Key Questions to Ask When Ordering Piston Wear Ring

May. 26, 2025

How To Choose the Best Piston Ring for Your Application

By Mark Houlahan 6/12/ Share Add Article To List

Piston Rings Have a Tough Job, Choosing the Wrong Ones Will Make That Job More Difficult

There has been a lot of advancement in piston ring technology over the last few decades. Piston ring materials, coatings, edge profiles, and even ring thickness have all seen great improvements in oil control, sealing, and wear. Of course, these enhancements in ring technology only work when they are used in the proper manner. A basic street engine built for a cruiser will use a much different ring package than a 1,000 horsepower turbocharged engine. There are many decisions to be made when choosing the right set of piston rings for your engine build. While some piston kits include rings, often the higher you go up the performance ladder the rings become a separate purchase decision.

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There is no one “best” ring package on the shelf. Determining the engine’s use, power level, compression, type of fuel, and of course any power adder, are all factors in choosing the proper ring package. The decision should factor in proper sealing, wear, and durability so that your engine produces maximum power with minimal blowby and proper oil control, all with a ring package that will wear appropriately for the intended use with minimum friction loss. What follows is a breakdown of modern piston ring materials, ring types, coatings, and more that will help you determine what type of piston rings are indeed best for your build. If you’re having the short block assembled by an engine builder, then obviously we suggest following the ring package guidelines that they have for your reciprocating assembly.

What Are Piston Rings Made Of?

When it comes to piston ring material types there are a few ring materials no longer used or only used in specialty applications now. Currently the most common piston ring material types for automotive engines are cast iron, ductile iron, and steel. While steel does have the highest tensile strength, don’t count out cast iron or ductile iron rings for the right applications. For example, if you’re performing a basic “hone and ring” job to drop back into your daily driver there is no need for the added expense of ductile iron or steel rings.

What Is the Benefit of Different Piston Ring Materials?

Cast Iron: Fragile piston ring material properties, best used for stock engine builds due to low tensile strength. Low cost, great option for a budget rebuild.
Ductile Iron: Stronger piston ring material properties with double the tensile strength of gray iron rings. Better option for performance engine builds.
Steel: Better still in tensile strength and fatigue strength over ductile iron rings. Better option for boosted and nitrous applications. Used in narrow ring width applications for better sealing and less blow-by.

What Are the Different Types of Piston Rings?

Now that we’ve discussed piston ring material composition it is important to explain how many types of piston ring are commonly used. Modern pistons feature three different types of piston rings. Starting from the top of the piston you have the top compression ring. This is the primary ring that seals the piston to the combustion chamber wall. Below this ring you have the second or intermediate compression ring. This ring backs up the top ring by sealing the combustion chamber while also aiding in heat transfer and scraping oil from the cylinder wall. Finally, you have the oil control ring at the bottom, which has the piston ring function of controlling the amount of oil delivered to the combustion chamber wall for lubrication and cooling. Know that you can have different top and intermediate compression piston ring material selection in various ring packages, such as a ductile iron top ring with a cast iron intermediate compression ring.

Top and Intermediate Compression Ring Types:

Conventional Ring: Top and 2nd rings with gaps that can be set for various uses (N/A, nitrous, etc.). This style of ring is often file-fit by the engine builder to a specific final specification. See the section on ring gaps below for more details.
Gapless Top Ring: Provides increased horsepower and crankcase vacuum, used mostly on N/A engine applications to help fill the cylinder due to better ring seal. You want the gapless ring as close to the intake valve as possible. We offer Total Seal Gapless rings for your engine project build.
Gapless 2nd Ring: Preferred ring for turbo or supercharged applications as well as boxer engines. With a turbo or blower helping to fill the cylinder the gapless 2nd ring is utilized to keep heat and contaminants out of the oil pan. A gapless top ring can be used in boosted applications as well but is certainly more effective in N/A setups.
Gas Ported Top Ring: Increases horsepower by improving ring seal. The gas ported top ring features lateral gas ports machined into the top of the ring, which adds the benefits of gas porting to any piston. Works for both street and competition engines.

