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What are the Reasons for the Abnormal Noise of the Diesel Engine?

A loader in good technical condition can hear a uniform and slight exhaust sound when idling, and a smooth roar when running at high speed. If the sound increases, accompanied by a decrease in power, increased fuel consumption, and increased vibration, it can be judged as an abnormal sound.

con rod bearings

Common Abnormal Noise and Diagnosis Methods:

  • Valve knocking sound There is a crisp metal knocking sound at the cylinder head cover. When the diesel engine is shifting at medium and low speeds, the knocking sound is more obvious and crisp. The regular “click, click” sound is mainly caused by the excessive valve clearance. The sound does not change when the temperature of the diesel engine rises or when tested by the “broken cylinder” method.
  • The main reason for the sound of the piston pin is the wear of the piston pin, the connecting rod bushing, or the hole of the piston pin seat, resulting in an excessively large fitting clearance, and the piston pin collides during movement and makes a sound. The characteristics of the sound of the piston pin are: the sound is more obvious when it is transferred from the idle speed to the medium speed operation; the period (frequency) of the sound changes with the rise and fall of the engine speed.
  • The common and most important reason for the sound of the piston knocking on the cylinder is that the piston and the cylinder wall are worn, and the matching clearance exceeds a certain limit. Sometimes, although the fitting clearance does not exceed the limit, if the connecting rod is bent and deformed, it will make a noise. The sound of piston knocking is obvious when the temperature of the diesel engine is low, especially when idling. The sound decreases or disappears when the temperature rises. This is the characteristic of piston knocking.
  • The main reason for the sound of the connecting rod bearing is that the journal and the bearing are worn, the bearing alloy layer is burnt out and falls off, the bearing cover (shoe cover) is loose, and the bearing rotates (the bearing bush goes on the outer circle), and the moment of work collides with each other and makes noise. The characteristics of the connecting rod bearing noise are: the noise is obvious at medium speed, but not obvious at high speed due to the increase of other mechanical noises, and the noise is weakened at idle speed.

connecting-rod-bearing-

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  • The reason for the sound of the crankshaft bearing is the same as that of the connecting rod bearing. Its characteristics are: the sound is duller than the knocking of the cylinder, piston pin, and connecting rod bearing. When refueling or decelerating suddenly, the sound is obvious and clear; if the bearing alloy layer is burnt out or falling off, the diesel engine will vibrate.
  • The most common and most important reason for the sound of camshaft bearings is that the camshaft and the bearing (sleeve) are worn, and the matching clearance is too large; the bearing alloy layer is burned out, falls off, or the outer diameter of the bearing and the seat hole bearing “walk the outer circle”.

Therefore, the fitting clearance should be checked regularly and good lubrication should be maintained for the running machine. For the diesel engine with abnormal noise, it should be removed in time before use, so as to prevent the wear and tear from aggravating and causing mechanical accidents.

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