Causes of Engine Crankshaft Fracture (Part 1)

May. 18, 2020

The repair of the crankshaft is equivalent to the repair of the engine life after long use of the engine. Crankshaft in use for many reasons will cause crankshaft damage, in addition to the crankshaft for trucks its material, shape and size, processing quality, nitriding treatment, and other factors, will also appear abnormal damage, neck surface scratches, burns, cracks, and crankshaft deformation, fracture, and other faults or accidents. This article will analyze the cause of crankshaft damage, as well as the preventive measures in use.

Part of the crankshaft flywheel is mainly divided into the spare parts such as crankshaft, main bearing, and the flywheel, MERCEDES crankshafts role is to receive connecting rod transmission to come over to the force, torque, and power into travel through the flywheel output power. And drive the other nearby parts of the engine by means of a gear or pulley. The crankshaft consists of a spindle neck, a connecting rod journal, a crank, a front end of the crankshaft, and a rear end of the crankshaft.

MERCEDES crankshafts

MERCEDES Crankshafts

The spindle neck is supported by the main bearing. When working, the connecting rod neck rotates around the Central Line of the spindle neck. There is an oblique oil channel connecting the spindle neck and the connecting rod neck. A counterweight is added in the opposite direction of the crank to offset the centrifugal force when the crankshaft rotates so as to reduce the vibration of the diesel engine.

The connecting rod journal of some diesel engine crankshafts has a net oil chamber, as the name implies, used to filter impurities from the oil. When the engine works the crankshaft rotates, the oil impurities in the oil chamber will be thrown onto the oil chamber wall by centrifugal force, causing the clean oil to enter between the connecting rod journal and the bearing bush. The processing hole of the clean oil chamber is sealed with a screw plug, so it is necessary to open the seal regularly to clean the oil chamber.

The front end of the crankshaft is equipped with starting claw, crankshaft timing gear and pulley. The rear end of the crankshaft is provided with a flywheel connector, which is connected with the flywheel through bolts.

● what are the causes of common injuries

Crankshaft due to the use of a long time is bound to cause different degrees of wear and tear, we will take stock of the following, a few common crankshaft damages, and analysis of its causes. Provide a reference for friends to find similar situations in practical applications.

1. After the crankshaft journal is worn, the matching gap between the crankshaft and the bearing bush increases. It makes abnormal noise during operation, and the working condition deteriorates.

The reasons for this situation are concentrated, the first may be due to too little oil or oil in the presence of hard abrasive, oil deterioration containing acid. Secondly, the matching gap between the shaft neck and the bearing bush is too large or too small, resulting in the formation of oil film is difficult, the occurrence of dry friction will be early wearing, will also lead to this result.

In addition, when the crankshaft rotates, under the action of centrifugal force, the mechanical impurities in the oil tend to one side of the oil hole and become abrasive, making the journal wear uneven and producing taper. Connecting rod bending, twisting and cylinder sleeve deflection, so that the action on the crankshaft force distribution is not uniform, will also produce taper. All of these reasons will cause the crankshaft journal to wear after the increase of clearance with the bearing bush.

2, crankshaft journal surface scratches or strains

First, whether the oil in the sump has not been replaced on time, which will make the oil containing large metal particles mixed into the cracks between the bearing bush and the shaft neck to carve and pull the friction surface. Second, the maintenance of the air filter is not in place, cylinder liner, piston, and piston ring wear gap increased, with sand, impurities, and other abrasives with air inhalation cylinder combustion after channeling to the oil pan, circulation into the shaft neck and bearing clearance. It also has this kind of possibility, does not pay attention to the cleaning when the factory assembles, causes the diesel engine to bring in the dregs, the metal thing, and so on the abrasive particle.

3. Crankshaft journal burns

Burning tile is easy to cause the crankshaft shaft neck burn wear, burns will have blue ablation marks. This situation will cause severe friction between the shaft neck and the bearing bush, and the lubricating oil film will be destroyed. As the temperature rises, the surface of the shaft neck will appear blue. The surface hardness of the journal decreases and the bearing alloy often adheres.