Piston rings, rings or segments: types, functions and placement

Segments of an engine piston

The engine rings or rings they are basically some steel segments which are inserted into slots made in the piston. Thanks to them, the engines have sufficient tightness in the combustion chambers to take advantage of the explosions that occur in them and thus generate movement.

In current models there are normally 3: two of them are the compression rings and the last one oil scraper ring. Although there are very different configurations depending on the type of engine. For example, in two-stroke engines there are usually only two compression rings, due to the type of lubrication they have.

Types of piston rings and their functions

compression segment

single piston compression rings

The compression rings, also called fire rings, are in charge of seal the combustion chambers. In this way, the air-fuel mixture does not pass into the crankcase during the compression phase of the engine cycle, and neither do the combustion gases during the expansion and exhaust phases.

Another of his missions is to transfer part of the heat from the piston to the cylinder walls, during the time the engine is running. This helps to distribute the temperature more evenly and dissipates some heat from the piston head. Also, also serves as a buffer To some degree. They must be made of carbon steel that is very hard but porous at the same time.

Unitary and total displacement of an engine
Related article:
Unit displacement and total displacement

scraper segment

scraper segments

El oil scraper ring, on the other hand, allows some of the oil to pass through to the top of the cylinder and remove excess by sweeping. At the same time, it also scrapes off the lubricant that adheres to the bottom of the cylinder from splashes generated by the movement of the engine.

On many occasions, the scraper segment is made up of several parts. there are with two rings: a double ring with a groove in the middle in which a second helical-shaped ring will be inserted. and there are with three rings: one called an expander ring, which has a wave shape to create a spring effect, and two thin steel sheet rings, one above it and one below it.

The piston inside the cylinder of an engine
Related article:
The piston, heart of the engine: what is it, function, parts, characteristics, price

expander ring

expander ring

As we have indicated before, this type of pieces complements other segments. It is a wave-shaped ring, which is placed in the corresponding groove first. After scratching rings are placed on it corresponding, which are placed against the wall of the cylinder thanks to the spring effect of the expander.

We can distinguish both types of rings visually, because the compression ones are smooth, to avoid holes through which the pressure escapes. Instead, the oil scraper rings have openings on their periphery to facilitate the equal distribution of the lubricant (expanding ring).

Number and position of piston rings

Placement of piston rings

Piston rings and their placement in a 2t engine

The segments of a two-stroke engine (2t) normally there are only two dedicated to compression. This is because the lubricant is mixed with the air and fuel and, before reaching the combustion chamber, goes through the crankcase, camshaft, the connecting rods… and also the pistons from below. In such a way that they remain lubricated without the need for drag rings that distribute the oil along the walls. For example, this is what the piston rings of a 49 cc moped look like.

Related article:
The connecting rod: what it is, what parts it has, types, function and materials

Piston rings and their placement in a 4t engine

Piston rings in place

In four-stroke engines (4t) the most common is to find two compression segments that go on top and one scratch below. As we have indicated before, the latter is usually made up of an expander ring and two steel sheet scrapers.

in kits of piston rings the precise order is usually indicated where they should be placed. You should follow the instructions of your model scrupulously. However, a common collocation is as follows:

  • top ring: is a chrome ring that acts as a seal against the great pressure that is generated in the cylinder. The chrome coating serves to withstand high temperatures.
  • Middle ring: is a black ring due to its zinc phosphate coating. It serves to control the oil and to help the chrome to seal the cylinder.
  • bottom ring: rings to maintain adequate lubrication for the piston.

Again we show you a video in which you can see what these segments are like, what their distribution is on the piston and how easy are they to put on. Each one has its method to insert it and its orientation so that it fulfills its mission:

How to know if a ring is damaged

The usual process is to place the segment that we are going to check inside the cylinder. It has to be perfectly horizontal, so it's better help yourself with a caliber so that it is perfectly placed. Then you just have to see how far the ends of the segment are from each other. For this you can use measuring gauges, such as those of BGS technology or those of kinstecks, though anything similar will do.

In this video you can see how they are made corresponding checks made easy, to know when to change segments. An operation that continues to be carried out on motorcycles or machinery, but has not been carried out on car engines for decades.


