1947 Johnson Seahorse outboard motor 16 hp

I bought a 1947 16hp Johnson seahorse motor, i got the motor cranked and running. But, I'm not sure if the water pump is working or if it even has one. How can I check if the engine is cooling? Does the water come out of the exhaust? Please reply asap!

Re: 1947 Johnson Seahorse outboard motor 16 hp

I am assuming you have a model SD-10 or SD-15?? Those were the first generation of larger alternating twins from Johnson after WWII. If I'm not mistaken, the waterpump is tied into the propeller. The prop should have some vanes in the blades that create a suction at the tail end of the system to draw water into the system. May not work well in a barrel or test tank...

Re: 1947 Johnson Seahorse outboard motor 16 hp

Yes, that's true Chinewalker. The SD models didn't have water pumps. You have to be careful that you only use the prop that comes with them, because of those water vanes. I've been kinda interested in finding one of those.

Re: 1947 Johnson Seahorse outboard motor 16 hp

Zephyr - finding a prop or a motor?

Re: 1947 Johnson Seahorse outboard motor 16 hp

Remember, these motors had no neutral or reverse; basically it was like starting a typical motor in gear (hang on!). The assumption is whenever the motor is running, it is moving forward in the water. Because of that, they used what was termed a “pressure-vacuum” cooling system. No water pump to speak of. No impeller or moving parts at all in the cooling system. Water is picked up behind the prop and forced under pressure from the prop up into the cooling jackets in the block, then drawn out under vacuum through the slots in the prop cone. At idle or while trolling they were not so great at cooling due to not much pressure or vacuum. The post-war SD gained a small additional water inlet on the forward part of the lower unit to help with the marginal cooling.

Those motors changed from natural aluminum color before the war, to Sea Green after WWII. There was a heat shield to the rear of the lower unit on the postwar models. That heat shield was painted green in 1946 but left unpainted for 1947 to the end of production in 1950. Apparently the heat shield could get hot enough to discolor the paint!

Those were kind of fascinating motors, and a stepping stone in the evolution of outboards. They marked the start of the streamlined motors with the cowling. Also they pioneered the pressurized fuel system. Since much of the 2?-gallon fuel capacity of the built-in gas tank was below the carb float level, at less than full the fuel needed to be pressurized in order to force fuel up into the carb (or low-speed fuel inlet since it is a rotary valve 2-stroke). Remember, you can’t get pressure if the cap is loose or missing!

That pressurized fuel system made it very easy to convert the motor to the remote 2-line pressurized gas tank when they were invented for 1949. The advent of the F-N-R gearcase on the 10-horse Johnson QD-10 for 1949 revolutionized the outboard industry. The SD and the archaic 22-horse model PO opposed twin hung on long enough for Johnson / Evinrude to bring out the shiftable 25-horse Bigtwin for 1951. One must remember that prior to the QD-10 there was no such thing as neutral, and reverse was limited to small outboards and was accomplished by pivoting the motor 180 degrees. Larger motors from 9.8 horse upward were purposely limited to 70 degrees of turning so as to not flip over the boat they were powering.

Re: 1947 Johnson Seahorse outboard motor 16 hp

Thank you all so very much. My model is a SD-15. Ya'll have been very helpful!

Re: 1947 Johnson Seahorse outboard motor 16 hp

Chinewalker said:

Zephyr - finding a prop or a motor?

Click to expand...

Oh no, finding a complete motor. Never seen any of those around here. I see scads of TD/TN's though for cheap.

Excellent post, TN-25....as always. This is a motor I wouldn't mind learning more about. If I can find one locally, I'll probably snag it.

Re: 1947 Johnson Seahorse outboard motor 16 hp

IMPORTANT POINT!
Just to clarify, in answer to the original poster, there is no water pump per se. Because of this, you cannot run these motors in a barrel! They must be on a boat, moving through water, otherwise no water goes to the powerhead.

That, plus the dockbreaker tendancies due to no neutral or reverse (just "on" or "off") are the reason you haven't seen these motors around... They were super modern looking in 1940 though, and did pioneer the streamline styling and the pressurized fuel system. They even have exactly the same bore, stroke and 22.09 c.i.d. as the later 18-20-25 FD motors, but are definitely not the same motor. Rotary valve vs. reed valve, plus totally different casting.