Key Takeaways
The following are the key takeaways from this article:
- Piston rings are present in the outer diameter of the piston crown and act as a seal between the piston and cylinder wall.
- Piston rings also return the engine oil to the sump from the cylinder walls.
- The piston rings can be damaged due to the accumulation of dirt/oil, fuel flooding, and melted piston head.
- The symptoms of bad piston rings include excessive black smoke, poor engine performance, increased oil consumption, and poor vehicle acceleration.
- It usually costs around $750-1000 to replace the piston rings of common vehicle models in the US.
Introduction
Piston rings are metallic rings attached to the piston around the outer diameter. They are designed to act as a seal between the piston and cylinder wall. As a result, the combustion gases are sealed and do not escape.
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An optimum gap is kept between the piston and cylinder wall for the proper functioning of the piston. Usually, a smaller gap will result in the piston seizing, impacting other engine components (1). Similarly, a larger gap will cause the combustion gases to enter the crankcase, and as a result, less pressure will be maintained within the cylinder. This will eventually reduce the power output of the engine. So, an optimum gap is maintained between the piston and cylinder walls, with piston rings acting as a seal between the two. This article will shed light on the function, common problems, and symptoms of bad piston rings.
The function of Piston Rings
As the name indicates, these rings are in the piston, which seals the gap between the cylinder and piston. The top and second piston rings within the piston accomplish this sealing task.
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These rings press tightly against the cylinder walls, so the lubrication oil remains out and the combustion gases do not enter the crankcase. Another important function of the piston ring is to return the engine oil from the cylinder wall to the oil sump. A thin oil film is present between the piston and cylinder wall to facilitate the piston motion (1). The third piston ring/oil ring collects this thin oil film from the cylinder wall and returns it to the oil sump. During the combustion process, some of this oil is burnt due to high engine temperature. And the remaining engine oil is returned to the sump for further lubrication (2).
Piston Rings and Friction
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The major problem with piston rings is that the sliding motion of the rings within the cylinder results in friction. Resultantly, around 24% of the engine power is lost during this function. So, the piston rings are considered a compromise between friction and achieving good engine power.
The major problem with the piston ring design is that it has an oscillating motion instead of a continuous motion, making lubrication a major problem. A result of this problem is an improved quality motor oil that survives high-temperature and harsh conditions of high-speed sliding contact (5). However, the piston rings must float in the grooves to remain in contact with the cylinder. Restraint movement or binding of rings in the piston can result in engine damage and eventual failure.
Common Causes of Piston Ring Damage
Following are a few common problems of piston rings:
Accumulation of Dirt/Oil Contamination
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The major reason for piston ring damage is the dirt or oil contamination within the piston grooves.
As explained above, the rings need to move freely in the groove for proper sealing, and their restrained motion will impact the piston ring’s lifespan and cause internal engine damage. First, the dirt accumulating in the piston grooves is one major reason that restrains the movement of the piston rings (1). Secondly, the piston rings scrap oil off the cylinder wall so that some oil particles can remain within the piston grooves. This also restrains the free movement of piston rings within the grooves, impacting their lifespan.
Damage due to Fuel Flooding
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Fuel flooding is another important cause of piston ring damage. During combustion, certain faults result in condensation and fuel accumulation on the cylinder walls.
The fuel particles wash off the lubrication oil resulting in mixed friction, and the piston rings wear completely after driving a few kilometers (3). Not only the piston rings are impacted due to mixed friction, but the cylinder surface also scraps off. A common symptom of fuel flooding is the rapid decrease in engine oil levels in the vehicle. It is to be noted that the wear on all piston rings will not be of equal level due to fuel flooding (2). If the wear on all piston rings is of equal level, then it is due to the accumulation of dirt/oil and low-quality lubrication.
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Fuel flooding occurs due to faulty fuel injectors, fuel pumps, blocked air filters, and poor fuel quality.
