Bad Engine Valves – How To Spot Them?

Bad Engine Valves – How To Spot Them?

July 22, 2021 3 By CarGuy

Have you noticed recently how your engine starts to misfire or lose compression? If you have one of these symptoms, you may have a bad engine valves issue.

This is one of the most common issues that plague car owners, especially on higher mileage cars. These problems usually start to appear above 100,000 miles. Although in some cases they start to appear even sooner than that.

The most notable symptoms of bad engine valves are loss of power, misfires, low compression, burnt spark plugs. We are going through all of them later in this article. We also going to discuss the possible fixes and how to fix bad engine valves DIY.

This can also be an expensive problem to fix. But in this article, I’m going to explain how to fix this issue by using common tools and some new parts. We will learn how to bring back the valve seals and valve seats in mint condition, so you can regain the power of your engine. So, if you want to learn more about how to fix burned or bad engine valves. Follow along.

How To Tell The Difference Between Intake And Exhaust Valves

It is fairly easy to tell the difference between the intake and the exhaust valves. The Intake valve has a bigger diameter than the exhaust valve. Around 30% larger to be more exact.

Although in some simpler single piston engines the size can be the same. In these cases, you can tell which one is which based on the timing. When one valve opens the other valve closes.

It is also worth noting that these valves are made out of different metals because they have different roles that need to do. The exhaust valve needs to be stronger because there is a lot of psi of pressure 40-100 times stronger than the intake pressure which is around 14 psi.

An engine can be a dual valve and multi-valve. The dual valve incorporates one intake and one exhaust valve. The multi-valve engine incorporates four valves, two intake, and two exhaust valves.

There can be five and six valves, but they are not that common as two and four-valve applications.

Intake And Exhaust Valve Function

As their names say. One valve is intake and one is exhaust. When the intake valve is open, air and fuel mixture is inserted inside the cylinder.

Then a big boom happens inside the cylinder and the intake closes. After the intake valve closes the exhaust valve opens and collects the exhaust gasses from the burned fuel.

All this happens in one revolution. Remember, intake opens, fuel and air get injected into the cylinder, and the intake valve closes. Then the sparkplug makes spark causes an explosion. and the exhaust valve opens to collect the exhaust gasses.

By this example, we can conclude that intake and exhaust engine function is very straightforward. When one valve opens the other valve closes. All this per one revolution.

How To Check For Bad Engine Valves

In order to check for bad valves, the first thing you need to do is to remove the cylinder heads. In order to get there, you need to remove a lot of things.

1. Remove Intake Manifold Fuel Lines And Ignition Coils

First, you need to remove the intake manifold, fuel lines ignition coils. And then you can reach the heads. This process will take you around 3-4 hours if you don’t have experience. If you have already taken apart your engine, you can do this job fairly easily.

If you haven’t done this, it is useful to watch some videos with instructions on how to do this job for your specific engine.

2. Remove The Head Covers

Nevertheless, after you remove all of the necessary components to get to the engine head. Now it’s time to remove the headcovers.

3. Remove The Head Bolts And Rocker Arm

After you removed the head covers, now it’s time to get a torque wrench and untorque the head bolts and remove them, also remove the rocker arm. Also, the camshaft bolts if your engine is an overhead camshaft engine.

If you have an overhead camshaft engine you will also need to remove the timing chain. You can do this by relieving the chain tensioners. But remember not to mess up the timing when reassemble.

4. Inspect The Head Valves For Damage

Once the head is disconnected from everything. Now you can dive deeper into inspection and see what is wrong with the head.

Check the carbon buildup and how much the valves are sealing. See if your valves are in good condition. If they are not, you will instantly notice. If your valves are leaking oil, you can change your valve seals. But we will leave that for a next article.

Since we learned how to check for bad valves, now let’s see what are the burnt valve symptoms.

Burnt Or Bent Valve Symptoms

Burnt intake valve symptoms can be many. We are going to cover the most common ones and list them. Although intake and exhaust valves are doing a different job, the symptoms for both of them when fail are pretty much the same.

1. Misfires

Bad valve seals will cause the engine to misfire. Your engine will probably have some trouble running properly if there are bad engine valves. This also includes increased fuel consumption in the process. If you notice that your engine works unevenly and is trying to stall. That means that the misfires are strong and if you run it like this for a long time, the problem can become worse.

If you have misfires in your engine the best thing is to check your car with an OBD scanner and the tool will tell you which cylinder is misfiring. You can find these tools online for very cheap. But if you want to get a more quality scanner you will also have to pay a bit more.

2. Low Compression

Low compression is also one of the symptoms of bad engine valves. If there is no compression in one of the cylinders the car will also be down on power and will start to sound very strange. You will probably hear some tapping sound from the engine if there is no compression. This is because the valves or the piston rings do not seal properly.