Oil Control Ring Types:

One-Piece Oil Control Rings: Rarely used today, they are like a compression ring where the tension against the cylinder wall is taken from the ring’s cross section. A U-shaped design, the groove in the center moves excess oil back to the crankcase. Available with various ring profiles.
Two-Piece Oil Control Rings: A coil spring is placed into the oil ring groove of the piston first and a special oil control ring is then placed over the coil spring. The spring provides the tension of the oil ring to the cylinder wall. Available with various ring profiles.
Three-Piece Oil Control Rings: A pair of support rails with an expander between them for rail tension. The expander pushes the two rails, which act as scrapers, against the cylinder wall to remove engine oil and return it to the crankcase. This is the most used oil control ring design today.

Oil Ring Tension: When ordering piston rings, you often have the option of choosing the type of oil ring tension you desire for your engine build specs. You can choose from standard tension, low tension, and high tension oil ring offerings.

Standard Tension: Varies by oil ring thickness, so a standard tension 3/16 oil ring is not the same tension as a standard tension 3.0mm oil ring. The thicker the oil ring, the higher the standard tension for that size.
Low Tension: Also varies by oil ring thickness but does not always drop below the next size down in oil ring. For example, a low tension 3/16 oil ring is 15 lb/ft while a standard tension 3.0mm oil ring is 12 lb/ft. Utilized correctly, a lower tension oil ring increases horsepower and extends cylinder bore life.
High Tension: Also varies by oil ring thickness, but inversely. For example, a high tension 3.0mm oil ring is 15 lb/ft and a standard tension 3/16 oil ring is 23 lb/ft. High tension oil rings are recommended for boosted and nitrous applications to reduce motor oil related detonation.

What Are the Different Types of Piston Ring Coatings?

Piston ring coatings are applied to the face of the ring (the side of the ring where it contacts the cylinder wall) to improve durability and lower friction. These coatings also provide faster break in. No longer do you have to drive 500 careful miles to break in your piston rings. With modern coatings they can break in quickly and provide a long service life. Ring coatings do affect piston ring price a bit, but we feel the added expense is well worth it for a modern performance engine build.

Uncoated Cast Iron: Very soft for an easy break-in but doesn’t offer good durability.
Hard Chrome Coating: Very hard for good durability but is very difficult for break-in with lower scuff resistance.
Plasma Moly Coating: Rings bed in faster with higher scuff resistance, normally use a ductile iron base ring. Not for use with nitrous applications as the moly coating can fracture and break off the face of the ring.
PVD Coating: Physical Vapor Deposition coatings provide a lower coefficient of friction, better adhesion and increased hardness compared to other coatings. Ideal for boosted and nitrous applications.

Are There Different Types of Piston Ring Profiles and How Are They Installed?

When we talk about piston ring profiles, we are referring to the outer edge of the ring that seals to the combustion chamber wall. Different profiles, or faces, are used for varying reasons, including increased sealing, greater oil control, and more. These ring profiles are often hard to see clearly, which is why all manufacturers mark their rings with a dot or the word “top” on the ring face so that the ring profile can be installed in the proper direction. This does not mean it is the top ring on the piston, but the orientation of the ring itself. Always install rings with the dot or “TOP” facing up.

Square Face: Seals well but has higher wear, eventually wearing to a barrel shape, used on top ring.
Barrel: Best sealing properties with longer life/lower wear, used on top ring.
Taper Face: Used on 2nd compression ring, usually 2-4 degree taper of ring face to help scrape oil off cylinder wall.
Napier: Groove machined under 2nd compression ring to improve oil removal from the cylinder wall.

The top compression ring will usually be a barrel face, while the second ring will often be a taper face or Napier face ring. The reason for the different profiles is to optimize the performance of the ring for the job it must perform.

How Do I Know What Size of Piston Ring I Need?

A piston ring’s diameter is directly proportional to the cylinder bore. If an overbore of the cylinder has occurred, then the proper piston ring size (and piston) must be ordered to properly fit. For example, a standard 4.00-inch bore that has been machined .030-inch to remove wear or wall damage will now require both 4.030-inch pistons and rings. A file to fit ring is +.005 over the bore size to allow the fitting of a tighter end gap in performance engines.

