No compression-next move?

Big Block A body Tech

  1. RockinRobin

    RockinRobin Well-Known Member

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    If they are only slightly bent spring pressure can pull them back flat against the seats. I'm having them checked.
     
  2. mygasser

    mygasser FABO Gold Member FABO Gold Member

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    if the car's a keeper it'll be best long term :thumbsup:
     
  3. RockinRobin

    RockinRobin Well-Known Member

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    Just had new paint job, so yeah, it's a keeper.
     
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    • RockinRobin

      RockinRobin Well-Known Member

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      UPDATE: front cam bearing spun so cam journal and chain were not getting oiled. New cam/lifters/timing set. Oh and almost every valve was bent, they are toast.
      And if you think it couldn't get worse, we found a small crack in the block, so the block is toast. Now waiting on machine work to get done: valve job, tank and prep block from junkyard, check and polish crank, clearance new block for stroker crank.
       
    • my68barracuda

      my68barracuda Well-Known Member

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      Post # 50 # 51 mentions that valve spring pressure can pull slightly bent valves back flat against the seats.

      What? No way an closed valve with spring pressures in the xxx
      Ft Lb will pull a bent valve head / stem flat that has steel tensile strength in the xx,xxx Ft Lb.
      If there is wear in the valve guide, that may allow the stem to cock and the valve head to close. Even then the valve head will not be concentric with the heads valve seat.
      Not saying that I would not have them checked, I would get the valves chucked in a rotary spindle then lay an indicator on them. I am saying the reasoning given in posts 50 and 51 is B.S.
       
      Last edited: Aug 14, 2019
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      • Bobzilla

        Bobzilla Well-Known Member

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        Where was the crack found in the block? Wondering if it was unrelated to the original issues.
         
      • RockinRobin

        RockinRobin Well-Known Member

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        It was under the bearing in the front journal. Totally unrelated. Probably had more to do with it being drag raced and revved over 7000rpm constantly for 5+ years.
        It's probably fortunate that we found it when we did, a bare block cost me $210 dollars, the motor coming apart at 100mph plus and 7000rpm plus would have been much more costly!
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        You put enough spring load on a valve and it will seal. Absolute fact.

        Had a customer bring in his heads for a freshen up. So I pulled a vacuum on them and they were sealed right up.

        When I took them apart, every intake was bent so bad you could set the valve on the bench and see the crooked stems. 5 exhaust valves were bent, but not that bad. All sealed up.

        I had him pull the short block and bring it in. He was a home assembler. He didn't have the cam times correctly AND he didn't measure piston to valve clearance. And that's what you get.

        So you can have a bent valve and have it seal. Seen it so many times I can't count it. So the solvent test, pulling vacuum on the port or using a flash light in the port only tells you it's sealed. Nothing else.
         
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        • my68barracuda

          my68barracuda Well-Known Member

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          spring pressure with the valve closed is the attainable spring pressure at the installed height.
          Typically in the high 2 digits to low 3 digits Ft lb.
          Not enough to straighten a bent valve stem. But I agree, with a worn guide or a very slight bend in the stem, it would be possible for the stem bend to be contained within the guide diameter. That is why the stems need to be measured for straightness.
           
        • yellow rose

          yellow rose Doctor of Thinkology.

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          You don't need enough spring to make the valve straight. All you need is enough spring load to make the valve head conform to the seat. 100 pounds on the seat will seal a valve that is bent. Undercut stems, smaller than 3/8 stems all make it even easier to seal a bent valve.
           
        • RustyRatRod

          RustyRatRod Weenie idiot loser. FABO Gold Member

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          Who in the WORLD told you that? If you have a bent valve, YOU HAVE A BENT VALVE. Ain't no valve spring gonna pull it back straight. Ain't happenin.
           
        • RustyRatRod

          RustyRatRod Weenie idiot loser. FABO Gold Member

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          That's total bullshit to be acceptable. Lemmie splain, Lucy. Even if you had enough spring pressure to pull a slightly bent valve to seal, what are you doing with it EVERY CYCLE? You're flexing it, that's what. There's going to be one side of the valve that hits the seat first, and then it gets pulled down tight. Do you see what's happening here? The valve head is flexing on the stem as it's being pulled closed by the spring. Over and over and over. You can kiss that valve goodbye in short order when the stem gets fatigue from flexing.
           
          Last edited: Aug 19, 2019
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          • RustyRatRod

            RustyRatRod Weenie idiot loser. FABO Gold Member

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            Total bullshit. You shouldn't be spreading this nonsense. It might make somebody cut a corner and cost them an entire engine.
             
          • mygasser

            mygasser FABO Gold Member FABO Gold Member

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            i think he's actually telling us not to cut corners as a vacuum test can hide a bent valve so they should be stripped and checked. that's how i read it anyway. :thumbsup:
            neil.
             
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            • fishmens67

              fishmens67 Well-Known Member

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              Oh my O my. Bent valves will not seal unless the guide is totally wasted, even then I doubt it. lol
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              It's not bullshit rusty. Seen it many times. You don't think it be like it be but it is.

              I've never advocated for running bent valves. I'm telling you that a solvent test, or a light test, or a vacuum test may show the valve is sealed. You can still have a bent valve and have it seal.

              Happens all the time. Bent valves can seal. And do.
               
            • RustyRatRod

              RustyRatRod Weenie idiot loser. FABO Gold Member

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              I'll put it like this. "I" will not run one "LIKE THAT". How's that?
               
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              • fishmens67

                fishmens67 Well-Known Member

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                How are the guides ?
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                I'm not advocating running with bent valves either. Don't know where you got that.

                I'm saying I've seen it enough times to know just because someone brings in a head and says I did a solvent test and it passed doesn't mean the valves aren't bent. That's all I'm saying. Bent valves can seal. And do.
                 
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                • yellow rose

                  yellow rose Doctor of Thinkology.

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                  Had a 572 BBC come in for a surface. A couple of the valves just looked funny. So I pulled one. Bent. All 8 intakes bent. 4 exhausts bent.

                  Customer said I was just trying to sell him new valves! Found out later he didn't know how to degree a cam, hence the bent valves.

                  Also found out later when he brought in the short block that he had killed an externally balanced flywheel and replaced it with an internally balanced flywheel.

                  When the crank went up on the balancer it about shook me right out of the shop. I'm like WTF???? So I had him come by and see what was happening. He leaves and comes back an hour later with the original.

                  So I ask him..."dude...did it not shake like a dog shitting peach seeds?????"


                  Customer..."nope...smooooooooth as butter!!!!!"

                  Oh ok. 100 grams out and the engine didn't shake?
                   
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