There will also going to be a lot of blowby. Just remove the oil cap and give it a few revs, if it blows out of the oil cap, it means that the engine has a lot of blowby and low compression.

If you want to be sure, you can get a compression tester. In our previous article, we explained how you can use these testers and where to find them. They are fairly inexpensive tools and will tell you which cylinders in your engine are affected by low compression.

3. Poor Performance

Since your engine does not have compression, you will be down on one cylinder. And running on one cylinder means that you are low on power. This will reduce your horsepower level and make your engine very sluggish.

3. Burnt Valve Sound

Your engine will also be going to start to make a burnt valve sound. If you try to listen to the cylinders and hear how they work, you will notice that one of them is making a weird noise that is not characteristically for an internal combustion engine.

4. Bent Valve Sound

If your valve is bent you will hear how the cylinder is hitting the valve. This will be a hard metallic sound like something really bad is going on inside your engine.

Bent valve sound will be like someone is hitting a metal with a hammer. Especially the first time when the valve gets bent.

Running your car with a bent valve is not recommended, and you need to solve this issue.

How To Fix A Burnt Valve

How to fix a burnt valve is a pretty straightforward job. In one of your previous chapters, we have explained what needs to be removed in order for the engine head to come out from the block. And now we shall continue with our repair tutorial.

Step 1: Remove Valve Springs

In order to do this job, you need to get a special tool to remove the valve springs. Valve springs have high tension on them and you need a tool to release this tension for them in order to be popped out from their place. You can get these tools almost everywhere, there are many places that sell them like Amazon or your local parts store.

Now let’s begin with how to fix a burnt valve tutorial. Let’s say you have the tool. And now you need to install the tool above the spring and relieve the tension that is on the spring. After this, you remove the clip that is holding the spring in place and pop the valve.

Step 2: Remove The Valve

Check the condition of the valve and also the condition of the valve seat. Make sure that your new valve sits tight on the valve seat. If not, you will also need a new valve seat.

Step 3: Replace The Burnt Valve

Replace the valve and the valve seat if needed. Just remember that these new valve seats are not machined and you will have to look at some videos on how to machine them to seal your new valve properly.

Note that if you are not skilled to mount the valve seats and make them flush with the new valve, you can take your head to a machine shop where they will do proper machining and will install all your valves correctly and you will have a perfectly running engine head.

Step 4: Replace The Valve Seats

After you install these components, it is also useful to use a new valve seal and replace all the old ones. This will make sure that you don’t have an oil leak inside the cylinder. Valve seals tend to fail. You can check how to do this in our new article about valve seals.

Step 5: Reassemble The Head

After this job, you can start the assembly process. You need to put everything back together and make sure that you don’t have leftover parts. If you have leftover parts it means that you messed up something.

How To Fix A Bent Valve

Bent valves are unfortunately a worse problem than burnt valves. If your valves get bent, it means that there is damage inside of the engine. And if you run your car runs like this, the damage will get bigger and bigger.

If you hear a tapping noise from the engine, turn it off and call the roadside assistance service to pick your car up. If you don’t do this your engine will mangle on the inside.

When valves get bent, they start hitting the piston. Almost in every case of bent valves, you will need a new piston and a new valve. And you should consider yourself lucky because of this.

Because if the situation gets worse. Your head and cylinder walls may get mangled and destroyed. If this is the case in your car. The cheapest solution will be to get a new engine. Because this damage is unfixable. So, pay attention when your engine starts to make some weird noises and try to act as soon as possible in order to prevent these outcomes.

Burnt Valve Repair Cost

Burnt valve repair cost is not high if you are only replacing the valves. A single valve is like $15-$30. But if you replace also the valve seats and stem seals it can add up to $70-$100. This is only for the parts. We don’t count the labor that needs to be put into this job, and also machining if needed.

When all this adds up at a mechanics shop, depending on the severity of the issue it can cost from $700 up to $1500. These numbers are approximate and it really depends on where you take your car to and how expensive is the shop

Bent Valve Repair Cost

Bent valve repair cost can be a bit higher. Because you need the valve, and also a new piston and O-rings. New bearings for the piston. New piston rod. This job can get even up to $2000 at a mechanics shop. Only the piston and all of the components can cost around $200 plus the valve and the seal $70-100. It doesn’t come cheap. Also, these numbers are approximate and prices may vary from engine to engine.

If your engine is too far gone and everything is mangled inside, you will probably going to need a new engine, and in my opinion that is a cheaper way instead of rebuilding an old engine with compression issues.


In this article, we have summed up everything when it comes to bad engine valves. We learned a lot about how to disassemble the engine and find our issue with bad engine valves.

We also learned what are the main symptoms of bad engine valves and how to recognize if your engine valve has failed.

And lastly, we looked at the possible outcomes for this problem. How you can solve this by yourself or by visiting a professional mechanic.