The Merc shift shaft has six splines and can go any one of six different ways. Mercury has always stated in their manuals that the lower units should be removed and installed with the lower unit in forward. I have found over the years that this is pretty much baloney and neutral is really the way to do it, if you are gentle. What the problem is, is that the Merc sliding clutch is spring loaded in forward. This is great, because when have you ever seen a worn forward gear and clutch on a Merc? ( I didn’t say, “rusted;” I said worn!) The mechanism that moves the clutch is a cam, that the the vertical shift shaft twists back and forth. If you remove the gear case in neutral, there is the chance it can be bumped off the cam’s neutral position and the shift will slip into forward. If the mid section is still in neutral, this could end up being a problem; so they say to do it in forward. The trouble is, in forward, the shift cam detent is not well defined and can go too far past the forward direction, making it very hard to line the splines back up. Some people get the lower shaft position so far out of whack that lower unit will actually shift backwards, because the cam is now working off its back side. Anyway, if you remove and install the the lower unit in neutral and be careful not to jar it too much, the splines will go back together pretty easy, because the unit will stay almost perfectly in neutral, due to the nice, defined step on the cam. Just be sure to check the shift operation before going boating. In forward, the prop should lock one way and ratchet in the direction that the prop would normally drive the boat forward, in the other.
The clutch-dog-looking thing on the shift rod is part of the reverse lock mechanism. That is a whole other story. The way it is supposed to work, you may ONLY lower and raise the motor in FORWARD gear, engine off. That’s right; you shut off the engine, THEN push it into forward gear and tilt the engine up. Conversely, you lower the engine in forward gear and then shift to neutral and start up. Despite what it looks like, that ramped piece on the lower shift shaft is not really supposed to lift the reverse lock into neutral.
Always remember Mercury’s long standing (to this day) engineering motto: Look around, see how everybody else does it, then do the opposite.
Long live American manufacturing!
