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Reasons for Abnormal Sound in Diesel Generator

Aug. 23, 2019

When diesel generator is running normally, it will make a loud noise, but the normal sound should be continuous and uniform. If the diesel generator has an abnormal sound, this indicates that a part of the unit has failed. The source of abnormal sound mainly include the following:


1. Mechanical knocking

Due to the wear of the moving parts of the diesel engine, the fit clearance is increased, and a large impact is generated during operation to generate a knocking sound. This knocking sound began to be slight and gradually became worse as the wear increased. Such knocking sounds generally occur periodically, accompanied by increased vibration of the diesel engine.

In addition, the diesel engine parts are damaged, or the installation is improperly adjusted, there is an uncoordinated phenomenon during work, and abnormal knocking sound may occur, and this kind of sound generally appears suddenly.


a. The knocking sound of main bearing

When the main bearing nut is not tightened or loose, the main bearing bush wears seriously or burns out, or the improper adjustment of the assembly will increase the clearance between the bearing bush and the neck shoulder of the main shaft bushing. When the diesel engine is working, it will have an impact effect and knocking sound.


b. The knocking sound of connecting rod bearing shell

When the connecting rod bolt is not tightened, loose or broken, the connecting rod bearing bush is badly worn or burned, which will increase the gap between the connecting rod bearing bush and the connecting rod pin. When the diesel engine is working, a large impact load is generated between the connecting rod pin and the bearing bush, and an abnormal knocking sound is emitted.

The knocking sound of the connecting rod bearing is similar to that of the main bearing, but it is lighter than that of the main bearing, and the tone is clear and a "bong" sound is emitted. When the diesel engine raises the speed or increases the load, the sound is more obvious, but it is not obvious when there is no load.


connecting rod


c. The knocking sound of piston pin

When the clearance between the piston pin and the connecting rod small head bushing is too large or the piston pin and the pin seat are too loose, there will be an impact effect and abnormal impact sound.

It is a very sharp, high-pitched and obvious metal knocking sound. When the speed of the diesel engine changes, especially from a high speed sudden drop to a low speed, a sharp "bong" metal impact sound can be heard from the upper position of the cylinder. When the speed is low, the sound is slow and obvious. When the speed is raised, the sound will also increase. When the temperature of the diesel engine rises, the sound will not weaken.


d. Piston ring knocking

Because the piston ring is broken; the gap between the piston ring and the ring groove is too large; or because the cylinder liner wears, the convex shoulder appears on the top of cylinder sleeve, which causes the first piston ring to collide with the cylinder sleeve shoulder. If the piston ring breaks, it will make a "Shua shua" sound; if the gap between the piston ring and the ring groove is too large, it will give out a dull hammering sound, and as the rotation speed increases, the sound will also increase, and will become a noisy sound;


e. The impact sound between valve and piston

Because the valve clearance is not adjusted correctly, the valve is stuck in the open position; or the piston connecting rod group is not installed correctly, causing the valve to collide with the top surface of the piston, emitting a heavy and uniform, rhythmic knocking sound. The diesel engine is running with load for a period of time, and the sound is louder after the temperature rises.

If the valve collides with the piston, the valve clearance should be re-adjusted and the installation position of the piston connecting rod group should be checked.


diesel generator piston


f. Valve knock

Because the valve clearance is too large; the clearance between the valve rod and the valve guide is too large; the valve is stuck; the cam wear is severe. When the diesel engine is running at a low speed, it is easier to hear continuous, rhythmic, and slightly "Tap-tap" sound. As the speed increases, so does the sound.

If the valve knocking sound is found, the valve clearance should be checked and adjusted in time.


diesel generator valve


g. The knocking sound of the valve spring

The knock is caused by the valve spring being too soft or broken. In severe cases, the valve falls and collides with the top of the piston to make a loud noise. At the same time, a large amount of black smoke is generated in the intake pipe and the exhaust pipe, causing a destructive accident of the piston and the cylinder head.

If the knocking sound of the valve spring breaking is found, the qualified spring should be replaced immediately.

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