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1991 Honda CRX
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Discussion Starter #1
Just like the title says, whenever I installed any pistons I always do what the ring manufacturer says, like with my JE piston rings you just multiply the bore size by either 0.0045, 0.0050, etc... (depending on what it will be for nitrous, turbo, NA). So for example I did 2.97" x 0.0050 (turbo), and got 0.01485" for the top ring. But I was thinking is that the best way to do it or is there a general number I should shoot for depending on what the setup is? Any advice is appreciated.
 

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I'm running .018 for top and .019 for middle, this is for 75.5mm.
 

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Formerly weebeastie
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Run a happy median of what the ring manufacturer recommends. Ring end gap can help/hinder a setup by a wide margin. To wide and they won't seal properly (trust me on this one, experimenting with the whole "loose is fast" thing, which it is btw, but too loose is smokey and slow) and too tight can bind up the piston in the cylinder
 

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1991 Honda CRX
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Discussion Starter #5
I looked at D16A1 ring end gap (I have a DOHC ZC), and it said 0.006"-0.014" for the top ring, and 0.012" - 0.018" for the second ring. So I guess it's slightly wider, for boost. I guess I should just listen to the manufactuer, seem right. Thanks for the input guys.

The reason I ask is because my engine I built has about 1-2K miles on it and it still sort of smokes (oil smell and blue smoke, only under hard acceleration and if I'm sitting reving it up). I've rebuilt probably 3 or 4 other engines before and I never had a problem. I thought maybe the ring gap was wrong, but it seems okay as is (it's in NA form until I can afford the turbo, so the ring gap is slight wider but should it cause a problem?). The thing that kind of freaked my out was when I took my intake manifold off, there was oil in the intake port and about 2 inches up the intake runners. I have a breather box, so oil can't be getting in the intake that, the valve stem seals are new, and guides are newer (with good clearance). I don't really see how if the cylinder was leaking oil how it could go against the intake air and back into the intake runners. The valve cover gasket is new and isn't leaking, also I broke in the engine the same way I always do.
 

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Sounds like blow by to me, did you assemble the motor? What if one of the rings was damaged prior to running the motor?

How are you "feeling" the gap? I'm using a .18" and .19" and they are hard to fit into the gap, but they do go in just not smoothly. Wonder if I should file it or leave it.
 

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Formerly weebeastie
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Sounds like blow by to me, did you assemble the motor?
This statement is what you are experiencing. I know, I've experienced it myself. Normally two things can cause it. The rings are not gapped properly or the hone used to hone the cylinders was too coarse. What type and grit hone did you use?
 

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1991 Honda CRX
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Discussion Starter #8
This statement is what you are experiencing. I know, I've experienced it myself. Normally two things can cause it. The rings are not gapped properly or the hone used to hone the cylinders was too coarse. What type and grit hone did you use?
Machine shop did it, it didn't look that rough looked like the hones I had before. I figured it was blow-by, but how is there oil in the intake runners? I don't get how it could go into the intake valve, through the incoming air and go up there. If I had a PCV valve and hoses I would think of that, but I don't have them. I've gapped the rings before on other engines and got it down, I just put them into the cylinders, use the piston to press it down maybe an inch or so and may sure it's even, then use my feeler gauge to see what I got.

I do it until the feeler gauge has slight drag on it, like when adjust valve clearance.

Another thing I thought about was that when I got the block it was already bored out to 75.5mm, and I just had to have the machine shop hone the cylinders until the piston-to-wall clearance was what Wiseco said.

One thing I didn't do was check after to see if it was the exact right bore size in each cylinder, just got the ring clearance right and started assembly. They were always good before, and I was in a hurry. Maybe the piston-to-wall clearance is too much? I did notice that once it's warmed up all the way (like after 30 minutes of driving) it's not as bad, but still there. I will be pulling the engine/trans in a month to upgrade a few parts, maybe I should check out what going on in there. Also, compression test is 180psi all the way across (tested about a month ago), same since I rebuilt it. Guess I might do a leak-down test also.
 

