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Can a rod bearing spin on startup?

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  • Can a rod bearing spin on startup?

    Hi all,
    Roughly 150k on motor. Drove it Wed 10/6 for about 40 minutes. Great driving. No problems or weird noises. Engine temp gauge and oil pressure gauge showed normal the entire time I've been driving it and I've been anal as hell about keeping an eye on it. Parked it and engine sounded normal. It's been sitting since Wednesday around 5:30pm.

    I started the car this AM after being parked for 3 days. It turned over a few extra times on startup and immediately started making a solid metal on metal knocking/slapping noise at idle. Very loud and directly tied to engine RPM. Thought maybe water pump but the knock is solid, loud, and steady.
    I'm fearing the worst, but I've never totaled an engine before. What else could cause a knock like that? Piston slap? I'm too nervous to let it warm up for fear of doing more damage. Perhaps the engine is totaled anyway.

    Checked oil in dip stick and it looked normal and full. No leaks. Coolant at correct level.
    Started up temps were about 62 degrees F this morning. I only let it run about 30 seconds as I was in disbelief.

    I'd love to record the noise but I'm afraid to do more damage.
    Any thoughts to what that noise could be besides a spun bearing?
    Thanks for helping out an s14 noob

  • #2
    Can you tell where the noise came from? Front of the engine, back, bottom?

    could be the timing chain tensioner failed or is stuck.

    Comment


    • #3
      Thanks for your reply Todd.
      It seems like it's coming from the head of the motor under the valve cover but it's really loud so not sure at all. I will get an audio recording of it tomorrow at the mechanic so everyone can hear it.
      Hoping for the best. At this point a new tensioner would be a victory. I've never heard a noise this bad from a BMW engine. However, I'm no mechanic so I could be blowing this out of proportion.

      A little more info. 1990 S14B23. New rod and main bearings installed when PO installed oil pan baffle and high capacity oil pump. roughly 5-7000 miles ago (owned for 13 years, driven about 1,000 miles a year. Garage kept)

      I've owned the car for about a week . Bought it in TN. Did a 1 hour pre purchase drive with the owner. It drove solid as hell. Engine felt and sounded great. I then drove it home to VA 6 hours with no issues (sport driving through the mountains but never redlined). Drove it three days last week to work (super chill driving). Again, purring like a kitten and just a joy to drive. It's been parked since Wednesday. I reached out to the seller (very cool open and honest older guy) who suggested water pump or possibly a pulley issue but this is a solid "knock" metal on metal noise. It's not valvetrain sounding, It seems like bottom end. Oh how I'm hoping to be completely wrong on this.
      Last edited by pete914; 10-09-2016, 02:39 PM. Reason: Added info about rod and main bearings being replaced

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      • #4
        Honestly with a noise like you describe...the engine is almost certainly going to have to come apart to some extent at least. The only possible option to avoid that would be if you have a timing chain tensioner issue...and it doesn't sound like that is what you are describing.

        I know that is not what you want to hear....but we tend to waste a lot of time and energy (and possibly cause more damage) trying to diagnose things from outside when a teardown is probably going to be required regardless.

        The sad truth is that whatever it is....and it is indeed an internal engine issue....it is not going to fix itself.

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        • #5
          couple of things. has the engine ever been rebuilt? Did they use forged pistons? I have an engine that is loud rod knockish on startup but it goes away after warmed up. The forged pistons are looser in the bores than cast and have piston slap on cold starts. also check exhaust header gaskets. if one is loose the exhaust gas will make the header knock against the head and sound internal.

          T

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          • #6
            Thanks for the responses guys. I really appreciate you guys taking the time.
            I agree, it's all guessing until we open up the engine but I'm trying to prepare myself (and wallet). I'm assuming complete rebuild.
            I forgot the PO replaced the rod bearings which suggests this could be something else though.

            HANDBLT: No known history of rebuilt but no records before the person I bought it from. I was thinking to let the car warm up in idle to see if the knock went away but got spooked and shut it off. I was thinking, "oh this is piston slap!" However, it's never made this noise on cold start before. I will check the header gaskets in the AM. Good thinking! Thanks!

            Comment


            • #7
              Could be chain tensioner or chain guide if a new issue immediately on startup. Or, painfully could be a bearing. only way to know is to dig in. Hope it is a tensioner or guide! Good Luck!
              88M3 henna


              73T100C
              97 540\6-Gone
              2008 MINI Clubman S

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              • #8
                Sound like the oil has bleed from the timing chain tensioner and when that happens makes a dreadful rattle noise usually comes right by lifting the rpm above idle to smoothen it out and allow time for the oil to refill the tensioner.

                If it is tensioner you run the risk of stripping it down and finding nothing, better to either bleed the tensioner manually or start it up and take it for a short drive to bleed it.

                See here.
                https://s14net.vbulletin.net/forum/s...hain-tensioner

                E30 M3 1987
                Mini Clubman GT
                BMW E36 323 Msport
                Toyota Corona
                KTM 200EXC
                Honda CB50 (1979)

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                • #9
                  Dave, this sounds very promising! As the rod bearings were reportedly just done, I'm skeptical that's the issue but I keep jumping to that conclusion.
                  Here is a poorly shot video of the problem. I felt rushed because the the tow truck was blocking traffic waiting for me to pull it out.. Sorry, I meant to get a good video but this at least gives everyone an idea of the sound.

                  https://drive.google.com/open?id=0B9...XdsdHdZTHk3WDQ

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                  • #10
                    Drain the oil into a pan so you can review the contents. DO you see gold/sparkly dust or flakes? Those would indicate rod or main bearings. Also, cut away the metal jacket of your used oil filter an look for junk laying on the filter element.

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                    • #11
                      that is too high pitched and outside the motor sounding to me. I vote exhaust header gasket, spark plug loose, or something letting the compressed, exhaust air out under pressure.

                      T

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                      • #12
                        I dunno....to me that sounds mechanical rather than an exhaust leak...but it is hard to tell without being there. It does not sound at all like piston slap to me, and timing chain tensioner issues that I have heard sound more like a rattle than a "knock-knock-knock....". It sounds like the noise is only effecting one cylinder/rod.

                        I hate to be glass half empty guy but I vote rod knock.

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                        • #13
                          She's on the lift now. Hopefully I'll know something by Thursday. Checked the exhaust headers and unfortunately they're tight. My friend drove over his pristine 30,000 mile 1988 325is to take a look. He feels like it's coming from the head, not the bottom end.

                          Thanks everyone.

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                          • #14
                            Get a free oil test kit from http://www.blackstone-labs.com/ and send your oil in. The test will tell you if you have a bearing issue or not. Then it might be worth trying to get a new tensioner before taking the engine out and tearing it apart.

                            Is the tensioner in your car the e36 part? How does it look visually? Old or newish?

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                            • #15
                              any update? sounded like a backed out spark plug.
                              sigpic 95 M3 & 88 M3

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