I was working on some old outboards and noticed that the 10 hp 1956 Johnson gearcase, gears, water pump, etc are the same or very similar to the 22ci 18,20,25 models from about 1957 up starting with the 18 hp fastwin. I generally don't buy anything older than mid 60's but got a great deal on a couple 56 10 hp's. One needs a drive shaft and pinion gear as the circlip came off the bottom of the pinion and did a lot of damage. I happened to have a 1965 18hp gear case sitting next to me and is seems that all the internals are the same. The only real difference is the drive shaft on the newer 18 is recessed a little at the top of the splines for the pinion gear side but it all fits and works nicely. I can't find any parts manuals that far back so I can't cross reference most of the part numbers. It also seems that even though the design of the gearcase is a little different on the older 10 hp it looks like it will bolt on directly to an 18 hp mid section and vise versa. Anyone else come across this r have any input?
