Sonix

iTrader: (1)

What's the convention for the ring gap of the second ring?

From my bible, (David Vizards book) he mentions gapping the second ring slightly larger than the top ring. Now i've opened up my top ring gap considerably (future nitrous use), but i'm unsure about the second. I know it won't be seeing the heat that the top one will, but should I leave it gapped tighter than the top ring?

Just wondering if there was a logical convention one way or the other.

Thanks

sofakingdom

iTrader: (1)

Used to be, they were left with less gap than the top ring, precisely because they don't expand as much; but the conventional wisdom nowadays is to leave the 2nd gap slightly wider than the top one. Not a whole lot, maybe 15-20% wider. No matter what the top gap is.

Sonix

iTrader: (1)

Hmm, ok, fair enough. I'm doing the top ring at .028 or so, so I might go up to .035" or thereabouts then.
Thanks

Supervisor42

I don't understand Vidards reasoning to have a wider gap on the 2nd ring I guess a little more blowby is ok for insurance.
Speedomotive guidelines:
Top Rings (ductile iron, 4" bore)

Supercharged
Nitromethane .022 - .024"
Alcohol .018 - .020"
Gasoline .022 - .024"

Normally Aspirated - Gasoline
Street, Moderate Performance .016 - .018"
Drag Racing, Oval Track .018 - .020"
Nitrous Oxide - Street .024 - .026"
Nitrous Oxide - Drag .032 - .034"

2nd Rings (plain iron, 4" bore)

Supercharged
Nitromethane .014 - .016"
Alcohol .012 - .014"
Gasoline .012 - .014"

Normally Aspirated - Gasoline
Street, Moderate Performance .010 - .012"
Oval Track .012 - .014"
Pro Stock, Comp. .012 - .014"
Nitrous Oxide - Street .018 - .020"
Nitrous Oxide - Drag .024 - .026"

Sonix

iTrader: (1)

I was looking at KB's;
http://kb-silvolite.com/article.php?action=read&A_id=56

I don't have KB pistons, but their logic is sound. The excess gap isn't going to hurt anything (rings not sealing against walls would cause it to suck up oil, but a slightly larger gap is a microscopic change).
I wanted all the insurance I could get that I won't butt the rings together. .030" is NEVER going to butt together, even if I do grow the grapes to shoot that 250HP pill.

Ok, so your reasoning for a tighter second gap is ? It won't get as hot, so trap as much combustion gas as possible?

Wishmaster's87IROC

iTrader: (4)

hmm? well Ive got KB's and I gapped mine .035 it called for .033 with my bore size for nitrous use so I went alittle bigger just to play it safe. Im wondering now if thats where all my oil is going? I dont get any blow by out the exhaust that I can see but the oil is going somewhere. I mean like alot!

Supervisor42

I've seen plenty of engines with .030+ ring gap. All of them had over 150K miles on 'em though.
Let's revisit the stock spec just for fun. Top ring: .010-.020 ,service limit .030 .
Second ring: .010-.025 ,service limit .035 .

For Wishmaster, Speedomotive: "The second ring is primarily an oil control device. If the top ring is doing the job, the second ring will see fairly limited combustion pressure."

My reasoning is this: I know that nitrous will mandate a wide gap on the top ring, the only thing left from us building a brand-new "worn-out" engine is the second ring. So let's make it's gap even bigger?
Remember, the engine will also be run without nitrous a lot too.
Ring gap:
.010 = new
.020 = 80k miles
.035+ = 200k miles

sofakingdom

iTrader: (1)

Ring and piston designs and materials have changed, since alot of those "old standby" type books were written. Their details sometimes are obsolete as a result. Doesn't mean they're "wrong"; it just means that what they say, doesn't apply to the newer materials and techniques.

Used to be, the 2 (or more) top rings were both considered to be part of the compression seal, and the single "scraper" ring assembly took care of oil. However, better top rings seem to handle the combustion issue adequately all by themselves, and 2nd rings are now designed for improved oil control (this being, obviously, an emissions issue).

So, it seems that nowadays, it is considered better to use the wider 2nd ring gap such that any compression leakage that DOES occur past the first ring, can easily escape from that space between the 1st & 2nd rings; and the 2nd ring can then do its oil duty without interference from combustion pressure.

At least, that's how I'm understanding what I've been seeing.

Sonix

iTrader: (1)

Well see I don't get that. I can understand the rings wearing on the outside (sealing area), but I wouldn't think their gap would wear out much and become wider. I think losing the crosshatch on the cylinders would cause more oil consumption vs ring gap. According to that nifty chart on KB's site, they tested an engine with "normal" gap (KB specs), and .080" !!!! Oil consumption was barely effected.
.080" gap is about what you get when you use rings meant for an extra oversize bore, ie. one size up, .040" rings in a .030" bore. I'm taking all my info here from KB as gospel, and very little from personal experience.

Alright, so sofa you say that the idea behind gapping the second ring wider is to help the pressure relieve, this is the pressure between the rings. This pressure would help seat the rings though wouldn't it?
Hmm, i'm torn here. I think i'll just gap them identically, and see how it goes. My last build of this engine guzzled oil (or leaked it moreso I think). So this time i'm going to break it in LIKE I STOLE IT. Then i'll post back on how much oil it drinks with .030" top and 2nd gaps

Thanks guys!

Guest

The quoted ring gap service limits arent to determine if the gap is too big to let the ring do its job, but rather that the ring has worn down enough from scraping the walls that the gap increased significantly and its lost tension as well.

Guest

Just for confirmation on that, 1/2 quart over 5k miles with a LARGE top gap and larger second gap. New engine. It is running total seal rings, but... eh... still have a large gap in there on both and only one is 'gapless'.

Sonix

iTrader: (1)

Well... haha, we can't really compare gapless rings here eh? I'd love to do gapless though, best of both worlds.