Crankshaft ablation is mainly caused by the failure of the crankshaft journal and the bearing bush to form an effective lubricating oil film, which causes the crankshaft journal to directly rub against the bearing bush. When the crankshaft ablation occurs in the diesel engine, it will emit white smoke, emit a metal impact noise, and even cause the crankshaft and the bearing bush to be locked together and unable to rotate. Therefore, the cause of the failure must be properly analyzed and judged.
1. Poor engine quality 1) Inferior oil quality. The selected oil quality grade and viscosity grade are lower, or different grades of engine oil are used for blending, resulting in the performance of the oil oil not meeting the requirements; the oil is mixed with a large amount of dust during use, and the engine oil is oxidized and deteriorated due to the high working temperature of the diesel engine. . The oxidatively deteriorated oil is black and dull, and the concentration is increased. The oil is rubbed with two fingers, and there is dust and impurities in the oil. If the oil used is found to exhibit the above phenomenon, it must be replaced in time.
2) The oil is thin. Since some diesel engine fuel injection pumps are lubricated by pressure lubrication, once the fuel injection pump and the lubricating oil passage seal are ineffective. Diesel entering the lubrication chamber will dilute the diesel engine oil. In addition, if the water jacket has cracks or blisters, the penetration of cooling water into the oil will also make the oil thin.
Check the upper parts of the diesel engine (the upper surface of the cylinder head, the valve train, the cylinder cover) for water vapor or water droplets. If it is found that the oil capacity in use increases, the concentration decreases, the viscosity decreases, and the oily smell indicates that diesel oil is mixed into the oil.
2. Insufficient oil inventory, low oil pressure, insufficient oil inventory, and low oil pressure will cause insufficient lubrication of the lubricating oil of the diesel engine, and thus cannot form a lubricating oil film between the crankshaft journal and the bearing bush of the diesel engine.
Check the oil quantity in the oil sump and the reading of the oil pressure gauge to further check for abnormalities such as blockage and leakage in the oil pipeline.
3. The clearance between the crankshaft journal and the bearing bush is too large or too small. 1) The crankshaft journal and the bearing bush are too large, which causes the diesel engine oil pressure to be low, and it is impossible to form a sufficient lubricating oil film.
2) The crankshaft journal and the bearing bush are too small, and the oil film thickness between the crankshaft journal and the bearing bush is not enough or there is no lubricating film.
When the gap is too large or too small, you can check the size of the journal, bearing hole and bearing bush with a micrometer and cylinder gauge, calculate the matching clearance, and measure the fit clearance directly with the feeler gauge.
4. The geometrical dimensions of the crankshaft or cylinder are out of tolerance. 1) The crankshaft has a large radial runout error, which makes the gap between the journal and the bearing bush small or no gap, and the thickness of the lubricating oil film is not enough or there is no lubricating oil film.
2) The coaxiality of the main bearing bore of the cylinder is too poor, resulting in too small or no clearance between the main journal and the bearing bush. The thickness of the lubricating oil film is not enough or there is no lubricating film.
3) The verticality of the cylinder and the main bearing hole is too poor, resulting in too small or no gap between the connecting rod journal and the main journal, and the thickness of the lubricating oil film is not enough or there is no lubricating film.
In the case that the diesel engine is not used for a long time after the new machine or overhaul, the above phenomenon is often formed. To determine the geometrical tolerance, you can shake the diesel engine crankshaft by hand (rotate the force), then unload the diesel engine main bearing cap and the connecting rod bearing cap from the cylinder, and then rotate the crankshaft. According to the magnitude of the rotating crankshaft torque, the difference is determined specifically (but to determine the size of the over-difference, the diesel engine needs to be disassembled and measured with a special gauge).
5. The shape and size of the crankshaft main journal and the connecting rod journal are out of the crankshaft main journal, the connecting rod journal or the main bearing bore of the cylinder, and the spheroidal or taper difference of the connecting rod big hole are large, which will cause the journal and the bearing bush to be broken. Continued (intermittent) or tapered. A good lubricant film cannot be guaranteed.
After the new machine or overhaul, the diesel engine is not put into use for a long time, and the above phenomenon is easy to occur, and the journal size can be measured. If the measured journal is ablated, the adjacent journals can be measured (since the adjacent corresponding journals are processed by the same equipment and the same cutting tool, which can represent the shape error of the ablated journal).
6. The surface roughness of the crankshaft main journal and the connecting rod journal exceeds the roughness. Due to the poor roughness, there are many metal peaks on the journal surface, which destroys the integrity and continuity of the lubricating oil film between the journal and the bearing. The metal ribs directly rub against the bearing pads, causing the crankshaft to ablate.
Failures often occur after a new machine or overhaul, and the diesel engine is not put into service for a long time. If the measured journal is ablated, the roughness detector can be used to measure adjacent adjacent journals (in general, the adjacent corresponding journals are machined by the same equipment and the same cutting tool, so that the measured roughness can represent its ablation journal Roughness).
7. When the crankshaft, flywheel, and clutch dynamic balance are out of tolerance, the inertia force generated by the high-speed rotation of the crankshaft 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 each other and cause the crankshaft to burn. eclipse.
The fault generally occurs after 10,000 km of mechanical driving. After the crankshaft is ablated, the residual debris on the journal can be removed, and the dynamic balance can be re-checked. The unbalanced amount can basically indicate the ablation journal dynamic balance excess.
