Many people make abnormal noises to the engine and think it is only a small problem, so they are negligent, regardless of whether they ask. As everyone knows, small hidden dangers may cause big problems.

The abnormal noise of the engine is mainly caused by the looseness, improper adjustment or improper use of the internal parts. It indicates that the engine has large or small faults. It should be diagnosed in time and take effective preventive measures.

First, the initial diagnosis, to determine the degree of impact of abnormal sound on the engine

In many complex engine sounds, you should first determine which sounds are normal and which are abnormal. What are the abnormal sounds have little effect on the working condition of the engine, and are allowed to exist temporarily; which are not allowed to continue to exist, and must be excluded immediately, otherwise it is likely to cause greater harm.

1. If the sound is slightly simple when the engine is running at low speed, it will appear to be stable and even when it is running at high speed, and it will be a normal sound when it appears smooth and smooth during acceleration and deceleration.

2. If the sound is only present at idle speed, it will disappear after the speed is increased, and there is no obvious change in the sound throughout the use. This is an abnormal noise that is not harmful, allowing temporary existence and repairing at an appropriate time.

3. If the sound occurs during sudden acceleration or sudden deceleration, and when the engine does not disappear during the medium and high speed operation, and at the same time it is accompanied by the shaking of the organic parts, then this is an abnormal sound that is not allowed to continue to exist. Explain why.

4. If the sound is suddenly appearing during operation and is more violent, it should not continue to operate or be diagnosed by audition, but should be immediately shut down for inspection. Generally, the oil pan is first removed, and then the cylinder head and the valve cover are removed.

Second, earnestly analyze and further identify the location, cause and extent of the abnormal sound

In the period of occurrence of abnormal noise and the time of continuous existence, abnormal noise generally exists in several periods such as idle speed or low speed operation, high speed operation, and entire driving period.

1. For abnormal sounds that occur during idle or low speed operation

(1) First check whether the abnormal noise is related to the work cycle, and further determine which mechanism the fault is in. If there is an association, the fault occurs in the crank linkage or the valve train. The initial judgment can be made according to the frequency of the abnormal sound. The sound caused by the crank linkage mechanism is twice the working cycle, and the sound caused by the gas distribution mechanism is once a working cycle. Therefore, the crankshaft bearing The abnormal noise frequency is lower, and the frequency of abnormal noise at the valve is higher.

(2) Gradually increase the engine speed, hear the change of the abnormal sound, and judge the degree of wear of the moving parts according to the change of the abnormal sound with the rotation speed.

(3) During the diagnosis process, attention should also be paid to observing the influence of changes in engine temperature on abnormal noise.

(4) For multi-cylinder engines, first check whether the abnormal noise is related to the cylinder position by means of single-cylinder oil-breaking and fire-breaking. If there is a significant change in the abnormal noise after a cylinder breaks the oil, the fault is in this cylinder; if there is no obvious change in the abnormal noise after a cylinder breaks the oil, the abnormal sound has nothing to do with the cylinder position.

Through the diagnosis of the above several processes, the relationship between the abnormal noise and the engine load, the working cycle, the rotational speed, and the temperature can be basically ascertained. If the abnormal sound is consistent with a certain abnormal sound characteristic, a definitive conclusion can be made.

2. For abnormal sounds during high-speed operation

(1) First, gradually increase the engine speed from low speed to high speed operation. In the process, pay attention to the timing of the abnormal sound.

(2) When the abnormal noise occurs, stabilize at this speed and listen carefully to the abnormal sound. Sometimes the abnormal noise may only occur in the case of sudden acceleration or sudden deceleration, and the engine speed should be rapidly changed to find out the timing of the abnormal sound.

(3) In the process of diagnosis, attention should also be paid to the changes in the accompanying phenomena such as oil pressure, oil filler port, exhaust pipe, etc., to assist in the diagnosis of the fault, and thus to conclude the diagnosis.

3. For the abnormal noise that occurs during driving

The abnormal noise of the engine in the driving can generally be reflected in the operation of the engine at the same speed after stopping, thus obtaining the conclusion of the diagnosis of the abnormal sound failure. But sometimes there are exceptions. The abnormal noise in the driving, after the parking, makes the engine run at the same speed, but this abnormal noise does not occur anymore. At this time, the rotation speed should be changed abruptly, and the abnormal noise can generally occur. Then look for the reason and come to a conclusion.

Sometimes the abnormal noise in the driving is not necessarily the abnormal noise of the engine, but it may be abnormal noise of other parts. You should step on the clutch pedal or disengage the transmission gear position, and then do the rapid acceleration test. If it disappears, it means that the abnormal sound is not in the engine but in the chassis or the body part.

The diagnosis of abnormal noise of the engine is an empirically strong maintenance operation. Since the abnormal noise of the engine is various and complicated, the abnormal noise reflected by different faults may be similar, and the same fault may also occur due to the degree of difference. It also reflects different acoustic characteristics. The normal sound and the abnormal sound are mixed together, which is difficult to distinguish at one time. Diagnostic personnel can only grasp the regularity by conducting thorough research and repeated analysis and discrimination, and then actively diagnose the abnormal noise.

The safety of agricultural machinery is very important, so we must take precautions. (Qan Lan)

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