How To Know Which Ring Set You Need For Your Pistons

So, you have a set of pistons that you want to re-ring, but you don’t which rings to order. Here, we go over the options you have for measuring your old rings or ring grooves so JE can get you the rings you need.

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Forged pistons are a durable, high-performance option for many engines, and last a long time in various applications. Because of the lasting quality of forged material, replacing the piston(s) is not always necessary. JE pistons has many customers that have been running the same pistons for a long time, and they’re still well within safe running condition. However, these customers still need to periodically replace rings as practice of proper maintenance to help maintain efficient sealing and keep blow-by to a minimum.

In many cases, forged pistons will last a long time and be remain safe to re-use, but replacing the piston rings periodically is important to retain performance.

Replacing piston rings is easy, but ordering the correct replacement rings is not always cut and dry. If you have a JE piston—or set of pistons—you need rings for, you can usually provide the part number or job number over the phone to a JE tech expert and they’ll be able to tell you what ring pack part number will get you going again. That’s the easy situation.

However, there are many racers, builders, and enthusiasts out there that have some JE pistons that don’t have any laser marked numbers on the bottom of the pin tower. When there is no number present, this means the piston was manufactured before laser marking was implemented in 2005.

If your JE pistons have a job or part number, simply call JE, provide that number, and they’ll get rings coming to you! If they don’t have any numbers, you’ll need to follow the steps below to narrow down which ring pack you’ll need.

Need help identifying other markings on your pistons? Check out our guides for Powersports and Automotive.

Analyze Your Used Rings to Identify New Ones Needed

So, how do you know what rings to order if you don’t have a reference number? Here’s some tips to help you be prepared with the data you need to order the correct replacement rings.

First, make sure your old/worn out rings are off the piston. With the rings off, measure the axial height (this is the thickness of the ring) and radial width (the width of the ring from the outer edge to the inner edge) of the oil ring assembly with a set of calibrated calipers or a micrometer, whichever you have easy access to. Make the sure the oil ring assembly is assembled correctly—like it would be when sitting in the ring groove—while measuring. It should be assembled with two oil rings sandwiching the expander ring. Measure and record the axial height of the assembly, as well as the radial width.

Measure and record both the axial height and radial width of the oil ring assembly while off the piston. Using either a set of calipers or a micrometer is sufficient.

After recording those measurements, perform the same axial height and radial width measurements of your compression ring(s). In addition to these measurements, you’ll want to look for specific compression ring characteristics, such as shape, bevels, notches, and markings, that can determine which type of ring(s) your piston originally came with. Note that ring characteristics will vary between top and second compression rings. Compare your compression ring characteristics to the JE chart below.

Analyze and compare your rings to these charts to help identify which specific style rings your piston(s) came with.

Want to know more about ring material and design? Read this!

After all your measurements are recorded and you have identified what style compression rings you have, you’re ready to call in and provide your information to a JE tech expert so they can get the correct part number coming to you.

Don’t forget to record measurements for your compression rings, too!

Don’t Have Old Rings? Measure Your Ring Grooves

In some cases, you may acquire a set of used pistons that are still in good condition, but did not come with the old rings. If these used pistons do not have a job number or part number laser-marked, you’ll need to take a few measurements of the ring grooves to accurately track down which exact ring set you’ll need for your pistons.

First, measure the axial height of each ring groove. Axial height refers simply to the height of the ring groove itself. For exact measurements and engineering purposes, JE uses precision-sized pin gauges to measure ring grooves.

JE uses pin gauges for more exact measurements.

However, not every person will have a set of pin gauges in their garage. In this case, use a set of calipers to take as accurate a measurement as possible. This will get you close enough for the JE tech experts to know which ring pack your piston was designed for. Take the axial height measurement for each compression groove and the oil ring groove.

Most people don’t have pin gauges, so using a set of calipers to get an approximation of ring groove axial height is okay. To measure the smaller, compression ring grooves, use a set of feeler gauges in conjunction with your calipers.

It’s important to note that some pistons are designed and machined with accumulator grooves. While they can be confused as a ring groove, they are not designed to house any rings. When present, accumulator grooves are set between the top and second compression ring, and are purposed to allow any gases that make it past the top ring to expand, preventing ring flutter and reinforcing ring seal.

If you see a V-shaped groove between the top and second compression ring grooves, note that this is an accumulator groove, and is not intended to house any rings.

