Changing the impeller

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    #1 Unapproved

    Changing the impeller

    We've had reliable service from our '74 Ericson 32's A4 over the now nearly nine seasons since we purchased the boat, but I hate to admit that I've never been able to change the water pump impeller. I've tried on two previous occasions with no success, and this is one of the reasons why I ordered your Service and Overhaul Manual last week. When I mentioned this to the very friendly fellow who took my order, he willingly walked me through what sounds like an easy and straightforward operation - "just take the cover off and pull". So armed with this professional knowledge I made another attempt over this past weekend and you may have guessed by now that the old impeller still remains in the pump housing. Thus I was looking forward to receiving the manual, convinced that somewhere in its pages there would be a clue - it arrived earlier this morning and sad to say, it provides even less information about this necessary operation than what I had already learned over the phone. Clearly our pump is a late model Oberdorfer and I understand the concept of the shaft and impeller coming out as a set - the problem is that I can't get enough of a grip on the impeller and even though I now realize that I can pull without damage, no amount of exertion has yet to free the shaft/impeller from the drive slot inside the engine. You must realize that attempting to change an impeller on this boat is a 'blind, one-handed operation', and that one hand is working backwards. I even made a 'puller' out of stiff wire in an attempt to reach through the blades to get a grip under the inner face of the impeller, but it's so tightly held against the housing that this had no effect. I also tried pulling on a blade with a needle nose pliers, but by that time I was afraid I'd end-up damaging the existing impeller to the point of disabling the boat. Obviously I gave up and put the cover back on. The engine is still pumping fine - it always has, but that impeller has probably been spinning much longer than we have had the boat. Do you have any ideas for a guy who's already purchased your book? I suppose we could just keep going and going, but at some point changing the impeller will become an emergency rather than what is now just perceived as an overlooked need. I can't believe that I'm the only person that has ever had a problem with this. Thanks in advance for anything you might suggest. Bill Dimmitt - Sioux City, IA
  • Don Moyer
    • Oct 2004
    • 2823


    I'm not sure why the impeller is fighting you in this way, but I think I'd give up and remove the pump.

    With the pump as old as you indicate that it is, the shaft may be a bit scoured, which would tend to make it a bit more difficult to remove. Once the pump is removed, you can simply push the shaft and impeller out of the housing quite easily.


    Don Moyer


    • vain
      • Jun 2007
      • 3

      Impeller retaining clip?

      Hi Folks,

      on the oberdorfer impeller -

      Is there a retaining clip that must be removed prior to the impeller being able to be pulled from the shaft - or is it just pressed onto the shaft and held im place by the cover?

      I also have never been able to pull my impeller out of the housing.




      • bayareadave
        Senior Member
        • May 2006
        • 73

        keep at it

        On my impeller, there was a clip that goes around the shaft that keeps the impeller on. I pulled the on the impeller blades and it came out with the shaft - no problem. To the original poster: I'd keep up with it until you get it replaced. The impeller on my powerboat failed and it was only 2 years old. I had to float on the current and then start up for short periods of time for steering / docking. Depending on how it fails, you may not know that water flow is reduced - resulting in melting some components of your exhaust (possibly causing fire), or damaging your engine.
        -Dave Whaley
        Pleasant Hill, CA


        • Don Moyer
          • Oct 2004
          • 2823


          If you have an Oberdorfer 202M series pump, there is a small snap ring that holds the impeller on the shaft (product number CSOB_05_66 in our online catalog at You'll find a snap ring pliers in the Specialty Tools section of the catalog to assist in removing and reinstalling the snap ring. There is no reason that you should not be able to pull the impeller and shaft out of the pump other than possibly wear on the shaft.



          • Keymastr
            Frequent Contributor
            • Feb 2007
            • 5

            take the retain clip off

            I just OH my Oberdorfer pump and you have to take the retain clip off to change the impeller. Use a fresh gasket when assembling DON’T use the old one IT WILL LEAK.
            Remember to put the drain plug back in the bottom of the pump. Trust me it fills your billage up in less than 5 minutes if you don’t. A dumb mistake on my part. That took all day to find. Get yourself a long extension bolt for the bottom bolt ,you won’t regret it.



