'79 Evinrude powerhead interchangeable with '81 Johnson?? 25hp

[bobtodd23]

I'm going to do some research, but thought I would ask in case someone could answer quicker than me searching around I've got a 1981 25hp Johnson. It's starting to get a bit of a knock at WOT...probably needs a rebuild. Was wondering if a 1979 Evinrude would be interchangeable as far as the powerhead? I found a '79 Evinrude 25hp that has a bad lower unit for cheap. Was wondering if I could swap some parts. Any info would be great. Thank you.

 

[bobtodd23]

Re: '79 Evinrude powerhead interchangeable with '81 Johnson?? 25hp

Looks like part numbers are different between the two motors? Anyone have any input? Thank you!

 

[hidef]

Re: '79 Evinrude powerhead interchangeable with '81 Johnson?? 25hp

They changed something in 1981. The only way to tell if it would work would be a direct comparison.

 

[Chinewalker]

Re: '79 Evinrude powerhead interchangeable with '81 Johnson?? 25hp

The only difference that would make them incompatible would be different crankshafts. Somewhere in that range they went from the exhaust coming out above the propeller to a unit with the exhaust coming out the prop. If that's the case between your two motors, then the crankshaft splines will be different as the earlier one would have a 4-spline driveshaft on the lower unit and the later one would have a fine spline driveshaft. The '79 Johnson parts motor I have has the 4-spline crank.