Overhaul of Common Damage to Tractor Linkages

To understand the common damage of tractor connecting rods, we first understand the working principle of connecting rods, and then understand the maintenance of tractor damage. This article analyzes the causes of common damage to the connecting rod, and introduces the maintenance methods of the connecting rod.

 

The connecting rod is an important component of the tractor crank connecting rod mechanism. It is connected to the piston and connected to the crankshaft. Its role is to transmit the huge combustion pressure endured by the piston to the crankshaft, make the crankshaft make a circular motion, transfer the thermal energy generated by the combustion of the fuel, and finally convert it into mechanical energy to output power. The main defects of the connecting rod are bending and distortion, wear on the large and small end holes, and damage to the joint surface of the large end hole and the bolt hole surface. The consequences directly affect the mutual position and mating clearance of the piston, the piston ring, and the surface of the cylinder liner, which reduces the compression pressure of the engine, reduces the power, and reduces the working performance of the engine. Therefore, the connecting rod should be carefully checked and corrected during repair.

 

Common damages to connecting rods include: mechanical damage to the large end disassembly surface of the connecting rod and the bearing surfaces of the connecting rod bolts and nuts; wear and deformation of the large and small end holes of the connecting rod; and deformation of the connecting rod body.

 

The main damage forms of the connecting linkage are fatigue fracture and excessive deformation. The locations of fatigue fracture are usually three high stress areas on the connecting rod. The working conditions of the connecting rod require the connecting rod to have high strength and fatigue resistance; it also requires sufficient rigidity and toughness. Strict requirements are required on the shape of the connecting rod and excessive rounded corners. Attention should also be paid to the surface processing quality to improve fatigue strength, otherwise the application of high-strength alloy steel will not achieve the expected results.

 

Specifically, the common damage of the connecting rod can also be divided as follows: ① mechanical damage at the big end disassembly surface of the connecting rod and the bearing surface of the connecting rod bolt and nut; ② large and small end holes of the connecting rod wear and deform;③deformation, bending, twisting and double bending of the connecting rod body.

 

The following introduces several inspection methods for common damage to the connecting rod.

Worn big and small end holes

Repair method for small end hole wear of connecting rod: due to the wear of small end hole of connecting rod, the tightness of the lining in the hole will decrease. At this time, the small end hole of the connecting rod should be repaired. After the small end hole of the connecting rod is worn, the hole is generally bored on a special boring machine to eliminate the wear marks, cones and ellipses on the surface of the inner hole, and then it is equipped with a bush with an increased outer diameter.

 

Repair method for the wear of the big end hole of the connecting rod: After the big end hole of the connecting rod is worn, generally, a metal layer more than 0.2 mm thick is milled from the joint surface I of the large end of the connecting rod, and then the metal layer larger than 1mm. Then install the tile cover with connecting rod bolts according to the specified torque, and boring large end holes on the tile boring machine according to the standard size.

Damage to the connecting surface of the connecting rod bolt and the large end hole

When the connecting surface of the connecting rod and the connecting rod bearing pad cover is slightly damaged, the connecting surface of the connecting rod or the connecting rod bearing pad cover can be directly ground and repaired on a flat plate sprinkled with gold sand. If the joint surface is severely damaged, the above-mentioned repair method after the large hole of the connecting rod is worn, remove some metal grinding from the joint surface, and then boring the large hole to a standard diameter.

Deformation of connecting rod end hole

The out-of-roundness of the large end hole of the connecting rod is detected in the vertical direction of the long axis, and most of the elongation occurs on the end cover. The roundness of the detection aperture can use a special connecting rod end aperture measuring instrument. It has two fixed and one floating pin on the back. The floating pin can be adjusted according to the specific size of the large end hole of the detected link.

Deformation of the connecting rod body

Due to the complex alternating load, the connecting rod undergoes bending, twisting and double bending in the shaft. Inspection of bending and bending deformation of the connecting rod: The bending and twisting of the connecting rod is checked on the connecting rod checker. In addition, the curved connecting rod can be straightened with a bending tool on the press; or on the corrector. The twisted connecting rod can be fired on the vise and corrected with the correction tool on the corrector. If there is no correction tool, it can be corrected with a long handle and pipe wrench.

Damage to the connecting rod

The bending and twisting of the connecting link will not only reduce its strength, but also change the cooperation relationship between the piston and the cylinder. Therefore, be sure to check the bending and distortion of the connecting rod during overhaul. The inspection method is as follows:

 

(1) First carry out a simple inspection, place the connecting rod flat on the inspection platform, slowly move and observe the contact between the head and the platform, reverse the connecting rod, and then observe the contact between the other surface and the platform. If the bending is abnormal, check it carefully with the instrument. Be sure to check the bending and distortion of the connecting rod during overhaul. (2) The bending and twisting of the connecting rod can be performed on the connecting rod checker. The inspection fixture should be calibrated before the inspection, and the inspection fixture should be calibrated with "standard" connecting rod. (3) If there is no connecting rod tester, dial indicator, V-shaped block, standard mandrel and flat plate can also be used for inspection.

Detection of connecting rod bushing wear

Excessive wear on the connecting rod bushing increases the clearance between the piston pin and the bushing. When the clearance is too large, metal knocks will occur when the diesel engine is working, and it is more obvious when changing the speed. The inspection method is as follows:

(1) The wear of the bushing can be checked and measured with an internal dial indicator, and the roundness and cylindricality of the bushing and the clearance with the piston pin can be calculated based on the measurement results. (2) Generally, the roundness and cylindricality of the connecting rod bushing should not exceed 0.02 to 0.03 mm; the clearance with the piston pin is 0.02 to 0.05 mm. Such a high degree of accuracy requires that general measuring tools are difficult to measure, and most repairers judge by experience. Push the piston pin gently into the copper sleeve of the connecting rod with your fingers, so as to have neither resistance nor obvious looseness. The contact area between the piston pin and the connecting rod bush is above 75%.