylinder hood. The finale was to install just to the right and below the beautiful brass Toro nameplate, a low tension circuit magneto shorting switch to stop the engine. The high tension spark plug shorting clip had not been invented yet.

In summary, the new MF Toro also had about a 20% reserve in horsepower, reaching 3 HP at 2,400 RPM. Planet Jr. Allen engines all had an emergency rope start notch in the flat belt pulley, while conventional starting was with a crank on the 6:1 reduction camshaft accessory drive.

The power take-off of my pictured engine is similar to Toro's very early years, but has a smaller 16-tooth sprocket and carries what I believe to be a Planet Jr. part number, TR-141, as well as being Planet Jr. olive green in color.

I now confirm that Planet Jr. model tractor production runs A through G1929-1948 were followed by just two other letters, T for Toro, and B for Briggs & Stratton. 1949 model H was with a B for Briggs or a W for Wisconsin.

When on Planet Jr. tractors Toro versus PB Briggs was replaced in 1934 or 1935 by Toro versus model B Briggs may have prompted Toro to come up with the more modern MF engine as the B Briggs was not quite as powerful (2 vs. 2 HP, MF-3 vs 2 HP), but a much better balanced, smoother running, engine that the operator on the end of the handlebars appreciated. The only other advantage that the Toro powered Planet Jr. had was that it always incorporated Toro's own larger fuel tank stating that (quote the 1929 brochure) 'The gasoline tank is of extra large size holding one and one quarter gallons. That means only one refill during the day at noon a great time saving feature.'

More to come on Toro in the future, readers please write me if I can help answer any questions.