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Myself and a few of my buddies ran the old vitara pistons with the outrageous .006 P2W clearance and never had an issue like that so I don't believe it's the P2W, but I could be wrong.
 

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Discussion Starter #10
I did a compression test again and I got 170-180 across the board. Also, the leakdown test showed that: #1 cylinder had noise out of the dipstick, but nowhere else, #2 had the same slight noise from dipstick, #3 had very slight noise from dipstick but also had noise coming out of cylinder 2(head gasket leaking maybe), and #4 had slight noise from the dipstick. So I guess it is piston ring related, the spark plugs were very clean with no sign of oil just light brown color and the pistons (looking down the spark plug holes)had some carbon build up but no oil. I really don't think the rings were damaged when putting them in, I got the ring gap right, clocked the rings correctly, compressed them and very lightly taped them into the cylinder. I had no problems at all.
 

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Discussion Starter #12
Yeah, I followed that for the piston rings, seems like the gaps are good compared to other peoples. I have the JE total seal piston rings and Wiseco pistons. So does piston-to-wall clearance not have an affect on if an engine burns oil? I would think it would, but I guess the rings will seal it.
 

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It does affect blow-by. But the measurement depends on how much power you are planning to make and also depends whether you are using forged or cast.
 

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()*#$(*$
93 Legend L Coupe.
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Too much P2W lets the piston rock too much at the top, which DOES effect the ring seal. However, the oil control rings are usually the least effected by this since there are two of them, and they are very thin and usually packaged more closely to the axis of rotation (the wrist pin) so they aren't subjected to as much angle as the rest of the rings.
 

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Discussion Starter #15
Too much P2W lets the piston rock too much at the top, which DOES effect the ring seal. However, the oil control rings are usually the least effected by this since there are two of them, and they are very thin and usually packaged more closely to the axis of rotation (the wrist pin) so they aren't subjected to as much angle as the rest of the rings.
Okay, that makes sense. But how much is too much P2W clearance?
 

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93 Legend L Coupe.
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Ask the piston manufacturer. GOOD pistons mean LESS clearance. This is one of the reasons why I prefer Wiseco, because they properly taper the pistons so that the clearance gradually increases towards the crown, but, the bottom of the pistons are close fit. (Usually .0015" clearance, I think.)
 

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Discussion Starter #19
Ask the piston manufacturer. GOOD pistons mean LESS clearance. This is one of the reasons why I prefer Wiseco, because they properly taper the pistons so that the clearance gradually increases towards the crown, but, the bottom of the pistons are close fit. (Usually .0015" clearance, I think.)
I found my spec sheet it said suggested clearance 0.0030, I remember it was around 0.0020 and the machine shop said it could just hone it to the 0.0030. Measured at the bottom of the skirt about 1.3" below oil ring just like wiseco said. So if the skirt is the widest part, as the metal expands does the skirt expand at the same rate as everything else?

I was also talking to a few people yesterday, and one guy had this same problem with his LS motor. He had a stock bore size and some forged pistons, he checked the cylinder walls for warpage and it was perfect. And the piston-to-wall clearance was just 0.0010 off, and the machine shop said they could just hone it to specs. He got it back, fitted the rings, and started assembly. He put it in, started it up and broke it in properly. He had it tuned right away and there was a ton of smoke pouring out (blue, so oil). He decided to just drive it a while to see if it would stop when it broke in. It never did, so he pulled the engine to see, he checked the cylinder walls and they were warped I forget how much but it was way over what it should be. He called up another machine shop and they told him that the machine shop might of screwed it up by not using the honing machine right. He had that shop bore it out and rehone it, and it was perfect after that. My engine isn't as bad as his was, but maybe that could be it? That would cause the ring gap to be wrong and piston to wall gap inconsistant.
 

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That's why I recommend NOT using stock bore pistons. I'd rather use a freshly milled bore surface any day, plus I get to choose my P2W clearance with my pistons.
 
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