Piston rings: types, functions, typical problems


Absolutely all internal combustion engines work due to the movement of pistons, which are affected by thermal energy, and ultimately we get mechanical energy. Piston rings are a vital element in the cylinder-piston group, the condition of which determines the stable operation of the internal combustion engine, fuel consumption, maintenance of the oil level, etc. Next, we will consider what piston rings are needed for, varieties and what problems arise with them during operation.

Piston rings: types, functions, typical problems

What are piston rings

Piston rings are parts that are mounted on pistons, usually using two compression rings and one oil scraper ring. The shape of the rings is made in the form of a circle, and a cut is used for mounting on the piston, which is reduced when the pistons are installed in the cylinders. If the engine pistons were not equipped with rings, the engine simply would not work due to the lack of compression, as well as due to the filling of the cylinder with oil and its rapid waste.

The main purpose of the piston rings is to ensure normal pressure in the cylinder by firm pressing on the cylinder wall, as well as to prevent oil waste, allowing it to drain into the sump. Also, the rings retain blow-by gases, but only if there is no wear of the cylinder-piston group.

Piston rings: types, functions, typical problems

Types of piston rings

Today there are two types of piston rings mounted on a piston:

  • compression;
  • oil scraper.

 Today, piston rings are made from cast iron, and molybdenum, which has an extreme pressure property, is added for reliability and extended service life. Chrome rings are produced a little longer, they are somewhat cheaper, but they also have anti-seize properties, although they do not differ in a long service life. Let's take a closer look at each of the rings.

Piston rings: types, functions, typical problems

Compression rings

Compression rings are installed above the oil scraper, in the amount of two pieces. It is important to understand that this is not just a metal ring that is designed to seal the combustion chamber, since the compression ring is involved in the heat transfer between the piston and the liner, and also absorbs piston vibrations due to lateral thrust. 


The upper compression ring can be of three types:

  • with L-shaped ledge in the area of ​​the lock;
  • with a flat area;
  • twisted section - both ends of the ring are oblique, touching only one ledge with each other.
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Products with an L-shaped protrusion can change the sealing ability depending on the operating mode of the motor: when the gas pressure rises, the force on the ring increases and it “encircles” the cylinder more tightly, and when the pressure drops, the force decreases, and the friction between the cylinders, respectively. This approach makes it possible to provide the necessary compression at the right time, and in the inlet and outlet modes, to reduce friction and increase the resource of the CPG.

The second compression ring is of the usual shape, it only complements the upper one in that it additionally ensures tightness, protects against detonation and prevents oil from entering the cylinder due to reverse thrust.

Some of these rings are made beveled in order to better drain oil from the walls of the liner, and in modern motors, rings are completely made without a gap.

Piston rings: types, functions, typical problems

Oil scraper rings

The oil scraper ring is installed below the compression. The essence of the work of the ring is in its name - to remove excess from the walls of the cylinder. As soon as the ring passes over the surface, it leaves a film several microns thick, which is necessary to extend the life of the CPG and keep the temperature within tolerances. To remove oil, the rings are made in the form of radial or axial expanders. Some car manufacturers use two oil scraper rings.

Piston rings: types, functions, typical problems

Functions of piston rings

Based on the above, the following conclusions can be drawn:

  • compression properties. Complete insulation of the combustion chamber, ensuring the required pressure inside the cylinder, thereby achieving stable torque and optimal fuel consumption;
  • saving engine oil. Thanks to the oil scraper ring, an effective film is provided on the surface of the cylinder, excess oil does not burn out but enters the crankcase through the ring;
  • heat exchange. Piston rings effectively remove heat from the piston by transferring it to the cylinders, which cool down due to external contact with the coolant;

practical absence of horizontal vibrations. Due to the tight fit of the rings, the piston clearly moves up and down.

What are piston rings made of?

Nowadays, ductile iron and stainless steel are used as materials. Since modern motors have become smaller and more powerful, respectively, the load on them has increased many times over, there is a need for the use of innovative materials. The leader among materials is molybdenum, which is distinguished by antifriction properties and increased service life. By the way, piston skirts are processed with a similar composition.