What Is the Standard Piston Ring End Gap?

End gap is usually specified by the ring manufacturer, but most fall back on the general rule of thumb of .-inch of ring gap per inch of bore diameter (for example, a 4.00-inch bore naturally aspirated engine would take a .018-inch top ring gap). Second rings are usually gapped at .006-inch per inch of bore. Again, for a naturally aspirated engine. The goal here is to have enough gap that as the rings are exposed to the combustion chamber’s heat that the ring end gap provides enough room for ring expansion without the ring ends butting up against each other, which will cause ring scuffing and even breakage. A piston ring end gap filing tool is the proper way to file both ends of the piston ring equally.

Boosted applications require larger ring gaps due to the increased combustion chamber temperatures these engine combinations see. Finally, some ring manufacturers spec the second ring to be gapped between .005-.010 more than the top ring to aid in preventing gas buildup between the top and second rings. Ultimately, we suggest going with the ring manufacturer’s specifications, for the ring material you’re using and the application. Be sure to watch our video on piston ring gap placement (clocking) for more details on proper ring installation.

Are Thicker Piston Rings Better?

Traditional piston ring sizing has been in fractional inch measurements. You’ll typically find top and 2nd rings in 5/64-inch, 1/16-inch, or .043-inch sizes, with oil rings typically in the 3/16-inch size. Modern engines moved to metric ring measurements of 1.5mm to 1.0mm for top and second rings with 3.0 to 2.0mm oil rings. These ring thicknesses have been the norm for decades, but moving to a thinner ring package has shown several advantages. With custom pistons, you’ll find types of piston rings as thin as .5mm (.020 inch). The thinner rings provide some great benefits, including increased horsepower and torque while reducing weight and compression height. Significant power gains can be had from utilizing thinner, modern rings and piston designs. While it has been more critical to use the proper piston ring installation pliers on thicker rings, we highly recommend that you use the same tool on thinner rings as well. The only types of piston rings that are OK to be “spiraled” onto the piston are the oil ring’s top and bottom rails. Never spiral the compression rings onto a piston.

As you can see, piston ring materials and piston ring function are just as critical to a successful engine build as the camshaft specs, cylinder head flow, and other major engine building decisions that you must make. We hope this guide has helped you understand what your piston ring options are and what is best for your build. If you have any questions on the types of piston rings your engine build should use, simply give our techs a call for expert assistance or reach out to your engine builder.

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10 Questions You Should to Know about Piston Wear Ring

Author: becky

Mar. 17,

Total Newbie Questions About Changing Piston Rings - Miata Forum

Third gear
Join Date: Oct Location: Baltimore, MD Posts: 784 Total Newbie Questions About Changing Piston Rings Since I have to put a new short block in my car, I want to get the engine in tip top shape while engine is out of the car and accessable. I've bought a new used short block from a low mileage 96 or 97 Miata. The bores are supposed to be really clean with no scores or the like. I want to change out the piston rings so I can get nice even compression since this engine will be FI.

A friend of mine is going to lend his expertise and his tools to help me with the honing process. That part is taken care of. Here's my newbie questions...

1. I called Rosenthal Mazda to get a quote for a ring kit. The first thing that was asked was whether I wanted stock, +25 over, or +50 over. Since I plan on only doing a light honing and keeping the stock pistons, is there any reason to order any size other than stock?

2. Is there any way to test the compression before putting the engine in the car? Do I need to or can I assume that new rings will most likely give me good numbers? I would rather fix a problem while the engine is still on the stand rather than in the car.

3. Is there any other advice you can give a newbie such as myself?

I do have the old block to fiddle around with while I wait for the new short block and piston rings. I plan on taking everything apart, honing the bad block, and putting everything back together just for practice.

