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Thread: rod knock?

  1. #1
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    rod knock?

    My daughter has a 2003 525i (E39/M54) 160k miles that developed what I first thought was a just a simple ticking sound. It would only happen at idle (750rpm) and giving it just a bit of gas in neutral or drive (to 1000rpm) will make it go away. It sounded like just an annoying rattle (almost like a heat shield vibrating). Seemed to be coming from the drivers side of the engine. I didn't think it was much more than an annoyance but after a while I decided to do some research.

    Google/YouTube led me to a DISA valve flapping so I replaced that (easiest thing I've ever replaced on that car!). But the ticking remained.

    Then maybe I thought it was lifter noise. But now that I listen closely it is louder from the bottom and rear and I fear it may be rod knock? It is quite loud from the bottom and really almost like a hammer tapping noise. It is low frequency (definitely <750/min seems about 250/min I guess it could be as high as 375/min (like half the RPM) but that seems a little high. It happens in neutral and drive with the car parked or say idling through a parking lot. It does not go away after the engine warms up. This has been going on for several months and several 1000 miles and not gotten any worse or better.

    What seems strange to me is that even just leaning on the gas a little bit will make it go away. I would think that rod knock gets worse with higher RPM or load. Maybe it could be flywheel related? I don't think it is coming from the front of the engine.

    What do you think?

  2. #2
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    Make sure your spark plugs are properly torqued down.

    I have seen at least 3 examples like this turn out to be loose spark plugs.
    -Abel

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  3. #3
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    ^^^
    First thing to check. If you remove the plastic covering over the coils and plugs and hold the palm of your hand on each coil you will be able to feel a loose plug as that cylinder fires. This one happened to me and it does sound all the world like a rod knock.
    You described it as a ticking and speculate it could be lifter noise. These engines ARE a bit sensitive to oil. If the plugs are tight and the noise persists an oil change has never hurt anything. Premium oil in recommended weight please.
    Your engine is middle age at 160k and if it's had any reasonable care I'd be surprised to see a bearing failure.
    Good luck, hopefully you will be able to breath a big sigh of relief also.
    Last edited by ross1; 12-31-2018 at 05:53 PM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  4. #4
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    Thanks. I'll have the plugs checked (car is 350 miles away now!) I should also have mentioned that the car runs fine. No power problems. No rough idle or rough running. Just this darn noise at idle.

  5. #5
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    MauiM3Mania is offline Observer/Master Skeptic Moderator
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    A rod knock is a deep noise, I wouldn't refer to it as a tick. My experience with several engines with loose big ends was noise was noticed under very light load and deceleration.

    As was mentioned, check the plugs and do an oil change, pulling a sample and have it analyzed Blackstone Labs. You might want to seriously not drive the car until the issue is determined. Replacing crankshafts and connecting rods is an expensive repair.

    Performance is not effected. At least not early on.

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  6. #6
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    In the oild days when there were distributors and wires if you had a rod knock, while the engine was running you would remove the spark plug wire and the noise would go away because there was no combustion load on the piston. Rapper noise on the other hand is so easy to hear because the camshaft moves at half the speed of the crankshaft

  7. #7
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    Quote Originally Posted by MauiM3Mania View Post
    A rod knock is a deep noise, I wouldn't refer to it as a tick. My experience with several engines with loose big ends was noise was noticed under very light load and deceleration.

    As was mentioned, check the plugs and do an oil change, pulling a sample and have it analyzed Blackstone Labs. You might want to seriously not drive the car until the issue is determined. Replacing crankshafts and connecting rods is an expensive repair.

    Performance is not effected. At least not early on.
    Another thought is to inspect the oil filter removed. Look in the pleats of the filter, little shiny flakes will be in them if you have a bearing going south.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  8. #8
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    Hmmm, bottom rear, maybe driver's side....I'm going to guess cracked flexplate. No, I can't explain why it would go away with revs....or the other possible items either. But I have replaced several flexplates on cars identical to yours.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, at an independent, formerly @ dealer
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  9. #9
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    So we had the spark plugs replaced. The tech said one or two seemed to be loose and they thought the sound was gone but just a few hours later it is back. My daughter recorded the sound and I uploaded it to youtube so you can here. This is with the car parked at idle.

  10. #10
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    I don't think it is a rod knock, perhaps valvetrain noise

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

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