How to determine that a valve has burned out in a car engine: signs and symptoms

Timing valves are located directly in the combustion chamber and are designed for high temperature loads. However, if the normal operation of internal combustion engines is disrupted, even the heat-resistant material from which they are made is destroyed over time. How quickly the valves burn out depends on the nature of the problem. Typical signs that a valve in a cylinder has burned out are rough operation and difficulty starting the engine, as well as loss of power. However, these same symptoms can also occur with other problems. This article will help you understand what a “burnt valve” means, why this happened and learn about ways to diagnose the timing belt without removing the head.

What is valve burnout?

Since the valves of internal combustion engines are made of high-strength metal alloys that are resistant to high temperatures, they, of course, cannot “burn” in the classical sense of the word. A valve burnout is a technical term that means that a crack or melting has appeared on the edge of the valve. As a result of such defects, the tightness of the seal between the plate and the seat is lost, which inevitably leads to problems in the functioning of the engine and can cause serious damage.

Adviсe

Check the valve carefully when purchasing. Check the size standards and inspect the part for visible defects. Purchase spare parts only from certified points of sale from reputable manufacturers. The money saved on a cheap purchase will result in expensive repairs.

Check the valve clearances in the engine. Too short a distance is a common cause of overheating. Reduced clearance indicates wear of the valve seat. Install stiffer motor seats to prevent damage.

Thermal clearance table

Do not fill your car with low-quality fuel or lean gas in order to save money. Because of this, the engine loses some power and excessive gas consumption occurs. At the same time, regularly check the condition of the valves. Gas engines do not make as much noise when the valve is burnt out as gasoline engines.

When the first symptoms of a breakdown appear, it is better to contact a service center. Disassembling an engine with your own hands is a difficult process, especially with untrained hands. Experienced mechanics will quickly identify the problem and save you a lot of time.

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Why do valves burn out?

What does a burnt valve look like?

Experts identify a number of reasons why valves in internal combustion engines burn out. The most common and widespread of them are the following:

• Factory defects of the parts themselves;
• Incorrect adjustment;
• Malfunctions of the cooling system of power units;
• Malfunctions and wear of other parts of the gas distribution system;
• Long-term engine operation on a lean fuel mixture.

Not long ago, one of the companies specializing in the production of automotive components cited statistics indicating that approximately 20% of failed valves are caused by manufacturing defects. Nowadays, many companies are engaged in the production of these parts, and among them there are those that do not fully comply with the technology of their manufacture. Valves from these manufacturers most often burn out. As for the defects due to which they fail, they are the heterogeneity of the metal; defects that appear during forging and improper heat treatment; microcracks; poor adhesion of the valve surface coating.

A fairly common cause of valve burnout is improper adjustment of their thermal clearances. It leads to overheating of parts with all the ensuing consequences. It should be noted that for this reason, valves burn out both in engines in which they are adjusted manually and in those in which this process is carried out automatically. In the second case, hydraulic compensators are responsible for adjusting the thermal gap, and if for some reason they fail, the valves begin to overheat.

Their temperature can also rise excessively in cases where the engine is poorly cooled. This may occur due to problems with the pump, thermostat, clogged radiator, or a simple lack of coolant.

It often happens that during long-term operation of the engine, the valve guides wear out. This, as well as such a defect as weakening of the elasticity of the clamping spring, often leads to incorrect positioning of the part and, as a consequence, its overheating and burnout. In addition, valves often burn out when engines run on a lean fuel mixture for a long time.

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Signs of burnt valves

The surest sign that a valve (or several valves at once) has burned out in the engine is that it begins to “trouble.” In principle, this also happens when malfunctions occur in the car’s ignition system, but if after checking it turns out that everything is in order with it, then it makes sense to check the valves.

Another symptom that indicates this malfunction is a loss of power and throttle response of the car. There can be many reasons for this behavior of a car, but burnout of valves is one of the most common of them. Finally, another sign is the appearance of periodic popping noises both in the intake manifold and in the exhaust system (muffler).

If it turns out that the valves have actually warmed up, then repairs should not be postponed. The fact is that operating an engine with burnt-out valves is fraught with even more serious problems.

How to determine a bad cylinder?

