No compression-next move?

Big Block A body Tech

  1. RockinRobin

    RockinRobin Well-Known Member

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    I know this is a Gen3 Hemi, but it should be the same for all motors:
    Car was idling in the garage, suddenly died. Not electrical or fuel. Removed valve covers, everything is moving. Zero compression on all cylinders. Does this sound like chain or sprocket slipped?

    It's a bitch to take off the front cover on this motor because it has a motor plate so I have to support the motor with a cherry picker. Sounds like the front cover needs to come off though.

    Once again, the cam is turning but the valve timing seems suddenly way off.
     
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    • Murray

      Murray FABO Gold Member FABO Gold Member

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      Interesting! If cam is turning then valves are opening and closing. If crank is turning then pistons are going up and down. I would think you would have to have compression even if the chain has slipped.
       
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      • RAT ROD AL

        RAT ROD AL I know just enough to be dangerous FABO Gold Member

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        I would bring #1 up to TDC and check valves on that cylinder first.
        Before you pull everything off.
         
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        • RockinRobin

          RockinRobin Well-Known Member

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          I have a wooden dowel that I can stick in the spark plug hole and get me pretty close. What exactly am I checking for? To confirm that piston timing and cam timing are suddenly off from each other?
           
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          • RAT ROD AL

            RAT ROD AL I know just enough to be dangerous FABO Gold Member

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            Piston at tdc valves should both be seated, no pressure on pushrod holding valves open slightly.
             
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            • RAT ROD AL

              RAT ROD AL I know just enough to be dangerous FABO Gold Member

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              I'm not familiar with the gen 3 hemi, but I assume it has timing Mark's some where. Line them at 0 degrees #1 piston should be at tdc, check with your dowel to make sure. Valves for #1 cylinder should be seated at that point.
               
            • RustyRatRod

              RustyRatRod Weenie idiot loser. FABO Gold Member

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              Does it have those dumbass bleed down lifters that cancel the cylinders out?
               
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              • RockinRobin

                RockinRobin Well-Known Member

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                No timing marks. Will have to figure that out some other way. Damper is marked every degree from 0 to 360, but there is no reference mark on the front cover.
                No, this is a non MDS motor and non VVT.
                 
              • Tooljunkie

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

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                Yup, dowel in cylinder, and watch valves as you roll it over. Both valves should be closed when piston reaches top.
                 
              • hemi446

                hemi446 Well-Known Member

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                If you don't want to pull the cover right away. Just pull the valve covers and see if any of the push rods flop up and down if so just pull the engine because most likely there is also valve damage as well
                 
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                • Cope

                  Cope Fusing with fire

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                  New build?

                  The gen 3 cam goes in with the dot at 12 and the crank at 12. They dont line up.

                  Wonder if you bent all the valves?
                   
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                  • RockinRobin

                    RockinRobin Well-Known Member

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                    It was idling when it went, we'll see.
                     
                  • RustyRatRod

                    RustyRatRod Weenie idiot loser. FABO Gold Member

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                    Then you "gotta problem".
                     
                  • Cope

                    Cope Fusing with fire

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                    It's an easy mistake to make. I'll give you one guess as to why I know that.....

                    :BangHead::mad:
                     
                  • AJ/FormS

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

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                    try another gauge?
                    If the valves are moving, and split overlap is close, I have never seen zero psi

                    If you stick anything in the hole, be aware what can happen if the valves begin to open.
                    I use a different method. I take the gauge off the compression tester (Quick disconnect),and screw the hose back into the plughole. Then I stick the other end in my mouth, but do not make the mistake of sealing it hard and cranking it with the starter; you could blow your eardrums out!!.No, instead, gently motor the engine by hand. You will be able to find TDC compression pretty close........ if everything is as it should be; certainly close enough if the damper is marked.
                     
                    Last edited: Jul 2, 2019
                  • fishmens67

                    fishmens67 Well-Known Member

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                    Please enlighten us, sounds very , very intwesting. lol
                     
                  • RockinRobin

                    RockinRobin Well-Known Member

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                    What mistake would that be? I just had it at the track Friday night. It was idling in the garage when this happened.
                     
                  • RockinRobin

                    RockinRobin Well-Known Member

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                    And what could happen on a gen3 hemi where the plug holes are in the top of the head?
                     
                  • kursplat

                    kursplat FABO Gold Member FABO Gold Member

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                    are you sure the gauge is good? hard to believe they're all flat and you didn't hear something destroy it's self
                     
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                    • Tooljunkie

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

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                      Timing chain, cant see it jumping if valves are still moving.
                      Recheck the compression tester...
                       
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                      • AJ/FormS

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

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                        Ohchit
                        but I'd still use the hose in the mouth deal
                         
                      • IQ52

                        IQ52 Well-Known Member

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                        And on the 2,190,000 day God created the leak down tester.
                         
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                        • yellow rose

                          yellow rose Doctor of Thinkology.

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                          LOL
                           
                        • RockinRobin

                          RockinRobin Well-Known Member

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                          Definitely going to borrow another compression tester before I do any more wrenching.
                           
                        • yellow rose

                          yellow rose Doctor of Thinkology.

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                          Borrow a leak down tester instead. Then you will KNOW where the air is going.
                           
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