PapaSmurf Posted June 1, 2013 Share Posted June 1, 2013 (edited) Honed my cylinders and started measuring ring gaps and they seem really big compared to FSM Old top ring gap was at .80mm New top ring gap is at .35mm New bottom ring gap is .50mm This is with std size itm rings. So do I need a new set of rings maybe ten thousandths over sized and filed down a bit or will these work without hurting my compression and increasing oil consumption too much? Fsm states a minimum top ring gap of .25mm but I'm not sure about the maximum/preferred obviously its best to stay close to the minimum spec but my wallet hurts. Edited June 1, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 1, 2013 Author Share Posted June 1, 2013 Forgot to mention this is for a n/a f54 with flat tops not a turbo which would nessicate larger gaps Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 1, 2013 Share Posted June 1, 2013 Monroe's "How to Rebuild..." book says top ring should be "OK" at .3 - .43mm for an 88.9mm bore, recommends a target of .36 mm.. Second rings should be .05mm less since they run cooler. Page 121. BUT - then he says to follow the ring manufacturer's recommendations. So if you have a brand name (ITM) maybe you can find a spec. for mm gap / mm bore. Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 1, 2013 Author Share Posted June 1, 2013 (edited) The itm instructions are hurting my head. It says gap should be .003" to .004" for every inch of cylinder diameter and that's all it says so they seem to imply that top and bottom gaps should be the same which makes no sense because these bottom rings have a larger gap than top. But according to their math 3.5in bore needs .010" to .014" or ~ .25 to .35mm which would fit the top ring gap barely Are you sure the second compression ring gap should be tighter? I can't understand why they would be gapped larger on this kit and they didn't specify a different gap size Edited June 1, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 1, 2013 Author Share Posted June 1, 2013 (edited) FSM says .30mm for second ring which would be a larger gap by .05mm why the discrepancy between this and your how to rebuild book? Seems like my bottom ring gap is going to be out of spec and my top is on the ragged edge according to the itm instructions I don't think I can trust itm since they gave me two different sizes of rings and one spec Edited June 1, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 1, 2013 Share Posted June 1, 2013 (edited) I checked my "How to Modify..." book by Honsowetz and he says .017" (.43mm) top, and .014" (.36mm) second. But Monroe and Honsowetz worked together, I believe. It was written in a different style though so it doesn't look like a cut and paste. I'm just repeating what I read. The 1976 specs. at the end of the Engine Mechanical chapter says: Ring gap Top .23 to .38mm Second .15 to .30 Oil .15 to .30 Honsowetz and Monroe recommend looser than factory spec. You have a dilemma. Edit - I see that the 1981 spec. is a little bit different, but not much. What is the diameter of the bore (after honing)? Weird though, that someone would ship rings with different gaps. Maybe they're reboxed returns. Aggravating to get bad parts that you can't evn modify to work. Edited June 1, 2013 by NewZed Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 1, 2013 Author Share Posted June 1, 2013 OK so my top gap is good enough but a bit wider than optimal and my bottom ring gap is horribly larger than it should be I guess I'll order an oversized set and get out the file. Im Still confused about why itm packed smaller bottom compression rings Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 1, 2013 Author Share Posted June 1, 2013 (edited) Oops my math was flawed 86mm unbored cylinders with only slight wear from use and a hone is 3.25in not 3.5in would call for a gap of .00975 to .013" according to itm which would make my gaps even larger relative to what's called for. I hate these conversions If I can find a ruler i'll measure to make sure nobody bored it before i got to it. It had std size rings in it but that doesn't mean anything... The 81 spec is different than the 76 because it has a larger bore. Edited June 2, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 2, 2013 Share Posted June 2, 2013 Umm... I get 86mm = 3.385". Maybe your 3.25 is a typo for 3.35? Your gaps match 3.35". The factory range is in the back of the 81 FSM. Looks like your top ring is good and the second ring too loose. Are all of the second rings the same? You have six of each right? 76 (N42 block) and 81 (F54 block) are both L28's with the same bore and stroke. Pistons are different. The last few pages of the Engie Mechanical chapter has all of the spec. with ranges tabulated. Good luck. Looks like fun even witth the problems. Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 2, 2013 Author Share Posted June 2, 2013 My conversion may have been off yes all the bottom rings measure the same and oops a 76 is a 2.8l too for some reason my tired brain plugged in an l26 there haha yeah I guess I'm gonna be buying an oversize set and modifying them or maybe I can scrounge up enough to get her bored ever so slightly and start all over to be sure these cylinders are true gap is tighter above the stroke of the rings by a few thousandths which I don't like. I'll probably cheap out and just file down oversized rings and make it go Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 2, 2013 Author Share Posted June 2, 2013 (edited) One last question I'm reusing these stock pistons and rods should I have the wrist pins replaced or are they usually good to go? They move freely on the axis they should but there is a very slight wobble in the other direction. The rods/pistons I pulled from my n42 block behave the same way Edited June 2, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 2, 2013 Share Posted June 2, 2013 Nissan Rings usually didn't have this problem. American Manufactured rings UNIVERSALLY needed filing out of the package to fit ANYTHING.. The reason your old rings had a big gap is RINGS WEAR in these engines, NOT the bore! It was designed and engineered for you to, at service interval, be able to use stock replacement parts for as long a possible. Do not overbore the cylinder. You deglazed them, did you get an actual measurement on the bore afterwards. Deglazing does NOT require oversize rings, and 0.010" oversize