If you observe the piston of an IC engine, you will clearly see three piston rings attached to its outer diameter at the top. All these three piston rings are of different type and perform different functions.
So, what are the types of piston rings? There are three piston rings placed on an engine piston.
- Compression ring
- Middle ring
- Oil scraper ring
Let’s discuss the roles of each of these rings one by one.
#1: Compression Ring
Compression ring is the top most ring in the piston attached to its outside diameter. The main function of the compression ring is to seal the gap between the piston and the cylinder walls.
Sealing this gap with the outer diameter of piston and the cylinder walls ensure that the air fuel mixture in combustion engine does not move down to the crankcase and cause low compression and power.
In addition, this sealing also makes sure that the engine oil in the crankcase, used for lubrication, does not move up into the combustion chamber and gets burnt.
Engine oil moving into the combustion chamber and getting burnt will effectively result in excessive consumption of oil in the engine and then to low engine oil levels.
So, essentially the compression piston ring ensures that the combustion chamber and the crank case are segregated.
The air fuel mixture in the combustion chamber is not allowed to trickle down into the crank case and the engine oil is not allowed to move up into the combustion chamber.
As for the advantages of compression ring sealing the gap between the piston and the cylinder walls include – maintaining high compression in the combustion chamber, high power and acceleration in the vehicle, and no unnecessary burning of engine oil.
#2: Middle Piston Ring
The second ring or the middle ring is an all rounder of sorts – performing the functions of both the compression ring and the oil scraper ring.
So, essentially, middle ring helps in sealing the combustion chamber from the crank case as well as guiding the engine oil back down to the crank case.
While it may look like the middle ring is just there as a back up for both the compression ring (the top one) and the oil scraper ring (the bottom one), we cannot stress its importance more since it performs the function both these end rings.
If the compression ring is failing or not performing, then the middle ring acts as the primary seal between the combustion chamber and the crank case. Thus, not allowing the air fuel mixture to enter the crank case and maintain engine performance.
On the other hand, if the oil scraper ring is not working, the middle ring will again perform to guide the engine oil down back into the crank case through the oil holes present below the oil scraper ring. This helps in keeping the crank case component and the piston lubricated and cooled down sufficiently.
That’s why the middle ring is such an important component since it acts as the backup for bot the compression ring as well as the oil scraper ring.
#3: Oil Scraper Ring
The main function of the oil scraper ring is to guide the engine oil scraping along the piston outer surface back into the crank case.
Engine oil lubricates the piston as well as all the components within the crank case.
Engine oil is essential for an internal combustion engine since it performs two functions – i) lubrication and ii) cooling of the components.
Without an engine oil or the oil at low levels, the engine will not be able to perform and there can be harmful effects on the motorcycle components.
That’s why the oil scraper ring which helps in guiding the oil along the piston as well as into crank case to lubricate and cool down the components is such an essential component in itself.
Now, how does this oil scraper ring help exactly?
Firstly, what the engine oil does is it moves up along the piston outer diameter as a result of piston’s up and down movements.
The oil scraper rings barricades further upward movement of the oil and forces it to move downward.
Now, this is where things get interesting. The oil scraper ring although forces the engine oil to move downward, it does not necessarily mean along the piston surface.
There are oil holes on the piston right below the oil scraper ring. These holes allow the engine oil which are forced to move downward to enter into the crank case through these holes.
Thus, the engine oil which was moving along the piston outer surface is forced back down into the crankcase by the oil scraper piston ring.
That’s why this ring is so vital for engine oil movement within the crankcase. Oil scraper ring helps the crankcase components from heating too much or getting worn out by facilitating smooth oil movements.
Other Functions Of All The Three Piston Rings
Apart from their designated functions, these piston rings together as a whole perform certain functions as well.
The foremost being – heat transfer from the piston to the cylinder walls.
All the three piston rings are connected from the piston outer diameter to the inner cylinder walls. The piston gets heated due to its continuous contact with the combustion chamber.
As a result, the piston needs to be cooled down and the heat should be transferred away. This is where all the three piston rings comes in handy. The rings transfer the heat from the piston to the inner cylinder walls – thus reducing piston temperature.
Other functions include maintaining high compression in the combustion chamber, higher power output in the engine, maintenance of engine oil levels and overall, maintaining optimum engine performance.
To Summarize
The 3 types of piston rings are – Compression ring, Middle ring, and the Oil scraper ring.
Compression ring is the top most ring in the piston attached to its outside diameter. The main function of the compression ring is to seal the gap between the piston and the cylinder walls.
Middle ring is the second ring and helps in sealing the combustion chamber from the crank case as well as guiding the engine oil back down to the crank case.
Oil scraper ring is the bottom most ring. It guides the engine oil scraping along the piston outer surface back into the crank case.
Apart from their designated functions, these piston rings together as a whole perform certain functions as well.
These include – heat transfer from the piston to the cylinder walls, maintaining high compression in the combustion chamber, higher power output in the engine, maintenance of engine oil levels and overall, maintaining optimum engine performance.
