Piston Ring Gap [Merged 5-7] gapping rings pistons end filing

[SlowSpyder]

thats a machine to size piston rings. If you want to be more precise than plastigauge then youll need to find a dial bore gauge. With a dial bore gauge set to the diameter of the crank/rod journals you can check clearances on more than just one axis.

 

[madscientist323]

i just got my block and crank back from the machine shop.they told me everything is fine.they honed the cylinders.and polished my crank. and sold me the rings and bearings all standard size.they also recommended an assembly lube.i asked if there was any special products or other procedures i need to do or get. they told me to oil the cylinders before i install the pistons and how to move the ring gaps and to put assembly lube on the bearings where the crank touches it. and to torque the rods and mains down and that would be fine.they never said said anything about plasticguage. will it work cause the bottom end is built already i need to find out before i go too far.
thanks
larry

 

[Big Woo]

A simple way to ensure that the piston ring is square in the bore is to use a old clean piston with the second compression ring installed. install the ring into the cylinder, and square it up close to the deck surface, then using the piston (dish side first) push the ring down until the installed second compression ring bottoms against the deck surface. This way you can be reasonably sure that the piston in not tipped in the bore.

For bearing clearance I install the bearings and torque the caps, measure the crank journal diameters, and set a dial bore Gage to the crank diameter. Then using the bore gage measure the installed bearing diameters. The resulting difference is the bearing clearance for that particular diameter.

 

[Red 2g GSX]

I did a quick search of the tech archives and couldn't find what I was looking for. I'm currently rebuilding my engine using stock pistons and rings and the block is bored .020.

Reading the tolerances of the piston ring endgap I noticed that they seemed very tight, .009-.017 to be exact for the top ring. Due to the fact that iron expands .0154 at 700 degrees F, Enough to nearly close the gap. Is 700 degrees an unrealistic temperature for a piston/ring to see under harsh driving conditions? Or what would be a proper ring gap for my application.

 

[Defiant]

What kind of iron, and what alloy is the ring? Go with the ring manufacturer's specs.

 

[Red 2g GSX]

It is Ductile Iron. What stock rings are made of. The shop manual has a range as to where they should be, and its .009 and .017 with a service limit of .003. I’m wondering if I should go with the large or small side of the range. They are at .013 right now. (The way they came). I want to get as close of a gap as I can with out being too small.

 

[Big Woo]

According to my machinery's handbook the linear expansion of cast iron is .00000655 per unit per degree F. so assuming you are starting from 0 deg. F that would be .00000655 X 700 = .004585. If you then subtract ambient from this you get .00000655 X 70 = .0004585. .004585-.0004585=.0041265. (if it is 70 deg. currently)

The handbook I have in front of me right now does not specifically call out ductile iron, but it does list several different types of iron. The total difference in linear expansion between them is .00000006.

I would use the manufacturers specifications as stated, I have never had a problem when following them.

You may want to check the expansion coefficient you are using.

 

[Red 2g GSX]

e linear expansion of cast iron is .00000655 per unit per degree F. /QUOTE]
Well the rings arnt made out of cast iron they are made of ductile iron that has a diffrent expansion rate.

 

[timloomis]

your using 20 over pistons right???you said stock so i hope you mean mistu brand 20 overs.

 

[Red 2g GSX]

your using 20 over pistons right???you said stock so i hope you mean mistu brand 20 overs.

Well what diffrence does it make if its 20 over or mistu or top line?

 

[timloomis]

it doesnt matter the brand.i was just wondering on overbore size is all.

 

[Defiant]

Is the iron in a ring going to expand more in the circumferential distance, or axially across the width of the ring, or both? How does the chrome or molybdenum surface affect expansion?
Rings wear from rubbing along the cylinder wall. The iron is tougher than the aluminum of the piston, so the top and bottom surfaces should see minimal wear. As wear is on the face of the ring and the cylinder wall, ring gap will increase over time. You want to start with as narrow a gap as the specs will allow. Of course, too little will lead to ring binding and breakage.

