Johnson FD15 and FD21 differences

[itstippy]

I'm looking at a 1961 18HP FD15 Johnson as a potential parts motor for my 1967 20HP FD21. I figure they are pretty much interchangable, same series and block etc. Are the lower units interchangable (bolt on)? I understand there was a Johnson engineering change in 1964 (changed oil mix recommendations, for one thing). Is a 1961 FD a reasonable choice parts motor for a 1967 FD? Should I keep looking? Thanks!

 

[WillyBWright]

Re: Johnson FD15 and FD21 differences

Howdy Neighbor. Go Bucky!<br /><br />The Evinrude and Johnson 18, 20, and 25 of the 60s and 70s are very much alike. Not much really changed until the 80s. Precisely what was changed to create what horsepower I do not know. The gearcase should work fine. 50:1 was introduced around 1964, but several models made prior to that can be run at 50:1 just fine. The crankshaft and wrist pin bearings all have to be ball and/or needle-type, no bushings. I believe the main engineering change was to make all of the model's powerheads fully needle & roller bearing.

 

[Chinewalker]

Re: Johnson FD15 and FD21 differences

Hi ItsTippy,<br /> You should be able to swap over about 90% of the parts if needed. The gearcases are functionally the same and will interchange as a unit, although not much may interchange between them internally. I think the big changes on the 22-cube motors was the big carbs in '68 or '69, so I think you're safe there. The primary difference between the 18 and 20 models prior to the big carb era was (and I was told this - never compared them myself) the reed stops on the 20 were opened up a hair more. You might be alright running the '61 18hp at 50:1, but personally I would richen it up just a bit to 40:1 to err on the side of caution.<br />- Scott

 

[itstippy]

Re: Johnson FD15 and FD21 differences

Thanks guys. I'll make an offer on the FD15. <br />My problem is that I buy or find "parts mowers" (B&S lawnmowers) and usually wind up fixing them instead of parting them out - "this wonderfull old thing is too nice to scrap . . ." Spend even more time & $ getting the "parts mower" going.<br />Basement and garage are FULL of lawnmowers. And now I've developed this intense interest in older OMC outboards. Wife's gonna kill me.

 

[Scaaty]

Re: Johnson FD15 and FD21 differences

Lawnmowers are fun, but they don't float!Keep an eye out on ebay...I'm soon parting out a FD12 (58 18 Johnny)...