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  • Weird knock

    My engine had developed all kinds of knocking noises after the summer mostly lifter in nature. Once the head was pulled off there was lots of wear and I ended up fitting a practically Audi rebuilt head.

    Now all is good with compression of 12bar across the cylinders ( 2 have 11.8bar) but there is still a knocking noise on idle once the engine is warm or once it has been thrashed a bit.

    Engine pulls hard and is very lively. We thought a lifter may have been stuck so we did an engine flush and new oil 0w40 Mobil 1. Again all is good oil pressure 2bar on idle and goes to 3+ by 1500rpm moving out to 4bar easily.

    We unplugged one by one the coil cables and noticed that once cyl 5 was without spark, the knocking goes away almost completely, while once the rest of the coil cables were removed the noise kept on happening.

    My mechanic seems to think that this is a piston issue rather than anything else. He has seen it before happening in punto's where there could be pin damage or bottom piston wear.

    Has engine encountered something like this before?

  • #2
    https://youtu.be/6hym3CSrUPo

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    • #3
      Sounds like lifter noise, but can't be sure as it only idles. How does it sound when you hit the throttle little bit? Usually rod knock is little bit "deeper and heavier" than lifter knock and not so even.

      New INA lifters are not much: https://spareto.co.uk/products/420-0...r-slash-tappet
      Audi UrS4 Avant 2.5 20vt - twincharged - Project
      Audi 80q B4 Sedan 2.2 20vt - Daily user
      BMW 320d Touring e91 M-Sport - Daily user
      BMW 740iA e38 - Project

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      • #4
        The complete head was new from audi. Sat on a shelf for 7 years but was checked before fitting. After this it was checked again and lifters seem ok. I do have a set of lifters if needed, but with this test if it were lifters, wouldn't they continue to knock even after I removed the coil plug?

        To me removing the plug while the engine runs and noise going away seems to make me thing that it's related to the spark and compression cycle of the cylinder, whereas lifter should always knock if it did regardless.

        When revs go higher it's not heard that much, only a little as it speeds up. Then goes away. Also makes me think if it's related to the higher oil pressure that it goes away. As it doesn't knock on cold start and higher revs

        Sent from my SM-P550 using Tapatalk

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        • #5
          Rod related by the sound of it.
          91 Modded 3B
          14 A6 Avant Black Edition

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          • #6
            Originally posted by A80Avant View Post
            The complete head was new from audi. Sat on a shelf for 7 years but was checked before fitting. After this it was checked again and lifters seem ok. I do have a set of lifters if needed, but with this test if it were lifters, wouldn't they continue to knock even after I removed the coil plug?

            To me removing the plug while the engine runs and noise going away seems to make me thing that it's related to the spark and compression cycle of the cylinder, whereas lifter should always knock if it did regardless.

            When revs go higher it's not heard that much, only a little as it speeds up. Then goes away. Also makes me think if it's related to the higher oil pressure that it goes away. As it doesn't knock on cold start and higher revs

            Sent from my SM-P550 using Tapatalk
            Ooh, I didn't look the last one, hah As steve says, propably rod bearing noise.
            Audi UrS4 Avant 2.5 20vt - twincharged - Project
            Audi 80q B4 Sedan 2.2 20vt - Daily user
            BMW 320d Touring e91 M-Sport - Daily user
            BMW 740iA e38 - Project

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            • #7
              I have a very similar knocking noise but on cold starts and seems to be less noticeable when car is warmed up. Knocking is more frequent as engine speed increases.
              '93 Audi 100 Avant - R.I.P
              '92 Audi UrS4 Avant - SOLD
              '93 Audi UrS4 Avant LPG

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              • #8
                Originally posted by hunker7
                I have a very similar knocking noise but on cold starts and seems to be less noticeable when car is warmed up. Knocking is more frequent as engine speed increases.
                Which is exactly the opposite to mine

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                • #9
                  Sounds like rod knock or piston slap.

                  Sent from my Moto G (5) using Tapatalk

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                  • #10
                    How can that happen after 60k kms?

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                    • #11
                      Hard to say. Are you rods rifle drilled? Upgraded pins? Aftermarket pistons? What bore to piston clearance?

                      Sent from my Moto G (5) using Tapatalk

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                      • #12
                        Pistons are stock, Kolben Schmidt with stock clearance of 81.51mm I have the 3d size up. Rods are scat and not rifle drilled, but rods have been used for more than 120k km without issues.

                        From memory piston is 81.48mm.

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                        • #13
                          Trusted Vems knock control?
                          Audi UrS4 Avant 2.5 20vt - twincharged - Project
                          Audi 80q B4 Sedan 2.2 20vt - Daily user
                          BMW 320d Touring e91 M-Sport - Daily user
                          BMW 740iA e38 - Project

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                          • #14
                            Haha funny.

                            This is not to do with the top of the piston, as the head was off recently and pistons were absolutely fine.

                            It would be nice to focus on an issue rather than acting like an i&;~& for once.

                            Thankfully the forum still remains a place of wealth of info not hindered by comments like the above

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                            • #15
                              Yeah, humor isn't something that has been given to all of us lol. Anyway, detonation can lead to bearing failure. I'm not saying that is in this case, but it's an alternative. Before you open the engine we all are just guessing here.
                              Audi UrS4 Avant 2.5 20vt - twincharged - Project
                              Audi 80q B4 Sedan 2.2 20vt - Daily user
                              BMW 320d Touring e91 M-Sport - Daily user
                              BMW 740iA e38 - Project

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