Re: removing the bearing from LU
Josh: I have never worked on a 91 lower unit and therefore don't know exactly what you have. Some of the things you write confuse me. That said, I will give you some generalities and you can interpolate them to your lower unit. OK?
Now! Typically, the lower unit gears have teeth curved in a way that pulls the pinion down when the engine is running. That is why there is a tapered roller bearing (cone) at the top of the case with the small end facing down. Thus, the cup or race has its large end facing up to mate with the rollers.There is typically some vertical play in the shaft, and if you pull up on it, there will be some side play between the bearing and cone. This is not there when the engine is running. There is usually a special steel ring on the bearing and a crush ring presses this down onto the cup, and holds everything together when the top plate is installed. Thus: you cannot pull up on the shaft when the lower unit is completely assembled. If this crush ring is missing, the engine will still run fine because the gears are pulling together but you will be able to pull up on the shaft. The factory did not spend money to put in the crush ring for no reason! Even though the engine will run without it, it is a necessary part.
Typically, the cup has shims underneath it because the pinion hole has some tolerance and the shaft length has tolerance and the shaft taper has tolerance. When you add these tolerances up, the installed length of the pinion is different in different gearcases. SO: you must adjust how far the cup of the top bearing lets the shaft go downward by shimming it up in the case.
Now: If you look at the gears themselves, you will see a "wear" pattern on the teeth. It is not really wear but a mark where the teeth have been meshing. There is a special tool to set gear lash, but if you check carefully, you should be able to see if the running pattern is at the proper mesh point.
If you still have the gears out, mesh the pinion and forward gear by hand. You will feel that at various depths of engagement, the gears do not mesh smoothly. There is however, one "sweet spot" where they mesh slicker than snot. This is where the factory shims the pinion to run and it has a tolerance of about 5 thousandths of an inch. Anywhere else, and the gears will chew up the teeth under load.
Now: When you find this sweet spot, look at where the teeth are meshing and how far the pinion is from the center of the forward gear. Once you put them in the case with the original shims, see if the mesh looks proper. Next, with no water pump installed but the reverse gear and spool installed, turn the drive shaft by hand while pushing down. It should turn smoothly with no noise. Turn it in the opposite direction from engine rotation and you will hear a "rattling or grumbling". This is because the teeth on the gears are now pushing the pinion up and it is no longer mating with the forward gear properly. Indeed, after you assemble everything, if you spin the prop by hand while the lower unit is in forward gear, you will hear the same noise since you are loading the gears in the reverse direction as they are designed to run. When the engine is running, this can never happen because it is set to run in one direction only.
This is why you cannot run one outboard in counter rotating direction in a twin engine installation. You must have a counter-rotating engine block with the lower unit gears cut opposite so they are loaded properly.
Hope this somehow clears things up and helps you. Frank.
