Replacing shaft in MMI flange pump every other season

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  • theredboat
    Senior Member
    • Apr 2010
    • 73

    Replacing shaft in MMI flange pump every other season

    Over the past 3 seasons I've had to rebuild the MMI flange pump in my freshwater cooled A4 twice. The symptom is I see oil leaking through the weeping hole and when I pull the pump I see that the shaft is scored and likely the seals are bad too. Bearings look fine and there's no obvious play in the shaft. So what gives?!

    After a rebuild, pump works great for a while (no leaks).

    Now after two rebuilds im reluctant to do it again without figuring out what could be causing this.

    - Alternator belt tension issue? (I just ordered a gauge so I'm not eye'ing it)
    - Pump housing no good, needs replacement?

    Any ideas?
  • Dave Neptune
    Afourian MVP, Professor Emeritus
    • Jan 2007
    • 5115

    Try rebuilding with a new shaft. The new seals won't last on a worn out shaft. Also be sure the bearing fit nice and snug. It really takes an awful lot of tension to stress the nearing in the pump or alternator.

    Dave Neptune


    • Mo
      Afourian MVP
      • Jun 2007
      • 4519

      I agree with Dave, good point. Buy a new shaft.

      I have a friend that's a ex RCMP in Canada. He took up sailing, then gave that up. Now he plays in his work shop....with big WWII vintage lathes and the like. He makes his own stuff. Milling machines etc etc. Sharp dude. I break stuff, he makes a new one.

      He made me a new shaft last year..." here, I have a project to keep you busy for an hour tomorrow". It's a wonder he doesn't pay me...and no, he won't accept a dime.

      1976 C&C 30 MKI

      The pessimist complains about the wind.
      The optimist expects it to change.
      The realist adjusts the sails.
      ...Sir William Arthur Ward.


      • joe_db
        Afourian MVP
        • May 2009
        • 4544

        My water pump has popped a leak. It is original to the engine AFAIK and I was thinking about getting the new Moyer pump with the grease-free bearings and nice thumb-screw backing plate.
        If it needs a new shaft every year I am not going to bother!
        Joe Della Barba
        C&C 35 MK I
        Maryland USA


        • Al Schober
          Afourian MVP
          • Jul 2009
          • 2034

          The Oberdorfer style pumps do wear out. You can replace the shaft and seals, but once the housing is worn, it's all over.
          I struggled with mine for years and lived with the sea water leakage to the bilge & the corrosion under the pump. This was no longer an option when I converted to glycol cooling. Instead of leaking sea water I was now leaking coolant. And, like your blood supply, there's only so much of it.
          The change to the ball bearing pump with the face seal was wonderful!