Reply To: Prop Shaft Identification Help

[nj-boatbuilder57]

OK…I’ve done a ton of research, cris-crossed a ton of part numbers, and reached some conclusions:

1.) In 1958, across the 25-35HP offerings, OMC made changes to their gear sets. The housing didn’t change, but the shaft did: 1.) prop-nut attachment and 2.) added a spline, going from 22 to 23. The dog changed too, as did the dog cradle.

2.) the gears changed, but how & why remains a mystery to me. The pinion gear changed in part number, but the actual gear remained the same. The forward & reverse gears changed, but…as stated…not sure how. The pinion is still 12-tooth and the drive gears remain at 21-tooth, so the gear ratios remain the same.

3.) All of the bearings, rings, seals & bushings remain the same from 57 through 59 (and maybe further, but I only researched to 59)

I have to suspect that the gears & dog were all “improved” in some fashion….and certainly more splines provide better engagement (though only one spline can’t make THAT much of a difference, can it?)

I’ve concluded that my ’57 housing could accept the 23-spline shaft, but I’d have to replace the drive gears, dog & cradle as well…and that’s a tall climb just to achieve commonality of prop nuts. The only reason to do so is if the later gear/dog/shaft arrangement is in some fashion superior to the ’57 set. But how many tens of thousands of hours have been run on stock 57 engines without issue?

My decision….unless there’s a true & provable proof that the 58-59 gears are superior…I’m going to reassemble the 57 in its stock configuration. Anybody need a 23-spline shaft? 🙂