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Rattle near the front of motor ~1500 rpm

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    Rattle near the front of motor ~1500 rpm

    Hey guys,

    I haven't visited the forums in many years but this ones got me stumped and I'm hoping to avoid tear down before diagnosis.

    My m20 has a resonant rattle from the front of the motor that you can hear just over 1500 rpms. It does not follow engine speed and can only be heard at that specific engine speed. I poked around with a screw driver and I'm confident it isn't the crank pulley or distributor. I removed the fan and all belts and the rattle is still present.

    I was thinking either the oil pump or the timing belt tensioner at this point. Anybody have any tips for diagnosing this?

    Might be worth noting that I blew the timing belt on start up a couple of years back and replaced the bent valves and broken rockers. I didn't notice any real piston damage so I didn't touch the bottom end.

    I'm also not sure I want to even bother with this motor any more - I've got a halfway built turbo project on an engine stand waiting to be finished so maybe this will be the motivation to make that swap...

    #2
    I had a very similar issue with my car and it ended up being a cracked camshaft seal dust cover, I changed it out when I did my timing belt and I’ve been vibration free ever since.

    Hopefully that’s all your issue is, no harm in continuing to run it beyond the annoying resonance if it is.

    https://www.r3vlimited.com/board/sho...d.php?t=428483
    Last edited by zwill23; 07-29-2019, 09:11 AM.

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      #3
      Edit, just realised zwill23 linked the the same thread as me.

      Have a read of this too,

      https://www.r3vlimited.com/board/sho...d.php?t=428483

      Note I haven't fixed mine yet. One of these years i will.

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        #4
        So I actually did have an issue with the timing cover before - the threads on the cylinder head were stripped and I repaired it with a helicoil.

        I shot a quick video with my phone to try and show the sound. I think it might be a little different than you guys had in mind:

        https://www.youtube.com/watch?v=5SxeFwGx2Tk

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          #5
          Originally posted by e30davie View Post
          Note I haven't fixed mine yet. One of these years i will.
          Heh! I don't blame you, that's a pretty awful fix for such a small issue.

          Originally posted by sleepswithe30s View Post
          So I actually did have an issue with the timing cover before - the threads on the cylinder head were stripped and I repaired it with a helicoil.

          I shot a quick video with my phone to try and show the sound. I think it might be a little different than you guys had in mind:
          Hrmmmm, you're right that doesn't sound the same as our issue. I wouldn't expect the oil pump, you might be onto something with the timing belt tensioner or potentially the water pump though.

          A mechanic stethoscope might help you identify if the sound is coming from behind the timing cover.

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            #6
            Testing the water pump should be easy - just pull the fan belt. I guess I will dig into it if I have time in the next couple weeks. I'll post if I figure it out and this thread dies.

            Not sure how I could test the timing belt tensioner other than to swap it out. Any ideas?

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              #7
              Originally posted by sleepswithe30s View Post
              Testing the water pump should be easy - just pull the fan belt. I guess I will dig into it if I have time in the next couple weeks. I'll post if I figure it out and this thread dies.

              Not sure how I could test the timing belt tensioner other than to swap it out. Any ideas?
              If the bearing in the tensioner is bad and is causing the noise, a spray of oil (WD-40 or something) will likely make the noise change. I've done this with the idler pulley on my M50 to find out which one was bad.
              sigpic

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