            • Fred
              Senior Member
              • Mar 2005
              • 18


              I replace my impeller every three years, but as I read through the correspondence, the 'snap O pin' is something that I have never seen on the shaft and have never installed. As a matter of fact, I can see where the snap pin goes, but there was never one there in the first place.

              I have had the boat for 14 years and only once have I had an impeller fail, a broken impeller blade, when I first purchased the boat.

              My first question: am I doing any damage to the pump or impeller by not installing the pin? (seems to work just fine)

              My second question: What is the gauge of the impeller gasket paper?

              I have a spare, but by the time I receive one from MM parts department, (it takes at least a week to clear customs) I'm confident that I can cut one using my spare as a template.


              • CalebD
                Afourian MVP
                • May 2007
                • 900

                Impellers and such

                I know that your post is related to the original topic which is a couple of years old. Thankfully the old threads on these subjects are kept around so we can get info from them. Sometimes it is a good idea to start your own thread though. Nobody here seems to care so I suppose I don't either.
                To answer your questions:
                1) I do not think that you are doing any damage to your pump or impeller by not installing the the 'snap O pin'. In fact, I wondered about this when I have replaced my impeller in the past. The impeller will still spin as it is slotted into the shaft (obviously) and the pump body has a pretty tight clearance so that it is not likely to move around on the shaft much, if at all. The one benefit I see to not using the 'snap O pin' is that once you open up the pump the impeller should be easier to remove (perhaps the problem experienced by the original post (OP)). I can't speak from Don Moyer's experience but I see no reason why this should be detrimental to your water pump in any way. If an impeller blade or blades break then all bets are off and the ring might help hold it in place longer even at a diminished rate of flow. I reserve the right to defer to the more experienced mechanics on this board on this point.
                2) I don't know the gauge of the gasket for the water pump impeller cover. I had a similar thought as you that I could make one. I also do not know how much it matters if the gauge is a little thicker or thinner. Perhaps others would answer this question for you if you started a new thread instead of hoping that people will scroll down to the bottom of a thread that was started nearly 4 years ago.
                Keep posting eh?
                Tartan 27 #328 owner born 1958
                A4 and boat are from 1967


                • Don Moyer
                  • Oct 2004
                  • 2823


                  According to Oberdorfer, the snap ring is all about keeping the shaft from moving freely within its limits of travel which would be from where its shoulder contacts the hub of the impeller to the roll pin in the center of the accessory drive gear (I estimate this distance to be approximately 1/4"). The impeller itself is securely contained within the confines of the impeller chamber itself.

                  My understanding is that design engineers feel a bit clumsy over allowing a shaft to "float" freely within an assembly. As a practical matter, I don't think anything bad will happen if the snap ring is eliminated as long as the pump is installed. The designer's worst fear is probably over the small likelihood that upon removing the pump from the engine, the shaft could try to stay in the accessory drive and end up falling into the bilge.

                  In designing the MMI flange pump, we did eliminate the snap ring because the shaft is held securely within the two ball bearings.



                  • tenders
                    Afourian MVP
                    • May 2007
                    • 1452

                    I would also think that permitting a small amount of fore-and-aft wobble in the shaft could wear out the pump seals more quickly. I do know that pulling the shaft in and out of the pump too many times runs the risk of wearing out the seals!


                    • dvdcnl
                      Frequent Contributor
                      • Nov 2004
                      • 7

                      impeller failure

                      Several years ago while motoring down the ditch, the A4 got hot. On investigating, the fresh water pump impeller rubber had separated from the brass which continued to turn with the shaft but the rubber quit turning. The impeller rubber was still in good shape; no cracks or broken fins.

                      Would this be caused by the antifreeze acting on the glue holding the two together?

                      Fortunately there was enough hose on board to hook the salt water pump to the engine and we continued to Beaufort where we obtained another impeller, flushed the engine with fresh water and refilled the cooling system with antifreeze.