I have a 1968 Mercury 650, the motor worked at the end of last season, but something has gone wrong over the winter. Either there was water in the lower unit oil, or as I left the motor tilted up, rain/snow got in froze and caused damage. When I started getting the boat ready this year I noticed the prop looked back further than normal. Once I removed the prop I found the spanner nut got pushed out of its grooves and split. I got a new spanner nut and cleaned up the grooves on the inside of the lower unit. I can get the new spanner nut to thread easily now and tighten to the specified torque requirement. But it seems to not be shifting gears now. Whether in forward/neutral/reverse the prop is always free spinning in either direction. Also the prop shaft has some springyness to it and can be pushed forward. When I push the prop shaft forward and try to spin it seems like it is catching the gears. Anyone have any ideas of what I can try to fix this, or am I looking for a new lower unit?
