Introduction to engine crankshaft

The crankshaft is the main rotating part of the engine. After the connecting rod is installed, the up and down (reciprocating) movement of the connecting rod can be accepted into a cycle (rotating) movement.

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It is an important part of the engine. It is made of carbon structural steel or ductile iron. It has two important parts: the main shaft neck, the connecting rod neck (and others).


The main shaft neck is mounted on the cylinder block, the connecting rod neck is connected with the big head hole of the connecting rod, and the small head hole of the connecting rod is connected with the cylinder piston. It is a typical crank slider mechanism.

Crankshaft lubrication mainly refers to the lubrication of the connecting rod big head bearing bush and crankshaft connecting rod neck and the two fixed points. The rotation of the crankshaft is the power source of the engine and the source power of the whole mechanical system.

Crankshaft working principle: 

the crankshaft is one of the most typical and important parts in the engine, its function is to convert the gas pressure from the piston connecting rod into torque, as power and output work, drive his working mechanism, and drive the internal combustion engine auxiliary equipment work.

Crankshaft processing technology: 

Although there are many varieties of crankshafts, some details of the structure are different, but the processing process is roughly the same.

Introduction to main process

1) External milling of crankshaft spindle neck and connecting rod neck

▶In the crankshaft parts processing, due to the influence of the disk milling cutter itself structure, the blade and the workpiece is always intermittent contact, impact.

▶Therefore, the whole cutting system of the machine tool control clearance link, reduce the vibration caused by movement clearance in the process of machining, thereby improving the machining accuracy and the service life of the tool.

2) Crankshaft spindle neck and connecting rod neck grinding

▶The tracking grinding method takes the center line of the spindle neck as the rotation center, and completes the grinding process of the crankshaft connecting rod neck in turn (it can also be used for the spindle neck grinding) by clamping once. The grinding rod journal is realized by CNC controlling the feed of the grinding wheel and the two-axis linkage of the workpiece rotation movement to complete the crankshaft feeding.

▶The tracking grinding method adopts one clamping and completes the grinding process of crankshaft spindle neck and connecting rod neck successively on a CNC grinder, which can effectively reduce the equipment cost, reduce the processing cost, and improve the machining accuracy and production efficiency.

3) crankshaft spindle neck and connecting rod neck fillet rolling machine

▶The application of rolling machine is to improve the fatigue strength of the crankshaft. According to the statistics, the crankshaft life of nodular cast iron can be increased by 120% ~ 230% after the round corner rolling. The life of wrought steel crankshaft can be increased by 70% ~ 130% after fillet rolling roll.

▶The rotary power of the pressure comes from the rotation of the crankshaft, which drives the roller in the roller head to rotate, and the pressure of the roller is implemented by the oil cylinder.

1.The most common fatigue failure of engine crankshaft is metal fatigue failure, namely bending fatigue failure and torsion fatigue failure, the former is more likely than the latter.

2.Bending fatigue cracks first appear in the connecting rod journal (crank pin) or the round corner of the spindle neck, and then develop to the crank arm. Torsional fatigue cracks occur at poorly machined oil holes or rounded corners and then develop toward the axis.

3.The fatigue failure of metal is the result of the variable stress which changes periodically with time. Statistical analysis of crankshaft failure shows that about 80% is caused by bending fatigue.

The main cause of crankshaft fracture

1)oil deterioration after long-term use; Serious overload, overhang, resulting in long-term engine overload operation and the occurrence of burning tile accident. The crankshaft suffered severe wear due to engine shingle burn.

2)After the engine is repaired, the loading has not gone through the running-in period, that is, overload and overhang, and the engine is overloaded for a long time, so that the crankshaft load exceeds the allowable limit.

3)In the repair of the crankshaft, the overlaying welding is used to destroy the dynamic balance of the crankshaft, and the balance check is not done. The unbalance exceeds the standard, causing greater vibration of the engine and leading to the fracture of the crankshaft.

4)Due to poor road conditions, the vehicle and serious overload overhang, the engine often in the torsional vibration critical speed line, shock absorber failure, will also cause the crankshaft torsional vibration fatigue damage and fracture.

Notes for crankshaft maintenance

1)In the process of crankshaft repair, the crankshaft should be carefully checked whether there are cracks, bending, twisting and other defects, and the wear of spindle tile and connecting rod bearing bush, to ensure that the clearance between the spindle neck and the spindle tile, the connecting rod journal and the connecting rod bearing bush is within the allowed range.

2)Crankshaft cracks mostly occur at the transition corner between the crank arm and the journal, as well as the oil hole in the journal.

3)The flywheel operation balance should be ensured when repairing and installing the crankshaft.

4) The crankshaft should be comprehensively overhauled after serious accidents such as burning tiles and pounding cylinders in the internal combustion engine.

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