6 Bent Valve Symptoms Every Vehicle Owner Should Know

An engine is generally a complex machine that needs numerous parts working together to make it run smoothly. Such components include the engine valves. So, when the engine valves are bent, the engine is expected not to run great. As such, what are bent valve symptoms?

Bent valves can lead to problems such as loss of engine power, continuous engine misfires, low fuel efficiency, difficulty starting the engine, and more. We will discuss these symptoms in this guide to help you understand more.

We also talk about what can potentially cause the bent valves, how you can diagnose the bent valves, and the best solutions to the problem.

Understanding Bent Engine Valves

Engine valves are essential for controlling the flow of fuel and air mixture into the combustion chamber. Also, it helps with the expulsion of the exhaust gases. These valves have to open at the right time for optimal engine performance.

A bent valve simply means it has been physically deformed or bent and is no longer in its original shape. The deformation can occur because of many factors, which makes it hard for the valve to perform optimally.

When the valve is bent, there is no longer a tight seal against the valve seat. The result is that the engine losses compression, and the performance is generally low. There can be engine damage depending on how severely the valves have bent.

How To Recognize Bent Valves (The Symptoms)

How To Recognize Bent Valves

The bent valves can lead to many symptoms a person can experience while driving. It is vital to know these symptoms so they can be addressed early enough and handled quickly. Here are the common symptoms to watch out for in your engine.

1. Loss of Engine Power

The engine’s combustion process is affected when the valves are not working as expected. This potentially leads to a loss of engine power.

The bent valves do not usually close properly, leading to low engine compression within its cylinders. Low compression leads to low power output.

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Also, the bent valves would leave the engine running at a reduced air-fuel mixture in the combustion chamber. This also leads to low engine power. If you have been driving a car for a while, it is easy to know when there is reduced engine power.

2. Misfiring Engine

A misfiring engine is characterized by having irregular or complete combustion cycles in one or more cylinders.

You may notice the vehicle having rough idle, engine vibrations, hesitation in starting, and stumbling during acceleration. This should tell you there is a problem with the engine.

Having bent valves can be a reason for the misfires. This is because the valves are not opening and closing at the right time. This ultimately affects how the engine runs.

3. Valve Train Noise

Severe valve damage will require a distinct noise from the engine. It is commonly referred to as a tapping sound. Other sounds to watch out for include a ticking and metal clicking noise coming from the engine as it runs.

These sounds are because of the improper opening and closing of the engine valves.

The tapping sound is mostly prominent during the idle speed. It may also intensify if you put more strain on the engine.

Here is a video on how a tapping sound feels like coming from an engine

YouTube video

4. Backfiring

You can still consider checking your bent valves to see if they are the reason for the backfires.

Backfiring is when you hear a loud popping sound from the exhaust. Abnormal combustion in the intake or exhaust system causes this. This can happen if the valves are bent and the combustion process is disrupted.

Rough idling, misfires, and loss of engine power may also accompany backfires.

5. Low Fuel Efficiency

Many things may lead to low fuel efficiency, and bent valves can be the reason too. This is because if the engine cannot burn the air-fuel mixture as expected, you end up with fuel wastage. The result is decreased fuel efficiency.

The engine generally needs to use more fuel to compensate for the poor combustion of the fuel entering the combustion chamber. That is how you end up with reduced mpg.

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It is best to keep track of the vehicle’s fuel consumption and note any major changes. If there is a significant fuel efficiency drop, it is important to check for signs of bent valves and other related issues.

6. Check Engine Light

A check engine light can also be a symptom of bend valves. Each time you see the check engine light come on, run an OBDII scan to understand what could be the issue with the engine.

The scan gives you a report detailing what is wrong with the engine and seeing if it is related to bent valves. So, you should never ignore a check engine light because it can lead to further damage if not addressed on time.

What Causes Bent Valves?

What Causes Bent Valves

Now that you know more about bent valve symptoms, let us look at what usually causes such a problem.

1. Timing Belt/Chain Failure

A timing belt or chain is vital for the synchronized running of the engine. This means the valves can now open and close at the right time.

Remember, the camshaft controls the movement of the valves so that they work as expected. When the timing belt or chain snaps, then there is a disruption in this synchronization between the camshaft and the valves.

For an interference engine design, the valves will remain open when the pistons are moved to their maximum height. This results in a collision between the two. The collision leaves you with bent valves, damaged pistons, and a potentially damaged engine.

Here is a video on bad timing chain symptoms. It should help change it in good time to avoid such catastrophic failures.

