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

The design of the gas distribution system of most internal combustion engines includes a valve system. It regulates the timely flow of air or combustible mixture into the combustion chamber and the release of exhaust gases. The valve itself constantly operates in aggressive conditions under the influence of high pressures and temperatures, which destroy the body of the part, leading to engine failure. There are certain reasons and conditions under which valve burnout occurs much faster than the design period of operation.

Causes of high temperature damage

Experts identify various factors that have a direct impact on the integrity of parts. The most popular among them are:

• Extremely high temperatures. Automakers calculate the characteristics of the unit in such a way that it functions most of the time at 600-650C. In the case where there are malfunctions of the heat sink, excessive overheating is fraught with destruction.
• Manufacturing defects. Although all parts leaving the factory assembly line undergo strict control, there remains a low risk of defective parts. It can be determined independently by the heterogeneity of the metal, microcracks, defects in welding seams, etc.
• Low quality fuel. Running a lean fuel mixture may be the reason why valves burn out. The lack of fuel in the mixture is ruined by temperature fluctuations.
• Availability of connected gas equipment. Engines using gas as an alternative fuel are characterized by significant loads on gas distribution systems. Power plants with a poor gas supply are at risk. We recommend calibration at least every 12-14 thousand kilometers.

A high percentage of defective spare parts is a problem for the motorist

These are not the main reasons why valves burn out. The leading manufacturer of these parts conducted a small study, and the statistics were not happy - every fifth part that is produced breaks or burns out due to the human factor and defects. And even modern product quality control at factories does not guarantee that the part is free of any defects.

Another reason is metallurgical inhomogeneities that are included in the alloy. These irregularities make the valve weaker than it should be. In addition, there are manufacturing defects, namely forging. This leads to microcracks. Errors in the heat treatment process lead to changes in the dimensions of the product.

How will the engine work and what will happen if the valves are clamped?

How to understand that the valve is jammed

If after starting the engine runs normally, but during long operation the thrust drops - this is a symptom of pinched valves. Another sign of jammed valves can be shots into the muffler when releasing gas. Because The combustion chamber is not completely closed, compression decreases and a disruption in the working process occurs. When adjusting, it is better to exceed the permissible gap than to make it smaller.

A burnt valve must be repaired as quickly as possible!

The consequence of clamped valves is overheating, increased fuel consumption and, as a result, burnout. It is undesirable to operate the engine with a burnt-out valve; this leads to burnout of the valve seat. What the car owner will end up having to do is replace the entire head.

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.

Replacing burnt out valves

The operation of replacing the valves of different engines is similar, and differs only in the size of the parts and their placement on the cylinder head. Before performing the operation, prepare lapping powder, new valve seals and a new head gasket. After dismantling the cylinder head, operations are performed in the following order:

1. Valve desiccation. To do this, the head is laid out on a flat surface and a rubber mat is placed under the valve. A tube with a diameter of 13 mm is placed on the valve so that the crackers are inside, and blows are applied with a hammer. The valve desiccates, and the crackers remain in the tube. The operation is also easily carried out using a special device that compresses the vein and allows you to pull out the crackers.

1. The valve is pulled out, a new one is inserted, and the bushing guide is checked by shaking. If runout is up to 1 mm, the guide is not replaced.

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3. If it is necessary to replace the guide, use a special mandrel. The old part is knocked out in the direction of the camshaft using a half-sledge hammer with a heavy blow so that the part does not crumble. Afterwards, a new bushing is driven into the head, having first put a retaining ring on it.

4. The new valve is secured with a retaining ring and the assembly is lubricated with oil.

5. Valve grinding. The seat is initially treated with a special cutter, after which lapping powder is applied to the edge of the valve, inserted into the head, the other end is clamped into the drill chuck, and by pulling it up and down, the valve is provided with a tight fit to the seat. It is advisable to carry out the operation for all valves.

6. Drying of the valve. To do this, press the spring firmly and insert crackers. The cylinder head is attached to the engine cylinder block.

The described method allows you to replace the burnt valves of all models of the VAZ: 2101, 2102, 2103, 2104, 2105, 2106, 2107, 2108, 2109, 21099, 2110, 2111, 2112, 2113, 2114, Niva, Lada Priora, viburnum, Grant, Grant, Grant. Vesta and most foreign cars.

Let's sum it up

Let's start with the fact that the appearance of the first signs of valve burnout is a reason for immediate diagnosis of the engine. If the engine requires periodic valve adjustment, then this procedure must be carried out strictly according to the regulations. You should not wait for the moment when noise or knocking of valves appears.

The driver’s desire to save as much as possible on fuel after installing LPG is initially expressed in the fact that the owner asks the tuners to make the car economical. The technicians deplete the gas supply, as a result the engine noticeably loses power, but there is no significant reduction in gas consumption. The fact is that to maintain a dynamic driving pace, you have to press the accelerator more actively. At the same time, the lean mixture literally burns out the valves and seats with all the ensuing consequences. A high-quality LPG setup implies an almost complete absence of difference in throttle response when driving on gasoline or gas.

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What is burnout?

Metal destruction under the influence of high temperatures is typical for both diesel and gasoline engines. Even taking into account the fact that most of the important parts of the gas distribution mechanism are made of special high-strength steel grades, under certain conditions they are destroyed.

The actual combustion of the metal is not carried out in the classical form. Parts are destroyed from different sides.

It is important to know that a burnt-out valve can be identified by cracks formed on the edges or by obvious penetrations in the working surface.

Due to the fact that defects form on some coins, the tightness of the interface between the seat and the plate disappears. As a result, this results in engine problems, and can manifest itself in serious damage to the internal combustion engine.

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.

What to do if the valve burns out?

In the case of burnt valves, repair consists not only of replacing them, but also of finding out the cause of the burnout. Therefore, the ignition and cooling systems should be checked.

If you have replaced and ground in one valve, take the time to ground in the rest.

You can replace the valve not only at a service station, but also in a garage if you are familiar with the basics of repair.

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Thus, the valve is an important part of the engine, so in order to protect yourself from repairs, it is better to carry out routine maintenance on time.

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.

Video: Why valves burn