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471 Detroit Diesel Shake problem

Discussion in 'Engines' started by cleanslate, Apr 19, 2021.

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  1. cleanslate

    cleanslate Senior Member

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    My J & T 471 has developed a motor “shake /vibration “ between 1000 through 1400 rpm. Does it under any circumstances whether at the dock in neutral or underway in forward. Warm or cold engine.

    No shake under 1000 RPMs and the shake goes away over 1400 RPMs.

    no smoke whatsoever out the exhaust all pressure and oil gauges are stationary.

    Any ideas on what I should look at or check out?
  2. NYCAP123

    NYCAP123 Senior Member

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    Sounds like bad motor mounts or something much more serious (bent rod, bad cam, etc). Don't read too much into vibration not appearing at low RPM, where it's not noticeable or at high RPM where the speed smooths it out. One indicator of what's going on will be when you first noticed it (was it right after winter which might indicate the mounts, or after pushing high RPMs or striking bottom which indicate internal damage).
  3. cleanslate

    cleanslate Senior Member

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    No it started most of last summer I’m not worrying about it too much but obviously it’s something that’s not right I’ll check the motor mounts and then go from there I probably have 40 hours plus on it since it started happening I think it’s always been there since I’ve had the boat it’s just gotten a little worse and I don’t have a good Detroit mechanic right now which stinks.
  4. NYCAP123

    NYCAP123 Senior Member

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    Maybe someone here can help. Anyone know of a good DD mechanic in the Philadelphia / Camden N.J. area?
    In the mean time bring it up to where you've got a good vibration and check your motor mounts to see if one or two seem to be vibrating more. Even if it's that you'll need help changing or adjusting them. If it's internal you'll need that mechanic, if for nothing else then to give you peace of mind that it's normal.
  5. cleanslate

    cleanslate Senior Member

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    Cape may New Jersey Wildwood area that’s where I keep the boat....
  6. DOCKMASTER

    DOCKMASTER Senior Member

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    Hard to imagine it is a motor mount given it does it in neutral at the dock.
  7. NYCAP123

    NYCAP123 Senior Member

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    You should have no trouble finding a DD mechanic there. Check Utsch's, the commercial docks and West Marine for recommendations.
  8. NYCAP123

    NYCAP123 Senior Member

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    Actually that what leads me to hope that's what it is. We know it's not the running gear. So if not the motor mounts it gets very expensive.
  9. cleanslate

    cleanslate Senior Member

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  10. cleanslate

    cleanslate Senior Member

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    Not sure why my post looks funny?....I don't know what I did.
  11. DOCKMASTER

    DOCKMASTER Senior Member

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    When in neutral there should be virtually no torsional resistance (other than weight of crankshaft and items that rotate when in neutral) to impart load into the mounts. It should be pretty limited to the dead weight of the engine. Thus my comment that it is hard to imagine how an engine mount could be the issue in this case.
  12. cleanslate

    cleanslate Senior Member

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    what ever I did...if you just tap on it, the entire post pulls up...
    Ugh I’m not re-posting it.
  13. NYCAP123

    NYCAP123 Senior Member

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    You may very well be right. It's impossible to diagnose with a keyboard. I'm jut pointing him to possibilities that he can check himself. The mounts would be the easiest to to check. One other cheap possibility would be bad injectors causing the motor to run rough. After that he's heading to the mechanic.
    Btw, always try to observe work that's done. Consider it going to school along with keeping everyone honest.
  14. Capt Ralph

    Capt Ralph Senior Member

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    2-stroke Detroits are not smooth machines.
    When not bolted down, they are dancers at certain RPMs.
    Motor mounts are a maintenance item.
    If you see it shake, get new mounts.

    There is another American icon engine that shakes yet still as long lived as a Detroit Diesel.
    Old Hawg motor bikes have been shaking down the byways almost as long as the original 6-110s.
  15. Capt Ralph

    Capt Ralph Senior Member

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    How many had to look up 6-110?
    The forgotten work horse.
  16. cleanslate

    cleanslate Senior Member

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    Knew of a Trumpy or Mathis Trumpy with them ....when I was a young lad.

    Ok, ok...I will remove my big saloon hatch and start her up and get it shake RPM and observe all motor mounts at all points of connection and in between.

    what do you think on my blower comment above ?
  17. Capt Ralph

    Capt Ralph Senior Member

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    What blower comment above? Post # 9 is blank.
  18. Capt Ralph

    Capt Ralph Senior Member

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    How old are the mounts? Send pics or give us a style/model of them.
  19. cleanslate

    cleanslate Senior Member

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    Some how on my end my comment got all wrapped up in the previous comment from NYCAP..
    Try clicking on it see if it pops up..That's how I can open it all the way.
  20. cleanslate

    cleanslate Senior Member

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    Original. 1980. They are clean looking to me. No photos right now.