YouTube video

2. Over-revving The Engine

Over-revving the engine, in this case, means you are running the engine at high RPMs for a long time. This will stress the engine valves, valve springs, and many other valve train components.

The engine manufacturer intended to have the valve train components operate optimally within a certain engine speed. When you exceed such limits, the valves will not close in good time to the point that pistons hit the valves.

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As mentioned before, pistons hitting the valves leave you with bent valves.

Over-revving happens mostly during aggressive downshifting or sudden throttle blips. Also, the valves may fail if you keep using the engine beyond the recommended safe limits.

3. Engine Misfires

As much as an engine misfire is a symptom of bent valves, it can also be the reason for bent valves in the first place.

An engine misfire means that one or several cylinders in the engine fail to ignite the air-fuel mixture in the combustion chamber at the right time. The common reasons for misfires include faulty fuel injectors, sensor malfunctions, ignition coils, and spark plugs.

So, how do engine misfires lead to bent valves?

When there is sudden deceleration of the pistons during a misfire, then they can hit the valves. Something as simple as a misfire leads to bent valves.

4. Accidents or Collisions

It is possible to get into accidents or collisions, impacting the engine. This includes having bent valves. Accidents such as front-end collisions and side impacts on the engine can have this effect.

So, if your vehicle was involved in a front-end collision, the engine should be checked first to see if there is a problem with it or not. During the engine inspection, look at the valves to see if they are still in good condition.

Diagnosing Bent Valves

You must know how to diagnose the bent valves first to know how best to make the repairs. It can be a simple repair, or sometimes you have to replace the engine. Before replacing the engine, we recommend the following methods to diagnose bent valves.

Visual Inspection

This is the first step to take in diagnosing the bent valves. It involves removing the valves from the engine and physically checking to see if they are bent. This method can help determine if the other valve train components are damaged.

Compression Test

A compression test is vital to understand whether or not the cylinders are operating at low pressure. It can also help in understanding if the valves are bent or not.

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In the case of bent valves, compression readings will be low. Each engine type will have the standard compression ratings. As such, determine the pressure range to expect for each cylinder and compare it to your results.

Here is a video on doing an engine compression test

YouTube video

Cylinder Leakage Test

A cylinder leakage test is a more compressive method to help see the sealing capability of valves, cylinder head gaskets, and piston rings. This is the best way to see if there are bent valves and pinpoint the location of the leakage.

We recommend taking the vehicle to a verified vehicle model mechanic so you can get the right fix.

Solutions For Bent Valves

Since you now know the symptoms of bent valves, finding the best remedies for such an issue is also good. Below, we discuss how best you can deal with the problem of bent valves.

Valve Replacement

Most of the time, the bent valves do not have much of a repair route. Mechanics recommend replacing the affected valves, and you should have a smooth-running engine once again.

To replace the valves, the cylinder head has to be removed first. This is followed by disassembling the valve train before installing the new valves. This process must be done right to have proper valve seating and alignment.

Make sure to replace any other parts that might have been damaged along the valve train.

Cylinder Head Inspection And Repair

Other than replacing the damaged valves, make sure to also check the cylinder head for signs of wear or damage.

Sometimes the cylinder head can also crack, warp, or develop other issues when there are bend valves. So, repair the cylinder head if necessary for the best performance. The repairs for cylinder heads can include resurfacing and valve seat machining.


Can I drive with bent valves?

As much as you can drive with bent valves, it is not recommended. This is because it can lead to further engine damage and cost much more to repair the engine. You should consider replacing the whole engine, which can be avoided.

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Will the engine start with bent valves?

Yes. The engine will still start even if it has bent valves. However, you may notice a few issues, such as rough idling because of bent valves. Other issues include misfires, backfires, and more.

Can the bent valves lead to engine overheating?

Since bent valves mean there is no proper sealing in the engine; there can be increased heat generation during the combustion cycle. Too much heat can also potentially lead to engine overheating especially if there is also a problem with the engine’s cooling system.

What is the average cost of replacing bent valves?

It largely depends on the engine type and the extent of damage. The cost may range from $200 to $500 in most cases. It can even be more if you need to repair the cylinder head too.


Bent valves can be an issue in the engine’s performance. It is possible to experience misfires, backfires, loss of power, rough idling, and more as the symptoms of bent valves.

We always recommend that you take note of such symptoms and have the repairs done in time to avoid making it worse. Most of the time, the solution is to replace the bent valves to ensure the engine runs smoothly again.