What Are The Causes Of Crankshaft Bearing Damage?

Reasons for wear of crankshaft journal

In the working process of automobile engine, there is high friction between crankshaft journal and bearing. Especially when the engine is running at low speed or starting, dry 

friction is generated due to the difficulty of lubricating oil film establishment, resulting in bearing wear.

Reasons for crankshaft journal and bearing damage

The radial clearance between the crankshaft journal and the bearing is very small, which can make the crankshaft free rotation without opening and radial runout. If the radial 

clearance between the journal and the bearing changes, it often causes early wear and destruction of the crankshaft journal and shaft, so that the engine working vibration 

increases, noise increases, fuel consumption increases, and accidents increase. Crankshaft journal and bearing damage in the form of scratch, wear, fatigue spalling, corrosion, 

burning and so on.

1. Fatigue spalling：the crankshaft is constantly subjected to periodic gas force, alternating inertia force and rotating centrifugal force, which act on different parts of the 

crankshaft respectively, accelerating the wear of the crankshaft; Bearing under the action of long-term mutation load, impact load, alloy fatigue, and then crack, and to the 

depth of the expansion, so that the alloy spalling.

2. Corrosion: oil failure caused by its acid value is too large, it will have a corrosive effect on crankshaft and bearing. Especially when the bearing is exposed to copper, the 

corrosion rate is faster because of the lack of surface layer and nickel protective layer that are resistant to corrosion. The honeycomb structure produced by corrosion will greatly 

reduce the bearing strength

3.Burning-out: when the crankshaft journal and bearing between the oil, because of the low pressure oil oil duct plug, oil viscosity, the intense friction occurs between journal 

and bearing, the journal and the bearing temperature rise rapidly, to make the journal burns, serious causes the bearing metal melt, adhesion on the shaft, the crankshaft stuck 

even rupture.

4. Scratch: metal dust, lubricating oil filtration poor or foreign granular impurities with the flow of oil into the journal and bearing surface between these hard particles will make 

the alloy surface scratch, serious can be in the alloy surface and journal surface scrape out many ring grooves.

5. Defects of connecting rod geometry: when the geometric shape of connecting rod appears saddle shape, drum shape, not coaxial and not straight, the normal clearance 

between journal and bearing will change. If the clearance is too large, the contact radian between the journal and the bearing becomes smaller, which increases the pressure 

load of the oil film and aggravates the fatigue of the bearing. Too small clearance will limit the flow of oil, it is difficult to form an oil film, can not take away the friction heat 

generated, increase the tendency of overheating deformation and "holding tile".

6. Improper assembly of connecting rod: improper torsion of connecting rod bolt, assembly error of connecting rod bearing cover and assembly error of connecting rod bearing 

will cause damage to crankshaft in different degrees and in different forms. Crankshaft processing error Crankshaft geometry, such as journal step, cone, drum and saddle errors, 

will make the crankshaft journal and bearing clearance changes, reduce the thickness of oil film or prevent the formation of oil film, resulting in direct metal contact and 

abnormal bearing wear.

Crankshaft journal surface wear

crankshaft journal is the main working surface of the crankshaft, its wear is inevitable, the general connecting rod journal wear is mostly on the crankshaft center line side, and 

the main shaft journal wear is near the connecting rod journal side. Mainly related to the stress in the working process of crankshaft. If the connecting rod is bent and the 

cylinder sleeve is deflected, the eccentric wear of crankshaft journal will be aggravated. If the mechanical impurities in the oil are too much, due to the inclination of the oil 

passage of the spindle journal and the connecting rod journal, under the action of the centrifugal force of the crankshaft rotation, the abrasive is biased in the oil passage 

away from the rotating center of the one side, and concentrated on the one side of the connecting rod journal, resulting in larger wear of the connecting rod journal on the 

side. 

In addition, the deviation and deformation of the installation position of parts will also make the force on both sides uneven, and the larger side of the force is larger.

Crankshaft journal surface wear is not serious, can be used to restore the journal grinding. After crankshaft grinding, cylindricity error, surface roughness and fillet radius at both 

ends of crankshaft should meet the requirements; The parallelism error of the journal axis of each connecting rod to the journal axis and crank radius should meet the original 

factory regulations, and the allocation Angle deviation of the journal axis of each connecting rod to the center plane of the keyway of the crankshaft timing gear should meet 

the manufacturer's regulations. When worn journal size exceeds repair size, crankshaft must be replaced.