rings is a bad idea. Don't do it. You are obsessing on all the trees around you, and can't find the forest. The specs you gave are for all intents and purposes identical. People will tell you your ring gap is SAFE LARGE. Obviously if you ran at 0.80mm gap, then running new rings with good tension at that range would give similar results. TENSION against the wall for a given bore is what you are interested in, and the GAP is for thermal expansion. The top two rings are what is important. There are people who have run without the third ring...but let's not go there. If you run a tight gap on your first two rings, be prepared for a rebore eventually. Not enough clearance will have the ring ends touch, then continue expanding against the wall where scoring eventually occurs...or ring breakage. I would NOT say it's best to run near minimum spec, ESPECIALLY in an engine which may be used for competition or run hard. The heat will cause more expansion and binding will occur. Think of this using some common sense: how long did it take your current engine to go from .25 to .80mm gap? Now, you are fretting about gaps that are midrange. So what are we talking here, 100,000 miles to get to replacement point again? Or 200,000? I'd shoot for midrange if not upper end of all the gap clearances. Wider is better. You make them tight, you can ruin the engine. Make them big, and your gaps get big as the rings wear over the course of the next 200,000 miles. Is that really going to be a problem for you? Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 2, 2013 Share Posted June 2, 2013 If filing ring gaps up to size was such an uncommon procedure, the "Ring End Gap Filing Tool" would never have been invented. Look in Summit Racing, it's there for a reason! Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 2, 2013 Author Share Posted June 2, 2013 (edited) Are you saying my second gap of .5mm is good enough? This engine is a stranger to me I got it outta the yard so I really don't know anything about its oil consumption or mileage. According to the books the second ring gap is too large so I assume I need to buy an oversized kit to file down - tony you're confusing me ;p I can use these top rings at least less filing required Edited June 2, 2013 by PapaSmurf Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 2, 2013 Share Posted June 2, 2013 It is much better to have a larger gap on the top ring than the spec calls for. The top ring gets the most amount of heat from the combustion chamber. Less so for the second ring as it can be a tighter gap. If the top ring butts together when at optimum temperature, that will likely damage the piston ring lands. Ring gap Top .23 to .38mm equals .009" to .014 which is a little to tight. Set is at .016" to .018" to give it leaway to expand and NOT butt the ends together. Second .15 to .30mm equals .006" to .012" which at .012" is at the minimum or give it slightly more. Oil .15 to .30mm equals ..006" to .012" which is likely OK Quote Link to comment Share on other sites More sharing options...
Lazeum Posted June 2, 2013 Share Posted June 2, 2013 If it could make you feel better, I've filled my rings to get slightly bigger gaps than what's written in FSM. I've followed T. Monroe book if I remember well. Rings orientation is also different according to which book you refer to; FSM and "How to rebuild...." are not in agreement. +600mi after rebuilt, I haven't seen any oil consumption occuring that needed me to add some oil to the engine and I'm driving it hard - a WOT as soon as I can (but below 5000rpm). Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 2, 2013 Author Share Posted June 2, 2013 So .5mm on the second ring is OK? Or would I be better off getting an oversized set and filing them down? Its the $50 question Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 2, 2013 Share Posted June 2, 2013 .5 mm = .020" which is OK for the second and first rings. Don't need an oversized set of rings. Set ring end gap of both the top and second rings to .5mm i.e. .020" as long as the top ring has enough gap so that the two ends of the rings do not butt up to one another at maximum combustion chamber heat. As a rule of thumb, the top ring that gets the most heat should have the LARGEST gap. Then slightly less for the second ring. Quote Link to comment Share on other sites More sharing options...
PapaSmurf Posted June 2, 2013 Author Share Posted June 2, 2013 So why not just leave the top ring at .35mm and use the bottom at .5mm the top is in spec and according to the books is actually on the large size if I just give it a proper break in that gap will probably expand quickly due to wear in which I assume is accelerated in the beginning running against that deglazed surface. I don't intend to take this to the track anytime soon I'm going for optimal compression and minimum oil consumption as well as the longest possible time between rebuilds. If .35mm is in spec for top and .5 is good enough on bottom that's what I'd rather run. Is there any reason the second ring HAS to be gapped tighter than the top? Or do you really think that the top ring gap is too small at .35mm? Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 3, 2013 Share Posted June 3, 2013 (edited) We can not force common sense. I know engineers who jump because "seal air pressure too low" at 20psi into the panel, when we normally have 40.... They are amazed when the machine starts just fine, and loads up giving the 40psi eventually... Same for these ring gaps. Buying oversized rings is NOT how you get less ring end gap. It is, however a good way to screw up your cylinder bore and pistons... The "wear" you are talking and fretting over will take 100,000-200,000 miles to happen... You are talking about a .15mm disparity... Get over the hump, dude! Or take your ring set back, complain to the seller, and get another set, likely with the same clearances. Repeat ad nauseam until you: 1) find a set where you are happy with the fit. 2) realize you are wasting your time and just assemble it and find out you wasted days worrying over nothing. 45-35-35 or 18-14-14 if you prefer. Compression is the important thing. 0.005" "too much" ring end gap on an oil control ring (which is going to eventually stick ANYWAYS) is nothing to blink an eye over. Edited June 3, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
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