'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]

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

[hidef]

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

[Chinewalker]

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.