Bent Valve Symptoms – What Are the Causes and Solutions?

Bent valve symptoms signal issues with your car engines, especially the internal combustion chamber, resulting in decreased overall performance. Some symptoms include engine misfiring, rough idling, low power generation, increased oil consumption, etc.

Bent Valve Symptoms

Failure to rectify these issues may result in more severe complications requiring significant repair costs. This article explores these symptoms, their causes, and quick fixes, among other intricate details.

What Exactly Are Bent Valve Symptoms?

Bent valve symptoms are signs and defective symptoms your internal combustion engine displays when the valve gets bent or damaged. Such symptoms include engine misfiring, rough idling, excessive engine shaking or vibrations, increased oil usage, etc. The level of damage to the valve may determine the extent of such symptoms.

Engine Misfiring

A common symptom of a faulty valve is a misfiring engine. Your car engine will misfire when the intake or exhaust valve is stuck – either open or closed. False coordination of the valve opening and closing causes a disruption in the combustion process, which results in the observed jerking or hesitation during acceleration – a misfire.

For example, if the intake valve is opened for longer, it can cause the engine to run lean – consequently, a misfire. Likewise, an exhaust valve stuck open or improperly closed will cause the quick release of gasses before the complete combustion cycle.

Inadequate Power and Reduced Performance

As mentioned earlier, bent valves can disrupt the fuel-air mixture, causing the engine to run lean. It affects the normal combustion process, resulting in the engine not generating enough power and an overall decrease in performance.

This is evident in difficulty driving up a hill, overtaking maneuvers, hitting high acceleration, or maintaining high speeds. Also, there is an increased production of dark smoky fumes.

Rough Idling or Engine Shaking

Another symptom of noticing your car has a bent valve is you see the engine is idling. Even when your vehicle is stationary, you notice uneven idling speed or fluctuation of the RPM.

Car Engine Shaking

In other cases, a defective valve may signal an abnormal, overly engine shaking or vibration. It could also be car parts like the steering wheel or other components.

Excessive Oil Consumption

Another bent valve symptom is an increase in oil use. Even slightly bent valves can cause incomplete sealing or valve seat opening against the cylinder head. As a result, the oil may leak into the cylinder.

In addition, when your car is running, the oil in the cylinder mixes with the air-fuel mixture, joining the typical combustion process. Therefore, you notice that your vehicle needs more oil than it usually requires. However, an easy way to know that increased oil is burning is the presence of bluish-gray exhaust fumes.

Illumination of Check Engine Light

The illumination of your check engine light is always a signal of a deviation from normal car functioning. When car issues such as the engine misfiring – a result of bent valves, the engine’s onboard diagnostic detects it and causes the warning light to go on.

Car Check Engine Light

However, the illumination of the check engine light is not specific to a particular issue. The light comes on for various other car problems. Therefore, you need to check the vehicle’s OBD II scanner to detect the actual cause or contact an expert for help.

Reduction in Compression

As the car runs, pressure builds up – compression. But as earlier mentioned, a faulty valve disrupts the sealing of the valves against the cylinder head, allowing gas escape and reduced compression. This may result in other bent exhaust valve symptoms like low power generation and improper fuel-air mixture.

If you notice low compression when running a compression test, the main suspect is damage in your valves, often due to a bent or defective valve.

Loud Engine Backfire

A bent exhaust valve alters the expected release of fumes from the cylinder. It may even result in leakages that change the combustion process. When the engine control unit (ECU) notices this, it tries to rectify the issue.

Therefore, it may result in excess fuel combustion, causing the car to run rich and excess unburnt fuel in the exhaust. The result is a popping bent valve sound or a loud backfire.

What Causes Your Car Engine Valve To Bend?

Factors that cause your car engine valve to bend include issues with the timing belt, chain failure or prolonged engine overheating. It could also result from less complicated problems like collisions, hitting a large pothole or excessive engine revving, causing increased wear and tear of engine components.

Below is a more detailed review of the possible causes of a bending or defective engine valve.

Issues With Timing Belt or Chain Failure

A broken timing belt or chain failure is one of the leading causes of bent valves. Generally, the belt or chain plays a significant role in syncing the motion of the engine’s valves and pistons. Therefore, when the timing is not optimized, there’s a high chance of collision between the two components – the valve and pistons. The result is a damaged valve.

Excessive Revving of the Engine

Over-revving your car engine is another common cause of a defective valve. This is more common in interference engines where valve and piston paths overlap. Over-revving an engine causes a valve float.

In this situation, the valves become inefficient and unable to complete their open-close cycle, increasing the chances of valve-piston collusion. Therefore, when driving, you should be cautious of the engine’s RPMs and avoid unnecessary redlining.