Thanks in advance. Sixth Gear
Join Date: Jul Location: Mi, USA Posts: 8,832 Cylinder honing must be done correctly, and to the correct finish, for the type of rings being used. Along with this, the bores must be straight, round, and correctly sized to the rings and pistons. If not, wear and/or sealing problems will result. Adding a turbo or supercharger makes this even more critical. Unless you know your friend's hone is appropriate for this job, and that he? knows what needs to be done and how to do it, you would be well served to have this part of the job done by a qualified, experienced, professional. Because you are adding a supercharger you may want to use higher quality rings. Depending on boost, pistons may need up-grading as well.

1. Don't order any rings until the bores in your block have been inspected and measured.

2. You could do a compression or leak test, but until you have successfully broken in the rings the results of the tests are of limited value.

3. I don't mean this to sound rude, and I'm not trying to discourage you, so please don't take it that way. That said, you obviously know very little about what needs to be done, checked, and measured; and how to do it. While people in your position can and do recondition engines, a successful end result will happen only if a lot of things you are unaware of happen to be ok as is. I suggest you read everything you can get your hands on, and get all the help you can get from the most skilled and knowledgeable motorheads you know.

Good luck......Al English First gear
Join Date: Sep Location: Hampton, VA Posts: 73 Cylinder honing is really not that difficult. The main concerns are cylinder wear and if oversized pistons are required. If the hone marks remain from the original assembly, you probably (almost certainly) don't need oversized pistons and accompanying rings. If there is a cylinder ridge, caused by wear then the engine might likely need .025" (+25) dia oversized pistons and rings. They make measurement tools specifically for measuring the engine cylinder diameter.

Rings will not show good compression until they have been 'seated'. Sometimes, with chrome plated rings, this can take awhile because they don't wear much. Steel rings seat quicker but don't wear as well.

The most important part of installing piston rings is to put the ring in the cylinder and measure the end gap. The end of the piston can be used to keep the ring square in the cylinder for this measurement. Without proper ring gap the rings will never seat, or they will break when the engine gets hot.

The best advice I can give is to find (borrow, beg, or buy) measurement tools and learn how to use them. Don't trust 'Bubbas machine shop' to give you an engine you can just assemble. That said, if the clyinders still show hone marks, I doubt you can do much to improve the piston rings in that used engine. Just my opinion of course.

Good Luck!

Stan Third gear
Join Date: Oct Location: Baltimore, MD Posts: 784 I don't have to beg for the tool, thank gawd. The head of my employer's truck repair facility is loaning me all of the tools I would possibly need. Bearing mics, bore mics, honing tools, ring compressor. The only tool I will have to buy is the ring expander and that's because one of the machnics misplaced it.

So if I can still see hone marks in the cylinders of the used block, I should be good to go without honing and resringing? I don't know what mileage is on the used block other than the guys at Planet Miata are tearing down a lower mileage 96 or 97 engine for me because they weren't happy with the condition of the short blocks they had already in stock. If they are taking their time getting me a good short block and being picky about it, I can't complain.

Piston ring wear | Smokstak® Antique Engine Community*

What caused this type of wear? It's on a 1 1/2 economy engine. End gap was .018 and grove .003-.004. Center of ring face shiny only contact. Engine had lots of blow by and low compression, may why it won't run. Looks like the previous owner honed the heck out of it. New rings see what happens?

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looks like the rings where not flat on the outer edge....however before you put in new rings check the bore dimensions with a inside micrometer or other good thing like a bore gauge.
Measure the piston and see what you have...it may need a rebore and sleeve but need to check so you don't waste your time and a set of rings.
Those ones you show don't look too old.

Looks like the rings weren't sized for the cylinder, may have taken oversized and filed the gap to fit.

