How To Tell If Valves Are Bent After Timing Belt Broke?

Compression and air leaking tests are the most reliable tests to tell if the valves are bent after the timing belt breaks. Also, you can measure the valve clearance or do a resistance test to get the initial idea if the valves are bent or not. In addition, there are symptoms like engine misfire, poor engine performance, etc. also indicate that the valves might be bent.

This is just a brief rundown. To know how to tell if valves are bent after timing belt broke, continue reading.

Can a Broken Timing Belt Bent the Valve?

Yes, a broken timing belt can cause the valves to bend. This is because the timing belt syncs the timing between the camshaft and crankshaft. If the timing belt breaks, the camshaft and the crankshaft immediately lose their timing with each other, and as a result, the piston and valves may collide, leading to a bent valve.

However, this isn’t the usual scenario for all types of engines. Based on the clearance between the piston and valve, there are two types of engine, interference, and non-interference.

Let’s see what are the consequences for both types of engines.

For Interference Engine

An interference engine is one in which the valves and pistons occupy the same space within the cylinder, and there’s no gap at the top dead center (TDC). During the engine’s operation, the valves open and close in synchronization with the piston movement.

A broken timing belt will mess up the synchronization causing the pistons to collide with the valves. As a result, the valves are likely to bend.

For Non-Interference Engine

A non-interference engine has pistons and valves that do not come into contact with one another at the top dead center (TDC), regardless of whether the timing belt or chain fails.

Therefore, if the timing belt breaks, the pistons will not collide with the valves, and the valves will not be bent or damaged. 

What Are The Signs of Bent Valves?

While driving your vehicle, you may notice the following signs in case the engine valves are bent.

Check Engine Light On

A bent engine valve can cause the check engine light to illuminate because it can cause problems with the engine’s performance. An engine valve that is bent may not open and close properly, resulting in reduced performance. 

The check engine light may come on as a result of other issues as well. So, make sure to find out the root of the problem before jumping to a conclusion.

Excessive Emissions

A bent valve can prevent it from closing properly, which can allow fuel and/or air to escape into the exhaust system. As a result, the exhaust will emit more hydrocarbons (HC) and carbon monoxide (CO), resulting in higher emissions.

Furthermore, if the valve is not closing properly, it can allow air to enter the combustion chamber at the wrong time, disrupting the air-fuel ratio and leading to incomplete combustion. The exhaust can contain higher levels of HC and CO as a result.

In case, you want to know whether a timing belt affects air conditioning or not, check this out to know about it.

Engine Misfire and Excessive Vibration

When an engine valve is bent, the engine may misfire since the valve is not closing properly. It can result in a loss of compression in the cylinder if the bent valve can’t close properly. 

This can result in incomplete combustion of the fuel, causing the engine to misfire, eventually resulting in excessive engine vibration. 

Poor Engine Performance 

Bent valves can cause the engine to lack power and strength because they can’t close the cylinder heads properly. This reduces the compression inside the cylinders leading to poor engine performance.

Low Fuel Economy

The bent valves may not fit properly against the valve seat, allowing more fuel to pass through than usual. As a result, oil consumption may increase.

The bent valve can also cause the valve spring to lose tension, causing the valve to remain open longer than it should. As a result, oil consumption can increase as well.

Additionally, bent valves can cause the engine to run poorly and inefficiently, which in turn can increase oil consumption.

Unusual Noise

A bent engine valve can cause unusual noise in the engine because it can prevent the valve from properly sealing, allowing air and fuel to escape. This can lead to a knocking or ticking noise as the valve struggles to function properly. 

Additionally, a bent valve can also cause damage to other parts of the engine, leading to further noise and potential damage.


A bent engine valve can cause a backfire by preventing proper air and fuel mixture from entering the combustion chamber, resulting in incomplete combustion. This can lead to unburned fuel being expelled through the exhaust system, where it can ignite and cause a backfire.

So, these were the symptoms of bent valves. However, these symptoms may indicate other problems as well. In order to make sure the bent valves are the reason behind these, follow the next segment. 

How To Tell If Valves Are Bent After Timing Belt Broke?

There are a few simple ways to check if your engine valves are bent. Let’s take a look at them.

Warning: You will need to have the engine turned off and cooled down before attempting to do this.

Method 1: Compression Test

To properly check the compression on every cylinder, gather the following tools first:

  • Compression Tester And Kit 
  • Socket 
  • Spark Plugs Socket
  • Ratchet
  • Wrench 

As you have gathered these tools start proceedings.

Safety precaution

  • Remove the fuel injector fuse to disable the fuel line.
  • Remove the distributor coil to avoid engine combustion.

Step 1: Remove the spark/glow plugs 

Remove the spark plugs (for gasoline engines) or glow plugs (for diesel engines)( from your engine with a related size ratchet wrench and socket set. This is to attach the compression gauge adapter to the spark plug hole. 

Step 2: Inspect and connect the compression test gauge

Make sure your compression gauge is set for gasoline or diesel engines before testing.  Now, connect the compression test gauge adapter to the spark/glow plug hole.

