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    Engine noise 5.0 Merc-gctid465565

    I have a 2455 with a 5.0 that has an intermittent engine noise. First time this happened I took it back to the dock at idle and to a merc dealer. At the dealer it would not make the noise for them and I took it out with the mechanic and again nothing.

    I took the boat out on a couple of trips and no noise, then this weekend it came up again so I took some video to record the noise. The noise went away after I let it sit for a while and ran it again. It sounds like maybe a sticking valve or ?

    Here is a video of it making the noise

    https://www.dropbox.com/s/s5qi6n3ty2...2012.42.01.mov

    And a second when it goes away.

    https://www.dropbox.com/s/vx6bsh2ywb...2012.57.10.mov

    The engine was recently rebuilt less than 100 on it and not showing any problems with oil pressure or overheating. Once the engine noise went away I took it back to port, about 1 hour most of it at 3600 rpm with no issues.

    Anyone know what is causing this?

    #2
    Sounds like engine coupler failing, are you certain that the crankshaft thrust bearings were properly set during engine rebuild? Does the engine make this noise when revving in neutral?

    Comment


      #3
      Does the noise go away with the drive down.

      Maybe the ujoint.
      Be good, be happy, for tomorrow is promised to no man !

      1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

      '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

      Manalapan N.J

      Comment


        #4
        Warm the engine up until you can re-create the noise. Shut it down, and loosen the serpentine belt. Start it up again for a short duration, and see if you can re-create the noise.

        If no noise, it may be the serpentine belt idler pulley bearings, or the engine circulating pump bearings.

        You have an A drive, so you won't loose exhaust cooling water while doing this test.

        .
        Rick E. Gresham, Oregon
        2850 Bounty Sedan Flybridge model
        Twin 280 HP 5.7's w/ Closed Cooling
        Volvo Penta DuoProp Drives
        Kohler 4 CZ Gen Set

        Comment


          #5
          I should have tried running it in neutral but I did not. Unfortunately I have no idea how to get it to make the noise. For some reason after shutting the engine down and waiting a couple of minutes it went away. I figured shutting it down might get rid of the noise because the first time it happened it ran fine when I took it to the mechanic.

          I have tried running running it at different RPMs and it does not come back so it is hard to test anything. The leg was fully down when it happened and the noise does not appear to be comming from the front of the engine. It sound like it is coming from the port side but hard to tell for sure.

          Comment


            #6
            Amac35 wrote:
            I should have tried running it in neutral but I did not.
            While in neutral, all gears are still rotating.

            The only difference is that the prop shaft is not engaged to either of the two lower unit "driven" gears.

            I'll still suggest loosening the serpentine belt, and see if there's any excessive lateral movement at either the idler pulley or at the circ pump.

            The one draw-back to this test, is that it takes the idler pulley, the circ pump, the PAS pump, and the alternator all out of the loop.

            So you must still try to isolate the culprit.

            The one thing that I did not mention earlier, would be your power assist hydraulic steering pump.

            These are vane pumps, and occasionally the vanes will produce an intermitant noise.



            .
            Rick E. Gresham, Oregon
            2850 Bounty Sedan Flybridge model
            Twin 280 HP 5.7's w/ Closed Cooling
            Volvo Penta DuoProp Drives
            Kohler 4 CZ Gen Set

            Comment


              #7
              2850Bounty wrote:
              .

              I'll still suggest loosening the serpentine belt, and see if there's any excessive lateral movement at either the idler pulley or at the circ pump.

              The one draw-back to this test, is that it takes the idler pulley, the circ pump, the PAS pump, and the alternator all out of the loop.

              So you must still try to isolate the culprit.

              .
              I will give that a try.

              Comment

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