Johnson 25hp Powerhead Interchangability

[meathanger]

I would like to know if I could use a 1983 Johnson 25hp powerhead in the place of a tired 1977 25hp. I looked up the part numbers for the cylinder and crankcase but they do not match. I dont know if this means that they are not compatable or are merely a result of minor inconsequential changes. The powerhead that I currently have is on a 25R77S. Thank you.

 

[Dhadley]

Re: Johnson 25hp Powerhead Interchangability

Start by checking the powerhead mounting gasket (base gasket) number. If it's the same it will probably bolt up. Then you're going to have to look at changes in bosses, crank spline count etc. But the base gasket is a starting point. If they're different, you're probably done anyway. The older number may superceed to the newer one, be sure to check that.

 

[meathanger]

Re: Johnson 25hp Powerhead Interchangability

Unfortunately I do not have the opportunity to inspect the powerhead in person. I will not be able to take any measurements. Is there any rule of thumb for X year will generally fit X year?

 

[Dhadley]

Re: Johnson 25hp Powerhead Interchangability

Just go to the Evinrude site (shop.evinrude.com) and look up part numbers. If the base gaskets are the same then you can start to compare other things. If the base gasket numbers are different, you're done.

 

[meathanger]

Re: Johnson 25hp Powerhead Interchangability

Thank you so much you just saved me quite a bit of money. The gasket number do not match and neither do their dimensions so its a no go. Thank you.

 

[G DANE]

Re: Johnson 25hp Powerhead Interchangability

The reason for the different gasket is a different design of the water channels in the inner exhaust tube from 1981 and on. If you get that tube with the powerhead, it can sit on your mid-section. You will have problems getting your neutral-shift lock mechanism on the new powerhead, though, it will take a home made bracket, of creative design. Better ig you find a 1976 - 1979 powerhead. I am putting a 1984 powerhead on a 1997 lower end rignt now, minor differences, but no problem at all.