Help! Small block 360 has a knocking sound

Small Block Mopar Engine

  1. MOPAROFFICIAL

    MOPAROFFICIAL Well-Known Member

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    Pull the cover and run it to see if the noise is still there.
    The baffling comes loose on those cover sometimes and the rockers hit...they can be screwed on or pinned/riveted.
     
  2. CheeseRules01!

    CheeseRules01! Well-Known Member

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    The noise is still there with the covers off, I think it is a valve train issue with number 5. I need to pull the head off at some point and check the valves.
     
  3. 1970 TA

    1970 TA Member

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    I'm thinking flexplate bolts.
    My 340 sounded just like your motor.
    Bolt holes elongated in the flexplate.
    011012_a.JPG 011012_c.JPG
     
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    • CheeseRules01!

      CheeseRules01! Well-Known Member

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      Ok guys, I made a stethoscope and tested all kinds of different spots on the engine for noise. The engine checked out fine. I checked the fuel pump, as you guys mentioned, I checked the valve covers, the heads, none of it was making noise. I even put it on the oil pan just to see if there was anything going on in the bottom end, again, nothing. However, when i crawled underneath and put it on the bell housing, you can hear the knock clear as day, on both sides of the car. I checked the flex plate bolts, all of them are nice and tight. Didn't see any cracks on the flex plate, but there is an interesting thing I noticed, I think there is something wrong with the Transmission. When it is in park, the knock is there, but not very loud. Reverse, it practically disappears, you cant really hear anything at all. Neutral, it is atrocious, the video i recorded at the beginning of the thread was with the car in neutral. In gear, it is just as loud, but when you drive aggressively, it almost seems to go away. Part throttle or letting off the gas, it sounds hideous. I checked the transmission fluid, and for some reason there was almost none in there. Strange because I checked it not that long ago, and it was full. The car doesn't have any leaks that I know of, but I guess it obviously does for the tranny fluid to disappear like that. Didn't get a chance to add more, I don't have any extra at the moment, tomorrow I will get out there and fill the tranny back up and see what happens. Hopefully its not to badly damaged. I feel kinda stupid for running it low on fluid, but the weird thing is that it acted just fine. No slipping or anything, shifted normally as well. If you guys have any thoughts, please share them. Thanks.
       
    • diymirage

      diymirage HP@idle > hondaHP@redline

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      What gear was the tranny in when you checked the fluid?
       
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      • 408 swinger

        408 swinger FABO Gold Member FABO Gold Member

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        Crankshaft to flexplate bolts.
         
      • Cudafever

        Cudafever Well-Known Member

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        Still say it in the flex plate. you may not be able to see the crack.
         
      • CheeseRules01!

        CheeseRules01! Well-Known Member

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        Neutral
         
      • mbaird

        mbaird mbaird FABO Gold Member

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        Park pawl ?
         
      • CheeseRules01!

        CheeseRules01! Well-Known Member

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        If it was in the flex plate, then wouldn't it knock just as loud no matter what gear you are in? I'm not saying that I don't believe you guys, but it just doesn't quite add up. Like I said, the knocking is only there in certain gears, which is kinda strange.
         
      • CheeseRules01!

        CheeseRules01! Well-Known Member

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        Could it causes noises in other gears though? I'm not sure.
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        Not always. Had a Ford that was 3.5 hours from and and I specifically told the customer to double check the flex plate/flywheel and look at it very close.

        A few days later he called and was going to pull it and send it back. I burned a day and drove to his shop and what did I find?? Several small fractures that would make noise in weird ways.

        Lost a whole day of making money. Look very close. Very close at that flex plate.
         
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        • mbaird

          mbaird mbaird FABO Gold Member

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          You will have to pull the trany . Might as well do it now vs spending more time diagnosing.
           
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          • mbaird

            mbaird mbaird FABO Gold Member

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            A crack may be hard to identify.

            Last year I was having a problem with falling and tripping while playing hockey. WTF ! I thought I was developing an equilibrium related illness !
            Turned out there was a crack in my blade tower that was hard to see but would flex under hard maneuvers .
             
          • CheeseRules01!

            CheeseRules01! Well-Known Member

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            Thats the plan stan, in fact I have a 727 that I am going to freshen up to put in the car instead of the 904 that is in it now. So I was already planning on pulling the tranny at some point, I guess now I have a reason.
             
          • mbaird

            mbaird mbaird FABO Gold Member

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            If thats the case you must be relieved to know its a trany issue !
            Whew!!!!
             
          • rustycowll69

            rustycowll69 Well-Known Member

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            one thing you might try before you pull the trans: try pulling and pushing forwards and back on the front dampener/crank pulley. There should be minimal slop.
             
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            • Wyrmrider

              Wyrmrider Well-Known Member

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              yep bad thrust
               
            • CheeseRules01!

              CheeseRules01! Well-Known Member

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              I did, there was absolutely no slop at all, nice and tight. I think my spring/summer project will be tearing it apart and fixing everything on the car. It'll be fun.
               
            • Cudafever

              Cudafever Well-Known Member

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              My money is still on the flex plate.
              loosen you torque converter bolts and remove them. make sure that the converter will slide back into the transmission.
              should have about 1/4 or more clearance between the flex plate and the converter.

              Make sure the car is facing uphill so the converter stays put and START IT UP.
              Its only going to take 10 sec of run time to know if it there.
               
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              • George Jets

                George Jets 1967 Dart 2 Door FABO Gold Member

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                That is a good test Cudafever, going to keep that one in my "Diagnostic Tool Kit".

                Thumbs Up ! . . .

                Oh Wait . . Won't start without the torq converter with ring gear bolted to the crank shaft.

                Good attempt though . . .

                76 360 727.jpg
                360 external balance converter as example.
                 
                Last edited: Jan 20, 2020 at 7:55 PM
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                • George Jets

                  George Jets 1967 Dart 2 Door FABO Gold Member

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                  Cudafever, could still be that the Flex Plate bolts are tight but a tad too long bottomed out in their threaded holes in the converter.

                  This senario the flex plate could still walk on the bolts at the converter producing the knock.

                  Next test, put some flat washers on the 4 flex plate bolts and see if that tightens the flex plate to the converter.

                  Now start it up and test again and see if the noise/knock goes away. If it goes away, tells you wrong length bolts mounting the flex plate to the torque converter.
                   
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                  • George Jets

                    George Jets 1967 Dart 2 Door FABO Gold Member

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                    Good to take the 4 flex plate bolts out anyhow, like in Post 78 to see if the flex plate holes are starting to Egg Out.

                    All 4 . . .
                     
                  • Cudafever

                    Cudafever Well-Known Member

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                    Yeah that was dumb:BangHead: sounded good tho:D my fire wood guy showed up so i typed that real quick and hit send:rolleyes:

                    I think if he get the bolts off and pushes the converter back.
                    a flashlight will tell the story.
                     
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                    • Cudafever

                      Cudafever Well-Known Member

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                      two long of bolts would have caused the problem from the beginning.
                       
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