1978 Mercury Inline 6 90 HP Lower Unit Shims Below Water Pump Base

[kmk89]

I recently changed the gear oil in my lower unit and noticed some water in the oil. Before I attempt anything hard with the lower unit, I would like to try replacing the oil seals at the base of the water pump since I have replaced the impeller a number of times and I know how to do it. I have an entire new water pump kit with a new base, and the base already has the oil seals pressed into it. My question is how do I determine of the lower unit has the shims just below the water pump base without removing it. The shimming idea scares because of the small tolerances. I have the factory OB Maxi service manual but I can't determine if mine has the shims. It's also not that easy to understand how the shimming works or what the shims are for. Any help is appreciated.

 

[Texasmark]

In the lower unit the drive shaft has a pinion gear attached. This pinion is in contact with the F and R gears much like the drive shaft-axle connection in the differential of your car. The distance between the pinion and prop shaft drive gears is a measured dimension. Shims are added somewhere in the "circuit" to get the proper distance which is measured with a "use specific" tool at time of manufacture or lower unit overhaul.

Seems to me that under the water pump would be a good place to set this dimension or least one direction (up or down). Pull your old pump and look in the hole. If you have shims you will see them and if it were me I'd leave it be. Hopefully the spacing will be exact or close enough to work. Course everything manufactured has tolerances. Question is, will they matter to you. Otherwise you will have to pull your drive shaft rear bearing carrier and with the proper tool, set up your clearance.....something you will need a repair shop to do for you.

 

[racerone]

Measure the replacement pump housing and compare that to the existing housing.--------If it is the same than no shimming change is needed.

 

[kmk89]

I pulled out the pump base but it looks different than the replacement that I got from Sierra. The Sierra pump base is bigger with all the two oil seals pressed into it. My engine looks like there is another plastic pump piece beneath it pressed into the lower unit housing. One oil seal is In the pump base I pulled out the second is in this other plastic piece that I can't remove. This other piece has a small nub to line up with the pump base I can remove. Any ideas? It looks different than anything shown in the factory manual.

 

[merc850]

It sounds to me (without photos for certain) that the pump base has broken in 2, maybe where the groove for the Oring is, and the piece is the bottom of the pump. If you lift up the driveshaft it should bring the piece closer to the top of its cavity.

 

[Faztbullet]

Your OEM has a 2 piece lower base ..that why it looks broken. And you need to measure base dimensions as usually you have to replace with a 2 piece unit,

 

[kmk89]

Go figure I have the exception to the manual. Would you happen to know the part numbers for the two part base unit? All the parts in the manual and online look like the one unit base. I appreciate the help