raw water pump o-ring

[sailhog]

Ahoy! I replaced the impeller on my MMI raw water pump which has brass quick release thumb screws. Somehow in the process I lost the o-ring -- only to find two spares in the MMI packaging box. Whoo-hoo! When I tried to replace the o-ring, however, the both replacements were larger in circumference that the groove they're supposed to fit in. I placed the o-ring around the groove, secured it in place with some lithium grease, and fired up the engine. Unfortunately the pump wasn't moving any water.

I'm wondering if the o-ring could be the cause of the no-flow, or could it be something else.

I also cleaned out the raw water strainer which was filled with all manner of monkey crap...

Any input is much appreciated!

[Al Schober]

Sounds like you didn't get the o-ring into the groove and/or the cover didn't close properly. O ring packages for military use have a cure date (to the quarter year) and they DO go bad. Or perhaps the wrong o-rings were in the box - tough to tell from here.
Back when I worked for a living, we used to splice o-rings. We had a fixture that would clamp the two ends of the stock allowing us to slice the ends square with a razor blade, then hinges would bring the two ends together in alignment with a drop of CA glue. Worked fine. Don't know who made the fixture - perhaps Parker?
Second choice (no o-ring) would be to put the cover on with some silicone gasket compound. I like the blue stuff from Permatex for water. Should get you going until you find o-rings that fit.

[JOHN COOKSON]

The pump is supposed to be self priming. But maybe it didn't work this time. Try priming the pump and see if you have better luck. Also did you carefully compare the old impeller to the new one to be sure you have the right impelled? After cleaning the "monkey crap" did you check be sure you have free water flow? If you have an external strainer cleaning them can be a PITA when the boat is in the water.

TRUE GRIT

[sailhog]

Thanks, gentlemen. I'm going to try splicing the o-ring with a razor blade and add some of the blue Permatex at the seam.

The strainer is in the engine compartment, so it wasn't difficult to clean. There's free flow of water through the plumbing and strainer. I'll prime the pump and see where things stand.

Thanks, amigos!

[Administrator]

I'm going to try splicing the o-ring with a razor blade and add some of the blue Permatex at the seam.

You shouldn't have to do that. Suggest you give Ken or Don a call.

Bill

[ED.D]

I also have a MMI water pump with thumb screws and have always had to use a little gasket grease to keep it from leaking

[HOTFLASH]

Use a paper gasket too

I recall asking Don about the same issue and he said it was ok to use the paper gasket used for the original Oberdorfer pump cover along with the skinny o ring that comes with the newer Moyer pump cover on the Oberdorfer (that has the thumb screws). Works fine.
Mary

[sailhog]

Thanks for the replies...

While mucking around under the nav station, I found a second box with MMI parts in it -- along with an o-ring gasket that fit. Lo-and-behold, it all went together in five minutes. After priming the system, the pump was moving water like a firehose -- and without leaking.

The takeaway: the o-ring is a spare you want to have aboard.

Thanks again!

[Administrator]

Was the o-ring that didn't fit sourced from MMI?

Bill

[CajunSpike]

I've got the MMI thumb screw pump cover also.
Had no issues when i recently replaced the impeller.

[sailhog]

I think so but can't say for sure, Bill. I believe they were spares that came with the pump when I received it back in 2008 or 2009. This means they've been sitting in a hot boat in Florida for ten or eleven years. I'm wondering if this caused them to become malformed?

The other possibility is that they were from the previous Oberdorfer pump that I had. Perhaps the O-rings had a greater circumference?

[Al Schober]

My guess is the o-ring that didn't fit was from a different pump.
I'll try again on my advise about splicing o-rings - use CA glue, not silicone. A tool helps getting the cuts square and butted properly.
The blue silicone advice was for no o-ring.

[sailhog]

Thanks, Al. I got an o-ring installed that fits. I think it's probably a good idea to have both CA glue and blue silicone aboard.