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Onan MDKAF/MDKAD gensets water pump problem

Discussion in 'Generators' started by cdg, Jan 18, 2011.

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  1. cdg, Jan 18, 2011
    #1
    cdg

    cdg Member

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    Location:
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    I have these 27.5 kW and 17.5kW 60Hz gensets. They are a kubota diesel, 'marinised' with a sherwood raw water pump, gear/shaft driven.
    Nowhere on the Cummins Onan site is there help and the Onan agent here in NZ isn't responding. I have a refit coming and will likely replace both units (they are 17,000 and 22,000 hours); one would think they would try harder for some business. That's OK, Kohler seems quieter anyway. (Purchase advice anyone, btw?)
    The problem: the pump/impellor shaft has a flat blade or tang end, that links into a slot on the drive shaft/motor end. In the smaller genset, the pump shaft is narrower than the drive shaft and has mined a neat hole in the drive shaft the same dia as the pump shaft. The pump shaft tang is eaten away as a result. In the larger genset, the pump shaft has a blade or tang that is wider than the pump shaft. It is busy eating away the drive shaft as well, so that the slot is now an hour glass or X shape. It will completely mill out the drive shaft for sure. That the shafts should be joined or meshed together in a better design is clear; but what can I do to fix these now? Pulling the drive shaft end is a major (injector cams and so on). We've welded a new tang onto the pump shaft of one, but that's prob only temporary.
    I can't imagine we are the 1st vessel with this problem as its a design fault. Any ideas anyone? Thanks very much for your advice. C
  2. K1W1, Jan 18, 2011
    #2
    K1W1

    K1W1 Senior Member

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    Hi,

    Is there anywhere on the engine where you could mount a external pump and drive it off a belt on the engine by adding a multi sheave pulley to the FW Pump, Crankshaft Pulley etc?

    You could also look at bolting some type of drive to suit the external pump onto the front Crank Pulley and driving the pump directly off it.

    I have seen a few Hydraulic Pumps mounted this way on DD's and CAT's and they seemed to work ok.
  3. cdg, Jan 18, 2011
    #3
    cdg

    cdg Member

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    Location:
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    Thanks for the quick and useful reply K1W1. We should be able to make the weld fix work till re-fit, and don't have much additional room in/around the gensets. There must be a retro fit part fix that someone has considered to couple the two shafts together (a cap&collar/sleeve arrangement?).
  4. K1W1, Jan 18, 2011
    #4
    K1W1

    K1W1 Senior Member

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    Hi,

    Another way around the problem might be to use an electric cooling pump.

    You could either use an AC one if you can get the Gennie online pretty smartly after it starts or a DC one if you have a good capacity Start or House Battery setup to run it and an alternator/charging setup that will support a constant running pump.

    You could pretty well mount the pump anywhere it was convenient and run the hoses/cables to the engine /power supply.

    If I was a bit closer to Wellington I would not mind popping by for a look but alas I am not at the moment.
  5. cdg, Jan 18, 2011
    #5
    cdg

    cdg Member

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    Location:
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    Thanks again K1W1. (Are you a kiwi based in Florida, btw?) I have a Cape Horn 81 called Columbus - cruising top of South Island right now. The gensets appear to be 'on their last legs' and required a lot of attention; good clean oil, maintained on spec, but lots of niggling issues coming up, and more new ones than same old one repeated. The service agents here aren't coping well perhaps just lack of experience.....
    SO another question: I have a 60day refit scheduled soon, and was wondering on reconditioning the gensets vs purchase new. The ballpark costs of refurb are heinous, and encourage purchasing new. Murphy will be present during extraction/re-installation and spares availability (they are 10 years old) may create costs and hassles too. What sage advice do you have please? Many thanks in advance.
  6. Capt J, Jan 18, 2011
    #6
    Capt J

    Capt J Senior Member

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    With the amount of hours that you have on them, I'd recommend new. All of your accessories on the generators (the end, alternator, starter, exhaust, etc) are all old and with the cruising you're doing, personally I would replace.

    I would also go with Northern Lights generators in your application.
  7. K1W1, Jan 19, 2011
    #7
    K1W1

    K1W1 Senior Member

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    Hi,

    I would tend to agree with the post above.

    If they have done a good innings like that and are now starting to get unreliable I would lean towards replacing them and at the same time look to renewing the switch gear that serves them as everything is probably getting a bit long in the tooth.

    It may take you a while to find units that will fit into the space you have so you should start looking and getting things setup before you tie up for your refit period.
  8. cdg, Jan 19, 2011
    #8
    cdg

    cdg Member

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    Thank you Capt J and K1W1. New, is the way to go. The space seems to fit all of Kohler, Northern Lights and, ironically, Onan, so thankfully we have some choice. Will keep you posted. Your commentary has made a good difference - be sure to look us up next time in NZ. :) Cheers