.030 340 With KB Hyper Pistons, Ring Gap Info

Small Block Mopar Engine

  1. 340doc

    340doc Well-Known Member

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    Ok, so I have a .030 over 340 going together. I'm used to using file fit rings. My question is for those who have used the KB Hyper pistons. How did your ring gap come in? Being that these pistons require a larger gap, did you have to file a standard .030 non file ring? According to KB's chart I need a .027 top ring gap. Thanks.
     
  2. brian6pac

    brian6pac Well-Known Member

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    I don't like having such a big gap but hyper piston's require them. We built a 400 chevy and had a .028 gap and he overheated it and it scuffed the wall hard probably close to pulling the top off the piston. The piston is a lot smaller at the top putting more heat on the ring, that is why you need a big gap.
     
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    • Wyrmrider

      Wyrmrider Well-Known Member

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      yep ring is closer to the top and the hyper materiel does not suck the heat out of the ring
      you most likely can start with standard gap rings and file them
      but more important (IMHO) is to get a ductile or better top
      hyper gap when running is about the same as forged
       
    • moper

      moper FABO Gold Member FABO Gold Member

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      I believe KB says .006" per inch of bore for naturally aspirated rather than the "usual" .004. More if it's going to be driven hard. So I'd go around .028 for the top, and probably .24 on the 2nd.
       
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      • 340doc

        340doc Well-Known Member

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        Yes .0065 per inch of bore. I'm going with a moly ring. I'm hoping someone chimes in and can let me know if they had to file a regular .030 ring to hit those numbers. Otherwise I'm searching for a .035 over ring.
         
      • nm9stheham

        nm9stheham Well-Known Member

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        IIRC, yes we had to file the top KB moly rings that came with our .020" over KB 340 pistons. Piston-to-bore fit was set in the normal range fit for these pistons, nothing special.
         
      • 340doc

        340doc Well-Known Member

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        Thanks, this is what I was hoping to find out. Do you remember what the second ring was at?
         
      • rumblefish360

        rumblefish360 so close yet so far away

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        I’m file fitting my KB243 rings a little bit. Just a hair more than suggested.
         
      • nm9stheham

        nm9stheham Well-Known Member

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        Sorry, not off the top of my head... I won't be able to get to our notes for at least a week to see if I made notes on that. I don't recall touching them....
         
      • Wyrmrider

        Wyrmrider Well-Known Member

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        easier to get ductile in .035 over
        just saying
        cheap insurance
         
      • PRH

        PRH Well-Known Member

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        I never even try and run the ring gaps down at the min spec with the KB hyper pistons.
        I’ve used them a bunch of times, never any blow by issues.

        They’d be at .030 if I was doing it.

        .020-.022 for the second ring.
         
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        • 340doc

          340doc Well-Known Member

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          I agree but I'm having a hard time finding a file fit ring for a 4.070 bore. The KB's take the stock size 5/64 ring, not the more popular 1/16 ring. I started another post about that.
           
        • 340doc

          340doc Well-Known Member

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          Are you able to get by without the .005 over ring then?
           
        • nm9stheham

          nm9stheham Well-Known Member

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          Cannot ANY ring can be a 'file to fit' ring LOL? Am I missing something here? Why not start with the standard KB rings for that piston in +.030? 4000AM8070 for moly top ring. (No ductile in that size in their catalog unfortunately.)

          If you go with a .035" ring a stuff it into a .030" bore dimensioned for a hyper, that is going to be tightening the ring gap.... and (I think) would be increasing the ring tension over what is necessary.
           
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          • moper

            moper FABO Gold Member FABO Gold Member

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            Because the usual gap the stock replacement rings come with is based on the factory spec - either ring will work. A plain "+.030" ring will not need to be filed as much.
             
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            • Krooser

              Krooser Reform School Graduate

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              Better too big than too small
               
            • sireland67

              sireland67 Well-Known Member

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              You can file standard rings, just set them to the recommend gap.
              Make sure you have them a little more than KB recommends. Because your bore can have some taper.
               
            • MOPAROFFICIAL

              MOPAROFFICIAL Well-Known Member

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              .028 top ring
              .018-.020 2nd

              The top ring is spaced higher/away from the others...it gets the heat 95% .

              However...It wont hurt adding .004 to the 2nd ring, so do it it however you like.
               
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              • 340doc

                340doc Well-Known Member

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                That what I was wondering. I didn't want to buy a plain .030 ring set and find the gap too large. Standard ring gaps are usually large to make them error proof.
                 
              • 340doc

                340doc Well-Known Member

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                I know they can be filed, I just was worried about them coming in too big out of the box.
                 
              • 340doc

                340doc Well-Known Member

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                Yes any ring can be filed. Most standard ring sets have a built in larger gap to make them error proof in various situations. I didn't want to buy a standard .030 over set and find the gap too big out of the box
                 
              • rumblefish360

                rumblefish360 so close yet so far away

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                Only for women, fish, lotto winnings and margin of victory.
                :lol:
                 
              • nm9stheham

                nm9stheham Well-Known Member

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                Interesting... I can't say I have found that to be the case for fresh bores, properly sized. They always seem come pretty close to standard spec.
                 
              • 340doc

                340doc Well-Known Member

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                That's good to know. I'm gonna order the KB moly rings and hope for the best. Comments seem positive. Thanks to all!
                 
              • MOPAROFFICIAL

                MOPAROFFICIAL Well-Known Member

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                Buy/use the ring sized for your bore, .030 over bore....030 over ring set, file fit them... there is plenty of room to open them up...the 2nd is usually just right or .002 tight.
                If I'm reading what I think im reading...Do not use standard size rings on a .030 bore!
                 
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