Re: 1982 Mercury 9.8 Impeller change
Both shift shaft and the reverse lockout cam are splined, with an alignment flat machined into the shaft/cam. The shift shaft can only go back into the reverse lockout cam in one position.
It doesn't matter what gear you put it in (or Neutral). As long as you don't move the shift lever from that position and don't disturb the shift shaft, it'll be fine.
If you decide to put it in Reverse or Neutral, before you start you'll need to tilt the motor up, as it'll only release when in Fwd gear.
Since the motor is small, you can easily reach the flywheel to turn it as you're pushing the lower unit upwards, to engage the crankshaft/driveshaft splines. So there's really no concern about being in gear so you can spin the driveshaft with the prop.
It's a bit tricky as you reinstall, everything wants to line up at almost the same time. It's also easy to get the driveshaft at an angle, so make sure the gearcase mounting flange is parallel with the flange of the mid-section as you're installing the lower unit.
The copper water supply tube must 'catch' the plastic guide tube as you install the lower unit, best way to verify this is by shining a lite up there to observe the tube going in the guide. Once you're past this point, it should go right together.
The big nut in the front has to go on and be tightened down a ways before you tighten down all the way on the nut up underneath by the water intake screen. Otherwise you won't be able to get the nut over the front stud.
Once you snug down the (2) nuts, check shifting action. Easy way to do this is to shift while turning the prop, if you've got both gears and Neutral, you're ready to go!
Warning, be sure to disconnect both plug wires to prevent diced appendages!!
HTH & Have Fun........ed
