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I'm building an LQ9 short block with a mild cam. I bought factory / OEM pistons with ring lands of 1.2mm, 1.5mm, and 2.5mm for the oil ring. Not sure that makes a difference, but I need to come up with an ideal ring gap. I'm also an armature turner, will tune this engine myself so not sure if I need to figure in a fudge factor for my tuning abilities (may also try to do a lean burn tune later down the road).
Long story short I need to come up with a good ring gap. I have Mahle rings HERE. I understand rule of thumb is 0.004" per inch of bore. I'm at 4" bore with LQ9. However, from there I see conflicting info, some like wider gap and or tighter gap on second ring.
Second ring gap should be equal or greater than top ring to allow gasses somewhere to go. If they can’t get out, you’ll develop ring flutter which interrupts the seal process. Having said that, if it’s a mild street build, which it sounds like, with no boost in your future, I’d throw the rings in as-is if indeed your buying non-file rings as in the link you posted.
@RonSSNova , thanks, kind of what I was thinking, better safe than sorry. Your specs, seems pretty loose but super safe for the 0.026 / 0.028... I had been leaning towards 0.017 top and 0.020 bottom but no plans for power adders. Well I'm going to start gapping, can always enlarge a bit before I assemble, but I think it sounds that should be gapped to be safe. I assume this is the spec you were looking at for Mahle ring gap? Page 21 HERE
@Che70velle I didn't even know there were drop-in rings, pre-gapped until you mentioned them. I don't build engines but once a decade or so haha.
I've been referencing this website HERE which seems to say pretty much the same thing at the build book I bought, "How to Rebuild GM LS-Series Engines".
Where are you measuring the rings in the cylinder at? Are you using a square tool? .011 is on the tighter side, but not unreasonable for a stock or mild build. I’ve seen .009 in a LS1. Open it up some of your concerned about it.
@Che70velle I'm measuring about 1" to 2" from the deck in the cylinder. I just wondered if different placement would result in slightly different measurements. I used a piston to push them down in the cylinder / square them off.
I'm getting a little more comfortable with this. My last engine I built, I didn't even know this much, I just threw the rings in. I have All Data account for my factory 5.3L, it has tighter than the "rule of thumb 4tho / inch" too.
Thanks for the help. Perhaps I'll sleep on it haha
FYI ~ My immediate build goal is to get over 400 hp / 400 lb/ft... Then possibly do some better heads and exhaust. It's a low power / torque motor for truck. I will be towing and driving overland / off road with it. Short block is LQ9 with 578/587/213/220/114+4A spec'd camshaft and 317 heads.
Well talk about educational, I called Mohle. It's awesome to see great customer support is still alive with some of these parts companies. The tech said the rings come pre-gapped same as you said @Che70velle .... And that as @RonSSNova , you said, the marketing pieces / their instructions are out of date. The marketing pieces reflect 0.004" / inch bore. That hasn't held true for a long time and apparently they are wanting them to update that information but they haven't. Tech said even adding power to motor but naturally aspirated should have no problem at all with the pre-gapped rings. I'm going to double check with my machine shop if they open them up a tad anyways. They build some pretty awesome motors.
The factory typically builds em with less gap than people like Us would.
THIMK for a minute about it: if you have a .001" or 2 too much, you get an extra coupla molecules of blowby. Big deal, right? But if you have even ONE .001" too little, the ends butt together when they get hot, which results in INSTANT FATAL DESTRUCTION. The rings blow the lands off the pistons, seize in the bore, and otherwise aggressively misbehave. Since there's no such thing as "perfect", only "error" to one side or the other of that, which side would you rather have your "error" towards?
Rule of thumb for a "hot street" kind of build is around .0045" per bore inch on the top, and .001" - .0015" more than that on the 2nd. Add nitrous or a blower, and you'll want to add .001" - .002" to those. For a totally stock grandma's daily drive kind of deal, i.e. what you'd likely see in a "catalog" kind of spec, .004" top and .005" 2nd is completely normal. For a 4" bore motor like most of use here would be doing, which yours is pretty much solidly in that category, that means something in the neighborhood of .017" - .018" top and .020" - .022" 2nd would be a great target.
The factory typically builds em with less gap than people like Us would.
THIMK for a minute about it: if you have a .001" or 2 too much, you get an extra coupla molecules of blowby. Big deal, right? But if you have even ONE .001" too little, the ends butt together when they get hot, which results in INSTANT FATAL DESTRUCTION. The rings blow the lands off the pistons, seize in the bore, and otherwise aggressively misbehave. Since there's no such thing as "perfect", only "error" to one side or the other of that, which side would you rather have your "error" towards?
