Help with my 1973 Johnson prop

[Michael leblanc]

I have a 1973 Johnson 6hp it have a 2 blade prop don't really know what's the size and pitch but I just bought a 3 blade prop off a 63 model 8x7 it looks like same pitch but shorter blades and half inch maybe will this hurt it in any way just got it never put it on yet

 

[steelespike]

Re: Help with my 1973 Johnson prop

It normal for a 3 blade to be slightly less diameter than a 2 blade.
A 63 is a 5.5
It does appear that OMC changed the gear ratio in 76 or 77 to 2.08 older motors are 1.73.
1.73 is harder to turn the prop. 65-75 use a 2 blade 8 X 7 1/4" prop.
76 or 77 up have a 2.08 ratio and use a 3 bld. 8 X 7" prop.
I hope the 3 blade won't be too much for the 1.73 gear ratio.
Please give us a follow up.

 

[Michael leblanc]

Re: Help with my 1973 Johnson prop

Ok I'm going tomorrow after run it in the basin and I'll let y'all know how it does

 

[Michael leblanc]

Re: Help with my 1973 Johnson prop

Update on prop the 3 blade worked good but not as fast as my 2 blade it had good take off but no top end the 2 blade is a lot better

 

[Michael leblanc]

Re: Help with my 1973 Johnson prop

Like you said it felt like it wasn't turning it fast enought

 

[steelespike]

Re: Help with my 1973 Johnson prop

I would expect top end to be slower like going from 3 to 4 bld
sometimes does.Hopefully the gear ratio isn't the cause of rpm loss, maybe just the resistance
of the extra blade.
You may find it does better with a load.May have less slip with a load.
Maybe you could get a gps speed. Some cells have a gps app.
If you want to fiddle with it a prop shop may be able to remove some pitch.

 

[Michael leblanc]

Re: Help with my 1973 Johnson prop

Yes I find my motor wasn't getting to the rpms that it does with the 2 blade prop but it did push a load better ....that's for y'all help