Mercruiser engine aglinment

Discussion in 'Powerboats' started by Sprint 18.5, Aug 10, 2021.

  1. Sprint 18.5
    Joined: Aug 2021
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    Sprint 18.5 Junior Member

    The original motor ate a value so I replaced with long block with new exhaust manifolds and risers but haven’t made the exhaust connection being there kinda in my way to work.
     
  2. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    If there's an intractable level issue, I'd suggest getting a laser level in there, and measuring the exact height at each location below the plane of the laser beam. Then draw it on graph paper, to scale. The error will be immediately obvious. One mount will be out of plane.
     
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  3. Sprint 18.5
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    Sprint 18.5 Junior Member

    I’m going to reassemble one last time and and will try your method if I understand and get my hands on that tool.
     
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  4. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Do it with the engine out first. A carpenter's laser cross level comes from Lowe's or HD or really anywhere like that. Put it in one spot, dont move it. Ive done this recently in the forward cockpit for the under floor framing. Using a horizontal and vertical plane simultaneously you can get some real accuracy. Within a 1/16", easily enough. Say 2mm. Your issue seems larger than that, so that should really shine a light on it....literally.
     
  5. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    put the engine back in and take the gimbal bearing out.
    Put the alignment tool in to get a ball park of where the engine is.
     
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  6. Sprint 18.5
    Joined: Aug 2021
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    Sprint 18.5 Junior Member

    R&R the motor again checking bell housings, yoke etc. motor fell right into place all four mounts and adjusted opposite front motor mount to close the rear down even with the other rear mount. Front motor mount has more threads than the other. Looking up thru gimbal housing looks level but alignment tool seem to be hitting the left side about 9 o’clock position thinking could it be the gimbal bearing not seated correctly when pulled off lower unit. The motor stopped suddenly at 4000 rpm’s consuming a value. When I removed lower unit it was no harder than other times removing. I loosen all the bolts put a 2x4 under the skeg level pulled and dropping it about and inch high and separating normal. Out of things to try.
     
  7. Sprint 18.5
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    Sprint 18.5 Junior Member

    Sorry I didn’t see your post before my recent. I turned a pipe that fits flush into yoke and eyeball around the bearing turning it 4 time a 1/4 turn and it’s always closer to the 9 o’clock position having less space. I can raise and lower with adjustments at 6 and 12 o’clock position only and it pretty much level however the motor mount thread counts wer always close and now there off by at least 10 threads.
     
  8. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Dewalt laser level from Lowe's. Find out exctly what is off. There's no way 1 of 4 mounts is suddenly off unless something was distorted in the stop. What stopped the engine? Something seized hard in the leg?
     
  9. Sprint 18.5
    Joined: Aug 2021
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    Sprint 18.5 Junior Member

    It dropped a value about 35-4000 rpm with it knocking a hole in the cylinder loosing all power coming to a stop. ordered a long block marine motor to replace not getting the alignment tool to first enter.
     
  10. Sprint 18.5
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    Sprint 18.5 Junior Member

    The black factory paint on engine mount blocks look undisturbed with no clean markings. Took one motor mount at a time to bolt on me motor block. The looked the same and interchangeable.
    When I insert the greased alignment tool it hit the yoke at 9 o’clock horizon position and I can wiggle around with some force in but more difficult removing that Millimeter
     
  11. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Are the front mounts loose at the base, so they can move sideways, or are they fixed in position since the old engine? Merc front rubbers are quite stiff, if old engine stopped suddenly, it might have pushed something in horizontal direction. And you say the interference is in the 9 o'clock position, ie anything protruding into the alignment path is coming from the side, not in the vertical plane?

    If one of the rubber bush center sleeve is riding high on something, instead of entering onto the spiral washer, you might use marking blue ink on the sleeve when lowering into place. Lift off and see if there is a mark, probably on one of the fiber washers?

    Edit:
    Btw, what type of front mount do you have on the engine block? Have you got them back on their original side with the new engine? Are they absolutely symmetrical P/SB? There is one type which is adjustable horizontally, could be out of position?

    Sorry I keep nagging about the front, but apart from the one "gnawing", I have never come across a Merc rear mount causing trouble; its always the front end pointing ascew.
     
    Last edited: Sep 10, 2021
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  12. Sprint 18.5
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    Sprint 18.5 Junior Member

     

    Attached Files:

  13. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Take the front rubber mounts off and look at their mounting surface, they look like sitting tilting in the grp box. See if the rear mounts come down correctly without the front ones, if you can let the engine hang in the hook for a while.

    There might even be a crack in the hull "box" from the sudden stop.

    Sorry, got to leave you for now, its midnight here zzzzzznorkk!
     
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  14. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    ....and, since it looks like the front units have not been loosened: The correct mounting procedure requires the front mounts to be easily movable in the horizontal plane, then you lower the rear onto their seats and tighten slowly, while watching that the metal centers enter into the fiber washer correctly (some very slight "wiggling" sideways will ease the fit). This applies even if you reinstall an engine. If not following this scheme, you will build in strain into the installation. Result: undue wear and increased vibration level.

    That done, you can lower the front, while ascertaining that the mount's baseplate can move freely to "find" its position without any horizontal forces occuring. Finally, the front vertical adjustment is done; in this way there is seldom any adjustments necessary in the horizontal plane, only the final vertical "touch". The reason for this procedure is the very high horizontal stiffness in the Mercruiser rubber mounts; it takes several hundred pounds to move the rubber bush even a fraction of a mm horizontally. The accumulated dimensional tolerance chain just in play between bolts and holes is several mm's, and on top of that you have the hull change due to elastic and plastic shape change because of the unloading. Do it right and it is simple.
     
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  15. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    @baeckmo , that is so well written, so clear and methodical, that I could precisely follow what you mean, and I've never done it before. Just excellent.
     
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