How to Fix Low Compression in One Cylinder ✔️

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how to fix low compression in one cylinderDoes your car seem a bit under the weather? Maybe you’ve been hearing your engine misfire when you start it, or you’ve noticed that your car hasn’t been performing as well as it used to. Unfortunately, these are all low compression in one cylinder symptoms.

Don’t worry, low compression isn’t a death sentence for your car. It involves a lot of hard work, time, and will probably result in you getting so frustrated that you’ll want to drive your “piece of $&!#” car straight into the junkyard. You wouldn’t do that though–you love your car too much.

You may be wondering how to fix low compression in one cylinder? Well, put on your seatbelt and get ready for the ride because I’m going to tell you how to get your car back on the road.

Possible Causes of Low Compression

Your car’s low compression can be triggered by a number of mechanical problems. Even if you’re wondering how to fix low compression in one cylinder for an outboard engine, you can trace the problem back to these causes as well. Luckily, they can all be repaired.

1. Head Gasket Problems

If your gasket isn’t aligned properly or is dilapidated, it can cause low compression in one cylinder. Gas from the inside of the cylinder will escape through the small hole or gap between the head and the cylinder. This prevents your engine from functioning the way it should.

Take a compression tester and measure the compression level in the cylinder. Make sure to check your gasket if your readings come out different.

2. Deteriorated Timing Belt

Your car’s timing belt connects the camshaft and crankshaft. A worn timing belt won’t allow the camshaft to turn.

When the camshaft can’t effectively open or close the exhaust valve or intake valve, combustion in the cylinders won’t occur and no gases will be emitted. As a result, low compression can occur.

3. Decrepit Pistons or Piston Rings

Your piston rings can get overheated, which makes the piston rings break. Carbon gases will then seep through the rings because they aren’t secured in the cylinder.

The pistons themselves can also get damaged. Usually, pistons are made of aluminum alloy strong enough to resist any damage from combustion.

But when there is too much heat in the engine, holes can form in the pistons. This causes gas to leak out of the holes and lowers compression.

To test if your pistons are worn out, you can pour oil into the spark plug hole. Then, test the compression. If it’s higher, then the cause of the compression issue is the piston or piston rings.

4. Cracks in Cylinder Wall

A cracked cylinder wall can definitely contribute to low compression. To find out of the wall is cracked, you can turn on the engine and keep the cap of the radiator open. Look to see if any air bubbles come out.

The bubbles you see are gases that are coming out of the cracks in the combustion chamber and escaping into the cooling system.

5. Valve Issues

On top of every cylinder are exhaust valves and intake valves. The valves are secured on the valve seat that is attached to the cylinder head. Both parts are comprised of a finely ground metal that forms the seal.

To power the combustion process, air and fuel enter the intake valve. The gases that form as a result exit out of the exhaust valve.

If the valves get overheated, the valve seal can get worn. This can make gas seep out and cause no compression in cylinder.

To find out if you have leaky valves, run the engine and use a compression tester instead of a spark plug. Keep an eye on the inlet manifold or exhaust pipe to see if there’s a gas leak. Any sounds that indicate a leak will tell you if the valves are bad.

If you find that your valves are damaged, you need to remove the cylinder head and do a valve job.

6. Flattened Camshaft

Every valve has a camshaft lobe. Sometimes, the camshaft lobes can get worn out as well, which won’t allow the valve to open.

When the valve doesn’t open, the cylinder can’t get any air in or release any exhaust gasses. This results in compression issues.

Check out your valves by removing the valve cover and flipping the engine over. Watch the valve movement that occurs. If you notice a problem, you need to replace the camshaft.

Steps for How to Fix Low Compression

Before you go tinkering with your car, you need to make sure that low compression is really the problem. Take a compression tester to get a measurement. These tests usually take about 45 minutes.

If you find that there’s low compression, you need to check all possible areas where the problem came from including the gasket, valves, pistons, and cylinder. Any type of damage in these parts can contribute to your problem.  Below you will find the steps that may be needed to fix the low compression issue:

Identify the Cause

Low compression can result from several factors, including:

Worn Piston Rings: This allows air to leak past the piston.

Faulty Valves: Leaking or not sealing properly.

Blown Head Gasket: Can cause compression loss between cylinders.

Cylinder Wall Damage: Scoring or other damage can affect compression.

Piston or Cylinder Head Issues: Such as damage or excessive wear.


Inspect and Replace the Spark Plugs (if needed)

Sometimes, low compression can be caused by fouled or worn-out spark plugs. Inspect and replace the spark plugs in the affected cylinder to rule out this possibility.


Perform a Leak-Down Test

A leak-down test can help pinpoint the source of the compression loss. It involves pressurizing the cylinder and measuring the amount of pressure that leaks out. This can provide more information about the condition of the valves, rings, and other components.


Check the Valve Seating

If the issue is related to valves, inspect the valve seating for damage or wear. Valve clearance adjustments or valve replacements may be necessary.


Inspect the Piston Rings

Worn or damaged piston rings can contribute to low compression. If the rings are at fault, unfortunately, an engine rebuild or replacement may be needed.


Address Head Gasket Issues

If a blown head gasket is suspected, inspect for coolant in the oil or vice versa. Head gasket replacement is a complex task and may require professional assistance.


Cylinder Bore Inspection

If cylinder wall damage is suspected, the engine may need to be disassembled to inspect the cylinder bore. Depending on the severity of the damage, this could require cylinder honing or even engine block replacement.


The good news is that, once you find the issue, all you have to do is replace the damaged parts.

The bad news? You’ll likely have to take out entire engine.

Look on the bright side. Maybe you can use the opportunity to do a very thorough cleaning of the entire engine bay?

Other Compression Issues

You may find that there is no compression in your cylinders at all, low pressure in all cylinders, or no compression in one cylinder. These issues have some of the same causes that low compression in one cylinder has.

No compression in all cylinders is also caused by a broken timing belt or a broken camshaft, while low compression in all cylinders can be traced to damaged piston rings.

If you find that there’s absolutely no compression in one cylinder, then there’s a variety of other causes. A dropped valve seat, damaged valve spring, a damaged valve, and a dropped valve can all lead to no compression in one cylinder.

Get Your Car Up and Running

Don’t get discouraged by the amount of work that’s required to fix low compression. With the right tools and the knowledge of how to fix low compression in one cylinder, you can get your car performing great again.

You may be interested in our guide on how to remove a cylinder head.

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