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Twin Disc MG 506 RH 1980

Discussion in 'Engines' started by cleanslate, Jun 17, 2021.

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  1. cleanslate

    cleanslate Senior Member

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    So things are still the same after running the boat this weekend.
    Oil level way up on the stick in neutral with the engine running normal operating temperature and low oil pressure and fluctuating gauge.

    When things were completely cooled down the next day I checked the oil non-running cold ; The oil level was down around the low mark.
    Ok
    So I decided to check the round filter screen to make sure it was clean.
    As soon as I removed the oval cover plate for the screen there was a intake suction into the transmission.
    A minute or two went by I pulled the screen out which was clean as can be I decided to check the oil level with the screen out and the cover plate off now the oil was way up on the stick cold not running just like it should be.



    Somehow the clutch is creating a vacuum and not letting the oil drain back into the sump like it should when the engine is turned off and also it’s holding oil where it shouldn’t be while in forward low RPM I assume which is causing the fluctuating gauge in the low oil pressure.

    Oil pressure is fine in reverse idle rpm.

    Could be something wrong with the spool valve or the piston regulator that’s what I’m thinking something is stuck not opening up properly to relieve vacuum pressure?

    Oil fill and vent plug on top is clear and not blocked up.
  2. cleanslate

    cleanslate Senior Member

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    51C91422-480A-4C9F-848D-B6AACC0D987E.jpeg
  3. Capt Ralph

    Capt Ralph Senior Member

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    Just down loaded the 506 (1982) manual.
    I am so confused.
    The sump is open to the vent cap on top. That is how the clutch case is filled.
    However, there is a shoe the screen fits in, inside the case.

    PM me with an e-mail address that can take large PDF files.
  4. cleanslate

    cleanslate Senior Member

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    Well I removed about 3/4 of a quart of oil…no real change.
    I also tried to remove the spool thingy and piston etc. at the shift lever . I couldn’t pull it all the way out because it was hitting the underside of my inner cooler on the back of the engine by the turbo….
    Requires taking lots of stuff off the engine to get it out.

    anyway on my last trip last weekend it seemed to do a little better main thing that holds its pressure while underway and at high rpm.

    Going to live with it for a little bit.

    again got the oil to drain back into the sump the next morning by cracking open the cover plate over the filter screen on the bottom left corner of the transmission.
  5. Capt Ralph

    Capt Ralph Senior Member

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    How fine of a mesh is the filter made of?
    Is it under compression under the filter cover?
    Can you experiment/run for a minute with out the filter?

    That has to be the only place that a vacuum (post #21) can be had & held; oil pick-up to oil-pump..
  6. Capt Ralph

    Capt Ralph Senior Member

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    Could that have been pressure you noted in post #21?
  7. cleanslate

    cleanslate Senior Member

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    It’s very fine screen filter. Cylinder shape about the size of my thumb.

    I don’t see why not ? Run it a the dock for a minute with out the filter and see what happens . Check the oil both running and shut down.

    but remember in reverse things are all normal, pressure and no gauge fluctuation under normal operation.
    Only forward is when things act up.
  8. Capt Ralph

    Capt Ralph Senior Member

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    Not sure about reverse, just trying to figure out how a vacume or pressure develops on the screen cover. It's a vented sump.
  9. Capt Ralph

    Capt Ralph Senior Member

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    Oh, forward pack needs more oil, after all the shifts, all these years, I'm sure the forward pack has more wear.

    Just thinking and typing as I go here.
  10. chesapeake46

    chesapeake46 Senior Member

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    I have different gears than you but when mine were getting pressure fluctuations, the cause was slipping discs.