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Ohno (Onan) MCGCA 45 noise

Discussion in 'Generators' started by Pascal, Feb 26, 2024.

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  1. Pascal, Feb 26, 2024
    #1
    Pascal

    Pascal Senior Member

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    Another ohno issue: exhaust noise. While neither of them overheat or even run hot they are just way too loud as if not getting enough water to muffle the noise. There is good flow out the exhaust just not enough it seems

    everything has been checked from the external slotted TH to the heat exchangers as well as impellers, strainers, hoses etc. It just seems the raw water pumps aren’t up to the job.

    while they don’t show any sign of wear, I may replace one of them when we get back to miami since I have a couple of new spares.

    wondering if anyone has seen this before and if a solution was found. Bigger pumps? I had the same issues with 27.5 Ohnos on the previous boat.
  2. Capt Ralph, Feb 26, 2024
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Can you get a larger pump on a later gear driven OhNo?

    Years ago, I remember different sized cams in the raw water pump would change the flow rate.
    Maybe find a more aggressive cam for your pumps.

    We have installed a few Gas-Sep options with great results.
    https://centekmarine.com/solutions/generator-wet-exhaust/

    Baffles in the can muffler can wear away also.
  3. d_meister, Feb 26, 2024
    #3
    d_meister

    d_meister Senior Member

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    I had the same problem on a pair of 3406 Cats. The rubber raw pump vanes were 100%, but they had so much "curl" set that there wasn't enough tension against the pump bore.
  4. Capt Ralph, Feb 26, 2024
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    Are you running Globe impellers?
    Years ago, the soft vanes would sail past the cam and not pump as much water as stiff neoprene in various engine installs.
    I wonder if they still have this issue.

    OTOH, My bud luvs Globe impellers in his NL gen-sets.
    Moves water fine and out last the original neoprene impellers past 3 to 1.

    I just ordered a Globe impeller to try in my lil Kubota (ex-OhNo) gen-set.
    Last edited: Feb 26, 2024
  5. Capt Ralph, Feb 26, 2024
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    I'm sure your on top of this but just came to my mind and had to type it anyway.
    The front end of the heat exchangeer from the raw pump; Super clean and clear?
    Seems old impeller bits and a little of everything can collect here.

    And a question, Is it loud on the boat or noticed away from the boat ?
  6. Pascal, Feb 26, 2024
    #6
    Pascal

    Pascal Senior Member

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    HE inlet is clean. I did find some old impeller bits which a previous captain never looked for. It’s not really noticeable from inside the boat, just from the aft deck and within 100’
  7. Capt Bill11, Mar 12, 2024
    #7
    Capt Bill11

    Capt Bill11 Senior Member

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    You could change one to a larger volume electric pump and see if that helps.
  8. Pascal, Mar 12, 2024
    #8
    Pascal

    Pascal Senior Member

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    I just hate having to re engineer it. I wish there would be a bigger engine driven pump.
  9. Capt J, Mar 12, 2024
    #9
    Capt J

    Capt J Senior Member

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    DON'T. Without the amount of hours you put on generators, I suspect that the mufflers are worn out and would put new ones. Most likely why they're loud. I also do notice some of the Onans don't seem to have a copious amount of water flow out of the exhaust, but at the same time never overheat.
    Capt Ralph likes this.
  10. Pascal, Mar 12, 2024
    #10
    Pascal

    Pascal Senior Member

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    With water lift mufflers, isn’t it the water that muffles the noise, not baffles?
  11. Capt Ralph, Mar 13, 2024
    #11
    Capt Ralph

    Capt Ralph Senior Member

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    I have never diceted a lift muffler. I may have seen some cave drawing of it once.
    Either a baffle(s) or submerged tubes force the exhaust gasses under water once or twice before out the top.