What props will fit a 1959 Johnson 18HP?

asdasc

Senior Chief Petty Officer
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Aug 28, 2008
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I need to get a different prop for my 18hp Johnson as the boat I have it on is very heavy. Does anyone know what prop came stock on it (I am 99.5% sure it is the prop on there). I don't see any marks on the existing prop that shows pitch x dia. Will pretty much any Johnson prop from the 50's and 60's fit, or is there something special I need to look for?

Thanks,
 

asdasc

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Re: What props will fit a 1959 Johnson 18HP?

Wow, I feel a little stupid for not looking into that myself. I never considered that they would still sell new ones that fit. I was thinking this would be a hunt on eBay for a used one, or hunting thru all the old garages begging someone to part with their treasure.

Thanks for the help.

I will look again closer at my existing prop for any markings. I also need to figure out how to measure the RPMs and I want to double check the linkage is allowing it to reach full travel. I guess I have some work to do.

Is it safe to assume that the existing prop is ok to use in the interim, as long as I don't push it too hard and keep the RPMs down to just above trolling speed?
 

TN-25

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May 27, 2008
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Re: What props will fit a 1959 Johnson 18HP?

The existing prop on your motor can be used in the interim, but as you said you want to keep the throttle settings low as it may lug your engine.


Your 18 shares propeller interchangeability with the 10-horse 1951-1957, the 15 through 1956, 18s & 20s spanning 1957 ? 1976, and the 25 1969 ? 1976.

I'm going to quote some older OMC part #s. Who knows what they would cross reference to today.

The standard prop on 18, 20 & 25s generally in that period was part # 383629, a 3-blade, 9? diameter 10? pitch prop. OMC offered a free exchange when they were new for alternate props on those motors.

First was part # 592959 that had the same specs (3x9x10) but was intended for extremely weedy conditions. That won?t help you in your case.

Next was part # 379717, a 3-blade, 9? diameter 9? pitch prop (which just happened to be the standard prop for the 1951-57 10-horse). The 9? pitch was intended for 14? ? 16? boats with heavy loads when used on the 15-18-20-25. That sounds like the ticket for you.

Speed range for the 10? props spans 20 ? 30 mph as a peak speed. The 9? pitch will span 10 ? 22 mph peak speeds (hey, on a heavy boat...) You want a prop selected not especially for more speed, rather you want one that will allow your motor to reach it?s peak intended rpm range. If you use the shorter pitch on a light, fast boat and you?d over-rev the thing and possibly grenade the engine.



I notice on the i-boats link provided by Tashasdaddy that there is also a shorter pitch prop in stock. It is a 3 x 9.25 x 7. If your boat is quite big or especially heavy that one might also be worth considering. Still it might be easiest to just find a junked 1951-57 10-horse and grab the prop. The 1958 & later 10s had a different lower unit and shared props with the 1964-73 9.5 horse motors - not appropriate for your motor.
 

asdasc

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Aug 28, 2008
Messages
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Re: What props will fit a 1959 Johnson 18HP?

Thank you for all the information! That helps a lot. You are correct, the prop I have is a 9x10.

I will try to find the 9x9 from an older 10HP on eBay. If not, I can find the new ones on iBoat.

Thanks again,
 

asdasc

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Aug 28, 2008
Messages
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Re: What props will fit a 1959 Johnson 18HP?

Actually, I never was able to check the one on my running motor, I have a spare parts motor and grabbed the prop off of that assuming they were both the same. This prop is a 9x10 part number 315084 and is actually in pretty good condition. Since the other motor is still bolted to the back of the pontoon boat, and it is getting WAY too cold to stand in the water, I will pull the prop when I pull the boat out for the winter and check it then.

Thanks again!
 
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