Fellas, I'm building a .030 over 283 atm and ring gaps call for the usual 018" top ring gap etc. After squaring up the .030" up Hastings moly rings 1" down the bore I get .022" on the top ring, and .013" on the second. Anyone come across this ? While I would prefer to go with the "recommended" gap, I'm not super worried over the top ring being .004" over the recommended gap (.017"- .018" would be "nicer"- it's a muticarbed street engine deal). I'm wondering about the following : i. does anyone make a + .005" file back ring set (.035") for 5/64" rings? I have only been able to find them in my bore size (3.905") for the more High Perf 1/16", 1/16" ring sets and not the 5/64" OEM style rings. This way I could file the top ring for a tighter gap as recommended by the ring manuf. ii. today's thinking is to run the 2nd rings (more of an oil scraper really) slightly larger than the top ring to minimise ring flutter etc. Given my current ring gaps as checked, that would mean the 2nd ring would need to be gapped at around .024". What say you guys, go that way or leave it at .013"/smaller as it was done back in the day ? Given that I can't find any + .005" ring sets for 5/64" rings and applying the current thinking, I'm thinking to leave the top ring at .022" and given the second ring sees less heat, perhaps open it up from the current .013" to only .018" so it is closer in size to the top ring when it the top ring expands and closes the gap due to more heat. I'm not sure exactly how much the top ring gaps close up when running....I'd love to hear opinions. But in theory when running/hot, the top ring gap will close up a few thousandths to hopefully around what the 2nd ring gap is say .018" or so. Is my thinking sound ? What gap would you guys run on the second ring at and why ? Thanks
Well. .022 you are okay with, right? .013 you feel is too tight. Right? File the ring to the proper gap, or am I missing something?
I guess I should make it clearer, given what I stated above, what gap would you file the second ring to......and why ?
Cast ,forged or hyper pistons ? Odd there's that much difference between 1st & 2nd rings ? Never had any luck with hastings , switched to Mahle .
The reason for ring gap is because when the rings get hot, they expand in length enough to reduce the gap considerably...when it gets to zero, you have serious problems. So you can imagine that the ring gap when running will vary a bunch, as their temperature changes with load, etc. As long as they don't butt, and the gap is not real excessive, it'll work fine. You can expect the top ring to be hotter than the second ring, so it will have less gap than the second ring, even if it starts out with more gap when the engine is cold. Have fun....I would just put it together and run it.
I've been collecting parts for a .040 over 283, including KB hypereutectic flat tops and, coincidently, Hastings moly rings. The ring gap instructions that came with the pistons are pretty interesting, including this paragraph; "Modern piston design locates the top ring higher for improved performance. A high top ring operates at higher temperatures and requires a larger top ring end gap. To find the proper ring end gap, multiply your bore size by the ring end gap factor listed on the chart (i.e., Street Naturally Aspirated 4.000” bore x .0065” gap factor = .026” total top ring end gap Second Ring: Set second ring end gap at .004 per inch of bore minimum." They provide a chart with the top ring gap factor for various applications; it ranges from .0065 for NA street up to .0095 factor for drag supercharged/nitrous. So for my upcoming 3.915 bore, my top gap is to be .026" and the second gap is to be .016"
Thanks for the input guys, I'm using cast pistons. I understand ring tech etc, but my quns were specific as to O/S ring availability and the second ring gap tech. Deuceman, the gap factors are bigger on KB hyper slugs bc of their greater silicon content retaining heat in the piston therefore needing a bigger gap to avoid ring butting. Cast pistons on NA street engines are usually gapped with a factor of .004" - .0045". This factor would put my "ideal" top ring gap at .017" - .018". I'm not going worry about the .004" difference.....but, as I said in my OP, my main question is about the current thinking about the 2nd ring gap being run slightly bigger that the top ring. There are two distinct schools of thought on this and I'm curious if anyone done this and what did they find ?
I’m still maybe confused. Your 2nd ring gap it not greater but well less than the top ring gap. I’d go with the .004 per bore diameter for the 2nd ring.
I’d gap the second rings to your satisfaction, that .004 over on the top ring gap is inconsequential, you and the engine will never feel the difference.
After break in , you will pick up a couple thou. .022" top is ok. I would touch up the second rings closer to .018" . Break in creates heat and.013" is too tight.
I believe RB wants to know about the second ring gap mostly ...... QUOTE: This factor would put my "ideal" top ring gap at .017" - .018". I'm not going worry about the .004" difference.....but, as I said in my OP, MY MAIN QUESTION is about the current thinking about the 2nd ring gap being run slightly bigger that the top ring. There are two distinct schools of thought on this and I'm curious if anyone done this and what did they find ? .................................................................................................................................. I'm not sure exactly how much the top ring gaps close up when running....I'd love to hear opinions. But in theory when running/hot, the top ring gap will close up a few thousandths to hopefully around what the 2nd ring gap is say .018" or so. Is my thinking sound ? WHAT GAP would you guys run on the second ring at and why ? Ricky.
There has been a change it what was once considered correct. Old way was second ring smaller gap than top ring....not anymore. Now conventional thinking is you don't want second gap smaller than top gap....reason being, you don't want a tighter second gap to trap anything that gets past the top ring, trap pressure between second ring and top, and destabilize the top ring on the next intake and compression stroke. ......since the second ring IS NOT a compression ring and won't last long if expected to hold combustion pressure. You want anything that gets past the top ring to blow through to the crankcase so the PCV system can clear it out . Second ring is merely final oil preparatory ring for the layer of oil the top ring rides and seals on. Having a tight gap is not a requirement, and now the rule is second ring gap equal to or bigger than top ring gap. Call any ring company and ask.... Gap that second ring bigger.
But does the top ring gap stay bigger than the second ring gap, when it's running? I really doubt it. And I also guess that empirical evidence of ring gap while running is very hard to find...until it reaches zero, and the piston stops moving
I agree. I've never seen a second ring butt, and I've seen several cases of top rings butting and pulling the piston apart. That top ring sees fire and runs hot, even more so with a piston with raised top ring location as many KB Hypers have. I'd not hesitate to run a 283 with .013 gap on the second ring, but opening up a few thou surely won't hurt if you're so inclined. I built a LOT of engines when the thought was smaller gap on the second and none had any problems at all. Fly specks in the pepper IMO.
Are gapless rings still a thing? Even on a cruiser the benefits in seal and reduced oil contaminants has to be worth it. Or not? And don't freak out and get into a cosmic conversation of how they work, I know, I've used them in my builds decades ago. Just wondering.
Good info for sure....many even run the same gaps on the top and second rings. I think the point was made above that its almost impossible to quantify how much the top ring gap will tighten up when exposed to heat etc. Heaps of variables to contend with here. But let's say on a NA street deal, it tightens up around .004" with heat/load/friction and the 2nd ring, seeing less heat and being of a different material closes up .002". This would theoretically mean that if both were set at .0018" then the top ring's gap at running temp would potentially be .014" and the 2nd ring would be .016", meaning that at operating temp the 2nd ring's gap will be sightly bigger than the top ring's gap. Fly specs in the pepper for sure, but interesting nonetheless.
I’ve always tried to follow ring manufactures suggestions. I figured they spent the money on R /D this is assuming ( dangerous here from my past lol ) that the ring is specked for that application and intent. ( and no I haven’t always done that). But I will repeat something I was told at the track once. A little loose and no body in the stands will ever know. Too tight and everyone will know.
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