Piston rings have triple purpose



Piston rings seal the combustion chamber. They are set with precision so as to apply the correct pressure on the cylinder wall or liner, which ensures there is a consistent film of oil across the cylinder's working surfaces. This provides sufficient lubrication and protects against wear.


Piston rings from Perkins come as three rings. They are the top compression ring, then the intermediate compression ring and finally the oil control ring. These parts are relatively small in size but play a large role in the main cylinder block of your engine.



Their function is to seal off gases generated in the internal combustion process, help with transferring heat to the cylinder wall and then to both lubricate and scrape down oil from it. Getting the quantities of oil right is vital. Too much oil will cause it to burn off during combustion potentially making your engine produce blue smoke, too little will cause the engine ultimately to seize.


The primary role of the top compression ring is to seal off the majority of the combustion gases to ensure you get the maximum power output from your engine. Any failure or weakening of the piston ring in this area means your engine is working less efficiently than it should.


The bottom ring is responsible for most of the oil control, helping to make sure the right amount of oil is used to lubricate the working surfaces of the cylinder, while the intermediate ring helps with both functions, playing a finishing role in the combustion sealing as well as the downward oil scraping.


The result of these three rings working in harmony is sufficient lubrication within the cylinder bore, ensuring that no undue wear occurs at any time.


How Long Do Piston Rings Last?


Piston rings are a vital engine component since they seal the gap between the piston and the cylinder walls. High quality and long lasting piston rings are a must for all types of engines.


So, how long do piston rings usually last? Piston rings are typically built to last as long as the engine. As a result, piston rings usually last somewhere between 50,000 miles to 250,000 miles depending on their maintenance.


On an average, the life expectancy of piston rings is around 100,000 miles. One has to replace piston rings if they are damaged or worn out.


Life Expectancy Of Piston Rings


Piston rings are typically built to last as long as the engine. Since motorcycle engines last somewhere between 50,000 miles to 250,000 miles, piston rings should last around the same lifetime as well. On an average, piston rings should last around 100,000 miles.


Again, this is a highly subjective number depending on how good your maintenance is, the piston rings quality, and several external factors including engine oil levels, riding conditions (dusty regions are bad), etc.


If the piston rings are worn out or get damaged at a faster rate, then you might have to replace the piston rings far far earlier than their expected lifetime.


When Should You Replace Piston Ring


Firstly, if your engine has run more than 100,000 miles, then probably it is time for replacing the piston rings. But, do not go to all the lengths of removing the engine cylinder and taking the piston just to replace the piston rings if you are not facing any issues with the engine.


Rather, let things continue as long as there are no problems occuring.


However, as soon as you face a problem and have to repair an engine component, it is best practice to inspect piston rings and replace them if the engine has run more than 100,000 miles.


This is because if you are reworking on an engine component, its best to inspect all parts since you don’t want to go back to it again after sometime. Any work on the engine components like piston, piston rings, crankcase components, cylinder – are all cumbersome, time consuming and most of all, a costly affair.


Other times when you need to replace piston rings are when these rings are damaged or worn out.


Bad piston rings will cause more damage to both the cylinder walls as well as the engine itself. It’s better to replace the bad piston rings early rather than wait for it to damage other components.


Also, you cannot repair piston rings. Any sign of damage, just replace it. There is no easy way out here.


Replacement Cost Of Piston Rings


While piston rings cost around $50 to $200, replacement cost of piston rings is more than $2000.


This is because replacing piston rings is a laborious task. Although piston rings themselves doesn’t cost much themselves, the labor charges will be too high since piston rings replacement means taking out the engine cylinder head, removing piston from the engine, and then replacing the rings.


Typically, all this process will take around 10 hours altogether. As a result, the labor cost is far too high and costs so much for a simple piston rings replacement.


How Do I Know If My Piston Rings Are Bad


If the piston rings are damaged or worn out, there is no direct method to determine it. However, there are several symptoms which combined together will indicate that the piston rings have gone bad and should be replaced immediately.


