No compression-next move?

Big Block A body Tech

  1. RockinRobin

    RockinRobin Well-Known Member

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    Well damn. None of the local parts stores has a leakdown tester in stock. You have to buy it. I'll start by borrowing a compression tester just to confirm that mine isn't broken.
     
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    • RustyRatRod

      RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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      Does this engine run? If it doesn't run, then your compression tester is probably correct.
       
    • Tooljunkie

      Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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      A spark plug smashed apart and an air fitting welded to it works too.
       
    • pishta

      pishta I know I'm right....

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      They can drop valve seats holding up the valves, but zero across all? Are you sure the crank is turning? straight plug hemi could see the piston crowns down the hole, right?
       
    • Kendog 170

      Kendog 170 Well-Known Member

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      My buddy'truck did the same thing idling in driveway. No compression,motor spun real fast with starter. Wish I could help but he sold the truck broken .
       
    • RockinRobin

      RockinRobin Well-Known Member

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      UPDATE: Well here's a new one on me: The cam dowel pin is sheared off and the cam sprocket slipped about 70-80 degrees to the retard side. I think the dowel pin can be replaced, so I'll do that and see if it bent anything. It happened while it was idling, so maybe I dodged a bullet.
      20190708_111620[1].jpg 20190708_111609[1].jpg
       
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      • Tooljunkie

        Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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        That’s new. Glad you found it! That pin is going to be hard. And press fit. Need to find an old cam and see if it can be pulled out or driven out from the backside.
        Thats a new one for sure.
         
      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        Does the cam still turn?
         
      • jos51700

        jos51700 Well-Known Member

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        If that dowel broke, then the cam BOLT is the problem.
         
      • RockinRobin

        RockinRobin Well-Known Member

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        Yes, it slipped about 90 degrees and stayed in that spot.
         
      • RockinRobin

        RockinRobin Well-Known Member

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        Agreed, I was told I didn't need to put thread locker on it, but I think I should have. It came off pretty easy.
         
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        • PRH

          PRH Well-Known Member

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          Exactly. The dowel pin is only there for alignment, it’s not meant to carry the load.
          If it sheared off...... the bolt was loose.
           
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          • MobileCustoms

            MobileCustoms Well-Known Member

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            Glad you found the cause. Fingers crossed for you, for limited damage!
             
          • RockinRobin

            RockinRobin Well-Known Member

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            UPDATE:
            Motor is out of the car.
            I have one of those hoses that lets you pump air into the cylinder to hold valves up while you change springs. I loosened all of the rocker arms so there is no pressure on the valves and shot air into each cylinder. All cylinders held pressure! Except for a little leaking past the rings into the crankcase which is normal. I think I may have dodged a bullet! I guess I need to fix the timing chain and do a compression test to see what I really have, but this is hopeful! Advice? Don't want to pull heads if I don't have to. New ARP head bolts cost a lot of $$$
             
            Last edited: Jul 11, 2019
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            • PRH

              PRH Well-Known Member

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              I’m not a G3 guy..... but ARP head bolts for that application aren’t reusable?
               
            • RockinRobin

              RockinRobin Well-Known Member

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              You're right. Just found out they can be re used!
               
            • 408 swinger

              408 swinger FABO Gold Member FABO Gold Member

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              I had the same thing happen with my son's Scamp. He took it up to the local station to fill. Calls me up, won't start. Pulled it home. Replaced cam and crank sensors. No start. For some crazy reason, I pull the cam sensor and take a peek inside. Looked like the tone ring was going back and forth(front to back). Pull the front cover. Spun the cam bolt out by hand. The gear was loose enough, that with the movement, the sensor didn't pick up. I now loc-tite all hemi cam bolts.
               
            • RockinRobin

              RockinRobin Well-Known Member

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              UPDATE:
              Decided to pull the cam. There is enough general wear to justify replacement, so new cam, bearings, lifters are ordered.
              there are slight marks on the pistons/valves but they held air before I removed them. Tell me your opinion of the contact marks:
              20190717_194411.jpg 20190717_194418.jpg 20190717_194506.jpg
               
            • RustyRatRod

              RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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              I don't know man. The only way to know for sure is to chuck them valves up in a valve grinder and see how true they are.......by the time you do that, you might as well do a valve job. Now's the time.
               
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              • Bobzilla

                Bobzilla Well-Known Member

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                If it were me, I'd mock it all up again and measure valve to piston clearance to know how close they are. Kind of looks like it was kissing that piston for a while, although I could be way wrong on that.
                Either way, as RustRatRod said, must at least check those valves.
                No matter what, I'm so glad it did NOT have a catostophic failure with more damage. You dodged a big one this time.
                 
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                • mygasser

                  mygasser FABO Gold Member FABO Gold Member

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                  lay the heads flat combustion chamber up and fill the chambers with kerosene or similar. if it doesn't leak past the valves you're golden :thumbsup:
                  neil.
                   
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                  • RockinRobin

                    RockinRobin Well-Known Member

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                    Great idea, thanks!
                     
                  • PRH

                    PRH Well-Known Member

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                    Looks like fairly substantial contact to me.
                    I’m with RRR on this one...... pull em out and reface to be sure.
                     
                  • mygasser

                    mygasser FABO Gold Member FABO Gold Member

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                    contact or not if there's no leak with the above kerosene test then why? if there are bent valves they will leak, no question.
                    neil.
                     
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                    • RockinRobin

                      RockinRobin Well-Known Member

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                      I agree, but Machine shop explained to me why this is dangerous. Valves can be slightly bent, but spring pressure pulls them down flat to seal giving the impression that nothing is wrong. Need to confirm they aren't bent or they will eventually break. Off to the machine shop I go....
                       
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