The essence of the simplest test comes down to sequential shutdown of the cylinders. By simulating a malfunction, we observe changes in engine operation. After turning off the boiler in which the valve has burned out, changes in operation will be minimal. What are the best ways to do this?

1. Remove the high-voltage wire from the spark plug. At this time, the coil will experience increased loads, so the duration of such a stress test should not exceed 2-3 seconds. To avoid the risk of electric shock through a cracked GDP, such a check should be done wearing rubberized gloves or using pliers with plastic/rubber handles.
2. Physically disconnect the injector chip. If you have specialized diagnostic equipment, this can be done programmatically by connecting to the car via the OBD-II connector.

Possible consequences of valve burnout

As practice shows, the most harmless of all the consequences that come with operating a car with burnt-out valves is an increase in fuel consumption. The fact is that the power unit begins to operate unstably; as a rule, more fuel mixture enters the combustion chambers of the cylinders than necessary.

Much more dangerous is that when operating an engine whose valves are burnt out, fragments may enter its cylinders. Burnt valves lose their strength, steadily deteriorate, and metal particles may well get (and, more often than not, get) directly into the piston group and destroy it. This may lead to the need for serious engine repairs, including complete replacement of the cylinder head. If you continue to operate the power unit under such conditions, then, in the end, it will have to be changed completely.

Information for the consumer about preventing the valve grinding operation at the ZZA cylinder head.

When installing ZZA LLC cylinder heads on engines, it is forbidden to spill gasoline and grind the valves. Complete tightness of the combustion chamber is achieved during the running-in process by “tapping” the valves in the first minutes of engine operation.

The seat material used (heat-resistant powder material with a porous structure) and blade processing of the working chamfer with high precision in diameter, angle of inclination and roughness make it possible to eliminate the operation of grinding in the working chamfer of the valves.

During the running-in process, the valves are knocked against the seats and at the same time the tightness of the combustion chamber sharply increases compared to a new (unrun-in) cylinder head.

Carrying out valve lapping on new cylinder heads produced by ZZA LLC using lapping pastes with unknown characteristics does not improve, but rather worsens, the service life of the “valve sleeve-valve-seat” connection for the following reasons:

— the possible introduction of abrasive material into the porous structure of the seats and bushings leads to intensive wear of the surfaces of the valve and seat during operation;

— when lapping paste gets on the valve stem, the surface roughness of the valve stem inevitably deteriorates and the thin carbonitrated layer is destroyed, which is used to increase the hardness of the metal surface and reduce the coefficient of friction in order to increase wear resistance;

— in oil reflector caps the geometry of the working edge is violated, which requires 100% replacement of the caps;

— after the grinding operation, high-temperature washing with water under pressure with special detergent additives and subsequent drying is required, which is usually not used in a car service center.

Valve lapping is used in repair technologies for cast iron seats with high hardness (over 55 HRC), and for powder seats (hardness 35-40 HRC), it is necessary to use a special cutter based on the hole in the bushing for the valve stem.

Hi all! Let's talk today about such a holivar issue as grinding valves. The procedure in the vast expanses of Drive 2 is, to put it mildly, popular - I have not yet seen a single description of a major overhaul of an internal combustion engine that did not mention this “ritual”! Moreover, we will rather not even talk about the rubbing itself, but about those things that cause its need.

First, let's look at how the valve-seat assembly works in geometric terms:

We see a bunch of chamfers (and the saddle may not have a chamfer, but a radius)

Barik-CZ wrote a lot about the geometry of the seat and its influence on the operation of the internal combustion engine, but I want to draw attention to several key points for the life of the cylinder head: 1. The valve is pulled to the seat using a return spring

2. The ratio of the valve pressing force to the area of ​​the chamfer on the seat gives the specific pressure of the valve on the seat. 3. The valve is cooled through the chamfer on the seat.

As you can see, all the key moments for the operation of the cylinder head rest on two chamfers - on the valve plate and on the seat.

What happens if the chamfer on the saddle is uneven? The specific pressure at different points of the seat will be different; in the zone with maximum pressure, wear will be significantly faster than in neighboring ones. As a consequence, a violation of the tightness, a breakthrough of hot gases with a simultaneous sharp increase in the temperature of the valve in the zone of gas breakthrough and almost zero cooling in it. The result is valve burnout.

