How Long Do Piston Rings Last?

The piston rings of your four-stroke motorcycle engine have an important role in ensuring the efficient and smooth functioning of the engine.

This article is intended to make you aware of some of the important aspects of the motorcycle piston rings viz. how long do piston rings last, a brief about your motorcycle piston rings, and a few frequently asked questions on the topic.

The question “how long do piston rings of your motorcycle last” has a direct answer. The piston rings of your motorcycle can last 50000 miles and more, provided you maintain your motorcycle as recommended in the owner’s manual and do not skip any mandated periodical servicing. Experienced mechanics and motorcycle riders say it will last up to 100000 miles.

However, the above does not apply to a two-stroke engine motorcycle or a racing motorcycle due to their different engine design and working conditions. This article considers regular four-stroke motorcycles used on-road and off-road.

Let us explore more in the following paragraphs.

How Long Do Motorcycle Piston Rings Last?

The piston rings of your motorcycle engine can last 50000 miles and up to 100000 miles if you do the following:

• Take your motorcycle to the authorized service center at the intervals specified in the owner’s manual. Do not skip the recommended service check-ups.
• Use the recommended engine oil. The engine oil forms a thick layer between the piston ring and the inner cylinder surface to ensure good lubrication. If the oil quality is poor it may lead to metal-to-metal contact/friction and piston ring wear. This can also happen due to an insufficient quantity of engine oil.
• Keep the engine oil level as recommended in your owner’s manual and top it whenever necessary.
• Ensure the air filter and oil filter are clean (this will eliminate the dirt entering the engine).
• If you’re riding is in a dusty atmosphere, you may need to take additional care of the parts like the air filter, and fuel filter, and replace them more frequently.
• Flooding of the engine with a rich gasoline mixture can also contribute to the wearing of the piston ring. The unburnt fuel in the cylinder head /combustion chamber enters into the engine cylinder in place of the engine oil, and this hampers proper lubrication of the engine cylinder. Ensure your carburetor and engine are tuned to avoid flooding of the gasoline.
• If your owner’s manual specifies replacement of the piston rings after a certain number of miles are completed, consult your authorized mechanic and seek his advice if the replacement is needed or not.

Your motorcycle gives many indications to suggest the piston rings may be worn-out and the indications are:

• If the piston rings are not sealing the cylinder properly, the engine oil from the crankcase can enter the combustion chamber, and the mixture of air and gasoline can escape from the combustion chamber into the crankcase.

In the first case, the engine oil gets burnt along with the air gasoline mixture and the resultant exhaust smoke will be greyish blue or white color.  The exhaust gas of a healthy four-stroke motorcycle engine is normally non-smoky.

The result of the second case can be a reduction of the engine power. When you accelerate your motorcycle, if there is no corresponding increase in engine output/power, it may be due to worn-out piston rings.

• If the engine oil is getting burnt in the combustion chamber, it can result in faster consumption of the engine oil. So, if you are replacing the engine oil, more frequently, it may indicate worn-out piston rings.

The above issues can be due to other reasons also, but it may be wise to consult a trained mechanic who can conduct a compression test to determine if they are caused by worn-out piston rings. The loss of compression can happen if there is a crack in the cylinder head or similar issues. So, if the mechanic concludes there is a loss of compression in the cylinder, he/she can look for its causes.

Brief About Your Motorcycle Piston Rings

You are all aware that your motorcycle engine has a cylinder and a piston and the piston reciprocates inside the cylinder. However, if you make the piston directly reciprocate in the cylinder, the resulting friction between the piston and the inner surface of the cylinder generates overwhelming heat.

To minimize the frictional heat, piston rings are introduced between the inner surface of the cylinder and the piston.

So, when the piston reciprocates inside the engine cylinder, only the thin cross-section of the piston rings comes in contact with the cylinder, and this minimizes the frictional heat generated.

The piston ring has a thin cross-section and is split across its cross-section and the gap at the split is as per the design. The piston has grooves on its periphery to accommodate the piston rings. The piston rings on your four-stroke motorcycle engine can be a set of three or a set of two depending upon the number of grooves on the piston.

The basic function of the piston rings in your motorcycle engine is to preserve or control the compression of the air-fuel mixture in the cylinder, take care of the lubrication of the engine cylinder, keep the friction minimum, and dissipate the heat from the piston to the engine cylinder.

In a three-groove piston, the top piston ring is called the compression ring, and its function is to press against the inner walls of the engine cylinder and ensure good sealing. The sealing ensures the mixture of air and gasoline does not leak and enter the crankcase and the oil from the crankcase does not leak and enter the combustion chamber.

When the mixture of air and gasoline is ignited, the pressure inside the engine cylinder increase, and the high-pressure gas enters the top piston groove and expands the split piston ring uniformly to press against the cylinder wall.

The second piston ring works as a scraping ring and scrapes off the left-over oil into the crankcase when the piston moves down.

The third (bottom) piston ring is the oil ring and it has three parts (bottom ring, expander, and a top ring). This works to spread the lubrication oil around the cylinder.

In a two-groove piston, the design and function of the bottom piston ring/oil ring are the same as explained above. However, the top piston ring does the function of a compression ring as well as the scraper ring.

The material of the piston ring is cast iron or steel, and the piston is made of aluminum.

The gap of the piston rings never aligns on one line, it is always staggered as recommended in the owner’s manual. This is intended to avoid leakage. If the gaps are aligned, it may allow leakage of the compressed air-fuel mixture.

Due to the continuous rubbing against the cylinder, the piston ring undergoes wear and tear and loses its ability to provide the sealing. At this juncture, the piston rings need to be changed to ensure there is no leakage.

Frequently Asked Questions

A good set of piston rings ensures there is no leakage between the combustion chamber and the crankcase and also does the job of lubricating the cylinder. Maintaining your motorcycle properly and adhering to all the recommendations of the owner’s manual will make your motorcycle piston rings last longer.

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