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6 Symptoms of a Bent Engine Valve (And How to Test Them)

An engine problem is the last thing you want to deal with, but it happens. An embarrassing problem that can cause headaches is a bent engine valve. What are the symptoms of a bent engine valve and how serious is the fault?

Since engine valves are a critical part of the engine, it is important to fix these problems quickly. We look at the function of engine valves and address the symptoms when one is bent. Our guide also shows you how to test for bent engine valves. Let’s start with a quick look at the signs:

The most common symptom of a bent engine valve is a cylinder misfire with a check engine light on the dashboard. You may also notice other engine performance problems. If you see low compression with a compression test, that’s also a good sign.

Here is a more detailed list of the most common symptoms of a bent engine valve:

6 symptoms of bent engine valves

1. Check engine light

Flashing engine check light

Modern cars monitor all of your car’s engine sensors in real-time to make sure it is running at its best. If something is wrong with any of the sensors or a setting is out of range, the check engine light on your dashboard will come on.

If any of your engine valves are bent, this will definitely cause a check engine light. You can check trouble codes with an OBD2 scanner to find trouble codes related to the air-fuel mixture.

Engine valves are not electronic and therefore fault codes will not say that an engine valve is bent directly, but they may indicate something about a misfire or a poor air-fuel mixture.

2. Engine fails


If an exhaust valve is bent, it affects the way fumes exit the cylinder. Exhaust valves must open and close at specific times to ensure that the correct amount of pressure is always present.

A bent exhaust valve can end up in the wrong position. It may also not seal properly when closed. This failure causes an exhaust leak that affects the way fuel burns.

When the ECU notices the problem, it can overcompensate by changing the amount of fuel delivered to the cylinder. When the cylinder is rich, unburned fuel flows into the exhaust, creating a backfiring or popping noise.

3. Low compression

Comprehension test

When the engine is running, pressure builds up inside the cylinder, called compression. Bent engine valves usually cause a compression imbalance. When this pressure is too low, the combustion process is affected and the fuel cannot burn properly.

The bent engine valve creates low compression because it no longer closes properly, leaving the gasket with the head defective. As air or exhaust gases escape, compression is lost, causing a lack of power and other performance problems.

If you notice low compression during a compression test, it’s definitely time to check your engine’s valves to make sure they aren’t leaking.

4. Stirring motor

Bent engine valves are known to change the way the engine runs. If a valve is damaged by something like a broken timing belt, the engine could begin to shake due to a misfire. You may notice this more often when idling or driving at lower speeds.

Depending on the severity of the valve damage, you may be able to drive for a short time. However, severely damaged valves can cause the engine to shut down completely.

5. Lack of power

Bent engine valves almost always cause a lack of power. In many cases, these power problems stem from a reduction in cylinder pressure caused by the damaged valve. When the valve does not close properly or seat where it should, the combustion mixture will be expelled.

Additionally, power problems may come from running the engine to compensate for problems caused by the bent valve. Either way, it needs to be fixed, as the problem will only get worse over time.

6. Excessive oil consumption

Engine valves must be lubricated to function properly. Using the valve seal, the valve stem is lubricated with oil as it moves. However, the valve seal prevents oil from entering the cylinder.

A worn or damaged seal can occur when the valve is bent. These broken seals allow oil to leak into the combustion chamber. This failure causes an excessive amount of oil to be burned. It can also affect engine performance and damage the catalytic converter if not repaired immediately.

If you see blue smoke coming from your exhaust pipe, it may be due to a bent engine valve, causing the valve seal to leak.

RELATED: 6 Symptoms of a Bad Valve Seal

What are engine valves?

engine valves

Valves are the parts that help control the movement of air through the engine. During the intake stroke, the intake valves open to allow air to enter the combustion chamber. During the exhaust stroke, the exhaust valves open to allow the burned combustion to exit the chamber.

When the compression stroke occurs, the intake and exhaust valves must remain closed to build up pressure before the combustion mixture can ignite. This combustion force gives your car its power.

Inside the cylinder head are the exhaust and intake valves. Most vehicles have two of each per cylinder. Therefore, a four-cylinder engine contains 16 valves in total. However, some LS V8 engines used by GM contain only one intake and exhaust valve per cylinder, giving a total of 16 valves.

How to test bent engine valves

To test a bent engine valve, the ideal check would require you to remove the cylinder head and take a physical look at the valve. However, this is more work than most people want to do, so compression and leak testing are useful.

With a compression test, you can quickly see the amount of compression produced by each cylinder. It’s a simple way to see how the engine works.

If you find that a cylinder is low, you will move on to the leak test. With this diagnosis, you can tell when there is an engine air leak. The leak test is connected to the spark plug hole. Once this is accomplished, the crankshaft is rotated until the cylinder is on the compression stroke. This is when you listen to where the air is coming from in the engine.

If air is coming out of the intake, it is likely a bent intake valve. On the other hand, the air coming from the exhaust points to a bent exhaust valve. However, air leaking from these places could also mean that there is just a buildup of carbon in the valves, causing a poor seal. Further diagnosis from a qualified mechanic may be needed if you are unsure.


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