Toro/Planet Jr. Engine

By Staff
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1935-36 Allen engine: The new Toro front view, with oversize cotter pin for dipstick.
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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.
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1929 front view: now rear view, with Toro turn around.
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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.

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

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.

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