Step 3: Crank the engine and note the compression reading

To perform a compression test on your vehicle’s engine, the engine needs to be cranked. It is recommended to have a friend assist you during the test to ensure accuracy and avoid mistakes that can occur when working alone. Make sure to accelerate a few times for a more accurate reading.

Each time you check a cylinder, make a note of the reading. 

Step 4: Compare the test result 

A healthy gasoline engine typically has a compression pressure range between 125 and 175 PSI. However, this can vary depending on the make and model of a vehicle. In a diesel engine, optimal compression is generally between 275 and 400 PSI. For both types of engines, there should be no more than a 10% variation between the cylinders. 

The highest and lowest cylinder ratings should be no more than 15 to 20 PSI apart. A compression variation of 10 to 15% may indicate bent valves.

If you can’t manage a compression tester, move on to the next method.

Method 2: Air Leaking Test

Arrange the following tools for an air pressure test.

  • An air pressure hose according to the spark plug diameter
  • A long ratchet

Step 1: Place the cylinder piston top dead center 

Use a long ratchet to rotate the crankshaft and make sure the piston is in the top dead center (TDC).

Step 2: Close the valves

Once you’ve placed the piston at TDC, remove the timing belt and rotate the camshaft so that the respective valves remain closed.

Step 2: Blow pressurized air into the spark plug hole 

Put the air pressure hose into the spark plug hole. And then blow high-pressure air into it. See if the air passes through the valve area. If air passes from any cylinder then the respective valve is bent. So check each cylinder.

Both the compression test and the air leaking test are reliable and give accurate results. However, if you don’t have the pieces of equipment, you may perform the following tests to get the initial idea of bent valves.

Method 3: Resistance Test

To do a resistance test in the engine, you need to remove the timing belt first. Don’t lubricate the timing belt even if you feel like you need to do this (because it’s not recommended). Next, rotate the crankshaft twice with a long ratchet. While rotating the camshaft, inspect the resistance of the pistons as it reaches the top dead center (TDC).

If there is smooth movement and no significant resistance, the valves should be functioning properly. Inspect each piston as it comes to the top dead center while rotating.

However, sometimes in the case of a slight bend, the resistance may not be noticeable.

Method 4: Valve Clearance Test

The clearance between the valve stem and the tappet will be greater than usual if the valve is bent. So, you can determine the bent valve by measuring the clearance with a feeler gauge. 

You need the following tools to do the feeler gauge test: 

  • A feeler gauge 
  • A wrench set

As you have arranged these tools follow the steps below:

Step 1: Remove the valve cover

Remove the valve cover by using an appropriate wrench. Then, identify the valve you want to check and rotate the crankshaft to bring the respective piston to the top dead center (TDC).

Step 2: Measure the clearance with the gauge 

Insert the feeler gauge between the valve stem and the rocker’s arm. The gauge should be able to slide easily but with a slight drag. If you don’t find any resistance try with a bigger blade. And then read the measurement and verify with the manufacturer’s recommended clearance. 

You’ll find the recommended clearance in the service manual.  

Source: Wonkeedonkeetools

Compare the measurement on the gauge with the manufacturer’s specifications for proper clearance. high clearance deviation from the manufacturer’s recommendation may indicate a bent valve. Repeat the process for all valves to find out which ones are bent.

What to do If the Valve is Bent? 

If the valve isn’t totally broken or excessively bent, it may be possible to repair it. However, the repair procedure is usually quite complicated and requires the use of specialized tools. 

It’s typically not something that a non-professional would be able to do on their own. That’s why it’s generally recommended to repair the bent valves professionally.

Can You Drive With Bent Valves?

It’s not recommended to drive with bent valves as it can cause serious issues with the engine’s performance and potentially lead to further damage. By driving with bent valves, you can damage your engine completely and disrupt the engine’s compression, resulting in a loss of power and efficiency. 

It’s important to have the bent valves repaired or replaced as soon as possible to avoid further engine issues. However, in special cases when you must drive a short distance to a repair shop, it may be okay to do so, but it is not ideal.


What Does A Leaking Valve Feel Like?

A leaking valve can feel like a loss of power or decreased engine performance. Additionally, it may reduce fuel efficiency and increase exhaust emissions. A leaking valve can also cause the engine to make a knocking or tapping noise. 

Do You Need A New Engine If Your Timing Belt Breaks?

No, usually you don’t need a new engine if your timing belt breaks because the timing belt is a replaceable engine part. However, in extreme cases where the piston and valve collide due to a broken timing belt, it can cause severe engine damage and you may need to spend a lot to fix it.


Here’s how to tell if valves are bent after timing belt broke. After a timing belt has broken, let’s hope you’ll be able to determine whether the valve is bent.  

If you suspect the valve is bent, have it fixed by an expert without making any delay. Thanks for reading!

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Aaron Byrne

Hi, Aaron Byrne here. I'm an expert automotive mechanic with 10 years of experience. I work on engine parts especially timing belts for their repair, maintenance, and replacement.