1. Crankshaft bearing melting failure

When the crankshaft bearing melts, the engine's performance after the fault occurs is: the blunt and powerful metal knocking sound will be emitted from the melted main bearing. If all the bearings are melted or loose, there will be a clear "dang, pang" sound. The cause of the failure

(1) The lubricating oil pressure is insufficient, the lubricating oil can not squeeze between the shaft and the bearing, so that the shaft and the bearing are in a semi-dry or dry friction state, which causes the temperature of the bearing to rise and the anti-friction alloy melts.

(2) The lubricating oil passage, oil collector, oil strainer, etc. are blocked by dirt, and the bypass valve on the strainer cannot be opened (the preload of the valve spring is too large or the spring and ball valve are stuck by dirt, etc.), Caused lubricating oil supply interruption.

(3) The gap between the shaft and the bearing is too small to form an oil film; the bearing is too short and has no interference with the bearing housing hole, causing the bearing to rotate in the housing hole, blocking the oil passage hole on the bearing housing hole, and interrupting the supply of lubricating oil .

(4) The roundness of the crankshaft journal is too poor. During the lubrication process, it is difficult to form a certain oil film because the journal is not round (bearing clearance is sometimes large and sometimes small, and the oil film is sometimes thick and sometimes thin), resulting in poor lubrication.

(5) Body deformation or bearing processing error, or crankshaft bending, etc., make the center lines of each main bearing not coincide, causing the oil film thickness of each bearing to be uneven when the crankshaft rotates, and even become a dry friction state to melt the bearing.

(6) The amount of lubricating oil in the oil pan is insufficient and the oil temperature is too high, or the lubricating oil is diluted by water or gasoline, or the lubricating oil of inferior quality or inconsistent brand is used.

(7) Poor fit between the back of the bearing and the bearing seat hole or copper padding, etc., resulting in poor heat dissipation.

(8) The instantaneous overspeeding of the engine, such as the "speeding" of the diesel engine, is also one of the reasons for the burning of the bearings.

Fault prevention and troubleshooting methods

(1) Before installing the engine assembly, pay attention to the cleaning and inspection of the lubricating oil passage (wash with high-pressure water or air), eliminate the debris blocking the filter collector, and strengthen the maintenance of the coarse filter to prevent the filter element from clogging and the bypass valve Invalidate.

(2) The driver should observe the engine temperature and lubricating oil pressure at any time, and check for abnormal noise in the engine; check the quantity and quality of lubricating oil before leaving the vehicle.

(3) Improve the quality of engine maintenance and strengthen the pre-repair inspection of basic parts.

(4) The scraping of the crankshaft main bearing should make the center of each main bearing housing hole concentric. In the case of small deviation and eager repair, the scraping method of first correcting the horizontal line can be used. The scraping operation is related to the connecting rod bearing. It's roughly the same.

2. The crankshaft main bearing makes a noise

The performance of the engine after the noise from the crankshaft bearing is caused by the impact of the crankshaft main journal and the bearing. When the main bearing melts or falls off, the engine will vibrate greatly when the accelerator pedal is deeply depressed. The main bearing is worn, and the radial clearance is too large, and there will be a heavy and dull knocking sound. The higher the engine speed, the louder the sound, and the sound increases with the increase in load. The cause of the failure

(1) Bearings and journals are worn too much; the fastening bolts of the bearing cover are not tightly locked and loosened, which makes the matching clearance between the crankshaft and the bearing too large, and the two make a sound when they collide.

(2) The bearing alloy melts or falls off; the bearing is too long and the interference is too large, causing the bearing to break, or the bearing is too short to be poorly positioned and loose in the bearing housing hole, causing the two to collide.

Fault prevention and troubleshooting methods

(1) Improve the quality of engine maintenance. The fixing bolts of the bearing cover should be tightened and locked. The bearing should not be too long or too short to ensure a certain amount of interference.

(2) The grade of lubricant used should be correct, no inferior lubricant should be used, and proper lubricant temperature and pressure should be maintained.

(3) Maintain a good working condition of the lubrication system, replace the lubricating oil in a timely manner, and maintain the lubricating oil filter frequently.

(4) When driving, the driver should pay attention to the change of the oil pressure, and quickly check if the abnormal response is found. When the bearing gap is loud, the bearing gap should be adjusted. If it cannot be adjusted, the bearing can be replaced and scraped. When the cylindricity of the crankshaft journal exceeds the service limit, the crankshaft journal should be polished and the bearing should be re-selected.