First and foremost sign of bad piston rings is if you are seeing white or gray smoke coming out of the exhaust. White smoke is a clear indication that the engine oil is getting burnt in the combustion chamber. And the oil can only enter the combustion chamber if the piston rings are not sealing the piston and cylinder correctly.


In the same vein, if the engine is being consumed excessively and you are constantly seeing low engine oil levels despite several top ups, it is mostly likely because the piston rings are bad and are allowing the oil to moves into the combustion chamber to get burnt.


Apart from the indications from oil, you can also suspect bad piston rings from the engine. If the engine power and acceleration is consistently low, then the culprit is either the inlet and exhaust ports or the piston rings.


To pin point the culprit, you can test the engine compression. If the engine compression is considerably lower, then it is without a doubt certain that the piston rings are damaged and are not working properly. Here is a detailed post on on


To pin point the culprit, you can test the engine compression. If the engine compression is considerably lower, then it is without a doubt certain that the piston rings are damaged and are not working properly. Here is a detailed post on on signs of bad piston rings for more details.


One last sign of bad piston rings is piston slapping. If you hear piston slapping noise across the inner cylinder walls, then the piston rings are worn out and the gap between the piston and the cylinder walls have widened out.


Reasons for Cylinder Liner Wear and Ways to Measure it


All types of ship machines and parts get worn out due to continuous usage and working. Proper maintenance and routine checks are necessary to ensure that the machines work for a longer time. In this article, we will have a look at various reasons that lead to cylinder liner wear and how it can be minimised.


Reasons for Cylinder Liner Wear


The wear in the cylinder liner is mainly because of following reasons:-


1) Due to friction.
2) Due to corrosion.
3) Abrasion
4) Scuffing or Adhesion


Frictional Wear:


Whenever two surfaces slide over each other, friction is produced which leads to wearing down of both the surfaces. In liner wear, the surfaces are piston rings sliding over the cylinder liner. The frictional wear depends upon various factors like speed of movement between the surfaces, material involved, temperature, the load on engine, pressure, maintenance, lubrication, and combustion efficiency.


Corrosion:


The cylinder liner wear due to corrosion is caused due to these reasons:
– Burning of heavy fuel oil in the combustion space:
This happens because heavy fuel oil contains high sulfur content. During combustion, acids are formed inside the space which should be neutralised by cylinder oil which is alkaline in nature. The production of acids will be more if sulfur content is more, leading to the formation of sulphuric acid. Sulphuric acid is formed due to absorption of the condensate or moisture present inside the combustion space.


– Lower combustion chamber temperature because of reduced service load:


As the low load operation of the marine engine is gaining popularity, it also leads to low temperature in the combustion chamber. If the cylinder oil quantity is not matched properly with the load, it may lead to corrosion of liner.


Sulphuric acid corrosion is found more in the lower part of the liner as the temperature of jacket water is very low. Corrosion due to sulfur will be high due to the presence of water in fuel and condensate in the air. This wear is generally seen between the quills. The wear near the quills enlarges and gives a characteristic of the clover leaf shape to the wear pattern. This phenomenon is called clover leafing.


How the piston works
When the engine is running, the piston moves up and down in the cylinder. When the piston reaches the turning point, it slows down and then accelerates again suddenly. This produces inertia forces that act on the piston. When considered together with the forces generated by the gas pressure, this forms the piston force, which is transferred to the connecting rod and crankshaft. Connecting rods are only perfectly vertical at the upper and lower turning points. The angle of the connecting rod presses the piston against the side of the cylinder wall. The amount and direction of this force constantly change during the combustion cycle, as they depend on the piston force and the angle between the piston crown and connecting rod axis. Pistons are equipped with piston rings. They seal the combustion and working chamber in relation to the crankcase. They also remove the oil from the cylinder walls, thus controlling the oil consumption. Piston rings also discharge the heat absorbed by the piston during combustion to the cooled running surface of the cylinder liner.