Repair after burnout of valves

When, during the diagnostic process, it has become clear that the valves have burned out, it is necessary to stop operating the engine and begin repairing it. First of all, you need to eliminate the causes of the malfunction, because if this is not done, it will definitely arise again.

If it is determined that the cause of valve burnout was improper adjustment, then you need to replace them with new ones and adjust them correctly. In modern cars, to fix this problem, it is often necessary to change the hydraulic compensators.

If the guide bushings are worn out and the springs are weakened, they also need to be replaced along with the valves. To replace them, you should select only parts that are manufactured by well-known and reliable manufacturers in order to be completely confident in their high quality.

In cases where the cause of valve burnout is a malfunction of the engine cooling system, it is necessary to repair it first, and only then begin to replace the valves. Finally, in any case, you should stop using low-quality fuel and change the operating modes of the power unit so that it does not operate on a lean fuel mixture.

Compression check

Having identified a non-functioning cylinder, we must check the cylinder for leaks. There are several ways to do this:

measuring compression in the engine. Even the cheapest compression meter with a suitable measurement scale will be suitable for these purposes. The main thing is that there is an adapter with a suitable thread available. Without trusting the accuracy of the device, focus not so much on the number shown, but on the difference between the cylinders. Compression when the valve burns out decreases by 3-6 atm. in comparison with neighboring pots;

When cranking the engine with the starter, the throttle valve must be fully open, the fuel supply to all cylinders must be turned off, and the battery must be fully charged.

• checking the cylinder for leaks using a tester. The device is a gearbox through which compressed air is supplied to the cylinders. A pressure gauge installed nearby measures the actual pressure after the reducer, converting air loss into a percentage leakage rating;
• relative compression measurement. You can’t do such a test yourself, but a diagnostic technician with an oscilloscope will check it in no more than 15 minutes. You can measure relative compression using the starter current or using the CSS script by Andrey Shulgin.

Summarize

The first signs of valve burnout are a reason for prompt engine diagnosis. If the engine requires valve adjustment, then these operations must be performed strictly according to the manufacturer’s regulations. Don't wait for noise to start appearing. You should also know what compression should be in the engine in order to identify a breakdown in time and eliminate it without consequences.

Why valves burn out For those who want to save money and operate a car on gas, you should pay maximum attention to the adjustment. On such engines, it is recommended to adjust the thermal clearances every 10 thousand kilometers. Gas engines are at risk, while gasoline engines burn out less often.

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Fault localization

The most common and effective method for determining a burnt-out valve is compression measurements. If the results show low compression, then this is clearly a sign of burnout. But here you need to take into account a small nuance - using compression measurements it will not be possible to exclude CPG defects. Low compression is not only due to burnout. Various other defects can reduce it - for example, it could be broken rings. Therefore, if all the signs of a burnt valve are observed on a VAZ-2109 or on any other car, you will have to additionally diagnose the car.

The easiest way to help determine burnout after measurements is to pour a small amount of oil into the cylinder. Next, the compression is measured again. It should grow - this indicates that an oil film has been created. This is typical for a worn piston system. If the compression has not changed, then this is definitely a burnout. The way out of the situation is to replace the valves.

Another diagnostic method is a visual inspection of the spark plug from the problematic combustion chamber. If there is no characteristic deposit on the spark plug, then this is a clear sign of burnt-out valves. In addition, air or smoke will come out of the breather.

Causes

There are several reasons why valves can burn out:

• Manufacturing defects. The likelihood of deviations from the norm during the production of components is small, but still exists. Heterogeneity of the metal, defects in welding seams, microcracks are the first signs of defects.
• Critical temperatures. The operating temperature of the valves fluctuates around 650 °C. If the heat dissipation system is faulty, excessive overheating will cause the metal to quickly deteriorate.
• Poor quality gasoline. A lean fuel mixture leads to temperature spikes, which is even more damaging to the valves.
• Gas. Gas-powered engines are subject to greater loads than gasoline engines. Especially if the car is set to low gas supply. It is recommended to calibrate the valves every 10 - 15 thousand km.