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Causes of Knocking Noise from Main Shaft Bearing of Diesel Generator

Feb. 02, 2023

Today, we will briefly introduce the content about why the diesel generator produces the knocking sound of the main shaft bearing.


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Fault phenomenon: This is a kind of heavy, stuffy "bong, bong" tapping sound. The higher the speed of the diesel generator, the louder the sound. The sound is more prominent when the accelerator is suddenly increased, and the diesel generator vibrates greatly. There was a heavy "bong, bong, bong" noise when the speed was suddenly reduced. The noise of the diesel generator is obvious when it is loaded, and the noise does not change when the temperature changes.


Cause analysis: the knocking noise of the main shaft bearing is mainly caused by the excessive radial and axial clearance of the bearing and the bending of the crankshaft. Bearing cover fixing screws are loose. The lubricating oil supply in the bearing is insufficient or too thin, causing the bearing alloy to burn or fall off. The bearing bush and journal are seriously worn and the radial clearance is too large. The axial thrust washer of the main shaft is too thin and the clearance is too large. The bearing bush is too long or too short, causing the bearing bush to break or rotate. The crankshaft is bent and the journal is worn.


Treatment method: The knocking sound of the main shaft bearing can be judged by the following methods: make the diesel generator run at a speed below the medium speed, shake the throttle slightly by hand, and repeatedly increase the throttle, listen carefully, if the noise increases with the increase of the diesel generator speed, the noise is obvious at the moment of shaking the throttle, indicating that the main bearing is seriously worn, or even loose; If the diesel generator makes obvious noise when running at idle speed or below medium speed, and becomes disorderly when running at high speed, it may be that the crankshaft is bent; If the engine body vibrates greatly at high speed and the oil pressure decreases significantly, it means that the main bearing is loose or burnt seriously, and the bearing alloy falls off.


Open the oil filler cap and listen carefully. At the same time, change the rotating speed repeatedly. You can clearly hear the knocking sound of the main bearing. Find out the cause of the fault through inspection and judgment, and carry out targeted troubleshooting. Remove the oil pan, check whether the fixing screws of the bearing cover are loose, and tighten them if any. Remove the bearing cover and check the lubrication in the bearing. If the oil circuit is blocked and the lubrication is poor, the oil circuit should be dredged. If the lubricating oil is insufficient or too thin, add or replace the lubricating oil that meets the requirements to ensure good bearing lubrication.


If the fault is serious, the diesel generator shall be disassembled for inspection. If the clearance between bearing bush and journal is too large, but its surface is still good, the gasket can be adjusted properly to restore the normal clearance. If the bearing surface is slightly scratched or burnt, the good alloy layer can be exposed after scraping and grinding, and can be used again. If the alloy layer falls off or is seriously burnt, hang the alloy again or replace the bearing. When the axial thrust washer of the main shaft is too thin, it should be thickened to make the clearance meet the requirements.


If the bearing bush is too long, too short or broken, it should be replaced in time. If the crankshaft is bent, it should be straightened. When the taper and ovality of the journal exceed the limit, or the surface of the journal is seriously strained or burnt, it can be polished on the grinder. In case of slight strain or burn, apply oil on the fine abrasive cloth, roll it on the journal and polish the journal.


As a professional diesel generator manufacturer, we always insist on using first-class talents to build a first-class enterprise, create first-class products, create first-class services, and strive to build a first-class domestic enterprise. If you would like to get more information welcome to contact us via sales@dieselgeneratortech.com.

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