'77 85hp impeller plate

[iwombat]

Went and got a new plate and cup after the old ones failed inspection. The new lower plate (superseded number) does not have a knock-out to open up the chamber below the second water tube. For the moment, I just drilled a hole there big enough to do the job, but was wondering if there was some reason the new plate essentially disables the second tube.

 

[HighTrim]

Re: '77 85hp impeller plate

What part number was it? Was this OEM or aftermarket?

 

[ezeke]

Re: '77 85hp impeller plate

They probably sent the one that goes with the 1977 140 HP motor, that had the new midsection and only one watertube.

The picture below is a new one from a new OEM water pump kit and that is what you should have. Part number 317841 or Sierra # 18-3182.

 

[iwombat]

Re: '77 85hp impeller plate

Yeah, that's what the old one looked like. The new one is exactly the same except for the knockout. Think a drilled hole is good enough to do the trick?

Seems to be pumping good and strong.

 

[ezeke]

Re: '77 85hp impeller plate

The return water is sealed off from the housing, so only the water that goes through the hole you drilled will make it back to recirculate.

The intake part of the new plate is shorter by about 1/4 inch. And you added a tell-tale so you have another outlet that was not stock. Newer motors that are a lot bigger and hotter are running on that identical new plate, so I don't think that it could make a lot of difference.

I always thought that OMC had the second water tube to get heated water back to the the pump, otherwise it does not totally make sense to have the return.

 

[iwombat]

Re: '77 85hp impeller plate

Looking at the whole unit before I reassembled it that's kind of what I figured. It looked like that was some kind of return tube since it drains right into where the water vents draw in.

I'll run the one with the 3/8 hole in it instead of the knock-out. I can't see where it would make much of a difference since the hole in the LU from that side chamber is only about 3/8 anyway.

One less weird thing to worry about.