replace 2019 Yamaha F70 4 stroke aluminum prop with Johnson 90 stainless steel prop?

[Yamaha18]

Can I replace 2019 Yamaha F70 4 stroke outboard aluminum prop with 1982 Johnson 90 stainless steel prop?

How do I know the prop will fit before I try it on?

[zenoahphobic]

First I would look for numbers; that is the diameter and pitch of each propellor if they are in the ball park.
But usually they won't interchange without changing the hardware and or the prop hub.
I have a Johnston v6 prop that "nearly" fits a Yammy v6 twostroke. There is insufficient spline overlap to provide adequate engagement strength and reliable transfer of power, so in my case I would be stupid to just swap them like that.
The obvious advice would be to try to see if it fits; if nothing gained at least you would used the opportunity to regrease the propshaft on your Yamaha.

[walleye1]

Different spline if it has a rubber hub.

[Yamaha18]

First I would look for numbers; that is the diameter and pitch of each propellor if they are in the ball park.
But usually they won't interchange without changing the hardware and or the prop hub.
I have a Johnston v6 prop that "nearly" fits a Yammy v6 twostroke. There is insufficient spline overlap to provide adequate engagement strength and reliable transfer of power, so in my case I would be stupid to just swap them like that.
The obvious advice would be to try to see if it fits; if nothing gained at least you would used the opportunity to regrease the propshaft on your Yamaha.

Thanks for the excellent advice. I will report back what numbers I get on both motors shortly - was going to do that but just kind of anxious to test my new toy in the water first as is - lol

[Yamaha18]

Different spline if it has a rubber hub.

i will see whether it has a rubber hub. post some pictures of it

[Jason2tpa]

Remove johnson hub and replace w/Yam hub kit. Refer to your service manual for prop shaft specs...splines.