 

[Big Woo]

Yes I know you said ductile iron, but as I said at the time I did not have the correct thermal data for that alloy. However I did find some listings for thermal expansion on ductile iron. Type D-3 8.6 millionths per deg. F, type D-5.6 millionths, Type D-4 9.1 millionths, and Type D-2 10.5 millionths. Additionaly I did find some other information for you

The following is from the ductile iron society (on line) (yeah I know)
Ductil iron thermal expansion

"To iliustrate the wide range of thermal expansion exhibited by different types of ductile iron, and the influence of nickel content on the thermal expansion behaviour. High expansion types D-2 & D-4 are used to match the expansion of materials such as aluminum, copper, bronze, and austenitic stainless steels. Tpye D-3, with differnt nickel levels, is used to obtain the controlled, intermedate thermal expansion required to match the thermal expansions of a wide variety of steels and cast irons. Types D-5 and D-5B are reccomended for applications requireing maximum dimensional stability, such as machine tool parts, glass molds, and gas turbine housings."

 

[Red 2g GSX]

. You want to start with as narrow a gap as the specs will allow. Of course, too little will lead to ring binding and breakage.

That is what we are trying to do. We want a really small gap because we dont want blow by but we also dont want too small so the ring will close up. We might spray this engine and then the temp of everything will go up. We want as small of a gap as we could. We came up with this .019 on the top, .017 for the sec. Thats how we did it.

 

[NDgsx]

I never run tighter than .017 on the top gap. I ran .014 on a stock 7 bolt once and the rings butted up and I ripped a piston in half, that was fun. It was running 23lbs on a 20g.

 

[gsxitement]

I'm running .019 on top and .021 on the bottom with a .020 overbore a 2.0 with ross pistons. ross sent me a little formula to use with the moly rings i have, though i forgot what it was. i really hope you're running .020 over pistons in this motor, as that kind of clearance to the cylinder wall would be horrific.

 

[diambo4life]

RTFM & gap on the looser side.

 

[90TSIwhite]

Hey guys, My compression is hovering around 90 ish (running on Stock boost so it should be fine). What do I have to do to this motor when I replace new piston rings? Anything I should do? thanks!

 

[VelocitàPaola]

Unless you're upgrading the piston as well, you won't have to do anything to the block other than honing the walls (and thats only really necessary if the walls don't have much of the original cross-hatching left on them).

I saw a complete guide to overhauling the 4G63 before, but I can't remember where it was... I think VFAQ though. If I can dig it up, I'll post it.

 

[1993eclipseGS]

Um, If you did a compression test and the results came up , 90 across the board, Then you got serious problems. 130 is about the service limit..

 

[1BADASSEVO8]

Sweet info in here

 

[iwantawd]

I'm running .019 on top and .021 on the bottom with a .020 overbore a 2.0 with ross pistons. ross sent me a little formula to use with the moly rings i have, though i forgot what it was. i really hope you're running .020 over pistons in this motor, as that kind of clearance to the cylinder wall would be horrific.

arent you supposd to go down in gap from the first to second rings? less heat less expansion?

 

[gsxitement]

arent you supposd to go down in gap from the first to second rings? less heat less expansion?

no. you want to keep a tighter gap on top for this reason. if you run looser on top and tighter on the bottom, compression will get stuck inbetween the rwo rings causing "ring flutter". flutter is when you get compression waves in the space between the two rings, and they do exactly that, they flap around leaking compression, and in worst case scenarios, damage to the piston and cylinder wall. and i'd be running more heat cause more boost, bigger cylinder diameter, therefore more cyllinder pressure. hope that helps.

 

[sb7775]

You are wrong, u want a tighter gap on the oil ring( second ring). I have built a few 4g63 in the past year and i use .022 on the top and .018 on the second ring. This is a little on the loose side and they will chatter( use .020 and .016 to reduce chatter) a little more than normal. As far as using .009-.017 thats a little tight and might have a problem with them binding up after they expand a little. There is a formula i us and it matters if it's forced induction or naturally aspirated. I'm at work so I'll post it up later. Just to let u know i used weisco pistons and i believe they have the same type of rings as the stock ones.

 

[gsxitement]

uuuummmm, the oil ring is the THIRD ring down, with the scraper inbetween. so you have the top ring at .019", the second ring .020" and then the oil scraper. you want to have the second ring looser then the top ring. why does no one understand that you want to keep the compression on TOP of the piston....not on the side of it. i've been building motors for a while...including some nascar engines, and i can guarantee you want to have the top ring tighter then the bottom. and chatter and flutter are different things i believe. also, i'm using ross pistons with moly rings. you run tight on top to keep the compression up, but with the SECOND ring looser any blow by you might get is quickly released to the crank case with out putting any resistance on the top ring on the way down. you don't want chatter or flutter, so what you are saying is you are putting motors together knowing that there is going to be chatter. not a good strategy my friend. if you're building motors like that...i'm glad i don't have one of your motors in my car.