ring end gap & courting disaster - Page 2 - Vintage Mustang Forums
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post #16 of 32 (permalink) Old 07-05-2019, 03:23 AM
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.004” is what I use for a high performance street engine - top ring. I like Gapless second rings.

If you want an education on tolerances, go to an NHRA race weekend and watch them rebuild the top fuel engine between rounds. Of course it’s a unique situation, but wow. When you have that much nitromethane and blower pressure, who needs tight ring gaps!

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post #17 of 32 (permalink) Old 07-05-2019, 06:34 AM
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When I built my engine with Keith Black hyperutectic pistons they specifically called for a larger end gap on the top ring. For a 4 " bore on normally car its .026" for that piston. As bbmach said, there is not one answer. Follow what your piston and ring manufacture says.
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post #18 of 32 (permalink) Old 07-05-2019, 07:45 AM
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I don't see how you can generalize a ring gap. Expansion is a function of the metallic alloy composition and intended max operating temperature. I would follow the manufacturer's specifications over anything else unless you are using it outside its intended temperature range. Then I would use "local" knowledge of guys/gals running similar usages e.g. alcohol drag racing etc... I would not use a "rule of thumb" from this site.

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post #19 of 32 (permalink) Old 07-05-2019, 09:45 PM
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You sure come up with some doozies LSG. If you would be so kind, enlighten me on why a larger than necessary ring gap is beneficial. Other than machine shop liability.
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post #20 of 32 (permalink) Old 07-06-2019, 07:44 PM
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He didn't say bigger than necessary is beneficial, he said smaller than recommended is detrimental. Bigger than necessary is not as detrimental as previously thought.

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Last edited by Jeff351w; 07-06-2019 at 07:46 PM.
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post #21 of 32 (permalink) Old 07-06-2019, 07:51 PM
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Quote:
Originally Posted by 66coupe289 View Post
When I built my engine with Keith Black hyperutectic pistons they specifically called for a larger end gap on the top ring. For a 4 " bore on normally car its .026" for that piston. As bbmach said, there is not one answer. Follow what your piston and ring manufacture says.
KB Hypers are notorious for blowing out ringlands if the gap is set tighter than they recommend (ie to "normal" specs). They place the top ringland closer to the top of the piston than most other manufacturers exposing the top ring to more heat and therefore more expansion.

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post #22 of 32 (permalink) Old 07-06-2019, 09:25 PM
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[QUOTE=Jeff351w;10194322]He didn't say bigger than necessary is beneficial, he said smaller than recommended is detrimental. Bigger than necessary is not as detrimental as previously thought.

Well, he said "On our 289 & 302 engines I would like to see .030 or more...….". No mention of cast, hyper, forged, power adders, etc. Lot's of variables there. That's my question.
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post #23 of 32 (permalink) Old 07-07-2019, 08:18 AM
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For do it your selfers Ring Tech in this day an age is just a few key strokes away or in the ring packaging when you receive them. Following specs from days future past and applying those on today's ring and piston products doesn't make much sense. Here is an example of few key strokes (https://www.hastingspistonrings.com/...sion-ring-gaps).

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post #24 of 32 (permalink) Old 07-08-2019, 12:35 AM Thread Starter
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Tongue ring end gap

RickGTO, think of it like a math problem. If a cylinder for a 289/302 is bored .030 the circumference of that cylinder is pi x 4.030, or 12.660 inches. 1% of that would be ~.125 inches, 1/2% would be ~.065 and 1/4% ~.032 inches. So if you had my proposed .030 ring end gap, the top ring will catch more than 99 & 3/4ths of whats there. The second ring will catch 99 & 3/4ths % of what might get by the top ting. If your engine is running at 1000 rpm, thats 8 power pulse per second. There just isn't time for much to sneak through the end gaps. We have to remember ring tension comes from the shape of the metal ring, end gap does little or nothing for tension. So, if one wants to chase the 1/4 of 1/4 % percent,.....I guess you can do it if you want to. But if the gap is ever too small, for whatever reason, instant disaster ! If the gaps are large, you lose nothing but worry. LSG
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post #25 of 32 (permalink) Old 07-08-2019, 04:41 AM
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Quote:
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RickGTO, think of it like a math problem. If a cylinder for a 289/302 is bored .030 the circumference of that cylinder is pi x 4.030, or 12.660 inches. 1% of that would be ~.125 inches, 1/2% would be ~.065 and 1/4% ~.032 inches. So if you had my proposed .030 ring end gap, the top ring will catch more than 99 & 3/4ths of whats there. The second ring will catch 99 & 3/4ths % of what might get by the top ting. If your engine is running at 1000 rpm, thats 8 power pulse per second. There just isn't time for much to sneak through the end gaps. We have to remember ring tension comes from the shape of the metal ring, end gap does little or nothing for tension. So, if one wants to chase the 1/4 of 1/4 % percent,.....I guess you can do it if you want to. But if the gap is ever too small, for whatever reason, instant disaster ! If the gaps are large, you lose nothing but worry. LSG
Your reasoning is faulty. What about at 2,500 rpm where a street engine will spend a significant amount of time, say for 100,000 miles? Or a racing engine? Or a boat engine? Now do your “power pulse” math.

