1981 Mercury 75hp water pump question

[tkdrumr]

I'm replacing the water pump in my 81 75hp mercury ... while cleaning up the base gasket that sits on the top of the gear housing I found that there is a ridged section. It looks like the water pump base should be notched but it isn't, neither is the old one nor in the pictures I've found online (oem picture also attached). Any idea why this raised section is there?

 

[racerone]

I do not see a 75 HP listed for 81.----Serial # of your motor ?----Copper color decals ?-----I think an o-ring fits in that groove.----Best to get this correct as mistakes will be expensive.

 

[Chris1956]

I am not sure what you are asking. The water pump base has an oring, plus a base gasket. On top of the water pump is a gasket, wear plate and another gasket, then the pump cover.

A water pump kit comes with lots of gaskets and orings. Pick out the ones that fit the groove in the pump base, and match the cutouts in the pump base and wear plate and cover.

 

[tkdrumr]

My apologies, 70hp. Sn is correct. Not the o ring groove, the flat surface that will have a "paper" gasket under the flat surface of the pump base. Enlarge the first picture and you'll see the raised area in front of the bolt. That raised section looks like it will hold the base slightly off the flat.

 

[tkdrumr]

Sorry, I thought I posted the SN: 5755418 ... This is the raised area pointed out ...

 

[tkdrumr]

@racerone @Chris1956 Any idea why that "protrusion" exists near the bolt where the "paper" gasket will be laid? The pump that came out has marks from that raised area. It would seem to me that without an absolutely flat mating surface the gasket isn't going to do it's job, or worse it slightly changes the angle of the driveshaft/grease seal in the base.

 

[Chris1956]

I am not sure what you mean. The waterpump base has an oring and a gasket that seals the gearcase. Pick the right ones and grease them. Put the right gasket on the waterpump base and install it. A couple of nuts might be required to seat it into the gear case.
The waterpump base should be a snug fit. Orings that may be too thick are included in the kit. So pick the correct one. Now install a gasket that matches the waterpump base, the wear plate and gasket that also match the pump base.

 

[tkdrumr]

I am not sure what you mean. The waterpump base has an oring and a gasket that seals the gearcase. Pick the right ones and grease them. Put the right gasket on the waterpump base and install it. A couple of nuts might be required to seat it into the gear case.
The waterpump base should be a snug fit. Orings that may be too thick are included in the kit. So pick the correct one. Now install a gasket that matches the waterpump base, the wear plate and gasket that also match the pump base.

I would like to know what that area is. One more marked up picture to be absolutely clear.

 

[1960 Starflite]

Interesting, I've had my 75, 850 apart several times for water pump change. Never noticed that (step) of course I don't remove the base unless there's water in lower unit. How high is it? .005, .010 ?

 

[tkdrumr]

Here is a picture of that area on the pump housing that was removed. You can see the imprint of that raised area and the scraps of gasket.. The earlier picture I posted of a new OEM pump base was to show there is no apparent indent to allow for this "step". The gasket is flat, so no allowance for it either. I'm baffled as to it's purpose. Not sure of the height of it.