Lower unit

I have a Chrysler 55HP outboard. Model 557HC Serial 3188. I am changing the impeller and I noticed caked up oil just under the rear of the lower unit gasket, In front of propeller. I am pretty sure it is the lower unit gasket. First question. Do I need to change the gasket under the impeller plate when I change the impeller? Also, do I need to change any other gaskets, like where the leak is. I have the lower unit gaket but was wondering if it could be a seal under the propeller. I am thinking if that seal was bad it would not show all around the outer part under the lower unit gasket. It would show inside, under propeller.

Re: Lower unit

Well, you know that you don't HAVE to do anything. However, It is good practice to change the pump gasket when you change the impeller.

As for the lower unit, are you talking about the gasket between the gearcase and the upper portion? If so, this gasket does not contact the last 3/8 inch or so where the prop shaft gland plugs into the gearcase and a lot of crap collects there. If you are collecting lower unit oil there, it could be from a bad gasket or a leaking O ring on the gland itself. If you are not getting water into the lower unit through the gasket, you do not need to change it. HOWEVER: If you have disassembled the lower unit, because of the size, thickness, and composition of this gasket, It is a very wise move to use a new one.

If you are getting water into the lower unit, you need to check the driveshaft seal under the water pump, the shift rod seal, the drain and fill screw seals, AND the shift yoke pivot pin seal (The famous recessed screw on the side of the front of the gearcase bullet that you are never supposed to remove when changing the oil) Then you need to check the O ring in the prop shaft gland (part held on by two bolts) and the prop shaft seal itself inside the gland.