Why would you throw away efficiency and add contaminants to the oil by building a new engine already out of spec? If you think it’s a math problem, then spend the time to calculate the gap requirement for your particular piston and ring combo, and it’s intended usage. And then trust the expertise of those who manufactured the parts, and your experience.

There is a reason for the specification range, on both ends. By not following those guidelines, you’re just being lazy.

I assume you’re playing with semantics and trying to be cute, but if I used your shop for machining and/or building, and later found the ring gaps out of spec, we would have a problem. If your response was stated as above, we’d see each other in court.

Most of us know you get what you pay for on the internet, but the information here lives forever under Google. Why give out bad advice on purpose?

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post #26 of 32 (permalink) Old 07-08-2019, 06:58 AM
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post #27 of 32 (permalink) Old 07-08-2019, 09:30 AM
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.005 top ring and gapless seconds in my motor. Efficiency is power and I run this package in every performance engine I build. Even my 408 that huffed a lot of nitrous. I'd never run .030 in anything.
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post #28 of 32 (permalink) Old 07-08-2019, 12:12 PM
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The current industry standard is .0045-.005 per inch of bore for naturally aspirated engines. Power adders can require as much as .007/inch. The WORST thing you can do is run a ring too tight. It WILL butt and cause damage to the ring and the piston. Trying to run tight gaps to limit leakdown is silly. A leakdown tester is a "relative tuning aid". By that I mean if you assemble an engine and it has 4% leakdown and stays at 4% for a long time all is good. BUT if it goes to 14% in a short period of time , you have a problem. The amount of CHANGE is the important factor. A leakdown test NEVER gives the exact leakdown as the top ring is never at the actual operating temp OR gap as when it is running. Sure you can do a hot leakdown but guess what the ring does when it gets a blast of 100psi "cooler" air.
LSG is correct that "large" leakdown numbers are due to loss of "perimeter" seal , not a .030 end gap. Many years ago I did a leakdown test on 8 cylinders gapped from .018-.030 and the variance was about 2% between all 8. Excessive top ring gap does not cause oil smoke by itself.
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post #29 of 32 (permalink) Old 07-09-2019, 11:00 PM Thread Starter
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Tongue ring gap

BBM, not sure where you're getting specs, but my suggestions are based on what works and what doesn't, and what the piston manufaturer says. The copier at work doesn't work worth a s---, so I'll just tell you what our Icon/ KB/Silvolite book says, N/A street, .0065 per inch( .026 ) Street, towing or hi perf, .008 ( .032 ), Marine N/A, .008, again .032. I find it interesting that these numbers are listed as MINIMUMS, and none of the ring manufacturers list a max or 'do not exceed' gap.

I will say that probably 2/3rds or more builds get hypereutechtic pistons, with forged pistons needing more clearance than cast or hyper.

I did find but don't know how to show you a study that GM did with .018 gap consuming a quart of oil in 4 K miles. The same engine tested with .085 gaps sucked in a quart per 3,500 miles. I wish they or someone else would test an engine at .035~.040. Would that be somewhere in the middle ? What efficiency do you think you gain by going tight here ? Seems needlessly risky to me.

Would any of you like to discuss the difference between top and 2nd ring gaps ? Or how about 'gapless' top rings or zero gap second rings ?


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post #30 of 32 (permalink) Old 07-10-2019, 10:14 AM
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I would like to see some discussion on them. I'm always looking to learn and have not used gapless rings.

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