Re: Shifter shaft cam 1973 50hp mercury
Likely you're in FWD gear so just turn the shift shaft CCW to Neutral. If you turn the driveshaft or propshaft while you're shifting it'll go smoother. Use a pair of pliers cushioned with tape etc to turn the shift shaft.
Once you've located Neutral, turn the shift shaft the least amount possible in the CW direction that'll cause the gearbox to shift back into FWD. Leave it in that position, don't turn it any more in the CW direction.
If you're reinstalling the lower unit with the control box in FWD, this is the correct position for the shift shaft.
Now, you can install the reverse lockout cam. Take a look at the reverse lockout rod, sticking down from the center section. Note how the lockout rod will hit the shift cam. Position the shift cam such that the lockout rod will point towards the middle of the shift cam's ramp.
So what will happen when you shift to Neutral is, the flat spot at the top of the shift cam will block the reverse lockout rod from springing down. This keeps the reverse lockout hooks firmly locked around the tilt pin. When you shift to Reverse, the flat spot still blocks the rod.
Once you have the shift cam correctly installed, you can either leave in FWD and install that way, or shift to Neutral. Just be sure, if you shift to Neutral, that the control box is in Neutral also.
Some find it easier to line up in Neutral, you just need an assistant or long arms to turn the flywheel a bit to engage driveshaft with crankshaft on the way up. Be sure to disconnect the battery and pull spark plug wires when doing this work!
HTH & let us know how it goes.........ed