1984 Mercury 90HP 6 cyl lower unit

[wmpotter399]

I bought a boat a few years ago with a Mercury outboard. I finally finished everything in the boat. I am turning to maintenance now before the season starts. One thing that I noticed is that when running the engine at idle, there is no water from the tell tale hole. But it does start to flow as soon as you come off idle. I have been told that this is ok. But I do not know when the impeller was replaced last. So I was going to replace it. Thoughts????


Anyway.... After reading the manual and watching some people on You Tube, I decided to replace it. I Removed all the bolts and loosened the 2 nuts on the sides of the LU. I can only get the LU to move about 1/8" to 1/4". Some people are telling me that I have to disconnect the shift linkage up top under the carburetor. Some people are saying just those bolts on the lower unit and it pulls straight off. None of the marinas around here will touch it. They say it is too old. Can anyone point me in the right direction please?

 

[racerone]

Some people are just wrong with the idea of disconnection shift linkage on this motor !!-----It just slides apart.-----Did you remove the hidden bolt under the trim tab ?---There may be a nut at the front too.-----How many nuts are on your work bench now ??

 

[wmpotter399]

I took off the trim tab. I took off the bolt under the trim tab. A took a nut off at the very back of the LU. Took off the 2 nuts from underneather and removed the 2 washers. And I loosened the 2 nuts at either side of the LU. It does move a little. Just not much.

 

[racerone]

How many nuts / bolts do you count on your work bench ??

 

[wmpotter399]

I am at work right now. but working from memory...Trim tab, under tab, 2 nuts and washers, 1 nut from back. I think it is 2 bolts and 3 nuts on the bench. And 2 loosened that wont come out until unit can be lowered so I can loosen them the rest of the way.

It does move a little. but not much.

 

[racerone]

Use those 2 on the side to jack the lower unit down.

 

[wmpotter399]

Honestly never thought of that. Just to be sure. You mean try to keep loosening them using the force to hopefully push the LU down?

 

[jimmbo]

Honestly never thought of that. Just to be sure. You mean try to keep loosening them using the force to hopefully push the LU down?

I think Mercury designed it that way, as to have a way of pressing a gear housing off

 

[Texasmark]

You may be fighting corrosion between the drive shaft spline (male) and the female which is the bottom of the crankshaft in the engine block. Several ways to work at that in the archives.

Other thing is the shifter shaft at the front of the housing. The shifter rod female spline slides over a male spline in the lower unit. I like to shift into Neutral as it's easy to feel when going back together. Others like F gear which is to one side rather than in the middle of the shifter cam in the LU that the stubby shaft sticks into.

The point here is ensure that when you do the split, you keep the stubby shaft in position...holding it there, while you separate the units and in the process separate the upper shaft from the lower. If you pull the shaft out while trying to separate you will have a mess on your hands getting it back together usually requiring removal of the prop shaft and gear train to access the cam follower to hold it while you put the shaft back in it.