For those who have wanted to know, and YOU know who you are, it appears that a gearcase from a 1958 Montgomery Ward Sea King 12HP will fit on a 1954 Johnson 10HP outboard.
I had some water get into the gearcase of the 10 and the driveshaft and the bearing it runs on were slightly scored. I had the Sea King sitting around, and decided to try it. The drive shafts looked identical. Since I had already filched the gears from the 12 to use in my 56 15HP Johnson, I used the gears from the 10 - which inspection showed to be good yet. Actually, the gears fit into the "new" gearcase better than they did in the one they came from. I replaced the o-ring on the shifter and the seal under the water pump, as I believe one or both of them were the cause of the leak. I used the water pump from the 10, as I just replaced that 3 years ago.
I did have to use a file on the outside of the case before the prop would work (the prop from the 12 has too much pitch), but I only had to take off a minimal amount. So maybe I got lucky this time. We'll see, when I get it in a barrel.
I had some water get into the gearcase of the 10 and the driveshaft and the bearing it runs on were slightly scored. I had the Sea King sitting around, and decided to try it. The drive shafts looked identical. Since I had already filched the gears from the 12 to use in my 56 15HP Johnson, I used the gears from the 10 - which inspection showed to be good yet. Actually, the gears fit into the "new" gearcase better than they did in the one they came from. I replaced the o-ring on the shifter and the seal under the water pump, as I believe one or both of them were the cause of the leak. I used the water pump from the 10, as I just replaced that 3 years ago.
I did have to use a file on the outside of the case before the prop would work (the prop from the 12 has too much pitch), but I only had to take off a minimal amount. So maybe I got lucky this time. We'll see, when I get it in a barrel.
