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How to Tell if Motorcycle Piston Rings Are Bad

By Nidhi Nangia. Updated: August 28, 2019
How to Tell if Motorcycle Piston Rings Are Bad

Your motorcycle’s engine has piston rings which not only help your pistons work efficiently, but protect them from damage. If your piston rings do become worn out or damaged, you will start encountering a myriad of problems and issues. If left unattended, it will lead to several problems in your motorcycle’s engine and the result will be an expensive engine repair. This is why it's better to look out for the warning signs so that you can get them resolved in time. This oneHOWTO article will help you know how to tell if motorcycle piston rings are bad.

You may also be interested in: How to Clean a Motorcycle Chain

Symptoms of bad piston rings in a motorcycle

The piston rings fit round the piston head, the large part on top of the piston. The piston moves up and down a cylinder to compress the gas and power the engine. To aid in this process, the piston rings:

  • Seal the combustion chamber to keep as much gas in the cylinder as possible.
  • Maintain oil quality and regulate the amount of oil used in the cylinder.
  • Aid in heat transfer.

The piston rings move up and down the cylinder, so they need to be robust. To reduce wear they are lubricated with motor oil and are made from durable metals (mainly iron and steel). As durable as they may be, however, they can wear out or become broken. The main reason for this is wear over time. It is possible they will become loose or broken for other reasons, but these would need to be more specific.

If there is a problem with your piston rings, the motorcycle will experience various symptoms. These symptoms may be similar to other problems you may see when there is poor compression in your motorcycle. While these symptoms may not be a sure sign of having bad piston rings, they can be good indicators that you need to check your piston rings for damage or wear. If this is the case, they may need replaced immediately. Some of the symptoms to look out for are:

  • Grey or white smoke from the motorcycle’s exhaust: grey or white smoke from you exhaust system is a sure sign of burning oil. This can happen when oil leaks into your motorcycle’s combustion chamber and it gets burned alongside the gas.
  • Excessive consumption of oil: if your motorcycle’s piston rings are bad or worn out, the oil will start flowing into your bike’s combustion chamber, meaning you need to replace the oil more often.
  • Low power when you accelerate: when your piston rings are bad, compression will be deteriorated which leads to lessening the power of your motorcycle’s engine. The result will be poor acceleration.
  • Overall deterioration in performance and power: although loss of power is something caused by various possible motorcycle engine issues, damaged piston rings are one of them.

How to check piston rings of a motorcycle

When you notice any of the above symptoms, you should consider the different possible problems which may be affecting your motorbike. Damaged piston rings are only one of them. Ideally, you will take the motorcycle to a qualified mechanic. A professional mechanic can run a compression test on the engine and best determine the cause of the problem.

A compression test, also known as a leak-down test, works by introducing compressed air into a cylinder and working out the rate of leakage. This requires a compression gauge. This is similar to the gauge used to check tire pressure, but it is usually more durable and adapted to the cylinder itself. You can purchase this compression gauge yourself, but you will have to weigh up this cost with how much you would use it.

Whether you or a mechanic are testing the motorcycle cylinder's pressure, this is the process:

  1. Bring the motorcycle to normal running temperature by letting the engine run for a while, but turn it off afterwards.
  2. For fuel injection engines, disable the fuel pump by removing the fuel pump fuse. Otherwise turn off the petcock and release all the fuel.
  3. Remove all the spark plugs and the ignition fuse (if applicable).
  4. Attach the compression gauge to one of the cylinders, lubricating it first with come grease.
  5. Hold open the throttle and kickstart the motorcycle. You will probably need 3 or 4 kickstarts until the needle on the gauge moves.
  6. Record the reading and repeat with all the other cylinders.

Once the readings have been recorded, you need to check it against the motorcycle's manual to know what level it should be. If you do not have a manual, you should be able to look online. However, there are so many complicated parts to testing a cylinder's pressure that a mechanic should do it if you are unsure what you are doing. Also, although a compression test will help us to check if the piston rings are bad, there may be other reasons why the cylinder has lost pressure (e.g. a cracked cylinder head).

How to Tell if Motorcycle Piston Rings Are Bad - How to check piston rings of a motorcycle

Other ways to check piston rings

A more direct way to check if the piston rings are bad is to take a look at the them. As we said before, the piston rings are located around the piston head. You can look at their quality by seeing if they have any evident damage. Although they are made from durable metals, they can be worn.

Unfortunately, to check the piston rings directly is not an easy task. It will require removing the entire topend of the motorcycle. Once this happens, it is possible the piston rings look fine, but are actually letting oil slip or damaging the cylinder. This is why you experience any of the above symptoms, you should check the pressure first. If the pressure is fine, then it is likely to be another problem. For example, white smoke may be emitted due to a problem in the fuel line.

How to replace motorcycle piston rings

If your motorcycle’s piston rings are bad, you will need to get them replaced as soon as you spot the problem. The price that you will have to pay depends on a number of factors. The most important is the make and model of your motorcycle. The type and condition of your motorcycle’s engine will also determine the overall cost you will have to pay.

Replacing motorcycle piston rings could be very expensive. The reason for this is because it is very labor intensive. If a mechanic is charging around $100 per hour, the job could cost $500 to $1000 or even more. The process could take a day as the topend needs to be pulled apart. You could get a deal, but it is up to you to get a quote and judge the cost.

If a mechanic is sure the piston rings are the problem, they will need replaced. If they do this work, you should get any other issues looked at while the topend is off, such as checking the valves. This is because it is a big and expensive job, so you might as well lessen the chances of having to do it again.

How to Tell if Motorcycle Piston Rings Are Bad - How to replace motorcycle piston rings

Conclusion

There may be several reasons why your piston rings get damaged or worn out. But with regular maintenance and service of your motorcycle, the components will receive minimal damage. Poorly maintained motorcycles will wear out the piston rings more quickly. For example, not replacing the motor oil regularly will mean the piston rings are not lubricated and will damage more easily.

If you want to ensure your motorbike has a long and healthy life, then you can follow these 10 motorcycle maintenance tips to keep your motorbike healthy. You will also need to have your motorcycle checked regularly. In some countries, the motorcycle will require a road worthiness test every year. Some countries do not, but they are a good idea regardless.

If you want to read similar articles to How to Tell if Motorcycle Piston Rings Are Bad, we recommend you visit our Motorbike Maintance and Repair category.

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gokulbalaji
very useful
OneHowTo Editor
Thank you Gokulbalaji!
naveen kumar
hero splendour plus heavy black smoke coming from my bike.

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