2  
CLICK ON THIS IMAGE TO ENLARGE

After you drive out the pin holding the gear, you can
remove the axle. Usually this is easiest by replacing
the nut (leave it sticking out a little past the threads)
then lightly tapping it on the nut end to move the shaft
out through the box.
 

3 
CLICK ON THIS IMAGE TO ENLARGE

When you have replaced the gear, loosen the four screws
inside the box that hold it to the motor housing. this will
allow you to  move the gearbox around a little.
Push it upward as far as it will go and re-tighten the screws.
Feel the sharpening wheel by “rocking” it back and forth gently.
It should have about 1/4 inch or so of play. This is perfect.
Reassemble the wheel, reservoir and end plate as they were
and you are ready to go!