How To Fix Low Compression On A Motorcycle

Today we will learn everything about how to fix low compression on a motorcycle.

You might be experiencing that one of the cylinders of your bike is frequently misfiring. There will be a lot of roughness in it. And when you check the compression, you will be getting low readings as well.

If there is no compression, your engine won’t start altogether because all the cylinders have misfired. All in all, various symptoms will indicate low compression in your motorcycle.

So, what are its different causes, and what can you do to resolve the issues? We will discuss everything about it in this article, so keep reading.

What Causes Low Compression in A Motorcycle?

Causes of low compression in motorcycle

You might be thinking, what are the causes of a low compression? There are different causes due to which low compression occurs. You might be dealing with worn-out pistons or piston rings, which is the most common reason a motorcycle runs on low compression.

But there are some other causes as well. Faulty valves or valve seals can cause this problem as well. And if your camshaft timing has gone wrong, then it can also result in low compression.

This problem may also arise due to worn-out head gaskets or even if you have cracked as well as cleared cylinder walls. Any one of these issues can contribute towards low compression, and there might be more than one issue contributing to the problem.

Therefore, you need to run a check on all these before you start tearing your engine apart. You need to be sure about the cause so you can fix it and sort anything out simultaneously. Else, you might end up facing this problem again.

How Can You Fix Bike Engine Compression Without Going to Service Center?

Motorcycle service center

So, how to fix low compression on a motorcycle without going to the service center? This is something that several people ask because most of the time, the repairs are quite hasty, and you run into the same problem again but due to a different cause.

But doing it on your own must require that you have some experience in dealing with engines before. If you don’t have such knowledge, you should visit your mechanic.

As there can be different causes for low compression on your motorcycle, you will need a compression gauge to pinpoint the issue exactly. Using this gauge, you will run a compression test. But make sure you disable the engine so it won’t start when you are conducting the test.

You have to remove your ignition coil along with the spark plug from your cylinder (the one you are testing). Now insert the gauge extension and make sure to screw it in properly. You can ask for help in cranking the engine up for you. Keep looking at the gauge till you reach full compression.

A good engine needs to have 100 PSI compression per cylinder. If you have found that two cylinders are right next to each other and have low compression, then your culprit is a blow-up gasket.

If low compression is there, you will have to replace that leaking part no matter which part it includes anyone of the above mentioned. Moreover, if your motorcycle is old and prone to overheating, more than one part can be faulty.

The repair cost will depend upon the arts that have failed, and with more parts failing, the price will increase. But your options are pretty limited because you can’t ride your motorcycle running low on compression.

Why Perform a Compression Test?

Perform a Compression Test

You might be thinking, why a compression test when it is already running low on compression because of the misfiring cylinder? You know when your bike is misfiring in one or more cylinders, but you must perform the compression.

It is going to highlight what is the underlying cause of the problem. There can be more than one reason why your motorcycle is running low on compression. You need to identify the issue accurately, and its repair cost before you begin disassembling your engine.

Tearing your engine apart hastily can never be beneficial, especially if you don’t know how to get it back into your bike. If you have such experience, you need to run the compression test and work on the part right away. Even if you are taking your bike to the mechanism, you will know what problem needs attention.

Which Compression Gauge Should You Use?

Okay, compression gauge, but which kind of compression gauge should you go for? There are two types of compressions gauge commonly used for motorcycles. There is a screw-in compression gauge, and there is a rubber plug compression tester.

Screw-in compression gauge

This tester features a hose linked to it, and there is a fitting at the end of the hose. This fitting screws into your spark plug opening and can be fastened with an o-ring. This tester works well with all types of engines, and you won’t need any external help.

Rubber plug tester

There is a rubber plug tester as well, and you need to press the rubber nipple into the spark plug hole and then crank your engine using the starter. Therefore, you will need another person to crank the engine. This tester doesn’t work on most modern engines, so there are a few discrepancies here.

Dry vs. wet test

A wet test is just like a dry test, but there is a slight difference. A wet test is conducted by putting some oil in the cylinder under consideration. If you put some oil in and see that the compression is better, you will have worn out the rim or even worse. If the compression doesn’t get better, then there is some issue with the valve.

How to Perform the Test?

How to fix low compression on a motorcycle by performing the test? The entire process is pretty simple, and you won’t have to go through much to complete it. Just keep in mind that your bike engine must be hot during this period. The engine can be cold if your bike is non-running. But the values can be around 10 to 15 PSI lower in some scenarios.

Here are the steps you need to follow:

  • Turn your petcock off and run your bike until it burns all the fuel. For the fuel injector engines, you will need to remove the fuse of the fuel pump.
  • Remove the spark plugs and ignition fuse as well.
  • Now hook your tester, and don’t forget to grease your o-ring adapter to prolong its life.
  • Keep the throttle open all the way and crank your engine till the needles stop moving. You will need about three to four kicks.
  • Record the value and then compare it with the numbers given in the service manual.
  • Now repeat all the steps for other cylinders as well.

What Compression Test Results Indicate?

Now how to interpret the results? Engines need over 100 PSI to start; they won’t run properly. Most healthy engines have over 120 PSI. You might have to investigate further to find out the issue accurately, but on a 4-stroke bike, the low numbers are caused by worn-out exhaust valves, head gaskets, or piston rings.

Whereas on a dual-stroke bike, a head gasket or piston ring can be the issue. The test results will only show whether you have proper compression or not and don’t highlight the primary cause. On a 4-stroke bike, you will have to do a leak-down test to identify the issue.

How Do You Increase Compression on a Motorcycle?

Increase Compression on a Motorcycle

What can be done to increase the compression ratio? It’s an important question in resolving how to fix low compression on a motorcycle. Well, you can increase the compression on your bike by making smaller changes to its engine.

Skimming the cylinder is one way of doing it where you need to machine away from its bottom face where it pretty much feels right against the cylinder barrel. It effectively lowers the volume of the combustion chamber. You can also fit high compression pistons with a raised crown for increasing the compression.


Can bad spark plugs cause low compression?

Yes, bad spark plugs and even worn-out plug wires and cracked caps can also cause low compression. So, you need to keep the spark plug in good condition as well.

What causes no compression?

No compression occurs when all the cylinders of your engine misfire at the same time. The reason can be more than one worn-out component, and the cost of repair will be high.

Does higher compression mean more torque?

Yes, with better or higher compression there is a more significant turning effect on the cylinder crank. It means the engine will give more push to the piston, and due to this, more torque is generated.

Do high compression engines run hotter?

With high compression, more heat is generated as the engine is putting more push on the pistons. Therefore, its temperature will be higher. Diesel engines are hotter because they are pushing the pistons faster as compared to petrol engines.

Does more compression mean more power?

It means your engine will perform much better and generate more power without consuming much fuel. Plus, there will be lower exhaust gases as well.


So, fixing your bike’s compression isn’t that easy of a job. But if you have some prior experience with engines and accurately identify the issue, you will significantly reduce your costs by not going to the service center.

How to fix low compression on a motorcycle will require some serious attention because if more components contribute to the issue, you will have to bear more repairs.