Merc 800 waterpump seal confusion

[Moody Blue]

What a can of worms. In the process of replacing the waterpump assy on a 1971 Merc 800. Removed the old assy after fighting with the impeller that was seized on the driveshaft.

Replaced the lower pump driveshaft seals, O-ring, impeller and gasket. Bought new upper pump housing assy BUT, there is no seal in the upper pump housing. The SS insert is there but thats it. There is a space for a seal between the top of the insert and the housing, but no seal. Dealer verified that is how they come from Mercury.

I have three lower units of the same vintage and two are the same but one is different. Looks like two original pumps have the seal pressed into the outside of the housing. The third looks like a newer upper housing that is again missing the upper seal. I am not talking about the rubber slinger, but the shaft seal on/in the upper pump housing.

Has the upper seal been eliminated over the years? Is it not required? The seals can be ordered separately but in order to install them you would need to remove the SS insert from the housing then install the seal then press the insert back in place. Doesn't make sense.

What gives? My manual shows an upper seal on one page but not on another. POS Seloc manual - I hate it.

On-line parts diagrams all show an upper seal.

Arrrrrrg, this should be an easy changeout.

 

[Laddies]

Re: Merc 800 waterpump seal confusion

Since the early plastic replacement housing there has not been a seal for the housing just the slinger ring to help keep the dirt out, the bean counters decided they were a waste of money.

 

[Moody Blue]

Re: Merc 800 waterpump seal confusion

That explains it. So the upper waterpump seal is now longer used.

Was its purpose to keep water from getting out, or to keep things from getting in?

It doesn't seem right. The part I took out had a seal and the replacement does not. Does it matter to the vintage of the motor whether or not the seal is there? Should I re-use the old housing and put a new seal in it or just install the new upper housing assy without the seal?

 

[emckelvy]

Re: Merc 800 waterpump seal confusion

The only seal that's important at the top of the pump is the seal between the raised ribs at center of the impeller, and the pump insert. A seal on the external body of the pump is irrelevant to pumping action.

Apparently Merc decided that a slinger ring accomplished getting rid of trash from the top of the pump as well (maybe better, who knows?) than the seal in the older-style housings.

Use the new housing with a slinger ring on top. It'll be fine. No, really really it will !.............ed

 

[Moody Blue]

Re: Merc 800 waterpump seal confusion

Thanks Ed, you've put my mind at ease.

Never expected to encounter so many little problems working on this old motor. Sure hope its worth all the trouble.

Starting to regret selling my 1993 Mariner Magnum 40hp. I knew that motor well and it ran like new.