8. Improper maintenance If the diesel engine is not operated for a period of time after reasonable operation and maintenance, it will cause wear and failure of the oil pump pressure limiting valve and other parts. The oil filter element will be blocked by oil and sludge, which will reduce the oil pressure and cause the crankshaft to ablate.
1. Poor engine quality 1) Inferior oil quality. The selected oil quality grade and viscosity grade are lower, or different grades of engine oil are used for blending, resulting in the performance of the oil oil not meeting the requirements; the oil is mixed with a large amount of dust during use, and the engine oil is oxidized and deteriorated due to the high working temperature of the diesel engine. . The oxidatively deteriorated oil is black and dull, and the concentration is increased. The oil is rubbed with two fingers, and there is dust and impurities in the oil. If the oil used is found to exhibit the above phenomenon, it must be replaced in time.
2) The oil is thin. Since some diesel engine fuel injection pumps are lubricated by pressure lubrication, once the fuel injection pump and the lubricating oil passage seal are ineffective. Diesel entering the lubrication chamber will dilute the diesel engine oil. In addition, if the water jacket has cracks or blisters, the penetration of cooling water into the oil will also make the oil thin.
Check the upper parts of the diesel engine (the upper surface of the cylinder head, the valve train, the cylinder cover) for water vapor or water droplets. If it is found that the oil capacity in use increases, the concentration decreases, the viscosity decreases, and the oily smell indicates that diesel oil is mixed into the oil.
2. Insufficient oil inventory, low oil pressure, insufficient oil inventory, and low oil pressure will cause insufficient lubrication of the lubricating oil of the diesel engine, and thus cannot form a lubricating oil film between the crankshaft journal and the bearing bush of the diesel engine.
Check the oil quantity in the oil sump and the reading of the oil pressure gauge to further check for abnormalities such as blockage and leakage in the oil pipeline.
3. The clearance between the crankshaft journal and the bearing bush is too large or too small. 1) The crankshaft journal and the bearing bush are too large, which causes the diesel engine oil pressure to be low, and it is impossible to form a sufficient lubricating oil film.
2) The crankshaft journal and the bearing bush are too small, and the oil film thickness between the crankshaft journal and the bearing bush is not enough or there is no lubricating film.
When the gap is too large or too small, you can check the size of the journal, bearing hole and bearing bush with a micrometer and cylinder gauge, calculate the matching clearance, and measure the fit clearance directly with the feeler gauge.
4. The geometrical dimensions of the crankshaft or cylinder are out of tolerance. 1) The crankshaft has a large radial runout error, which makes the gap between the journal and the bearing bush small or no gap, and the thickness of the lubricating oil film is not enough or there is no lubricating oil film.
2) The coaxiality of the main bearing bore of the cylinder is too poor, resulting in too small or no clearance between the main journal and the bearing bush. The thickness of the lubricating oil film is not enough or there is no lubricating film.
3) The verticality of the cylinder and the main bearing hole is too poor, resulting in too small or no gap between the connecting rod journal and the main journal, and the thickness of the lubricating oil film is not enough or there is no lubricating film.
In the case that the diesel engine is not used for a long time after the new machine or overhaul, the above phenomenon is often formed. To determine the geometrical tolerance, you can shake the diesel engine crankshaft by hand (rotate the force), then unload the diesel engine main bearing cap and the connecting rod bearing cap from the cylinder, and then rotate the crankshaft. According to the magnitude of the rotating crankshaft torque, the difference is determined specifically (but to determine the size of the over-difference, the diesel engine needs to be disassembled and measured with a special gauge).
5. The shape and size of the crankshaft main journal and the connecting rod journal are out of the crankshaft main journal, the connecting rod journal or the main bearing bore of the cylinder, and the spheroidal or taper difference of the connecting rod big hole are large, which will cause the journal and the bearing bush to be broken. Continued (intermittent) or tapered. A good lubricant film cannot be guaranteed.
After the new machine or overhaul, the diesel engine is not put into use for a long time, and the above phenomenon is easy to occur, and the journal size can be measured. If the measured journal is ablated, the adjacent journals can be measured (since the adjacent corresponding journals are processed by the same equipment and the same cutting tool, which can represent the shape error of the ablated journal).
6. The surface roughness of the crankshaft main journal and the connecting rod journal exceeds the roughness. Due to the poor roughness, there are many metal peaks on the journal surface, which destroys the integrity and continuity of the lubricating oil film between the journal and the bearing. The metal ribs directly rub against the bearing pads, causing the crankshaft to ablate.
Failures often occur after a new machine or overhaul, and the diesel engine is not put into service for a long time. If the measured journal is ablated, the roughness detector can be used to measure adjacent adjacent journals (in general, the adjacent corresponding journals are machined by the same equipment and the same cutting tool, so that the measured roughness can represent its ablation journal Roughness).
7. When the crankshaft, flywheel, and clutch dynamic balance are out of tolerance, the inertia force generated by the high-speed rotation of the crankshaft 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 each other and cause the crankshaft to burn. eclipse.
The fault generally occurs after 10,000 km of mechanical driving. After the crankshaft is ablated, the residual debris on the journal can be removed, and the dynamic balance can be re-checked. The unbalanced amount can basically indicate the ablation journal dynamic balance excess.
8. Improper maintenance If the diesel engine is not operated for a period of time after reasonable operation and maintenance, it will cause wear and failure of the oil pump pressure limiting valve and other parts. The oil filter element will be blocked by oil and sludge, which will reduce the oil pressure and cause the crankshaft to ablate.
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