Yup. What's the PtW clearance OP. If it's been 'honed to crap' makes me wonder what with? Measure for out of round and taper of the bore. You've got to use a rigid hone when removing any defects. Those three stone spring hone are only ok(ish) for breaking glaze on a good cylinder. Otherwise they just make a bigger messes up cylinder.... Also the rings might be barrel faced which is why they're not worn all the way across. They should be worn all the way around though. This can happen if honed too fine. The cylinder glazes before the rings seat. I'd Hone no finer than 200 grit if it was me... The only history I know is the previous owner said it ran on battery but never on the Webster magneto. He had it rebuilt but never could get it to run. Timing and wouldn't trip but have worked that out (I think) So I measured the ring groove wear it's .003-.004. Rings seem fine in grove other than the end gap .018 measured at 3' from the back. I'll see if I can find someone to help measure the bore

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To be brutally honest, that hone job looks like crap. No cross hatch and pretty fine. The 0.018' end gap is fine. 0.004' per 1' bore diameter is absolute minimum so if it's a 4' bore, 0.016' gap is minimum. It's a ring seat issue causing blow by. The 0.003-4' land clearance is fine also. I've seen smaller rings far looser. I think you have the wrong diameter rings.

Slide the piston in the bore with no rings and see how large a feeler gauge you can fit between the skirt and cylinder wall. Will give a good idea of piston to wall without micrometers. I would use the proper ring size for the bore even if the eng gap is large. Ring fit in the bore and seating has far greater effect on compression than end gap. Thank you for all the good information. I should have mentioned it's a 3 1/4' piston with 1/4' ring .013 gap is what I should shoot for. With the suggestion of measuring piston and bore at the bottom, I get .008 with the feeler gauge. I'll remove the head later and measure at the top. Then maybe I can address the hone job. I didn't do And look at the rest of the bore. Good info all help is Appreciated Sounds like the piston to wall clearance is fine. I would suggest taking the cylinder to a shop with a proper sunnen home or see if you know anyone with a portable hone. Must be a guided, rigid hone sometimes called a 'plateau hone'. This will true the bore round and straight. If you use a portable you cross hatch manually. Take some light passes to get the 'feel' of the stroke rate required to make a nice cross hatch. 180-200 grit stones. Then measure the bore and order rings for that nominal bore size. Don't use over sized rings to get a file fit for the end gap. If the gap is over the 0.004/'bore, don't worry about it, it's not a race engine and the rings fitting the bore is more important than compression losses through the gap. Good luck with it! Maybe new rings in an oval bore. I've been at this over 50 years have not replaced rings in but a handfull. I'm currently working on a 6 horse "M" , had to drive the piston out with the prescribed 16# tool. All 5 rings were married to the piston, but about a half a day & probably a couple thousand taps with my little plastic hammer, they all came loose. Have been off the piston, cleaned & reinstalled. I have no doubt it will have good compression. The first thing people want to do is replace rings, & in my humble opinion, that's a mistake & usually unnecessary. [only worth .02 & you probably have change due]

Maybe new rings in an oval bore. I've been at this over 50 years have not replaced rings in but a handfull. I'm currently working on a 6 horse "M" , had to drive the piston out with the prescribed 16# tool. All 5 rings were married to the piston, but about a half a day & probably a couple thousand taps with my little plastic hammer, they all came loose. Have been off the piston, cleaned & reinstalled. I have no doubt it will have good compression. The first thing people want to do is replace rings, & in my humble opinion, that's a mistake & usually unnecessary. [only worth .02 & you probably have change due]

If they're not worn thin I'd leave em too. Just put a cross hatch in the bore to help them re-seat and go. OP is forced to do something as those definetly don't sit in his bore nice... The rings are not worn thin, just the odd uneven wear on the ring face. Who really knows how many other people have had there hands on this engine. It just one off may little things keeping it from running. I will do a nice light cross hatch in the bore and see what it looks like For me I've never seen wear like this. Thank you for all the good information and learning Just to clarify, I think those rings are the wrong size for your bore... Skip could also be correct that the bore is oval. Some proper measurements with an inside micrometer will tell.

I think Skip means (and correct me if I'm wrong Skip) that the rings probably didn't need to be replaced by the previous owner... if the new rings you have, that are worn funny aren't the right size for the bore, they're no good to you. I guess if you had a lathe and tool post grinder you could make a fixture to hold them and grind them round at your bore size... my guess is you need the proper sized rings in this instance though.

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Contact us to discuss your requirements of Custom Piston Ring. Our experienced sales team can help you identify the options that best suit your needs.

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