The core hints: the cause analysis and judgment of engine crankshaft ablation: when the crankshaft is ablated, the diesel engine will take the white smoke, send out the metal impact noise, even cause the crankshaft and the axle bush to lock together, and can not rotate. Therefore, we must correctly analyze and judge the cause of its failure.
Crankshaft ablation is mainly caused by the failure of effective lubricating film between crankshaft journal and bearing bush, resulting in direct friction between crankshaft journal and bearing bush. When the crankshaft is ablated by diesel engine, it will appear white smoke, send metal knocking noise, and even cause the crankshaft and axle bush to be locked together and unable to rotate. Therefore, we must correctly analyze and determine the cause of its failure.
1 poor quality of oil
1) the quality of the oil is inferior. The selection of oil quality and viscosity grade is low, or different grades of oil are used, the use of oil is not required; the oil is used in the process of using a large amount of dust, and because of high working temperature of the diesel engine, the oil is oxidized and deteriorated. The oxidized oil is black and lustrous, and the concentration is increased. It uses two fingers to twist the oil and feels that there are dust and impurities in the oil. If the oil used above appears above, it must be replaced in time. 2) the oil is thinner. As part of the diesel engine fuel injection pump lubrication pressure lubrication, once the fuel injection pump and lubricating oil seal failure. When diesel enters the lubricating oil cavity, the lubricating oil of diesel engine will dilute and deteriorate. In addition, if the water jacket has cracks or sand holes, the cooling water will be diluted into the oil. It is possible to check whether there are steam or water droplets on the upper part of diesel engine (cylinder head plane, valve body and cylinder head housing). If it is found that the oil capacity increases, the concentration decreases, the viscosity decreases, and the smell of oil is generated, it is indicated that the diesel oil is mixed with diesel oil.
2 oil stock is not enough, oil pressure is low
The insufficient oil stock and low oil pressure will result in the insufficient flow of the diesel engine lubricating oil, which can not guarantee the formation of lubricating oil film between the crankshaft journal and the axle bush of the diesel engine.
The number of oil in the oil pan and the reading of the oil pressure gauge can be checked, and the abnormal phenomena such as blockage or leakage in the oil pipeline should be further checked.
3 the gap between the crankshaft and the axle is too large or too small
1) because the clearance between crankshaft journal and bearing bush is too large, the diesel engine oil pressure is too low to form enough lubricant film.
2) because the clearance between the crankshaft journal and the bearing bush is too small, 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 long, the size of the shaft neck, bearing hole and axle bush can be checked with a micrometer and a measuring cylinder, and the matching clearance can be calculated by the gauge.
4 the difference between the geometric size of the crankshaft or the cylinder
1) the radial runout of crankshaft is very large, so that the clearance between journal and bearing bush is small or no clearance. 2) the coaxial degree of the main bearing bore of the cylinder body is very poor, resulting in too small clearance or no gap between the journal neck and the bearing bush, and the thickness of the lubricant film is not enough or there is no lubricating film. 3) the verticality of the cylinder head and the main bearing hole is too poor, resulting in too small clearance or no clearance between the connecting rod journal and the spindle neck, and the thickness of the lubricant film is not enough or no lubricant film is available. This phenomenon often occurs when diesel engines are not put into operation for a long time after new engines or overhauls. It is possible to shake the crankshaft of the diesel engine by hand, then unload the main bearing cover of the diesel engine and the connecting rod bearing cover by the cylinder, and then turn the crankshaft. According to the size of the rotating crankshaft torque, the difference of the crankshaft torque should be determined.
5 the crankshaft neck and connecting rod journal are of super size.
The spindle neck of the crankshaft, the neck of the connecting rod axis or the main bearing hole of the cylinder body, the cylinder degree or taper of the connecting rod big head are large, and the gap between the shaft neck and the axle bush will be interrupted (discontinuous) or conical. It can not guarantee the formation of better lubricating oil film. After the new engine or overhaul, the diesel engine will not be put into operation for a long time. If the journal is ablated by the measured axis, the adjacent corresponding shaft neck can be measured (the same equipment and the same cutting tool are used in the adjacent adjacent axis neck, thus the shape error of the ablative journal can be represented).
6 the surface roughness of crankshaft neck and connecting rod journal is super poor.
Because of the poor roughness, there are many metal peaks on the surface of the journal, which destroys the integrity and continuity of the lubricant film between the journal and the bearing bush. The friction between the metal edge and the bearing bush causes the crankshaft ablation.
Faults often occur after new engines or overhauls, and diesel engines are not put into operation for a long time. If the axis neck is ablated, the adjacent axis neck can be measured by the roughness measuring instrument (in general, the same equipment and the same cutting tool are used for the adjacent corresponding axis neck, and the roughness can be represented by the roughness of the ablative Journal).
7 crankshaft, flywheel, clutch dynamic balance overbalance
When the dynamic balance is over, the high speed rotation of the crankshaft produces the inertia force, which will cause the gap between the crankshaft journal and the axle bush to be damaged, and it will cause the crankshaft to be ablated by the shaft neck and the axle bush directly.
The fault usually occurs after the mechanical driving of 10000km. After the crankshaft is ablated, the residual impurities on the neck of the shaft can be removed and the dynamic balance of the crankshaft is rechecked. The unbalanced quantity of the crankshaft can basically indicate the dynamic balance excess of the ablative journal.
8 improper maintenance
If the diesel engine runs for a reasonable period of time without proper maintenance and repair, it will cause wear and failure of parts such as oil pump pressure limiting valve. The filter element of the oil filter will be blocked by oil and sludge. The oil pressure will be reduced and the crankshaft will be ablated.
