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Old 10-21-2007, 11:36 AM   #1
afmardve
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Default Piston ring end gap advice

I'm using 100mm cp pistons and i set the top ring gap to .025"
I started on the second rings and grinded more than i wanted .030" insted of .027"

CP recommends

top ring .024" - .027"

Second ring .027" - .031"

I know it's within the limits but am i going too see alot of blowby/oil consumption?

I run 20 to 22 pounds of boost.
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Old 10-22-2007, 07:29 PM   #2
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No you won't. Thru the gap you limited by the speed of sound, gap is smaller component than circumference blowby. CPs specs are very conservative.
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Old 10-22-2007, 08:43 PM   #3
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Thanks for the response!
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Old 10-27-2007, 04:17 PM   #4
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I just got a set of CP pistons... Should I use OEM Rings or CP? If OEM rings are used... What specification for gaping should be used?
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Old 10-27-2007, 06:17 PM   #5
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when you say gap them what exactly do you mean ??
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Old 10-27-2007, 07:09 PM   #6
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Carefully insert the ring into the respective, lightly lubed cylinder, let it expand tight to the walls, push it down a prescribed distance (using a piston so that it is correctly oriented), then measure the gap between the 2 ends. Remove it, file, re-measure, re-file if necessary, re-measure, done.
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Old 10-27-2007, 07:18 PM   #7
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I always re-measure until I have the ring gapped exactly as I want it...take baby steps
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Old 10-27-2007, 07:52 PM   #8
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Very true - we're talking thousandths here.
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Old 10-28-2007, 05:44 AM   #9
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Much better too wide than too narrow. If the rings butt you kill the engine!
Also take care that there are no burrs on the gap when you finish as they can result in sticking rings.

Larry

Last edited by hotrod; 10-28-2007 at 05:51 AM.
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Old 10-28-2007, 09:55 AM   #10
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wouldn't 100mm piston rings already have this gap established from the factory?

or are both rings the same?
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Old 10-28-2007, 11:37 AM   #11
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"Pre gapped" rings are usually gapped a bit too wide, so parts hangers don't butt their rings and lose engines. If you want the gap where you want it, you get file-fit rings.

Nothing mass produced this cheaply is super precise. Plus, the gap goes up by roughly 3x (pi times) the bore increase, so if your bores are .001" larger than their expected target, then the gap will be .003" larger. That just ate up the whole tolerance...
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Old 10-28-2007, 11:42 AM   #12
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Quote:
Originally Posted by noisycricket View Post
"Pre gapped" rings are usually gapped a bit too wide, so parts hangers don't butt their rings and lose engines. If you want the gap where you want it, you get file-fit rings.

Nothing mass produced this cheaply is super precise. Plus, the gap goes up by roughly 3x (pi times) the bore increase, so if your bores are .001" larger than their expected target, then the gap will be .003" larger. That just ate up the whole tolerance...
I guess its like "drop in" pistons... if you don't check it...you just gota pray that it works right !
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Old 10-28-2007, 11:46 AM   #13
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Nothing ever is drop in. Measure twice, cut once.

Or measure twice, make phone calls asking what they were smoking, wait two weeks or more...

We just recently got a set of rings in for a *common* large bore engine. The rings in the package were about a 1/4" rattle fit in the bores. Someone f'ed up when they packaged them. To the Bat-Phone!
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Old 10-28-2007, 11:55 AM   #14
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Quote:
Originally Posted by noisycricket View Post
Nothing ever is drop in. Measure twice, cut once.

Or measure twice, make phone calls asking what they were smoking, wait two weeks or more...

We just recently got a set of rings in for a *common* large bore engine. The rings in the package were about a 1/4" rattle fit in the bores. Someone f'ed up when they packaged them. To the Bat-Phone!
1/4'' ?? might be a little outa spec eh ?
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Old 10-28-2007, 02:25 PM   #15
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Quote:
1/4'' ?? might be a little outa spec eh ?
No those were just their "low friction" rings !

( J/K)

Larry
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Old 10-28-2007, 02:31 PM   #16
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I think it was putting rings for a Chevy 400 (4.125" bore) in the package for a Chrysler 400 (4.340" bore).

Checking is goood....
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Old 08-18-2008, 12:44 AM   #17
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I'm about to set the ring gaps too on my 100mm CP Pistons. I decided to do this myself so I know that it was done to the CP's specification, procedure, and orientation. Does anyone know which rings are which? Top, 2nd, oiling rings? I also noticed one of the rings has half of the ring end bent up. How does is this orientated? I bought a piston ring filer (a manual one that you have the ring up against the stops and a diamond disc with a lever you turn to grind the ring end) and a feeler gauge. I'll be setting the top ring to .026, 2nd ring to .028 and the oiling ring to .015. Do I need a piston ring compressor just to check the gap clearance in the bore or can I just compress the ring by hand and use the top of the piston to push it down into the cylinder bore? I know to deburr the ring ends so it doesn't scrape the cylinder walls. I also was told to just grind one side of the ring end since the untouched end will be perfectly 90 degrees square to the top and bottom surface of the ring. Anyone with pics helps also.

