Why Is Diesel Generator Crankshaft Ablated

During use of diesel generator, the crankshaft sliding bearing is ablated, commonly known as "burning tile". The main reason for this failure is that when the mechanical load and thermal load of the diesel engine are too large, and the oil supply is insufficient, an effective lubricating oil film cannot be formed between the crankshaft journal and the bearing bush, resulting in direct friction between the crankshaft journal and the bearing bush.

1. Specific causes of crankshaft ablation

(1) Poor oil quality

a. The quality of the engine oil is poor; a large amount of dust is mixed into the engine oil during long-term use, and the engine oil is oxidized and deteriorated due to the high working temperature of the diesel engine.

b. There is water mixed in the engine oil. Cracks in the water jacket or the water jacket have blisters, allowing the cooling water to seep into the engine oil.

c. The engine oil becomes thinner. Because some diesel engine fuel injection pumps adopt pressure lubrication, once the fuel injection pump and the lubricating oil passage are sealed to fail, diesel oil enters the lubricating oil passage to dilute and deteriorate the diesel engine lubricating oil.　　

(2) Insufficient oil capacity and low oil pressure

a. The oil capacity is not enough. Failure to add enough oil according to the specified capacity will result in insufficient lubricating oil flow of the diesel engine, and the formation of a lubricating oil film cannot be guaranteed.

b. The oil pressure is low. Due to the low oil pressure, no lubricating oil film is formed between the crankshaft journal and the bearing bush.

c. Due to poor cleanliness of the engine oil, the lubricating oil passage or oil hole is blocked, or there is insufficient or insufficient engine oil between the crankshaft journal and the bearing bush.

(3) The gap between the crankshaft journal and the bearing bush is too large or too small.

a. The clearance between the crankshaft journal and the bearing bush is too large to make the oil pressure low and it is impossible to form a sufficient lubricating oil film.

b. The gap between the crankshaft journal and the bearing bush is too small, resulting in insufficient oil film thickness or no lubricating oil film between the crankshaft journal and the bearing bush.

c. The bearing bush (camshaft bushing) moves axially. Due to the axial displacement of the bearing bush (camshaft bushing), the formation of the oil pressure chamber is destroyed, the oil pressure cannot be generated, and the lubricating oil film cannot be formed.

(4) The geometric dimensions of the crankshaft or cylinder block are out of tolerance.

A. The crankshaft radial runout (crankshaft bending) is too large, so that the gap between the journal and the bearing bush is small or no gap, and the thickness of the lubricating oil film is insufficient or there is no lubricating oil film.

B. Uneven angles of crankshaft connecting rod journals and uneven angles of crankshaft connecting rod journals of multi-cylinder diesel engines make the gap between the connecting rod journal and the bearing bush too small or no gap, and the thickness of the lubricating oil film is insufficient or there is no lubricating oil film.

C. The coaxiality of the main bearing hole of the cylinder block is too poor, resulting in too small or no gap between the main journal and the bearing bush, insufficient lubricating oil film thickness or no lubricating oil film.

D.The verticality of the cylinder hole and the main bearing hole is too poor, causing the connecting rod journal and main shaft journal clearance to be too small or no clearance, insufficient lubricating oil film thickness or no lubricating oil film.

(5) The dynamic balance accuracy of crankshaft, flywheel and clutch is out of tolerance.

When the dynamic balance accuracy is out of tolerance, the high-speed rotation of the crankshaft will generate a lot of inertial force, which will damage the clearance between the crankshaft journal and the bearing bush. In severe cases, the journal and the bearing bush will directly rub against the crankshaft and cause ablation of the crankshaft.　　　　

(6) Improper maintenance.

After the diesel engine has been running for a period of time, if reasonable maintenance is not carried out in time, it will cause the oil pump pressure limiting valve, oil pump and other parts to wear, fail and deform. The filter element of the oil filter will be blocked by oil dirt and sludge, which will reduce the oil pressure and cause ablation of the crankshaft.

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