Cause Analysis of Engine Crankshaft Damage (1)

1. Crankshaft journal wear

After the Crankshaft journal is worn out, the matching clearance with the bearing bush increases, and abnormal noises are emitted during operation, and the working condition deteriorates. The main reasons are:

① There is too little engine oil or there are hard abrasives in the engine oil, the engine oil has deteriorated and contains acidic substances.

②The matching clearance between the journal and the bearing bush is too large or too small, making it difficult to form an oil film, and dry friction will cause early wear.

③The diesel engine is overloaded for a long time, and the diesel engine will wear out quickly when it works under overheating.

④ When the crankshaft rotates, under the action of centrifugal force, the mechanical impurities in the oil are biased to the side of the oil hole and become abrasive, which makes the journal wear uneven and produces taper.

⑤Bending, twisting and deflection of the connecting rod and the deflection of the cylinder liner will cause uneven force distribution on the crankshaft and also produce taper.

2. Scratches or strains on the surface of the crankshaft journal

The main reasons are: (1) Inadequate cleaning during assembling has brought scum, metal and other abrasive particles into the diesel engine. ②The lubricating oil of the oil pan is not replaced on time, so that the lubricating oil contains large metal objects and other abrasive particles mixed into the gap between the bearing bush and the journal to scratch and scratch the friction surface. ③Improper maintenance of the air filter, increased wear gaps between cylinder liners, pistons and piston rings, and abrasives with sand, impurities, etc., which are sucked into the cylinder and burned with the air, escape to the oil pan, and circulate into the coordination of the journal and the bearing In the gap.

Crankshaft

3. Burns of crankshaft journal

There are bluish ablation marks on the journal burn. Burns and wear of Large Crankshaft journals are caused by bush burning. In this case, severe friction will occur between the journal and the bearing bush, the lubricating oil film will be destroyed and scratching will occur. The temperature will rise sharply and the surface of the journal will be oxidized to blue, and the hardness of the journal surface will decrease, and there will often be scratches. Bearing alloy stuck down.

4. Cracks on the surface of the crankshaft journal

Heavy  Duty Crankshaft cracks mostly occur at the fillet of the transition between the crank and the journal and the oil hole. The former is a radial crack, which is extremely harmful, and is easy to cause the crankshaft to break and cause a major crash. The latter is an axial crack, which develops along the axis along the oil hole. The reasons for the cracks are mainly caused by defects in manufacturing and repairing and improper use: ①During use, the shaft journal has poor surface roughness, and there are defects such as indentation, scratches, corrosion, and grinding pits. This is the source of stress concentration. If the ground is not eliminated in time, fatigue cracks will occur and develop first. ②Insufficient lubrication will cause serious bush burning, which will cause axial cracks. ③Long-term use, the metal fatigue transition on the surface of the journal will cause cracks in the circumferential direction. ④ After grinding, the shoulder fillet radius is too small, the transition is not smooth or the surface roughness is poor, causing stress concentration. ⑤When surfacing welding repairs the journal, excessive residual stress will be generated on the surface to cause cracks.