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      rudy torrisi said

    Marian:
    Perhaps this is controversial, but the important thing is to reach a conclusion with technical reasoning.
    The first ring, which, as you said, is known as the fire ring and it is a compression ring and in most cases it has a layer of hard chrome or similar on its periphery (friction area with the cylinder).
    The ring that sweeps up a large part of the oil that deposits in the cylinders is the second ring, which also contributes to sealing.
    The third ring, generally made up of more than one piece, is the lubrication ring, in charge of dosing the oil that lubricates the cylinders.
    I also told you that although there are steel rings, there are also centrifugal and nodular cast iron.

      David said

    Hi!

    Can someone tell me if, in 2-stroke engines in which there are basically 2 types of liners: gray cast iron and chromed (or nikasil), the rings are always different, that is, the cast iron liners can have rings of cast iron, or only chromed rings?, and the nikasil shirts, what types are the rings?, chromed or cast iron...
    Thank you:

         Victor said

      Hello good, does anyone know what heat treatment the ring has after being machined, I have a couple of lathes I made the rings but I don't know what heat treatment it has, the material I use is pearlite gray cast iron..

      Samir said

    the fire one is placed below all and the other two are placed above

         cristian said

      hello samir, I have an unarmed r1 with a cracked nikasil shirt, and it does not come as a spare part in arg, you tell everyone, can you tell me if I put steel shirts with hoops for nikasil, what happens? Thank you

           Throw said

        Samir is a joke, right?

        Piston crown rings in descending order, i.e. from top to bottom:

        1- Of Fire or Compression.
        2- Scraper (The one that makes the oil pass towards the upper or lower segment).
        3- Lubrication. (Remove unnecessary oil again.)

        I hope I have helped. Try to put them in order or you will end up burning "the cylinder cover gasket" (Fire Segment that is not fire and that is why it burns) of the renault cangoo.
        A greeting.

        Sources: Stark Industries 😀

      bryan strap said

    Check if you have the rings positioned correctly, the first common smooth compression ring can be chrome or black, the second smooth oil-scraper ring that sweeps the cylinder walls causing the oil to drop, the third and last ring is ventilated spring or barflex, which is two sheets and a caterpillar... it could be that you have the first ring in the second groove and the second ring in the first groove, and it is causing a lot of combustion and the joint bursts, otherwise it could be a problem with the joint...

      jose lopez said

    ok just for concern, the segments or rings of (the) pistons go in that order from top to bottom 1st ring of fire (compression), 2nd ring (oil scraper) here I want to ask a question this ring lets a small amount of oil so that it burns with combustion at the top of the cylinder in any of its phases or in certain phases (compression, exhaust) or in all of them, I understand that the oil comes from the crankcase upwards or is it above the chamber where the valves go, camshaft there are holes for a certain amount of oil to enter the cylinder (I know that only for the work to exist in the cylinder there must be air, gasoline and the spark, BUT NOT OIL or a minimum amount of oil) and the 3rd ring that is in the shape of a caterpillar or that is not linear is the one that really cleans the oil when the piston is in the admission phase …….. thank you very much and sorry for the paragraph

      jose lopez said

    ok just for concern, the segments or rings of (the) pistons go in that order from top to bottom 1st ring of fire (compression), 2nd ring (oil scraper) here I want to ask a question this ring lets a small amount of oil so that it burns with combustion at the top of the cylinder in any of its phases or in certain phases (compression, exhaust) or in all of them, I understand that the oil comes from the crankcase upwards or is it above the chamber where the valves go, camshaft there are holes for a certain amount of oil to enter the cylinder (I know that only for the work to exist in the cylinder there must be air, gasoline and the spark, BUT NOT OIL or a minimum amount of oil) and the 3rd ring that is in the shape of a caterpillar or that is not linear is the one that really cleans the oil when the piston is in the admission phase …….. thank you very much and sorry for the paragraph

      darwin said

    Could you tell me classes of hoops or rings
    Also what are types of hoops or rings

      LUIS ALFREDO GUILLEN said

    VERY GOOD MORNING, A GREAT GREETINGS FROM MERIDA VENEZUElA, I HAVE A NISSA PATROL 1980, 6 CYLINDERS IN LINE, BUT I CAN'T GET THE RINGS IN MY COUNTRY, WE ARE IN CRISIS, IF YOU CAN HELP ME WITH THE PISTON MEASUREMENTS AND MEASUREMENTS BETWEEN GROOVES , TO SEE WHICH ANOTHER ENGINE I CAN FIT THEM, A GREAT GREETINGS FROM MY DYING VENEZUELA./