318 engine noise.

Small Block Mopar Engine

  1. KEVIN LANGFORD

    KEVIN LANGFORD Member

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    Just started. Sounds like a dull thud after I let off the gas. (Screwdriver handle tapped on the valve cover type noise) just one thud, not consecutive. Valve train rocker is somewhat loose on the #6 cylinder. Wish I could upload the video...

    318 with a thumper cam.

    How long do you think it will last. I'm shopping for a rebuild of this engine and or upgrade right now.

    20190106_131924.jpg
     
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    • TrailBeast

      TrailBeast Slightly Twisted Member

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      Does it change at all with engine temp, and always there?
      Different RPM's make a difference?
       
    • KEVIN LANGFORD

      KEVIN LANGFORD Member

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      I do hear valve chatter and pin pointed to the #6 but the thud doesn't change that i know of.
      The thud is when i rev it and it comes back to an idle maybe half a second to a second after. and I can only make it repeat if I rev it up again. It is not repetitive with rpms. Plugs look clean, maybe running a bit on the lean side. But maybe the plug is fowled and I cant tell...
       
    • toolmanmike

      toolmanmike FABO Staff Staff Member FABO Gold Member

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      You will need to go through You Tube and post the link for a video.
       
    • Plymouth 65

      Plymouth 65 Floorable Deplorable

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      Those stock rockers tend to bend under high loads of high lift cams. 65'
       
    • Garry in AZ

      Garry in AZ Building a 9 second Valiant FABO Gold Member

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      Broken motor mount?
       
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      • KEVIN LANGFORD

        KEVIN LANGFORD Member

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        • Thanks! Thanks! x 1
        • toolmanmike

          toolmanmike FABO Staff Staff Member FABO Gold Member

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          Side to side isn't a problem. Those rockers are almost self centering. A flat lobe or collapsed lifter will be loose pulling up and down and will be noisy at idle or at all engine speeds. As Garry said sounds like a broken motor mount.
           
        • KEVIN LANGFORD

          KEVIN LANGFORD Member

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          I replaced a broken trans mount in October and I did buy motor mounts to replace over the winter because i saw a bit of cracking in the rubber... I can change those and see if it works.

          Thanks for the info.
           
        • toolmanmike

          toolmanmike FABO Staff Staff Member FABO Gold Member

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          With the help of a trusted friend, you could load the engine against the brake and then let off the throttle. The drivers mount is the first to go. The engine will jump and then settle with a thud.
           
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          • toolmanmike

            toolmanmike FABO Staff Staff Member FABO Gold Member

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            At about 2:40

             
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            • 69FBCuda

              69FBCuda Life in the Fast Lane

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              He can look from the drivers seat between the cowl and hood. no innocent bystanders will get injured> :)
               
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              • nm9stheham

                nm9stheham Well-Known Member

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                Another thought: Could be backfire in the the exhaust.. when you let off the throttle quickly, the carb will run rich for a good part of a second until the emulsion flows inside the carb re-adjust to the lower air flow; that's been a 'known' for decades. A little gas in the exhaust and a leaky exhaust manifold to let in some fresh air will do it.
                 
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                • toolmanmike

                  toolmanmike FABO Staff Staff Member FABO Gold Member

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                  As well ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                   
                • KEVIN LANGFORD

                  KEVIN LANGFORD Member

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                  I'll check that to. I do have a missing exhaust manifold bolt... Thanks!
                   
                • nm9stheham

                  nm9stheham Well-Known Member

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                  It's just an idea that may better explain the 1/2 to 1 second delay.... that factor does not seem as well explained by the mount.
                   
                • Slantsix64

                  Slantsix64 Well-Known Member

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                  Check the torque on the rocker arm bolts.
                   
                • TrailBeast

                  TrailBeast Slightly Twisted Member

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                  I thought exactly the same thing, and glad someone mentioned it.
                  When he said "like a screwdriver hitting the valve cover" I was going to ask if he meant the handle or the metal end.
                  Then reading through I saw you post and went YES out loud.:D
                  My Wife says "What?" from the other room.
                   
                • KEVIN LANGFORD

                  KEVIN LANGFORD Member

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                  Yep sounds like the handle end dull thud...lol!
                   
                • TrailBeast

                  TrailBeast Slightly Twisted Member

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                  If I had a farm I would almost bet the whole thing the noise is a pop inside the exhaust from winding down like nm9stheham mentioned.
                  Fresh air pulled in around a leak gives unburned fuel the oxygen to ignite.
                   
                • MopaR&D

                  MopaR&D Nerd Member FABO Gold Member

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                  I knew whenever my header collector bolts came loose on my Duster because it would start popping out the exhaust on decel, normally it never does that. I finally redid the down pipes because the first set were dragging and hitting everything.
                   
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