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Old 06-02-2012, 11:53 AM
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Piston Ring End Gap

Hello I have a sbc 400 thats bored .40 using a standard eagle crank that im building. Im at the step now where im trying to check the piston ring end gap before i install the pistons. The instructions with rings says "check end gap .004 per 1" bore diameter is the minimum" So what im trying to find out is what is my bore? Bore x .004 =

I able to fit .016 on the feeler gauge into the end gaps.

Also I have speed pro h616cp .040 pistons..I cant find the instructions i looked all over google. Im trying to find instructions that show the ring end gap position while installing the piston.

Please help

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Old 06-02-2012, 12:13 PM
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If i remember correctly a stock 400 sbc has a bore of 4.125 so being .040 over you should be at 4.165. As for ring gaps i put them 30 degrees from the piston pin make sure they are staggered. 0.016 ring gap should be ok for a mild street engine IMO.
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Old 06-02-2012, 03:47 PM
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.016 top ring and .018-.020 second ring will be good for a street/strip application.. a good formula for this is Bore X .0045 top ring Bore X .0050 second ring... now for mild nitrous or turbo go .005 bigger... hope this helps a bit.. some guys like there ring gaps different depending on there intended use.. but this is a good basic gaps thats commonly used
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Old 06-02-2012, 09:53 PM
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Quote:
Originally Posted by grandprix601
Hello I have a sbc 400 thats bored .40 using a standard eagle crank that im building. Im at the step now where im trying to check the piston ring end gap before i install the pistons. The instructions with rings says "check end gap .004 per 1" bore diameter is the minimum" So what im trying to find out is what is my bore? Bore x .004 =

I able to fit .016 on the feeler gauge into the end gaps.

Also I have speed pro h616cp .040 pistons..I cant find the instructions i looked all over google. Im trying to find instructions that show the ring end gap position while installing the piston.

Please help
Standard 400 SBC bore = 4.125" plus 0.040" overbore = 4.165"

4.165" bore X 0.004" = 0.0166, or rounded up, 0.017" minimum end gap. If the 0.016" feeler fits w/o friction, AND the ring is square in the bore, the end gap is sufficient for "normal" use. Place a ring in the bore, then use a piston inserted upside down into the bore to square the ring.

Generally, unless your instructions say otherwise, the second ring should be gapped 0.004" to 0.008" wider than the top ring according to Carrillo. Minimum of 0.015" for the oil ring rails, do not file them.

Also be aware that there are pistons like some made by Keith Black that use a wider top ring gap than what is normally recommended by ring manufacturers. So be sure to check the piston manufacturer's instructions to see if they differ from the ring manufacturer's instructions.

There are several different thoughts on end gap placement, the following diagram will work fine:

Ring end gap location.

Last edited by cobalt327; 06-02-2012 at 10:06 PM.
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