So, the drivers are recommended to resolve faulty fuel injectors/fuel pumps, air filters, etc., before fuel flooding occurs, and the piston rings also need to be replaced.
Melted Piston Head
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Another cause of piston ring damage is the overheated piston crown. The piston crown will overheat due to increased friction with the cylinder wall.
As a result of the melted piston head, the piston rings will also be damaged and deformed (3). So, the drivers are recommended to take care of the piston lubrication to enjoy a seamless driving experience.
Common Symptoms of Bad Piston Rings
Following are a few common symptoms of bad piston rings:
Excessive Black Smoke
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A common symptom of bad piston rings is the exhaust pipe’s excessive smoke. The smoke will mostly be black and dense. However, the color of the smoke can also be dark grey or blue depending upon the fuel type and its leakage.
This smell would also accompany the burning oil smell from the exhaust pipe. This is because bad piston rings will leak the oil into the combustion chamber (2). This excess fuel will be burnt in the combustion chamber resulting in excess smoke.
Poor Engine Performance
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Another common symptom of bad piston rings is poor engine performance.
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This is the worst case when the piston rings have failed, and there would not be enough pressure within the combustion chamber to generate power (4). In this case, the engine might not start, and you must tow the vehicle to the nearest service center to resolve the problem.
Increased Engine Oil Consumption
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This is another symptom of bad piston rings. When fuel flooding occurs, the fuel on the cylinder wall washes off the engine oil.
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Hence, the piston rings would not be able to return the oil to the sump. Similarly, when the piston rings are worn out, they would not be able to return the remaining engine oil from the cylinder wall to the oil sump (4). In this case, the oil level in the reservoir would be decreased. So, if you are experiencing a drop in the engine performance along with the decreased oil level in the reservoir, there is a chance that the piston rings have gone bad.
Poor Acceleration and Check Engine Light
The final symptom of bad piston rings is poor acceleration. When the piston rings have gone bad, they might need to maintain an optimum combustion pressure resulting in poor acceleration. As a result, the vehicle will not accelerate despite pressing the accelerator (5). Similarly, the check engine light will also appear on the vehicle’s cluster meter, indicating a problem with the engine.
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You can always connect a hand code reader with the OBDII module to check for a particular problem in the engine.
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Common Cost to Resolve Piston Ring Issues
The following table illustrates the common costs of resolving piston ring issues (5):
| Common Piston Ring Issues | Cost to Resolve the Issue |
|---|
| Bad Piston Rings | $750-1000 to replace the faulty piston rings |
| Faulty Fuel Injectors causing Fuel Flooding | $350-800 to replace the fuel injectors |
| Faulty Fuel Pump | $400-800 to replace the fuel pump |
| Low Engine Oil Level | $35-100 to fill the refill engine oil |
Conclusion
To conclude, piston rings serve an important function of cylinder sealing. So, the oil does not enter the combustion chamber, and the combustion gases do not enter the crankcase. There are three types of piston rings, where the first two piston rings serve the purpose of sealing and the third piston ring serves the purpose of returning the engine oil to the sump. Sometimes, the piston rings can go bad due to the accumulation of dirt, fuel flooding, and overheating. In this case, you will experience excessive smoke from the vehicle, poor engine performance, increased engine oil consumption, and poor acceleration.
FAQs
Usually, the piston rings of normal vehicle models in the US will range between $750-1000. However, replacing piston rings can be expensive if you own a supercar. Similarly, labor costs can also increase depending on the engine’s complexity. So, take care of the engine maintenance to increase the lifespan of piston rings.
There can be several causes for piston rings to break. The common cause includes excessive clearance in the piston and cylinder wall. This will increase pressure on the piston rings, and driving for increased distance can even break piston rings.
You can know this by a few symptoms, such as increased smoke from the vehicle, poor engine performance, increased engine oil consumption, etc. However, these symptoms can also be caused due to other engine component damage. So, always check the OBDII code before ordering new piston rings.