I just checked the instructions that came with the rings, so I guess I'll answer some of my own questions.

The 12 and 6'clock position would be the centerline of the wrist pin.

The top ring is the copper colored ring with a bevel on the inside. This one should have the bevel facing up and the gap located at the 8 o'clock position with 12 o'clock facing the engine front.

The second ring is black and has what they called a taper hook groove on the outside edge of the ring and this one should always face down with the gap at the 9 o'clock position.

The oiling ring consists of three rings. These rings are thinner than the top and 2nd ring. The top ring is black, the middle ring is copper colored with a hex shape going up and down throughout the diameter of the ring, the bottom ring is black also but one end has half of the end bent up. I read on another thread the bent up portion goes into one of the hex valley of the middle oiling ring.

Also when setting the gaps, should I mark each set of rings I measured in each specific cylinder bore just in case there where slight variances in bore diameter?

Let me know If I have anything wrong, although I'll also give CP a call tomorrow to verify this.

Last edited by methaddict; 08-18-2008 at 01:16 AM.
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Old 08-19-2008, 10:43 AM   #18
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Do the rings for each cylinder. I go ahead and put them on the piston that the bore has been fitted to and then nothing gets mixed up. Then when I put the pistons in I recheck the gap orientation. I don't like to wind the rings on the piston as it might put a twist in it. I use a ring expander and only spread them as much as needed.
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Old 08-19-2008, 10:59 AM   #19
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And use a SHARPIE to mark the front of each piston for # and orientation for installation!
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Old 08-19-2008, 11:44 PM   #20
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Well I gapped the rings today. I'm not sure how the cylinder's are numbered but I started out with front passenger side. I placed the top ring in the cylinder and with the piston pushed it down passed the first ring land gap, then measured with a .026 feeler gauge. Of course it didn't fit in there so I took it out then proceeded to place the ring end against the stops of the manual ring filer. I bought the Summit version model #SUM-906795 from carshopinc.com for $31.95.



I proceeded to grind one side of the ring since the untouched side is already perfectly square to the top ring surface. The top ring is a harder steel so I started with 5 turns at a time the put it back in the cylinder at the same depth and checked. I know it isn't much but I didn't want to go too fast since I was dealing with thousand's. It took several times grinding and checking then finally the gauge slipped in snug but now so much I had to force it in there.

Then I did the same with the second ring. Mike at CP said to be careful with the second ring since it's cast iron and prone to breaking if pulled apart to much. This material is alot softer too so I found that about 6-8 turns did the job to get it at .028"

I placed upper and lower oiling rings into the cylinders by lightly pushing them with the piston as deep as the oiling ring land on the piston was. Measuring with a .015" feeler gauge and noticed it didn't need any grinding. It was actually slightly larger than .0015" but Mike said .015" is the minimum gap. Then with the oiling rings there is one with one side where half of the outer edge is bent up. Mike said this goes into a groove on the upper portion of the oiling ring land that keeps the ring from spinning. The middle oiling ring with peaks and valleys hex shaped ring also do not need to touched.

After setting the gaps on the set of rings for each particular cylinder I measured I made sure to deburr the corners and edges of the ring ends so that it wouldn't score the cylinder walls and also that the ends would not catch in the ring lands with extended burrs.

I then inserted the rings into there perspective ring land gaps. The top brass ring had to have the bevel on the inside edge facing up with the gap at the 7 0'clock position with 12o'clock pointing towards the front of the motor. The second ring had to have the taper hook groove on the outer edge facing down with the gap at the 9 o'clock position. The oiling ring with the bent portion goes into the groove on the upper portion of the oiling ring land gap. Then goes the hex shaped middle oiling ring and then the bottom oiling ring with this gap at the 10 o'clock position. It takes a little wiggling finessing to get the three oiling rings in their gap, but it will and must sit in there with all the outer edges of the rings flush to each other and to the piston side ring land surface.

I marked each piston according passenger front, rear or driver's side front or rear and also to the set of rings placed in them that were measured to each particular cylinder with an arrow pointing towards the front of the motor. That arrow line is also the same line to the wrist pin centerline.

I took it upon myself to set the gaps so I know that everything was done to CP's specs and procedures.

Last edited by methaddict; 08-19-2008 at 11:56 PM.
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Old 10-15-2010, 07:51 PM   #21
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^ thanks for the great info.

quick question. Is there any way to do the grind the rings without the tool. I just don't feel like buying another tool I'm going to use only once...
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Old 10-15-2010, 08:25 PM   #22
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you can use a file. Just make sure as others have said that you go slow and make sure that the two ends of the rings meet flush and flat as well as make sure there are no burs on the ends of the rings. Nice and smooth is good
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Old 10-15-2010, 09:40 PM   #23
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Thanks for the help. I have a small thin finishing file I'm planning on clamping in a vice and use for the rings. Is there anything I can do to ensure that end gaps come out square?? I have about .006" I need to take off.

And not to get off topic, but do I need a ring separator or can I just stretch the rings by hand to install?
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