In addition to measuring axial height of the ring grooves, the radial depth will also need to be measured. Radial depth is the distance from the outermost surface of the ring groove to the inner wall of the ring groove. Radial depth may be difficult to measure to measure without pin gauges, but if a close measurement is taken and provided in conjunction with the axial height and bore size, JE tech experts should be able to narrow down the ring pack needed.

Bore size is another critical measurement to be taken and provided to help identify the correct rings.

JE would typically use a blade mic for quick and accurate groove radial depth measurements, but if you can get to a close measurement with the tools you have, JE tech experts can work on narrowing it down for you based on other measurements.

Whether you’re providing measurements of old rings or ring grooves, providing all critical measurements—axial height, radial depth, and bore size—is important to help JE figure out what rings you need. This is because there are some situations where two ring packs may have the same axial height, but varying radial depths.

Don’t Have the Means to Measure? Let JE Take Care of It

If you’re unsure about taking accurate enough measurements, or you don’t have the proper means to provide the measurements yourself, JE would be happy to take care of it for you. Simply contact JE and let them you know you need measurements taken for new rings, send in your piston(s), and JE will take exact measurements and let you know which ring set to purchase.

If you’d rather have JE perform the measurements to be sure you’re getting the correct ring pack, just give them a call to coordinate sending your piston(s) in!

Piston rings are manufactured and classified on the basis of function and usability. The primary usage of the piston ring is to seal the chamber (where the piston is moving), which can be a combustion chamber of a 2 stroke or a 4 stroke engine. Marine engines have three or more types of rings fitted on the circumference of the piston.

The piston ring is an essential piston part, and its numbers and functionality differ depending on the type and capacity of the engine.

In 2-stroke large engines, compression type piston rings are used to seal the combustion chamber and wiper rings are installed below them to wipe the deposits from the liner and distribute oil on the liner surface.

Related Read: Reasons for Cylinder Liner Wear and Ways to Measure it

However, in smaller marine engines, different types of piston rings are used for dedicated purposes. E.g. oil scraper ring is used in 4 stroke engine as it’s a trunk type engine, and the crankcase oil has direct access to cylinder liner and piston. In this article, we will have a look at the different types of piston rings used in marine engines.

Types and Functions of Piston Rings

Compression Rings or Pressure Rings

The compression rings provide sealing above the piston and prevent the gas leakage from the combustion side. The compression rings are located in the first grooves of the piston.

However, this may differ according to the design of the engine. The primary function of these rings is to seal the combustion gases and transfer heat from the piston to the piston walls.

The oil is controlled by shearing the layer of the oil left by oil ring, thus providing the top compression rings enough lubrication. Moreover, it also provides help to the top compression ring in sealing and heat transfer.

Wiper ring

The wiper ring also called a Napier ring, or backup compression ring, are installed below the compression ring. Their main function is to clean the liner surface off the excess oil and to act as support back up ring on stopping any gas leakage further down which escaped the top compression ring. Most of the wiper rings have a taper angle face which is positioned toward the bottom to provide a wiping action as the piston moves toward the crankshaft.

Related Read: How Internal Forces in Marine Engines Affect Their Operation?

If the wiper ring incorrectly installed with the tapered angle closest to the compression ring, it results in excessive oil consumption. This is caused by the wiper ring wiping excess oil toward the combustion chamber.

Oil Control / Scrapper Rings

The oil control rings control the amount of lubricating oil passing up or down the cylinder walls. These rings are also used to spread the oil evenly around the circumference of the liner.

The oil is splashed onto the cylinder walls. These rings are also called scraper rings as they scrap the oil off the cylinder walls and send back to the crankcase.

These rings do not allow the oil to pass from the space between the face of the ring and the cylinder.

Related Read:  Intelligent Cylinder Lubrication for Modern Marine Engines

In the oil ring, holes or slots are cut into the radial centre of the ring which allows the excess oil to flow back to the reservoir.

Oil rings can be one-piece or two pieces. To increase the contact pressure between the ring and the liner surface, the rings can have chamfered edges on either the outer sides of the lands or facing the combustion chamber to reduce the oil consumption through improved oil scraping from the bore.

Two-piece oil control rings consist of a cast iron or profiled steel ring and a coil spring which is made from heat-resistant spring steel to act around the whole ring circumference for maintaining the pressure and contact.

Piston ring material

One of the most prominent materials used in making piston rings is cast iron. This is because it contains graphite in the lamellar form which itself acts as a lubricant assisting the sliding motion between the rings and the liner.

Alloys and coatings are done on the piston rings, and it will vary as per the type of the ring as the functionality of these rings are different from each other.

