Ring end Gap
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Ring end Gap

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    Boat Nut sleekcrafter's Avatar
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    Default Ring end Gap

    I'm in process of fit fit of the piston rings. Whats the end gap on a 4.5 bore BBC, in a jet boat application, going to be? Since we don't fall into any perticular category on the JE/SPR chart. I'm figuring .025 on the first ring, and .030 on the second, but looking for some guidance. Thanks in advance

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    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by sleekcrafter View Post
    I'm in process of fit fit of the piston rings. Whats the end gap on a 4.5 bore BBC, in a jet boat application, going to be? Since we don't fall into any perticular category on the JE/SPR chart. I'm figuring .025 on the first ring, and .030 on the second, but looking for some guidance. Thanks in advance
    Not sure what to tell you I run mine pretty tight in my v-drive. I use .0045 x bore dia. so for my 4.311" bore I use .019" ring gap. so I would figure .020" or maybe .021" for yours to be safer?? Not sure about engine temp and load differences. You NA only or will you be using any nitrous? I'm using the same gap top and bottom, they recommend the bottom tighter on the old set ups but I'm trying to make sure their isn't any pressure between the top and second rings and I have a machined grove on my pistons so I didn't figure the second gap needed to be any wider than the top gap.

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    Boat Nut sleekcrafter's Avatar
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    I popped in some of the old rings, Top was .022, and 2nd ring was .024. these were C&A ZGTF gapless 2nd ring. I'm looking to run the bigger gap on the 2nd ring. If I figure using the .0055 on top, it's .022. If I figure 25% larger on the 2nd ring, .0062 it's .028. The original build was for occasional Nitrous, this is still the intent on the refresh.

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    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by sleekcrafter View Post
    I popped in some of the old rings, Top was .022, and 2nd ring was .024. these were C&A ZGTF gapless 2nd ring. I'm looking to run the bigger gap on the 2nd ring. If I figure using the .0055 on top, it's .022. If I figure 25% larger on the 2nd ring, .0062 it's .028. The original build was for occasional Nitrous, this is still the intent on the refresh.
    If I read above you have a 4.500" bore correct? If so I think your math maybe off some where because I get the following.

    4.500 x .0055 = .02475 rounding to .025" ring gap (not the .022")
    4.500 x (.0055 x 1.25) = .030938 rounding to .031" ring gap (not .028)

    Did you use the 4.500" bore or 4"? I'd say your original rings were set up for NA with that 022/.024 ring end gap. Then they just opened up a couple of thou with normal wear. Just my .02.

    BTW the boats looking real nice in your avatar.
    Last edited by Carnivalride; 01-20-2009 at 04:24 AM.

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    Boat Nut sleekcrafter's Avatar
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    Thanks Carnivalride...I see the error in my formula, was adding + 25% to the first ring gap, not multipling by 1.25.

  8. #6
    just a ski boat with bark Carnivalride's Avatar
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    Quote Originally Posted by sleekcrafter View Post
    Thanks Carnivalride...I see the error in my formula, was adding + 25% to the first ring gap, not multipling by 1.25.
    Glad I could help

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