Quick Diagnosis of Valve Abnormal Noise

Valve abnormal noise is a typical fault of the engine valve system, which is often caused by metal knocking and can be easily confused with abnormal noise from the crankshaft and timing system. If not diagnosed in a timely manner, it can exacerbate wear on components such as valves and rocker arms, affecting engine power and smoothness. The core of rapid diagnosis is to "listen to the sound, observe the working conditions, and determine the location", combined with simple operations to accurately locate faults. The following are detailed diagnostic methods.

1、 First identify the characteristics of abnormal noise: distinguish valve abnormal noise from other abnormal noises

Valve abnormal noise has obvious exclusive characteristics that can be quickly distinguished from other abnormal noises. The typical valve abnormal noise is a clear "dada dada" metal knocking sound, with a rhythm completely synchronized with the engine speed. The higher the speed, the faster the frequency of the abnormal noise, and the clearer the sound; The abnormal noise is most pronounced after cold start, and may slightly decrease after hot start, but it will not completely disappear.

Attention should be paid to distinguishing: abnormal noises from the crankshaft and connecting rod are mostly dull "thumping" sounds, coming from the lower part of the engine; The abnormal noise of the timing system is a "clacking" sound, and the rhythm deviation is obvious with the change of speed; And the abnormal valve noise is concentrated in the engine cylinder head. After opening the oil inlet cover, the sound will be clearer, which is the most intuitive distinguishing point.

2、 Condition testing: Accurately locate the root cause of the fault

By changing the engine operating conditions, the core cause of valve abnormal noise can be quickly determined, with simple operation and no need for professional equipment.

Idle speed and speed test: There is obvious abnormal noise during idle speed. Lightly press the accelerator to increase the speed, and the abnormal noise intensifies with the increase of speed. There are no other chaotic sounds, mostly due to excessive valve clearance; If the abnormal noise is chaotic and even accompanied by idle shaking after the speed increases, it is most likely due to aging of the valve tappet and pressure relief.

Cold and hot car comparison test: abnormal noise appears immediately after cold start, but decreases after hot start but still exists, which can be basically judged as excessive valve clearance; If the abnormal noise worsens after the car is heated up and accompanied by the flashing of the oil pressure indicator light, it is mostly due to lubrication system failure, resulting in dry wear of valve components.

Cylinder disconnection test: Disconnect the spark plugs of each cylinder one by one. If the abnormal valve noise significantly decreases or disappears after disconnecting a certain cylinder, it indicates that there is a fault in the valve components (rocker arm, tappet, valve spring) of that cylinder, and the cylinder can be inspected as a priority.

3、 Simple inspection: further confirm the fault

No need to disassemble the engine, the diagnostic results can be further verified through simple inspection. Open the cylinder head and valve chamber cover, visually inspect whether the valve clearance exceeds the standard, observe whether there is wear and deformation on the surface of the rocker arm and tappet, and whether the valve spring is broken or deformed; Check the oil level and quality. If the oil is insufficient or deteriorated, it can cause poor lubrication and abnormal valve noise. It is necessary to replace the oil in a timely manner.

The key to quickly diagnosing valve abnormal noise is to grasp the three core characteristics of "speed synchronization, cylinder head position, and cold and hot vehicle changes", combined with working condition testing and simple inspection, which can locate faults in a short time, save time for subsequent repairs, and avoid blind disassembly and waste of parts.