Re: 1951 Evinrude M4443 7 1/2 hp

[frankr]

Correct, the keyway is a rotary valve for pumping the oil up to the upper bearing. If you look closely, you will see a couple of small holes in the bearing and the keyway joins those holes when the lower crankcase chamber has pressure and the upper chamber is partial vacuum.

EDIT: Actually, on that motor the two small holes I mentioned are slots milled in the case, one joining with the oil line.