Diference between 25 28 and 30 hp Johnson/Evinrude motors

[boggtrotter59]

Was just wondering what the difference is between these 3 motors... 1951-1955 25 hp, 1956 30 hp and 1962-1964 28 hp. They all have the same displacement yet the horsepower ratings are different... Carburetion I'm guessing? Are there any other differences? I am currently restoring on a 1956 30 hp and the block I have is heavily scored... can I use a power head or block from a 25 or 28 hp and still retain my 30 hp or are the blocks (port sizes) different? I was told the ports are slightly larger on the 30 hp 1956 version.

 

[kodibass]

Re: Diference between 25 28 and 30 hp Johnson/Evinrude motors

from what I can see in my books it looks like the 28 & 30 are the same but not the 25. are all your power heads, Jonny's or all rudes? I think this can make a bit of a difference also, for things like bolting on the engine cover etc.

 

[Chinewalker]

Re: Diference between 25 28 and 30 hp Johnson/Evinrude motors

The 28 and 30 are essentially the same. The 25s used different cylinder heads and pistons and had a lower compression ratio. A 30hp cylinder head will NOT fit on a 25hp powerhead unless you put 30hp pistons in it. 1954 & prior 25hp blocks had slightly different bolt pattern on the base as the exhaust housings were different than 1955 and later... Might be able to make them work, but it would involve drilling stuff out to fit...

 

[boggtrotter59]

Re: Diference between 25 28 and 30 hp Johnson/Evinrude motors

O.K. thanks for the replies... I currently have at my disposal a complete 55 Johnson 25 hp powerhead (good condition) as well as a 62 Gale 25 hp powerhead (pistons and block are good but rods and crank are toast (rusted). The original 56 30 hp pistons, rods and cyl head are good but the block is no good. So the 56 30 hp pistons, rods and cyl head should work with either of the 25 hp blocks I have.... and still retain 30 hp?

 

[Chinewalker]

Re: Diference between 25 28 and 30 hp Johnson/Evinrude motors

In theory... Use as many of the 30hp parts as you can. The later 25hp Gale rods would have been the best - better bearing arrangement, but if they're toasted, go with the 30 rods...