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Lower Unit Swap

***  Note:  These tips are based on a Mercury 200 ..........

This job can be done in about 30 minutes once you have done it a couple of times.

Here is how to do it:

Put it in gear.  Remove the prop.   If you have a trim tab remove it, this will gain you access to an allen head bolt that needs to come out.  Tilt motor as high as you can.  This will keep the lower unit from coming out too fast once all the bolts are taken out.  Remove the allen head bolt that is hidden by the trim tab. 
Remove the two nuts (with a deep well socket)that are up under the cavitation plate.  All nuts are 5/8".  Loosen the two hard to get at ones that are midway of the lower unit.  You will not be able to take this all the way out yet.  Loosen them until they ALMOST come in contact with the midsection.  There is one more nut on the front of the lower unit with a funny washer, remove this nut and keep any eye on that washer!!
Now wiggle the lower unit, it should drop about 3/8", the middle bolts will catch it.

You will now be able to take the two middle bolts out.  The lower unit may want to slide out so be ready for it, it all depends on how high you were able to tilt the motor.
You should have her out now!
While the lower unit is on the ground, slide your prop back on the shaft.  Take a firm grip on the driveshaft and turn the prop.  One way it will click (clutches), the other way it will turn the driveshaft and you will not be able to hold the driveshaft.  Make a note on which way it turns and which way it clicks. 
Take a pair of pliers and turn the shifting linkage on the lower unit ONE CLICK,(shift linkage on the lower unit is a rod that sticks up toward the front about an inch with 6 or more splines on it), this will be neutral.  Check it by turning the prop, it should be easy to turn either way.  Make a note on which way you turned the shift linkage!

On the lower unit that you are putting on......
Slide your prop on the shaft and get a firm grip on the driveshaft.  Turn the prop to see if it is in neutral (like before).  Put the shift linkage in the same position as the old one.  Turn the prop again and make sure the clicking and the rotation of the driveshaft is the same as your old lower unit, (there are right and left hand rotation gearcases.)
If everything is the same and you have it in the same gear as you took the old one out you are almost ready to install it.

First, grease the splines on the driveshaft and shift linkage.  When you took the lower unit off of the motor a pipe that is bronze may have stayed in the water pump; most times it stays in the motor where it belongs but sometimes it will come out with the lower unit.
It it came out with the lower unit (water pump), pull it out and take a flashlight and shine it up in the midsection.  About 1 1/2" from the splines of the driveshaft you will see a hole with a rubber gasket.  Install the pipe into this hole.  On the water pump or on the bronze pipe you should see a plastic pipe.  All this is for is a guide to get the water pipe started into the water pump.  If you do not have one (sometimes they melt away), GO GET ONE!!

Now put the driveshaft up in the lower unit.  The first thing you do is line up the water pipe with the plastic pipe that is in the water pump.  Next thing you will have to do is line up the splines of the driveshaft; do this by turning the prop slowly.  Once the splines line up the lower unit will go onto the midsection.  DO NOT FORCE IT!!
Just barely start the two middle nuts, this will hold it in place while you line up the shift linkage.
Take a screwdriver or something small and push the shift linkage that is in the midsection over onto the splines of the lower unit and then push upward on the lower unit and LIGHTLY snug the middle nuts up!

Install the rest of the nuts and tighten up the same way that you would a car wheel or a set of heads on a motor; a little at a time and work your way around.  Tighten them all up evenly.  This will pull the lower unit up. 

Congratulations, you have just changed your lower unit !!

But, wait a second, let's check it.  Put the motor in neutral and the prop should spin in either direction, put it in reverse and forward and see if it is shifting properly.
If you have followed all of these directions it should be shifting properly !!

.......... J.B.