Rule of thumb for a "hot street" kind of build is around .0045" per bore inch on the top, and .001" - .0015" more than that on the 2nd. Add nitrous or a blower, and you'll want to add .001" - .002" to those. For a totally stock grandma's daily drive kind of deal, i.e. what you'd likely see in a "catalog" kind of spec, .004" top and .005" 2nd is completely normal. For a 4" bore motor like most of use here would be doing, which yours is pretty much solidly in that category, that means something in the neighborhood of .017" - .018" top and .020" - .022" 2nd would be a great target.
Thebplot thickens... I spoke with machine shop. They said absolutely do not listen to tech at mohle, he recommended .020 and .026.. I will open em up I like your err on safe rather than sorry.
.020" & .026" is pretty conservative. Sounds like he's expecting that you'll get The Itch sooner than later. Won't cause any trouble in the meantime though, so it's not wrong.
Okay so running into some questions here. First ring was easy and consistent to measure. All the first rings measured like this: 0.017" feeler swipes through, 0.018" feeler goes through with a little resistance and 0.019" won't fit at all so I stopped grinding calling that a 0.017" to 0.018" gap.
The second ring allows a 0.017" feeler to swipe through the gap w/o touching. However, I can fit up to a 0.022" gauge with minimal resistance. Then 0.023" will fit with more resistance but 0.024 will not at all. So what's the measurement is it 0.023 to 0.024" or is it 0.017 to 0.024"?
I'm assuming the ring is expanding against cylinder wall as I slide in the larger feeler gauges?
Few additional notes:
I also noticed, the materials comes up much faster filing the second / bottom compression rings.
First ring is 1.2mm and hard as a rock. Second ring is 1.5mm and has a cupped surface on outside diameter, bottom of ring, cylinder side. Really cool but it seems to behave much differently than the top ring.
Formerly I had ordered wrong rings. The other rings were for a factory LQ9 piston as well but different ring land design. Those rings had 1.5mm / 1.5mm compression rings and the two rings looked identical, top and bottom (perhaps different material though). There was no cup on the bottom ring for them.
Okay, stupid me... I read the instructions that came in the box with these rings. It said 0.004" for each inch of bore, and 0.002" extra for bottom ring.
Okay so running into some questions here. First ring was easy and consistent to measure. All the first rings measured like this: 0.017" feeler swipes through, 0.018" feeler goes through with a little resistance and 0.019" won't fit at all so I stopped grinding calling that a 0.017" to 0.018" gap.
The second ring allows a 0.017" feeler to swipe through the gap w/o touching. However, I can fit up to a 0.022" gauge with minimal resistance. Then 0.023" will fit with more resistance but 0.024 will not at all. So what's the measurement is it 0.023 to 0.024" or is it 0.017 to 0.024"?
I'm assuming the ring is expanding against cylinder wall as I slide in the larger feeler gauges?
Few additional notes:
I also noticed, the materials comes up much faster filing the second / bottom compression rings.
First ring is 1.2mm and hard as a rock. Second ring is 1.5mm and has a cupped surface on outside diameter, bottom of ring, cylinder side. Really cool but it seems to behave much differently than the top ring.
Formerly I had ordered wrong rings. The other rings were for a factory LQ9 piston as well but different ring land design. Those rings had 1.5mm / 1.5mm compression rings and the two rings looked identical, top and bottom (perhaps different material though). There was no cup on the bottom ring for them.
Okay, stupid me... I read the instructions that came in the box with these rings. It said 0.004" for each inch of bore, and 0.002" extra for bottom ring.
You’ve got .018 and .023 gaps. I’d leave it alone if it were mine, but it won’t hurt anything to go on out to .020 or top rings and leave second ring alone. Your instructions there call for a .016 top ring gap... Again, I’ve seen much, much tighter gaps run for a hundred thousand miles.
Thanks everybody... I settled on 17 to 18 thousands top ring... 20 to 22 thousands bottom ring... With first number being a zero resistance feeler, last being last feeler to fit at all. The only oddball was cylinder 3, for some reason the second ring would fit all the way to a 24 thousands feeler.
I also called my genius builder friend. He said seldom does it ever make any difference but the gap insurance is a good one haha
Pistons in short block for better or worse
Last edited by weinerschizel; 03-21-2021 at 10:04 PM.
03-18-2021, 06:14 PM
NA 6.0 LQ9 Ring Gaps 
I like your err on safe rather than sorry. 
Won't cause any trouble in the meantime though, so it's not wrong. 
