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89 325i Knock Knock, can anyone hear this?

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    89 325i Knock Knock, can anyone hear this?

    Last year I broke a rocker and decided to refresh the engine in my 89 325i. New valve seals, rod bearings, rings, new rubber all around. I had a machine shop do the bottom end. I put it together, it sounded great, and about a month later, I get this noise. lol. Knowing that I'll be tearing it back down in the spring, possibly even scrapping the bottom end for eta crank and rods, I drove it a little around town this winter.
    I know.
    As you can see in the video, once it gets past 2.5k, the noise disappears, and as long as it's in gear, stays gone.

    https://www.youtube.com/watch?v=BdS5...ature=youtu.be

    This morning the oil level light AND the coolant level light turned on the dummy panel. After adding about a half quart and checking the dipstick, I see the tiniest bit of milkshake on the top of the fins. So I guess I'll be dropping the engine sooner than I planned. What I'm wondering is if the apparent HG failure might have anything to do with what I suspect is rod knock or a spun bearing. Has anyone heard such a slow knock or is this super basic? Should I go ahead and buy a new set of bearings or just use this as a sign to source an ETA crank and rods? The HG was Goetze, BMW bolts.
    Last edited by fahr'n fahr'n fahr'n; 01-15-2020, 04:08 PM.

    #2
    Hello,

    I've heard such a slow knock and it turned out to be my flexdisk and CSB on the driveshaft. Before you tear down the engine, make sure the problem lies within it. That milkshake you saw, could it be due to condensation because the car had sat for a period of time?
    '85 Alpine Weiß 2-door with m20b30 ground up build

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      #3
      The video shows the car was parked, in neutral with it making the noise. Also, the flex disk is about 6 months old. But I wish. Thanks for the suggestion.

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        #4
        How certain that it's coming from the motor? $10 from the local auto store will help to pinpoint the exact area

        Click image for larger version

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          #5
          I tried listening at the oil cap and listening at the dipstick and neither sounded louder. Its the loudest inside, at the feet, right about where the bell housing and back of the engine meet. As long as I'm within those RPM coming from idle, it will knock. If I bring the RPM past the knocking, to lets say 3.5k and then gradually back down to the knocking range, it will be gone. But once I let it go to idle and raise it to that point again, it reappears. Pushing in the clutch does nothing to stop the sound.

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