piston ring gaps



piston ring gaps

Postby grumpyvette » February 7th, 2010, 10:49 am

the general rule is that for normal use a pistons top ring should have a minimum of .004 thousandths end gap for each inch of bore diam. ie a 4" bore requires a minimum of a .016 end gap, to prevent the ring ends from bearing on each other after heat expansion,expanding them, so as to prevent the ring locking in the bore and pulling the top of the piston ring lands off, resulting in catastrophic engine failure.
but in high heat applications increase ring end gap is HIGHLY recommended
keep in mind oil flow and oil splashed on the cylinder walls does a great deal of the cooling on piston rings
for about the first 30 years we built engines with the top ring gap set at slightly larger than the second ring gap because it operates at higher heat levels, usually the top ring gaps were set at a minimum of 4.5 thousands per inch of bore diam. and the second ring gap, at a minimum of 4 thousands per inch of bore diam.
BUT RECENT TESTING HAS CONFIRMED
that pressure that bye-passes the top ring that gets trapped between the first and second compression rings tends to significantly reduce the top ring seal, thus the current recommendation is for the second ring to have a slightly larger end gap to significantly reduce that
now years ago, we were instructed to leave the second ring gap at a tighter .004 per inch of bore with the upper top ring having the larger end gap due to the higher heat levels, it operates under ,well extensive testing in recent years shows that
(1)the second ring gap needs to be larger because if significant cylinder pressure builds between the top and lower ring the upper ring seal is quickly lost
(2)theres very little cylinder pressure lost thru the ring gaps in the thousandths of a second the rings are compressing the fuel/air mix, or during the power stroke, because most of the blow by, is the result of less than effective ring to cylinder wall seal
(3) ring seal is destroyed if the ring gap allows the rings to contact, or the rings butting destroys the piston lands
(4) ring gaps up to about .045 have very little effect on blow by or oil use

http://www.kb-silvolite.com/article.php ... ad&A_id=64
Application

Bore x
High-Performance Street / Strip
.0045”Top Ring
.0055”2nd Ring
Street-Moderate Turbo / Nitrous
.0050”Top Ring
.0055”2nd Ring
Late Model Stock
.0050”Top Ring
.0055”2nd Ring
Circle Track/Drag Race
.0055”Top Ring
.0060”2nd Ring
Blown Race Only
.0065”Top Ring
.0070”2nd Ring
Nitrous Race Only
.0070”Top Ring
.0075”2nd Ring


READ THESE LINKS, THEY CONTAIN A GREAT DEAL OF USEFUL INFO


http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

http://www.kb-silvolite.com/assets/kb_installation.pdf

http://www.stockcarracing.com/techartic ... index.html

http://www.aa1car.com/library/ring_end_gap.htm

http://www.circletrack.com/enginetech/c ... index.html

http://www.circletrack.com/howto/1818/index.html

http://www.kb-silvolite.com/assets/auto ... ctions.pdf

http://www.kb-silvolite.com/article.php ... ad&A_id=56

http://www.aa1car.com/library/ar293.htm

viewtopic.php?f=53&t=509&p=632&hilit=+compressor+rings#p632

viewtopic.php?f=53&t=1797

viewtopic.php?f=53&t=2795

viewtopic.php?f=53&t=247

http://www.muller.net/sonny/crx/rings/index.html
viewtopic.php?f=51&t=588

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you may want to keep in mind cast iron or moly faced cast iron piston rings expand with heat and that .018 gap in a running engine with a piston temp of lets say 450f would drop to, near 10-12 thousandths of an inch, get into detonation, and heat could reach a temp range where the rings lock in the bore

http://www.engineeringtoolbox.com/therm ... d_859.html

http://www.enginebuildermag.com/Article ... mance.aspx


you may want to keep in mind that once an engines up to operational temperatures, the piston to bore clearance is rather tight and the ring gaps are significantly reduced due to heat expansion, in the metals, at just 1000rpm idle speeds , theres 8.3 compression /power strokes PER SECOND, and that almost all the peak cylinder pressure is incurred during the upper 2" of piston travel, as the piston approaches or recedes from tdc, theres not a great deal of the cylinder volume that can leak past a properly functioning ring thru a gap that's maybe 12 thousandths wide, in the .07 of a second that peak compressions potentially occurring, speed the rpms up to 6500rpm and your down to only .011 seconds per power stroke in the higher pressure range, again, a minimal ring gap has almost no effect, everything , Ive read states that gaps up to about .45 thousands of an inch have a minimal effect on compression or power, or even oil consumption if the rings are sealing to the bore effectively.
youll be far more concerned with the ring seal, bore hone, and having the block honed with plates simulating the bore stress tightened head bolts produce to reduce ring blow-bye
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read this

viewtopic.php?f=51&t=588


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worthless P.I.T.A. to use

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GOOD and VERSITILE

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WORKS GREAT BUT LIMITED TO A NARROW BORE RANGE AND EXPENSIVE

http://www.amazon.com/KD-Tools-850-Diam ... 0002STSMG/
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this type (ABOVE) handles many applications but the cheap versions are a P.I.T.A. to work with