Engine Overheating

Prolonged or severe overheating may also affect the integrity of your valves. As the engine overheats, the valves also experience this intense heat. This may cause warping of engine components, including the valve, or the expansion of the valve head and stems to expand beyond their intended tolerance.

Car Engine Overheating

Therefore, the valve won’t be able to close or open properly, resulting in contact with the pistons, which can result in valve bending or eventual breakage.

Inadequate Lubrication

Valves, like other engine components, require sufficient lubrication for optimum functioning. They operate within two metal contact points – the valve guides and the valve seat. Therefore, the parts are liable to wear and tear conditions without adequate lubrication to reduce friction and heat build-up.

And we already mentioned that increasing heat (and friction) may cause the valve to experience warping or deformation and eventual bending. Also, insufficient lubrication may cause the dragging of engine valves within their guides, increasing the possibility of a valve-piston contact.

Intrusion of Foreign Objects

Beyond collision, physical damage to the valve may also arise from the presence of foreign objects like bolts, screws, or debris in the internal combustion chamber. These objects may hit the pistons or damage the valves.

Incorrect Valve Configuration

After routine maintenance or engine assembly, if you fail to configure the valves correctly, they may open and close at the wrong time. This may interfere with the pistons or misalignments, causing the valve to bend or more severe engine issues.

Incorrect Car Valve Configuration

Therefore, visiting a reputable auto shop or contacting an experienced mechanic for all your auto repairs or maintenance is vital.


Rare, but a hydrostatic lock may also mess with your vehicle valves. This occurs when liquids like water penetrate the internal combustion chamber. Since water can’t compress, it just causes pressure to accumulate, which may damage or bend the valves. The easy way to avoid this is to avoid driving in flooded areas.

Beyond all this, it’s also possible that the valves just experience wear and tear of specific valve components after prolonged use and become ineffective as they ought to be. These components include the valve springs, pushrods, rocker arms, etc. Any issue with either of these parts may affect the valve’s functionality.

How Can You Fix Bent Valves in an Engine?

You can fix bent valves in an engine by first identifying the engine valves that are affected. This may involve visual examination or performing a simple compression test. The test consists in removing all the spark plugs from the cylinder. Then you crank the engines on multiple occasions.

You then check the compression in each cylinder; the one(s) with low compression has a bent valve. After determining the defective valve, the next thing you do is to detach the cylinder head using appropriate tools. Once you remove the cylinder head, you can replace the defective valve with a new one; then, ensure to install it properly and seal it.

When carrying out a valve replacement, you should incorporate new valve seals, along with valve keepers and springs, into the assembly of the cylinder head. To ensure the engine’s optimal performance, ensure meticulous adjustment and verification of valve clearance.

Once the cylinder head is properly reassembled, reattach it firmly to the engine. The process is pretty tasking and time-consuming, so we recommend you consult with an expert.


How Often Should You Change Your Engine Valves?

You should change your engine valves whenever they get damaged, bent, or worn out beyond repair. Generally, the engine valves are not supposed to require replacement. They are meant to last your vehicle throughout its lifetime. Depending on car models and make, variations may exist.

Still, we recommend you replace them after every 100,000 miles, as by then, they may start showing signs of wear and tear.

Can a Bent Valve Cause Bad Idle Control in a Vehicle?

A bent valve is one of the causes of a bad idle control valve in a vehicle. When a valve becomes bent, it fails to close properly, disrupting the airflow and fuel mixture required for smooth idle control. This can result in erratic idling, stalling, and overall poor engine performance.


This article exposes you to various symptoms of a bent engine valve, including their causes and how to repair them.

Let’s make a quick recap of all we mentioned in the article.

  • The common symptoms associated with bent engine valves include engine misfiring, inability to generate enough power, rough idling, increased oil consumption, etc.
  • Driving a car with a valve may be frustrating, as you cannot hit high speeds, even while driving on the highway. Also, your vehicle may continue to shake excessively.
  • The leading causes of this car issue include over-revving your car engine, timing chain or belt failure, overheating, and inadequate lubrication.
  • Bent valves may sometimes arise by collision with a deep pothole or wear and tear after prolonged car use, especially with poor maintenance practices.
  • We provided you with a step guide on repairing a bent valve. However, we must emphasize that it’s a tasking procedure, and you may wreak more havoc in your car if you make a mistake. Therefore, we recommend consulting an expert’s help.

Ideally, with good maintenance practices, you can avoid experiencing faulty valve symptoms, but cases including collision, debris penetration into the internal combustion or hydro lock may be problematic. Whenever you notice any of the bent valve symptoms, do not hesitate to visit a professional auto repair shop for proper fixing.

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