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Piston rings: types, functions, typical problems

Typical piston ring failures

During the operation of the internal combustion engine, the pistons and rings gradually wear out, after which they become unusable. The main malfunction is an increase in the gap between the ring and the cylinders, which causes problems with starting the engine, fuel consumption increases, power drops sharply, excessive pressure forms in the oil sump. 

Often, drivers are faced with such an effect as the occurrence of rings. The process is explained by the fact that due to engine overheating or oil deposits, the rings lose their elasticity, which means that all the properties of the rings are lost.

Piston rings: types, functions, typical problems

Despite the fact that in most cases, the occurrence of rings can be corrected by applying engine decarbonization, to prevent this process, use the following rules:

  • try to use the car as often as possible, and also do not neglect the rules for warming up the engine;
  • use only high-quality engine oil with tolerances according to the classification for a particular engine (especially if it is a diesel engine with a particulate filter and unit injectors);
  • do not allow the engine to overheat, because the consequences of this are too expensive, at least in changing the oil and coolant, as well as replacing the cylinder head gasket with grinding the plane of the head.

Do not forget that the quality of the rings also affects not only the resource, but also the resistance to critical temperatures and loads.

Piston rings: types, functions, typical problems

Consequences of piston ring wear

The consequences of piston ring wear are often similar to other malfunctions, so a high-quality diagnosis should be made in the form of measuring the compression and checking for air leaks in the cylinder. 

More details about the consequences:

  • difficult cold start. When the engine is not warmed up, an increased gap forms between the piston and the cylinder and it decreases only due to warming up, respectively, the expansion of rubbing parts. The initial wear of the rings manifests itself only on a cold engine, after which the engine runs stably. You can observe the effect due to the bluish smoke at idle speed;
  • increased fuel consumption with reduced power. An increased clearance means a loss of compression properties, which means a low pressure - low efficiency, which requires more fuel to achieve;
  • triplet motor. Low compression is necessarily accompanied by triplet, and this is not only discomfort for the driver and passengers, but also accelerated wear of engine mounts and other attachments.

You can check the condition of the rings by placing your hand to the exhaust pipe or a clean sheet, and if you find an oil stain, the problem is more likely in the rings.

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Piston rings: types, functions, typical problems

Selection and replacement of piston rings

Please note that it is highly discouraged to change the piston rings separately from the pistons for the following factors:

  • during operation, the cylinder wears out unevenly, and becomes elliptical;
  • pistons can also deform, especially if overheated. Piston ring grooves can grow larger, making it impossible to install new rings;
  • the block of cylinders must be given for inspection, where after it it will be clear whether the cylinder is within the ellipse tolerances, whether it is necessary to apply fresh hon or whether boring is required to a repair size.

What criteria should be used to choose piston rings? If your budget does not allow for overhaul to the maximum, then you can install budget pistons, but always high-quality rings - advice from experienced minders. As for the selection factors:

  • cost. The cheaper the rings, the less they are of high quality, and there is no other way here. Cheap rings are made of low-quality cast iron, which already during installation can manifest itself in the form of ring breakage;
  • manufacturer. I strongly recommend that you pay attention to manufacturers such as Mahle, Kolbenschmidt, these are top-quality companies. If you want to save money without a sharp loss of quality, then look at a manufacturer such as Goetze, Nural, NPR;
  • the appearance of the packaging and the rings themselves. Pay special attention to how the rings are packed, what quality the packaging is, whether there is a hologram, installation instructions, and how the rings themselves are made.

How to replace piston rings

The procedure for replacing rings is no different from the overhaul process. It is important to understand that in modern cars the method of “tossing rings” will not end well. You need to send the cylinder block for troubleshooting, and if it so happens that the rings require replacement at an early run, while the pistons and liners are in tolerance, you can replace the rings separately.

In other cases, it is necessary to make a full overhaul by this method:

  • disassemble the engine, defect the block, and give the cylinder head for pressure testing;
  • after receiving data on the condition of the cylinders, purchase the piston group assembly or rings separately;
  • assemble the engine and, depending on the type of rings, run the internal combustion engine for a certain number of kilometers.
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