Engine Vibration 3k RPM

Small Block Mopar Engine

  1. plumkrazee70

    plumkrazee70 Well-Known Member

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    Hi everyone, I'm chasing an engine vibration (or at least that's what I think).

    70 Dart
    68 340
    A500 OD transmission
    Neutral converter
    Neutral balancer

    The vibration can be felt in Neutral when revving the engine to 3-3500k. It's not as pronounced as when it's wheels on the ground, at speed though.

    The vibration goes away when the OD kicks on, which drops it to about 2200 RPM.

    I thought it was driveline or pinion angle related, but I took it back to the guy who built the driveline and rear end and after we went for a drive, he doesn't believe it's driveline related. He even had another guy come by and get his opinion.

    The trouble is, this is a new build (8+ years in the making) so I don't have anything to go off of.

    Here are things,.I was planning on checking:
    1. I was thinking maybe a misfire (not sure how to check)
    2. It's got Fuel injection with timing control (maybe rotor phasing is off)

    I wanted to remove driveline to be absolutely sure it's not rear end or wheel related, but not sure the best way to plug the trans. Will these work? https://www.oreillyauto.com/detail/...le-transmission-transaxle-plug-set/lis0/23400

    Thanks for any suggestions.
     
  2. Murray

    Murray FABO Gold Member FABO Gold Member

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    This can be many things. I have had new convertors vibrate and had to be removed for re-balance.
     
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    • T56MaxTorq

      T56MaxTorq Well-Known Member

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      If it’s worse in neutral, it is not the driveline or the rear axle.

      check ignition timing at point of vibration

      what are the motor mounts condition? All 3 ok?

      Is the exhaust secure?

      How about the harmonic balancer? What’s that condition and age?

      If the engine received new pistons but didn’t get balanced (which is sometimes ok to do) than it may vibrate like this all the time at that rpm.
       
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      • plumkrazee70

        plumkrazee70 Well-Known Member

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        I wouldn't say it vibrates worse in N, I would say the opposite. Its worse when driving at that RPM.

        All three mounts are new and in good shape.
        The exhaust was just welded up (Summit kit w/clamps)
        The balancer is new, but I would like to recheck the timing to be sure it hasn't jumped.
        I can't remember if the engine was balanced when it was put together as that was 8+ years ago. I do remember KB hypers +.040, the crank and rods were what came with the motor (stock stroke). It was a very mild build as I wanted to have a nice driver.

        What is the best way to verify engine balance? Does the motor have to come out and take apart?
         
      • dadsbee

        dadsbee FABO Gold Member FABO Gold Member

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        Vibration or a miss/stumble that feels like a vibration. My 340 Dart doesn't like 3200. Just fine 100 rpms above or below
         
      • T56MaxTorq

        T56MaxTorq Well-Known Member

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        Oh, you said in the original thread post that it was less pronounced with the wheels on the ground, at speed. And that it can be felt in neutral.

        As for your engine balance, go through all your documents and see if it was balanced. You’d surely know if you bought a balance job or not. It’s at least a couple hundred $. And with a good balance, they want to also have the flywheel/flex plate, balancer, and sometimes the torque converter. Not just a crank and block.

        it would be my assumption that if the engine was not balanced, it would vibrate and has a resonance at that specific rpm range. I had a 360 with KB pistons, no balance and it would have a certain rpm spot it would resonate at.
         
      • pishta

        pishta I know I'm right....

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        try a carb spacer....really.
         
      • dadsbee

        dadsbee FABO Gold Member FABO Gold Member

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        Umm.. no, it's up there high enough now! :D
        1969dartcleanupweek18.5 007.JPG
         
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        • pishta

          pishta I know I'm right....

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          could change the powerband slightly and possibly move your resonant vibration. Peace of mind that its intake related instead of balance.
           
        • dadsbee

          dadsbee FABO Gold Member FABO Gold Member

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          I know mines fuel/carb related. Was just offering it as a suggestion to the OP that thinks he has an engine vibration.
           
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          • plumkrazee70

            plumkrazee70 Well-Known Member

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            Ok, you're right. I know for sure I didn't provide.them with the flex plate or balancer, because I didn't have the balancer yet. So it wasn't balanced.

            This weekend, I plan on checking the rotor phasing and pulling the plugs to see what they look like.
             
          • plumkrazee70

            plumkrazee70 Well-Known Member

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            I already have a 1" spacer. Mine could be tuning related. It has EFI and I haven't messed with it at all yet. Yesterday, when I was getting it up to RPM in the garage in N, easing into the gas, I could see the tach stumble right around 2500. It would drop to 2k and then it would rise back up to whatever RPM I was after. I didn't notice this when I would rev, but easing in it was noticable.
             
          • mygasser

            mygasser FABO Gold Member FABO Gold Member

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            did the trans come from a 360/5.9 vehicle, if so the convertor may have a weight on it? remove that and you 'should' be golden.
             
          • replicaracer43

            replicaracer43 Grumpy Old Man

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            If it wasn't balanced, and you used KB pistons, there is your problem. The KB pistons DEFINITELY effect the Bob weight, your only fix is to disassemble the engine and get it balanced. Running it out of balance like you are, can destroy the bearings also.
             
          • plumkrazee70

            plumkrazee70 Well-Known Member

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            I am not sure what it came out of, but the converter I have was built for the combo and I know I specifically said Neutral balance. I'm sure there are no weights on it.
             
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            • plumkrazee70

              plumkrazee70 Well-Known Member

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              Understood. At least winter is around the corner. Thanks for the help.
               
            • T56MaxTorq

              T56MaxTorq Well-Known Member

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              Man I wouldn’t tear it apart for that. Is it really that bad?
               
            • dadsbee

              dadsbee FABO Gold Member FABO Gold Member

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              Sounds like a fuel delivery stumble and not an engine vibration to me, why I questioned it in my first post.
               
            • 512Stroker

              512Stroker We are all here because we are not all there.

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              Lets do the easy things first.
              Check the torque converter bolts make sure they a tight and loctite has been applied.
              Remove all the drive belts from the front of the engine, water pump, alternator, etc with the car in park check for your vibration you may have a fan or pump that's going south. Make dam sure you do not overheat the engine doing this, start with a cold engine.
              Post some close up pictures of the spark plugs so we can see the timing mark on the ground strap.
               
            • PRH

              PRH Well-Known Member

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              KB flat tops for a 340 are over 150g lighter than factory pistons...... each.

              If the rotating assy wasn’t balanced, it really should be.
               
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              • replicaracer43

                replicaracer43 Grumpy Old Man

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                I pointed that out in post 14, but people are advising all sorts of other nonsense
                 
              • 512Stroker

                512Stroker We are all here because we are not all there.

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                "nonsense" hold on there partner, we/I are only giving the OP suggestions to check for it is up to the OP which path to follow. I agree that the rotating assembly could be the issue, but I would try everything else before I take the engine apart.
                 
              • plumkrazee70

                plumkrazee70 Well-Known Member

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                Oh yea. It's like a WAA WAA WAA. I called the machine shop and he said to bring it by and he could tell me if it was a misfire or an engine vibration. I don't really want to tear it apart, but I want it to be right.
                 
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                • T56MaxTorq

                  T56MaxTorq Well-Known Member

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                  yeah absolutely - you should be satisfied!
                   
                • Dartswinger70

                  Dartswinger70 Only thing I ever bought new was a Fender Strat

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                  if you can verify it isnt a misfire, Id say its your rotating mass. i had a similar problem and it was a defective pressure plate.yes I know yours is auto but I m just saying it sounds similar. Mine was so bad the dash rattles sitting still
                   
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