Toro/Planet Jr. Engine

| December/January 1995

  • 1935-36 Allen engine
    1935-36 Allen engine: The new Toro front view, with oversize cotter pin for dipstick.
  • 1935-36 Toro Planet Jr. engine
    1935-36 Toro Planet Jr. engine: sporting 5' x 5' muffler, 3 x 3 S. L. Allen flat belt pulley and bronze Toro I.D. tag.
  • Toro model MF engine
    1929 front view: now rear view, with Toro turn around.
  • 1935 PCV system

  • 1935-36 Allen engine
  • 1935-36 Toro Planet Jr. engine
  • Toro model MF engine
  • 1935 PCV system

1701 N.W. 114th Street Vancouver, Washington 98685-3741

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.


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