Root Cause And Fault Diagnosis of Valve Abnormal Noise

Root cause and fault diagnosis of valve abnormal noise

The valve is the core component of the engine valve system, and abnormal noise is a typical manifestation of its malfunction. If not judged and dealt with in a timely manner, it will exacerbate component wear and affect engine power and smoothness. Valve abnormal noise is mainly caused by abnormal clearance, insufficient lubrication, or component aging. The root cause can be accurately located through the characteristics of the abnormal noise and the occurrence of working conditions. The following are the core judgment methods.

1、 The core root cause of abnormal valve noise

The essence of valve abnormal noise is often due to abnormal component coordination or lubrication failure. Excessive valve clearance is the most common reason. The cold clearance of the valve exceeds the standard due to wear and improper adjustment, resulting in a hard impact between the valve and the rocker arm or tappet during operation, causing a metallic knocking sound; Lubrication system failures such as insufficient oil pressure and engine oil deterioration can lead to poor lubrication of friction parts such as valve lifters and rocker arms, resulting in dry grinding noise; In addition, aging and damage to valve components, such as pressure relief of the tappet, wear of the rocker arm, and deformation of the valve spring, can also disrupt the normal fit of the valve train and produce irregular abnormal noises. Partial abnormal noise is also related to timing transmission deviation. Loose timing chains/belts can cause misalignment of the valve timing, indirectly leading to valve knocking.

2、 Fault diagnosis method for valve abnormal noise

To determine valve abnormal noise, it is necessary to combine the characteristics of the noise with changes in operating conditions to achieve precise positioning.

From the perspective of abnormal noise, the noise caused by excessive clearance is a clear "dada dada" metal knocking sound, synchronized with the engine speed. The higher the speed, the faster the frequency of abnormal noise; The abnormal noise caused by poor lubrication is mostly a dull "rustling" sound, which does not change significantly with the increase of engine temperature, and even worsens due to the decrease of oil viscosity; The abnormal noise caused by component aging has no fixed pattern and may be accompanied by idle shaking and decreased power.

Judging from the operating conditions, the abnormal noise that appears immediately after cold start and slightly reduces but does not disappear after hot start is mostly due to excessive valve clearance; The abnormal noise intensifies after the car is heated up, and at the same time, the oil pressure indicator light flashes, most likely indicating a lubrication system malfunction; There is obvious abnormal noise during idle, and the abnormal noise is chaotic after acceleration. It is necessary to check vulnerable components such as valve lifters and rocker arms.

3、 Key points for distinguishing easily mixed and abnormal noises

Attention should be paid to distinguishing valve noise from other engine noise to avoid misjudgment. Valve abnormal noise often comes from the engine cylinder head, and the sound will be clearer after opening the oil inlet cover; The abnormal noise from the crankshaft and connecting rod comes from the lower part of the engine, and the sound is more muffled; The abnormal noise of the timing system is accompanied by significant rhythm deviation with changes in speed. In addition, although the abnormal noise caused by spark plug failure and intake manifold leakage is similar to valve noise, it will not disappear with the maintenance of the valve mechanism, and can be further distinguished through cylinder cut-off testing and air tightness testing.

The core of judging abnormal valve noise is to "listen to the sound, observe the working conditions, and determine the location". It is necessary to regularly check and adjust the valve clearance according to the maintenance manual, replace high-quality engine oil to ensure lubrication, and promptly investigate any abnormal noise to avoid serious damage to the valve mechanism caused by minor faults.