ROTARY VALVE MOTORS??? What is it?

[jerry]

I recently picked up a motor with the sheave showing "OUTBOARD MOTOR CORPORATION"..It has a funky looking carburetor with some sort of plunger on top and a shroud where the Venturi should be….I was told it was a 1933 model.
Can someone tell me if the rotary valve motors are better runners than reed type? What is the advantage? It appears to be about 3 or 4 horse.I have no idea how to prime it since I can’t see the Venturi to inject fuel for testing…Jerry

[1946zephyr]

Rotary valves were most common in motors before 1936. As a mater of fact, the carbs on the old Sportsmans, Scouts and Mates were more or less the beginning of the "reed valve" concept, with the exception that the valve was in the carburetor itself an not in the manifold.
The rotary was a cut out in the crank that allowed air to be inhaled into the motor during the compression stroke As the piston nears TDC , the valve closes. On the power stroke, the rotary is still closed, therefore the fuel/air vapor is forced into the combustion chamber as the piston goes toward BDC
Any accessive internal wear, will effect the function of the rotary valves, unfortunately.

[frankr]

Improvements in spring metals made reeds practical and more or less universal. In addition to the wear and fit problem, rotary valves allow backfiring through the carburetor and sometimes fires result. Related to the subject were the Martin Motors with cam operated poppet valves. They were notorious for fires resulting from backfiring through the carburetor (combined with leaky gas tanks). But they were very good motors, otherwise.

[1946zephyr]

quote FrankR:

Improvements in spring metals made reeds practical and more or less universal. In addition to the wear and fit problem, rotary valves allow backfiring through the carburetor and sometimes fires result. Related to the subject were the Martin Motors with cam operated poppet valves. They were notorious for fires resulting from backfiring through the carburetor (combined with leaky gas tanks). But they were very good motors, otherwise.

Holy Sheep sh– Batman 😮 :o. That is a scary thought

That spells disaster as Donald Trump would say

[The Boat House]

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• This reply was modified 6 years, 1 month ago by The Boat House.
• This reply was modified 3 years, 9 months ago by The Boat House.

[jim-moffatt]

Jerry

I have had a whole series of 1930s rotary valve motors, including your 1933 Lightwin. The Lightwin had a rotary valve only in 1933 through 1936 (I think
). The advantage is that it will run faster than a poppet valve Lightwin. The disadvantage is that they wont idle as slow because the rotary valve doesnt seal perfectly like a poppet valve. They are not good fishing motors but a lot of fun to run.

Your carb does not have a choke only the primer plunger. The primer works extremely well, better than a choke in my opinion. The plunger squirts fuel into the crankcase through a separate tube at the back of the carburetor. you can test it with the carb off the motor.

[canoecrafter]

quote 1946Zephyr:

quote FrankR:

Improvements in spring metals made reeds practical and more or less universal. In addition to the wear and fit problem, rotary valves allow backfiring through the carburetor and sometimes fires result. Related to the subject were the Martin Motors with cam operated poppet valves. They were notorious for fires resulting from backfiring through the carburetor (combined with leaky gas tanks). But they were very good motors, otherwise.

Were Martin outboards susceptible to occasional fires? Read on…

I grew up in Eau Claire, WI where Martin motors were made at Presto Industries, so there were lots of them around.

In the 1950s, when wooden boats were king, I recall being out on a local lake fishing when someone started yelling for help. A lone fisherman’s black Martin motor was flaming and the fire had spread to the transom and rear wooden seat of his Shell Lake boat. He was screaming and franticly splashing water on the fire with his hands, progressively moving further toward the bow as the fire spread forward towards him. By the time we got to him, he was hanging waaay over the bow and still hand-splashing water on the now totally-aflame boat. He swam over and we took him aboard, then watched the Shell Lake boat burn. Things got pretty spectacular when the rubber gas tank stopper burned through and the tank exploded in a showy ball of flame–just like in the movies.

Finally, so much wood was gone that the weight of the Martin sank the whole thing. All we could see were a few bubbles rising and a little blue smoke to mark the spot. Ever seen a wet fisherman cry?

We dropped him off at the shore–sopping wet, sobbing, and swearing at the damn Marin Motor Company and Presto Industries.

Canoecrafter.
Rice Lake, WI

[jeff-register]

FIRE on the boat has been my greatest fear. I highly respect fuel & what it can do. At 12 years old my friend got burns all over his face. We were playing with fire & GASOLINE!!

[garry-in-michigan]

Ole’s first row boat motor used a pressure actuated intake valve. He called it a check valve carburetor. Later he added a float bowl so you didn’t have to adjust for varying amounts of fuel in the tank. Others used the piston skirt as a valve. These "third port" outboards were prone the back fire through the carburetor when run at slow speeds with a lean mixture. Third port motors in particular spit back into the intake passage at an idle. Flame arrestors put out the fire by reducing the temperature of the charge using aluminum or copper. Johnson countered this backfiring by adding aluminum flame arrestors to the bypass passages in the cylinders. They all added air horns to direct and contain the fuel and flame away from the boat. Some had flame arrestors on the front of the carburetors. The rotary valve increased efficiency by opening and closing sooner, but could also backfire if run lean at slow speeds. At high speed the motor benefits from a longer open time because of the ramming effect of the velocity of the incoming charge. At idle speed this is minimal to nonexistant. The light and effective reed valve overcomes these deficiencies by being faster acting than the check valve and at the same time (unlike the third port or rotary valve) automatically adjusting to the various engine speeds. These improperly adjusted motors (Lean adjustment backfiring) are the leading cause of broken reed valves. (In my opinion) Second is running over speed.

[The Boat House]

• This reply was modified 6 years, 1 month ago by The Boat House.
• This reply was modified 3 years, 9 months ago by The Boat House.

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