How Does Piston Wear Ring Work?

At some point, every budding gearhead or curious motorist asks, What are piston rings? And what do piston rings do?

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Simply put, piston rings form a seal between the piston and cylinder wall, which prevents pressurized combustion gases from entering the oil sump. They also regulate oil consumption by preventing excessive oil from entering the combustion chamber and burning. Properly functioning rings are vital to maximum engine power and efficiency.

Let&#;s take a deeper dive.

What do piston rings do?

Most stock automotive pistons have three rings, as shown here on this new automotive piston.

The top and second rings are responsible for pressing tightly against the cylinder wall and sealing the combustion chamber, keeping combustion gases in and oil out.

The oil ring scrapes oil off the cylinder wall on the way down the cylinder, depositing it back into the oil sump. Because an extremely thin film of oil lubricates the ring/cylinder wall interface, it is normal for some oil to burn during combustion. What constitutes &#;normal&#; oil consumption, however, depends on the engine.

When good piston rings go bad

Worn rings can allow a gap to form between the ring face and cylinder wall. During combustion, the pressurized gases that drive the piston down the cylinder and turn the crankshaft can blow by the piston and travel down the cylinder wall and into the oil sump, taking horsepower and efficiency with it. Blow-by also contaminates the motor oil, reducing its performance and service life.

Stuck rings can result in the same scenario. Extremely hot combustion gases can break down oil, forming carbon deposits in the ring grooves. Gasoline byproducts can form deposits, too. Heavy deposits cause the rings to stick in the grooves rather than stand proud of the piston, allowing a gap to form between the ring and cylinder wall, which invites blow-by and oil consumption.

Blue smoke, hard starts and power loss

The negative effects of bad piston rings are often easy to notice. Excessive oil consumption can lead to blue smoke billowing out of your tailpipe, especially at startup before the engine has warmed and the rings have expanded in the cylinder. Burning oil also means you&#;ll also need to top-off your oil more frequently.

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Worn or stuck rings can also result in hard starts and reduced horsepower.

As the engine is turning over, the piston compresses the fuel/air mixture prior to combustion. Bad rings, however, allow some of the fuel/air to escape the combustion chamber, effectively reducing engine compression and making the engine more difficult to start. Once it is running, reduced compression robs your engine of power.

In the above image, the top ring is stuck in its groove, indicated by the fact it doesn&#;t stand proud of the piston. Stuck piston rings reduce engine power and allow combustion gases to enter the oil sump, contaminating the oil.

The piston rings in the above image are free in their grooves and working properly

Prevention is best practice

Preventing worn and stuck rings is vital to maximizing your engine&#;s power, efficiency and life. It starts with using a high-quality synthetic oil, like AMSOIL Signature Series Synthetic Motor Oil, that fights wear and withstands extreme heat, keeping pistons clean.

If you suspect your rings are worn or stuck, consider using the highest viscosity oil the original equipment manufacturer (OEM) recommends. Some OEMs recommend a range of viscosities, depending on your climate (e.g. 5W-20 when it&#;s cold, 10W-30 when it&#;s above 0ºF). Using the highest recommended viscosity can help close the gap between the rings and cylinder wall.

You can also try freeing stuck rings by using a quality engine flush or fuel additive designed to clean deposits, such as AMSOIL Engine and Transmission Flush or AMSOIL P.i.® Performance Improver.

Updated. Originally published July 8, .

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BHPian  
Join Date: Dec Location: SINGAPORE Posts: 266 Thanked: 7 Times How do piston rings work? Here is a brief description of " How does a piston ring seals the combustion chamber from crankcase? "

The piston rings have two type of clearances in their grooves. One is radial and other axial. Due to this clearances, the piston ring is free to move in the groove. Also the piston rings have some springness and they will always be pressing against the liner wall. But this springness is not enough to seal the combustion chamber against the gas forces.

When working, the piston is sitting on the bottom of the piston ring groove and they are pressing against the cylinder liner wall. Due to this there is a small clearance at the top and at the back (towards centre) of the piston ring. Due to this clearance, the gases can go to the back of the piston ring from the top clearance and press the ring hard against the liner. This causes it to become almost gas tight.

