Re: 1970 20 hp johnson lower unit problems...
That style lower unit was introduced in 1949, on the Johnson QD-10 and 1950, on the Evinrude Fastwin 14hp. It was in production, on the 25hp Johnyrude till 1976. There have been changes made on it through the years, but has remained the same basic design for 27 years. Clutch dogs for your year of motor should be pretty much the same, from the late 50's all the way through your era, but just make sure you check your parts dealer for the part numbers and compatibility years. For your 1970 Johnson 20hp, you should be easily covered from 1966 - 1976 as far as being the same design of lower unit. The earlier ones had a slight difference in the mold for the halves. I believe the 1966 model, they did away with the ridges at the seam and made them smoothe. Requardless of that though, you can take the lower unit off of a 1957 18hp and put it on your 1970 20hp and it'll work fine. There is a possibility that the inner parts may be different, but I doubt it. I see the part numbers are different, from 1955 to 1966, but it doesn't necessarily mean the part is different. To be sure, just order the part by your year and you'll be safer.
