Re: 1957 Evinrude Big Twin 35 flywheel keyway

[twinrudes]

Frank,
It seems to fit only one way, in other words, it appears that there is a top and bottom? Maybe I’m nuts. But I’m a little paranoid here. I had to replace the flywheel and key because it spun, don’t want to have to deal with this again!
Any idea what size thread the shaft is?

Clearly the round side goes into the shaft first, but boy oh boy, there isn’t much of a protrusion to go into the flywheel.