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BTW when you go to buy a ring compressor....this type(ABOVE & BELOW) works far better than the others, but its specific to a very limited range in bore size applications

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http://store.summitracing.com/partdetail.asp?autofilter=1&part=PRO%2D66766&N=700+115&autoview=sku

Proform 66766 $31
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: piston ring gaps

Postby grumpyvette » April 4th, 2010, 10:38 am

filing ring gaps correctly, takes a bit of time and effort, it can be done with a very fine file by hand but there are tools designed specifically for the job.
a dremel tool can also do the job in experienced hands, don,t worry about cutting the ring gaps a bit to large, if the ring gaps are a bit to tight and the ring ends touch under high heat conditions or butt it will destroy the engine, but if the ring gaps are even 5-7 thousands too large, the results on power produced or ring seal and burning oil are negligible at best compared to having them exactly right, compared to the charts.
be aware rings can,t seal correctly to the cylinder walls unless the block was honed with deck plates simulating the distortion a cylinder head and mount bolts produce on the block, and the surface finish used during the hone is also critical.

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btw most rings have a dot or mark showing the side that faced upward


when your setting the ring gap theres been a few changes in whats been found to work best, over the years
for most of my 40 years of engine build experience most builders gaped the top rings for a
Normally aspirated
.0045 per inch of bore top
.004-.0045 per inch of bore second (slightly tighter end gap on the second ring)
because the second ring was not exposed to the same intense heat so it needed less gap to prevent the ring ends from touching as the heat expanded the rings and lowered the resulting end gap, remember that .0045 per inch of bore results in about a .019-.020 " end gap on the rings of a 427-454 bbc with its 4.25" bore

lately thats changed to

.0045 per inch of bore top
.005-.0055 per inch of bore for the second ring second

this is the typical approach nowadays that most builders use.
the reason for the change is that its been found that the compression, and combustion tends to build pressure between the rings and that pressure build up,tends to significantly reduce the effective seal of the top ring
A fairly recent development with the second ring has been to open up the ring end gaps more to allow more trapped gases to escape from between the top ring and second ring, The larger second ring end gap flow area, allows any potential pres sure build up keeps the top ring from fluttering, it also allows trapped oil to escape back to the crankcase.
greg_moreira posted this info
"[Inter-ring pressure] is somewhat minor but all of the little things add up," says Sealed Power's Gabrielson. "The flow gap on the second ring should be twice the flow gap on the top ring. That doesn't necessarily mean the ring gap is twice as large. The flow area is that little bit of area that includes the ring gap and part of the end that hangs over the land underneath the ring. Everything else is closed off because the ring is sitting on the piston ring land. So you actually have only that little spot that is hanging over the edge."


READ THESE
viewtopic.php?f=51&t=588&p=764&hilit=hone+plates+block#p764

viewtopic.php?f=51&t=976&p=1706&hilit=hone+plates+block#p1706

viewtopic.php?f=53&t=509&p=632&hilit=hone+plates+block#p632

viewtopic.php?f=50&t=1249&p=3752&hilit=block+epoxy+plugs%E2%80%A6#p3752

http://www.summitracing.com/parts/SUM-C ... /?rtype=10
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another ring file tool
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deburring the ring edges
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using ring file tools
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using ring file tools
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read this
http://www.chevyhiperformance.com/howto ... index.html

http://www.aa1car.com/library/ring_end_gap.htm

http://www.muller.net/sonny/crx/rings/index.html

http://chucker54.stores.yahoo.net/pisringapfil.html

http://www.jegs.com/p/B-B/Piston-Ring-F ... 5/10002/-1

http://www.popularhotrodding.com/engine ... rings.html


btw heres typical detonation damage, and in this case, resulting from a bit of nitrous, that boosted the pressure, but the results would be similar on a high compression engine subjected to crappy fuel and high loads at high rpms without nitrous, notice the sugary/frosted appearance and rounded edges of the melted areas
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damage to the ring lands can be caused by detonation or just the ring gaps set too tightly, if the piston shows no frosted appearance its usually the ring gaps too small, or excessive heat, to lean a mix, to much ignition advance,etc.
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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