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Author Topic:   How to determine propeller pitch?

whalerron posted 10-19-2000 11:24 PM ET (US)
I have a 1969 Minot whaler with a 1975 Johnson 70 hp outboard. The prop is the original prop but the pitch and diameter are not marked or stamped anywhere on this prop. I have pulled the prop and check all hub and blade surfaces but there are simply no numbers anywhere on it. Finding the diameter of this prop is easy but does anyone know how to calculate the pitch of a prop?
Thanks,
Ron
Lil Whaler Lover posted 10-20-2000 08:01 AM ET (US)
Whalerron,
There should be numbers on the end of the hub under where the nut goes to hold the prop on. There may be a washer stuck to the hub that is blocking you from reading the numbers. Check and see if that is the situation.
You have a 1975 70 hp and the most likely prop on a Minot of that vintage was an OMC aluminum 13 1/4"diameter by 17" pitch. This size was 382764 and a later version was 391199. The 17" pitch for your engine is now a 14 X 17 but I am not sure of the part number.
To answer your real question, if there are no numbers anywhere on the propeller you would have to take it to a prop shop and they can check the pitch with a pitch block which is used in reconditioning.
Good luck, Dave

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Author	Topic: How to determine propeller pitch?
whalerron	posted 10-19-2000 11:24 PM ET (US) I have a 1969 Minot whaler with a 1975 Johnson 70 hp outboard. The prop is the original prop but the pitch and diameter are not marked or stamped anywhere on this prop. I have pulled the prop and check all hub and blade surfaces but there are simply no numbers anywhere on it. Finding the diameter of this prop is easy but does anyone know how to calculate the pitch of a prop? Thanks, Ron
Lil Whaler Lover	posted 10-20-2000 08:01 AM ET (US) Whalerron, There should be numbers on the end of the hub under where the nut goes to hold the prop on. There may be a washer stuck to the hub that is blocking you from reading the numbers. Check and see if that is the situation. You have a 1975 70 hp and the most likely prop on a Minot of that vintage was an OMC aluminum 13 1/4"diameter by 17" pitch. This size was 382764 and a later version was 391199. The 17" pitch for your engine is now a 14 X 17 but I am not sure of the part number. To answer your real question, if there are no numbers anywhere on the propeller you would have to take it to a prop shop and they can check the pitch with a pitch block which is used in reconditioning. Good luck, Dave