How to detect malfunction of the exhaust valve

First, the valve is to be visually inspected, and its condition evaluated. Check whether the component is located correctly, and whether the valve face size is sufficient. Ideally, the width of the latter should be 1.15-1.5 mm. After that, measure the clearance between the component and the piston. To do so, pull out the piston as much as possible. The optimum clearance is 2.5 mm. If the measurement result is less than this value, the valve may hit the piston, which will immediately destroy the valve.

Besides, it is necessary to check how much the component is fouled. If the component has considerable carbon deposit, or combustion residues and oil decomposition products, the component is to be cleaned. For cleaning, use compositions that contain alcohol.

You may notice that the exhaust valve may need diagnostics by the following symptoms:

• the pressure of exhaust gas has increased;
• the combustible mixture spontaneously ignites in the cylinders of the engine;
• fuel consumption has increased;
• Check Engine lights on the dashboard;
• the engine gets overloaded quickly;
• too much moisture gets condensed on the engine;
• smell of exhaust fumes in the passenger compartment.

The reasons of the exhaust valve malfunctions

Exhaust valves are intended for operating in an aggressive environment: they are constantly exposed to high pressure, chemicals and extreme temperature, which sometimes exceeds 650°C. Therefore, their manufacturing requires especially strong materials and careful observance of the technological process. Even the slightest errors during manufacturing significantly reduce the service life of the components. Today, factory defects are the most common reasons of exhaust valve failure.

In many cases, the failure of the valves is caused by their systematic overheating. It may be caused by various reasons, including the use of poor quality fuel. Low octane fuel causes detonation during combustion. This results in an abrupt increase of the temperature, and in premature wear of the component. Similar consequences may be caused by malfunctions in the fuel supply system, which hinders the process of forming the combustible mixture. Constant exposure to critically high temperature may result in deformation of the valve stem, and the component may get jammed.

Incorrectly adjusted valve clearances, incomplete seating of the valve head in the valve seat, accumulation of carbon deposit on the contacting surfaces, wear of separate elements and their fouling, and slackened return spring significantly reduce the efficiency of heat exchange processes. As a result, the head of the valve exposed to constant overheating burns through, cylinder tightness is lost, and the engine malfunctions.

Repairing and replacing the exhaust valve

Repair cannot eliminate damage of the component.  Despite the fact that the valve is made of a very strong metal alloy, if the valve is melted or deformed, it should be replaced.

To install a new component, remove the cylinder head. Therefore, replacement should be entrusted to a service station.

After replacing the valve, it should be seated in the cylinder head. A special grinding compound is used for this purpose.

In order to properly assemble the engine, we recommend marking its elements during disassembly. After the engine is installed, a trial drive should be made at a medium engine speed.