The most common form of alloying cast iron is chromium, molybdenum, vanadium, titanium, nickel, and copper.

The piston ring material is kept harder than the cylinder liner to provide maximum life.

Related Read:  How are Piston Rings Made?

The Piston of Main Engine

The combustion chamber of a 2 stroke marine engine is a large space producing an enormous amount of heat and stresses.

The upper rings of the piston are directly in contact with the combustion chamber, hence they need better protection and coating to tackle the thermal stress and provide proper sealing.

Many new designs were introduced specially for the large two-stroke marine engines. Some of the important design introduced are:

MAN engine

The uppermost piston ring is of Controlled Pressure Relief type in which several oblique shallow grooves (hard chrome plated) are provided on the face allowing some gas pressure to pass through to the 2nd ring thereby reducing the load on the top ring. It has ‘S’ type joint at the ring ends.

A new design was also recently introduced which is a modified version of CPR rings known as CPR Port on Plane rings (CPR POP).

The modification is done on the position of the grooves which are now placed in the lower side of the ring as it was noted that the wear of CPR rings grooves in the running side was faster than usual.

Second or Intermediate Rings

The other rings have an oblique cut at the ring ends. All the piston rings are aluminium-coated on the outer surface for helping in running-in.

Wartsila Engine

In the Wartsila 2 stroke engine, the piston ring grooves on the piston surface are hardened for excellent wear resistance. The top piston ring (also known as Gas Tight (GT) ring in Wartsila) have overlapping ends to avoid gas leakage with an asymmetrical barrel shape. They are chromium- ceramic (CC) coated along with running-in coating (RC).

Goto Dongya to know more.

The number of piston ring will vary depending on the size of the engine. E.g. an RTflex 35 will have a very short skirt and is equipped with three piston rings, but an RTA engine may have 5 piston rings.3

Four-stroke engine

The piston ring requirement in a 4 stroke engine is different as the piston liner assembly is open to the sump. Hence, oil scraper rings are additionally needed in the 4 stroke piston ring-pack. It typically consisting of 2-5 rings depending upon engine type and specification. Usually, 2-4 compression rings are provided to seal the gases from the combustion chamber, and 1-3 oil-control rings are provided to excess avoid oil ingress in the combustion chamber.

The compressor rings are usually of barrel type with taper face for efficient gas sealing. The oil-control ring profiles comprise two lands and an inserted coil spring to support the pre-tension of the ring.

How Do Piston Rings work?

As explained, there are different types of rings provided in a piston at various levels, which perform different tasks.
The topmost groove of the piston consists of a compression ring whose main function is to seal any kind of leakage inside the combustion chamber during the combustion process.

When the air-fuel mixture is ignited, pressure from combustion gases is applied to the piston head, forcing the piston toward the crankshaft.

The pressurized gases travel through the gap between the cylinder wall and the piston and into the piston ring groove.

During the combustion process, the force of high-pressure gases presses the piston ring against the cylinder liner wall which helps it to form an effective sealing. This pressure pushing the piston ring is proportional to the combustion gas pressure.

The next set of rings in the piston which are placed below the compression ring and above the oil rings are called wiper rings.

They have a tapered face construction and it is used to further seal the combustion chamber. As the name suggests, they assist in wiping the liner wall clean of any excess oil and impurities. If any of the combustion gases were able to pass by the compression ring, these gases will be blocked by the wiper ring in a good condition.

The last set of rings are oil rings which are located at the bottom grooves of the piston closest to the crankcase. The main function of the oil ring is to scrape any excess oil from the walls of the cylinder liner when the piston is in motion.

Majority of the wiped oil is directed into the crankcase back to the oil sump. These oil rings come with spring fitted at the back in a 4 stroke engine to provide an additional push for wiping the liner.

Why Piston Rings Fail?

The combustion chamber exerts tremendous pressure on the piston rings. If the combustion pressure of the gas produced inside the chamber is higher than the usual, it may affect the ring performance.

This can be due to detonation and pinging of the fuel from the leaky injector or when the fuel is mixed with dirty air.

Contaminated fuel oil or wrong grade of cylinder oil will also affect the performance of the ring. As the ring starts wearing down, their ability to seal the combustion gases will become apparent.

Bad fuel or cylinder oil quality, bad combustion process, wrong fuel timing, worn liner etc. are the normal cause of piston rings worn out. The most common indication or sign of a worn ring is gas passing into the crankcase or under piston area known as blowby.

