quote Chris_P:
I am converting a 5.5/7.5hp OMC gearcase to be used with a 1958 10hp Johnson (never did have a gearcase for this motor). I realize the shift rod will need to be changed, but what about the drive shaft? I know they have different part numbers, but not sure if that is simply because the 5.5/7.5hp shaft has the hole drilled in it for the carbon seal assembly. Im wondering, if I pull the pin and use it, do the crank splines differ? Cannot think off hand, and Im sure someone on here has done this.
OK, well the driveshafts are definitely different and can not be interchanged. The prop shafts are different as well, leaving the old prop shaft in place and using the 7.5hp prop will result in over revving.
In 1958, the gearcase housings for the 5.5/7.5/10hps were the same, but not necessarily so in later years. You will need to change the upper bushing/seal housing as well…
In short, try to find a complete serviceable 10hp gearcase!
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