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1972 Johnson 20HP - What exactly do I have?

S

shinola

Contributing Member
I posted a few weeks back about a Johnson 20 I picked up, model 20R72R (1972). I haven't spent much time on it yet, but have noticed a few unusual things.

My first post was just wondering if the 20 and 25 hp were close enough cousins that I could upgrade it easily. Quickly found out the blocks were quite different, with different cranks, pistons, cylinder heads, and maybe a few other items.

I had noticed when I picked it up that the block was painted in Evinrude blue instead of the Johnson green of that year, which made me think again what might I have. Particularly since Evinrude didn't produce 20HP versions that year. So I looked up the part number from the casting marks on the head and find that it was a common part from (I think) ~1964 forward on Evinrude and Johnson 18HP motors. There is no part number/serial number in the boss on the side of the cylinder assembly, so I couldn't trace that.

So what were the differences in the 18hp Evinrude/Johnsons and the 20 hp Johnson from 1972? Trying to figure out what I bought.

If it works (have had trouble posting pics lately) I'll add a picture of in the next post.
 
Don't be misled by casting numbers. 18hp/20hp have different cylinder heads, 378557 for 18hp, 381151 for 20hp (both 1968). You are correct, 25hp is a whole different motor.

BTW, you might not even be able to tell the seat-of-the-pants difference between 18-20hp. One MPH on the average boat. It is more of a marketing gimmick.
 
Casting number on this cylinder head is 306160. Google search shows it as maybe identical to 378557 which is why I thought it was likely an 18. And yes, probably not really important, just wondering what I had. Will try a little later to get a picture up.
 
You would not notice the difference between 18 and 20 HP.----Evinrude marketing thought 18 HP sounded good I suppose.-----Wonderful motors that are easy to maintain.----New and used parts are everywhere.-----Many parts common from late 1950's to 1976 models.
 
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