Sticky ring due to carbon or sludge deposit and breaking or crack on the ring can result due to wear down.

Things to be Checked During Inspection of Piston Ring

Inspection of the piston rings is an important task to determine the proper working of piston rings followed by either cleaning or replacing piston rings (if broken or worn out).

In 2-stroke cycle engines, the port containing the top ring usually is at a higher position than the 4- stroke engine’s top ring groove.

During Routine Inspection

During normal scavenge space inspection, the piston rings are pressed with the help of a screwdriver. This is done to check the spring action or tension of the rings. This also tells whether the ring is broken or not. If the ring is broken there will be no spring action.

The rings are checked for their freeness in the grooves, as they might get stuck due to carbon deposits and might finally break causing a lot of damage to the liner.

The clearance between the ring and the groove is also checked and the wear is calculated. The ring is checked for scuffing marks and damage, and the overall condition is also assessed.

Related Read: Essential Marine Engine Maintenance Guide For Marine Engineers

During Major Overhaul

During major overhauls, the piston rings are changed completely with the new set. But the following steps need to be considered for scrapping the rings:-

1) If the piston ring is found stuck in the groove.
2) If the axial height of the rings is reduced and the clearance in rings and groove is large.
3) If the chrome layer is peeled off or damaged.

During the overhaul, the grooves have to be properly cleaned off carbon deposits and checked for damage in the ring grooves.

Before putting the piston rings, it should be first rolled rounded in the grooves. In this process, the ring is entirely moved inside the grooves.

With this test, we can check that the grooves are more in-depth than the radial width of the ring.

While inserting the piston with replaced rings in the liner, use the adequately lubricated piston ring compressor tool which will ensure the rings will not stick to the liner face while going inside the combustion chamber.

The piston rings are put inside the worn liner, and the butt gap is also checked. For rings of the small piston (e.g. compressor), the ends can be treated using a piston ring filer, but for marine engines, the rings have to be sent to shore workshop for reconditioning if the butt gap is unusual. While putting rings, they should be checked for markings as to which part is up or down and also check different marking for different positions.

Rings should be put with the help of proper toll, i.e. with the help of ring expander. The clearance between the ring and the groove is checked with the help of the feeler gauge.

The axial and radial clearance of the old ring is checked and recorded to assess the amount of wear for a number of running hours.

How Piston Ring Installation is done?

Before installing the piston ring, the new or spare ring is checked for its marking and compared with the old one for the same grade or position. If the old piston ring marking is wiped out, check the manual for the identification of the piston ring so that it can be placed in its appropriate groove. 

The groove must be cleaned properly to ensure no carbon and sludge deposit are present in it. While cleaning, it is to be kept in mind that some piston grooves are coated with a special protection film. They should not be damaged by the use of a chipping or grinding tool. 

Once the groove is properly cleaned, the piston ring is installed using the piston ring tool which expands the ring to be inserted in the groove by sliding it from the top of the piston head. Ensure to insert the ring keeping the top marking on the upper side.

Most of the piston rings are provided with marking “TOP” or the identification number stamped surface is considered as the top face if no specific marking is present. 

It is extremely important to use the ring expander tool appropriately as wrong use may damage the ring or it may hurt the operator as the ring is under constant tension. 

In small 4 stroke engines, in case the tool is not available, the ring can be expanded by use of clothes or rags available in the engine room.

Two rags are placed on each side of the ring ends and they are pulled so that rings can be expanded and inserted from the top of the piston. 

After fitting all the piston rings, ensure the opening or the butt end of all piston rings are not aligned to avoid gas leakage from the chamber. 

Life of piston rings

Similar to all the other machinery parts, the piston ring will also have a set time period of overhaul and replacement. The life of a piston ring entirely depends on the piston ring type, the size of the engine it is fitted on, and the operational condition of the ring and the liner. 

For a large two-stroke piston ring with a bore of approximately 900mm, the overall life of the ring can be up to 24,000 hours and for smaller engines of 500mm bore, it can be up to 16,000 hours. 

For auxiliary marine 4 stroke engines having high speed, the piston ring life is usually lesser than the 2 stroke engine. The average lifespan of a marine 4 stroke high-speed engine is approximately 8000 hours, post which renewal is required. 

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Disclaimer :
The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of data or profits arising out of, or in connection with, the use of this website.

About Author

An ardent sailor and a techie, Anish Wankhede has voyaged on a number of ships as a marine engineer officer. He loves multitasking, networking, and troubleshooting. He is the one behind the unique creativity and aesthetics at Marine Insight.

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