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Onan Mdl4 Generator

Discussion in 'Generators' started by Lunderic, Jul 15, 2025 at 10:11 AM.

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  1. Lunderic, Jul 15, 2025 at 10:11 AM
    #1
    Lunderic

    Lunderic Member

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    My otherwise perfectly running generator had the rear main oil seal fail. My mechanic can't source the parts and doesn't want to proceed. Any suggestions? I was thinking of removing and just measuring and order from Grainger or other. Does anyone know of a source for obsolete Cummins/Onan parts? Cummins stated I need to replace the generator. I will eventually replace but just trying to finish out season if possible. Thanks for any suggestions!
  2. Capt Ralph, Jul 15, 2025 at 10:32 AM
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Any numbers still readable on the old seal?
  3. Lunderic, Jul 15, 2025 at 10:39 AM
    #3
    Lunderic

    Lunderic Member

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    I didn't take it out yet. I'm a little tight on time so I hired mechanic but now he doesn't want to continue without being able to source parts.
  4. Capt Ralph, Jul 15, 2025 at 11:14 AM
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    My notes show 509-0203 as the original OhNo rear seal part number (spec A).
    That includes a wear sleeve.

    Sadly, these engines are way past end of life and parts are near non-existing in North America.
    The last time I ordered MDL* parts, they came in from South America.
    Verify this part number, call your Cummins rep back up and ask for a world wide search.
    Maybe Cummins can offer the original vendors part number.

    I do understand why your tech is in no hurry to jump in there.
    It is a shame, when running, they are darn good engines but every time I work on one, it turns into a Pandora's Box. Splitting yours for a rear seal may turn into an ugly ordeal for you and your tech also.

    How bad is the leak? Will it last till you get home or end of season?
    Maybe some snake oil or thicker straight weight oil.
    Last edited: Jul 15, 2025 at 11:20 AM
  5. Lunderic, Jul 15, 2025 at 4:56 PM
    #5
    Lunderic

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    It's leaking bad... after running for 10 minutes it leaks probably a pint. I can't run it as is.
  6. Capt Ralph, Jul 15, 2025 at 5:36 PM
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    Ouch.
    No backup gen-set?
    Leaks in a tray, with a drain port?
    Have you been gen-set shopping lately?
    Where is your ship?
    You probably have an ole Hatt, what model ship?
  7. Lunderic, Jul 15, 2025 at 11:07 PM
    #7
    Lunderic

    Lunderic Member

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    The boat is on Long Island. No backup Gen-set. She's a 93 53' Viking. It does leak into the tray but no drain port. I did start shopping, but I would like to get it going to at least get through the season.
  8. SplashFl, Jul 16, 2025 at 12:16 AM
    #8
    SplashFl

    SplashFl Senior Member

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    Previous boat had 8kw Onan. Turned out to be same Kubota motor as in Phasor Generator and the local dealership stocked parts priced way below Onan's.