ring gap for a 4.281 mild engine BBC
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ring gap for a 4.281 mild engine BBC

  1. #1
    Senior Member ol guy's Avatar
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    Default ring gap for a 4.281 mild engine BBC

    I have always gone with the old rule of .004 per inch of bore which would put me at a gap of .0018. This mild N/A mild engine. Any thoughts?

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    Village Idiot fc-Pilot's Avatar
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    For marine stuff I always give it another thou or two due to the cooler water temp. But that is just me. It also depends on the ring manufacturer recommendations. Knowing how a boat is always loaded vs a car engine, it also gives me reason to keep it on the safe side. Who’s rings and what do they recommend? What are the pistons made of (cast,hypers or forged)?

    Paul

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    Senior Member ol guy's Avatar
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    I go along with what you are saying. I set them today at .021. the pistons are hyper's and the rings are sealed power KX rings Chrome moly on top and cast iron 2nd's. The season for the question was I had very little time on the engine but pulled it apart for a cam swap and do to the fact I got it HOT thanks to the water pump I felt it wise to ring and bearing it. When I pulled it apart I was kind of pissed cause it came apart like it was brand new. Better safe than sorry I guess. I just wanted another opinion and I am glad you piped up! Thank you. Mark

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    Village Idiot fc-Pilot's Avatar
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    I don’t know “what is right” I just know what I do. Funny thing is I will be asking the same question before long. Getting ready to start assembly of another build as well. Good luck on yours.

    Paul

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    Senior Member Bubbletop409's Avatar
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    Just freshening my SunsetRaceCraft 565 after 11 years of flawless service. In pulling the original build sheet I found the gap for both the top and second ring on my 4.6" bore was set at .024.

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by ol guy View Post
    I go along with what you are saying. I set them today at .021. the pistons are hyper's and the rings are sealed power KX rings Chrome moly on top and cast iron 2nd's. The season for the question was I had very little time on the engine but pulled it apart for a cam swap and do to the fact I got it HOT thanks to the water pump I felt it wise to ring and bearing it. When I pulled it apart I was kind of pissed cause it came apart like it was brand new. Better safe than sorry I guess. I just wanted another opinion and I am glad you piped up! Thank you. Mark
    Sorry I didn't see this earlier. Hypereutectic pistons usually require a larger ring gap, particularly KB Pistons. I don't know the number since everything I put together is with forged pistons.

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    Distinguished Member David 519's Avatar
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    I follow the directions from the ring mfg. I typically like total seal (non-zero-gap) or Hellfire for power adder combos. My feeling is you lose less HP with a slightly bigger gap than making them tight and lift a land.... Of course I beat my stuff like a rented mule, so YMMV...

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