Re: 1978 115 evinrude crankshaft swap
In looking thru my parts books (1978-1980) for the original part numbers, then searching thru my various price books for the final superseded numbers of both crankshafts, I can see where the confusion would sit in.
The 1978 115 C/S 386281 supersedes up to 396689 and is listed as Not Available as of 1997, and of course omitted from later price books.
The 1980 115 C/S 389599 supersedes up thru 393751 to a final number of 396623. It does not appear in thr 2004 book, therefore also assumed as being Not Available at some earlier date.
Judging from the part numbers of the two crankshafts not interchanging at some point, it would appear that there is some difference between the two that would prohibit their interchange.
HOWEVER.... Back during those years, for some reason, there would be be a change of part numbers between a crankshaft of say a 90hp and a 115 hp of the same year, the difference being that one hp crankshaft would include the top bearing housing or perhaps one would include the sealing rings where the other would not. We in the trade, at that time, would of course know that the crankshafts would be identical and why... BUT thirty years later or so, the memory has a tendency to fade. This addition or parts to a unit could be the reason for the part number failure to interchange.
I realize that this reply is of no help to you but it does get it back to the top of the pile for other members to re-read. The only advice I can give is for you to inspect the two crankshafts thoroughly... rod throws & their position, mains, D/S spline count and depth, top taper, everything.
Whatever you find, I'd be interested in hearing about it.