Re: Shift Shaft Neutral
On most of the older Mercury lower units the shift shaft can spin in almost a full circle without much resistance.
If turned all the way till resistance is felt in one direction then a little more you will find it gains resistance then falls into neutral.
A little further in that direction is reverse.
This is done by a "cam" pushing against a pin at the end of the drive shaft.
This cam is mostly round with a ramp, dip (neutral) and a lobe (reverse).
If only wants to turn in one direction and go up the ramp, through the neutral detent and into reverse. Keep turning and it will fall back into forward for almost a full turn.
try to turn it the wrong way against the reverse cam and it probably won't go.
Use a pair of vice grips carefully clamped onto a piece of belt leather wrapped around the splines to test this theory.
I prefer to assemble with lower unit and gear shift in neutral, but often it will pop into forward on it's own while I'm putting it together and may take a couple tries.