There is another clearance provided at the ends of the rings. This is to compensate for the change of length of the piston ring due to temperature changes. Due to this, the small amount of gases leak past the rings. Just like a air leaking through small hole. So to redue the pressure to a small level, number of rings are provided. Each one reduces the pressure a fair amount and the last one reduces it to crankcase pressure.

If these gaps get blocked due to carbon deposits and piston rings are not free to move in there grooves, the gas pressure do not act from inward side, but due to taper on the rings will act from outward side towards inwards. This will lead to sudden collapse of the ring and breakage. Last edited by Rehaan : 5th November at 07:31. BHPian  
Join Date: Dec Location: SINGAPORE Posts: 266 Thanked: 7 Times My god! What a reaction!!

Sorry guys if I have offended you. Did not realise that posting such an innocent thing will attract so much attention.

hellspawn:
How did you guess that it is a copy and paste thing? Well! almost everybody is copying pasting here on this site. Isn't it? So I decided to try my own copying and pasting;-) I tried to make it as simple as possible for everybody to understand.

esteem_lover:
There is neither a question nor a lecture. While going over many posts, I realised the there are quite a few here who would like to know or if given a start will find out more on piston rings performance. Reasons are very simple. If you are interested in performance, fuel efficiency or simply longer life to the engine, pistons rings are one of the weak links.

Bullfrog:
Working of piston ring is not a rocket science. But believe me, for desgin consideration, it is still a nightmare for design engineers. If you go in details of working of piston ring, you will realise it. Just ask yourself following questions:
Which is the ideal place for piston rings - at the top end of piston or bottom end of piston?
How do you control the temperature of piston rings?
How to avoid or reduce the taper (sloping) wear down of piston grooves in which the piston rings moves? How to lubricate the piston rings when they are TDC with such high temperature and pressure and not much speed to piston rings? And how to get the lube oil in good quantity to such a place without overlubricating the bottom part? In diesel engines, how do you avoid sulphuric acid corrosion at low load operation and high humid areas? etc etc

DRC:
Thanks. And sorry, I could not provide link because I typed it on my own and hence cannot provide any linky to it.

Anyway, thanks to you all for the feedback. Don't take it otherwise. I will ask one question again which I have asked before. Why can't we make our own site a complete database for which everybody in the world will refer to instead we going to other sites? Definitely, it has pros and cons about it. But we can think over it. Right guys! Last edited by jat : 27th October at 21:28. Newbie  
Join Date: Jan Location: FARIDABAD Posts: 11 Thanked: 0 Times Ok.. a Good Explanation.
But u forgot to mention.... There r basically 3 Types of Piston Rings!!

1. The top Piston Ring - which is made of Hard metal and is coated with hard Metal.

2. The Middle Piston Ring - Which is made of Cast Iron.

3 The Bottom Piston Ring - Oil Scrapper Ring, has a zig zag type scrapper ring and two rail rings on both side.

The Function of 1st ring is in initial period of engine life, wen the wear and tear is maximum. At that time the hard metal coating comes off and mixes with lube oil and smoothens the wear and tear areas!

The function of 2nd Ring is to Dissepate heat quickly from piston to cylinder. that is y made of cast iron which is good heat conductor.

The 3rd ring makes sure that the Lube oil sprayed from crankshaft on to the cylinder walls does not go above the ring in excess!

Besides that the rings are generally fitted at 120 Degrees wid each other from the clearance in the ring.
This is to ensure that oil or gases do not leak easily. BHPian  
Join Date: Oct Location: Bangalore Posts: 108 Thanked: 3 Times In the past, when the sealing methods were not advanced enough, there was a tendency for design teams to put a number of rings on there!!
The oil ring which is the bottom most ring as Vipul has pointed out, aids in adequate lubrication of the liner and on the downstroke, ensures the oil gets scraped off the liner to ensure it doesnt get burnt off and add to combustion/emission nightmares.
I have seen pistons of past design that have had 5 rings with 2-3 oil control rings.
Nowadays, the mantra is to move towards having as few piston rings as possible. (Its simple, more the rings, more is the friction as the rings press against the liner during operation)

It would be interesting to know why is it that we cannot eliminate the second ring i.e. go with just the top ring and the oil control ring...??