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Abnormal sound of engine crankshaft main bearing

wallpapers Tech 2020-05-27
The engine crankshaft main bearing is also one of the everyday abnormal noises of the engine.
 
The main characteristics of the main bearing ring:
(1) There is no noise when the engine is idling; it appears only when the load is large. It increases with the increase of the throttle.
(2) The sound is dull and dull, and it is the sound of "Li Chi." It seems that the sound of tapping a large rock with a sledgehammer, when severe, the engine body vibrates.
(3) The oil pressure is lower than usual, and the sound does not change when the temperature changes.
(4) There is no noticeable change in the sound when the single-cylinder is cut off. When the two adjacent bottles are cut off at the same time, the noise will be reduced.
 
The main reason for the noise of the main crankshaft bearing:
(1) The fit between the leading journal and the bearing is too large. The regular fit between the leading journal and the bearing is generally between. .03mm ~ 0.12mm, if the clearance exceeds this standard, it is easy to produce noise.
(2) Inadequate lubrication of the main shaft. Burning of the main bearing. Insufficient lubricating oil, clogged oil passages, deterioration of lubricating oil, etc. will cause inadequate lubrication, causing the main bearing to burn and produce noise.
(3) The crankshaft is bent, or the bearing is too small, causing the main bearing to consume and produce a loud noise.
 
Diagnostic check method:
(1) Run the engine at medium speed, shake the throttle by hand, repeatedly increase the oil test and carefully listen to the change of the sound. If the noise increases with the increase of the engine speed, it is generally the sound produced by the loose main bearing.
(2) Then conduct a single-cylinder flame-out test. If the cylinder is not fired and the adjacent cylinders are simultaneously flame-out, the noise will be significantly reduced. This main bearing between the two bottles is the fault location.
(3) If you touch the position of the crankshaft on both sides of the cylinder block with a stethoscope, the noise is more reliable than other parts.

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Tag: main bearing