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
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.
scraper segment
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.
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
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, the 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.
Piston rings and their placement in a 4t engine
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.