**Correction of the Reverse Rotation Support of a Hydraulic Excavator**
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*Created on 2018/5/16*
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**1. Fault Description and Cause Analysis**
A Sumitomo S2800FJ hydraulic excavator had been in operation for 8,664 hours when it was involved in an accident at a construction site. A dump truck collided with the counterweight of the machine, causing damage to the reverse support system. Several sealing components were found to be damaged, and abnormal noises were heard during reversing. When the machine turned to the front and left side, a creaking sound was emitted.
After lifting the excavator with the bucket and removing the tracks from the ground, it was discovered that the axial clearance of the reverse bearing was excessive. Further inspection revealed a significant radial gap when the boom was extended. The reverse motor and speed reducer were functioning normally, leading to the initial assumption that the steel balls and cage inside the reverse bearing were damaged, increasing both axial and radial clearances, and damaging the seals.
Upon disassembling the reverse bearing, it was observed that the outer race was connected to the upper chassis, while the inner race was attached to the lower chassis. After removing all oil pipes and sealing their ends, the excavator was lifted using a crane, and the bolts securing the outer ring of the reverse bearing were loosened and removed. The upper and lower parts of the machine were separated.
As shown in Figure 1, the taper pin was driven out, followed by the removal of the plug using a Screw. The steel balls and cage were extracted using wire. Only two intact cages were found, while the rest were crushed. More than 30 steel balls showed severe pitting and deformation, while others had varying degrees of damage. The grease on the inner and outer raceways was cleaned, revealing pitting on the raceway surfaces visible under daylight.
The impact caused by the collision applied a large radial force to the reverse bearing, resulting in damage to some of the nylon-based cage components. If the machine continued to operate, the damage would worsen, increasing the gap between the inner and outer races, allowing grease to escape, and further damaging the raceway, cage, and steel balls. This led to abnormal noise and sticking during reversing.
**2. Repair and Replacement of the Reverse Support Components**
**2.1 Replacing the Reverse Bearing Components**
Replacing the entire reverse bearing is expensive, costing around 100,000 RMB, and has a long delivery time. Since the excavator is an older model, replacing the full bearing was not necessary. Instead, the original reverse support was repaired.
The inner and outer raceways were not severely damaged, but there was noticeable pitting. The original steel balls had a diameter of 28.48 mm, while locally available ones were 28.60 mm—0.12 mm larger. With 136 steel balls and cages in total, this increase added up to 16.32 mm across the raceway. To compensate, the thickness of each cage was reduced by 0.12 mm, ensuring the steel balls fit properly into the raceway. It was crucial to select steel balls with a diameter less than 0.002 mm smaller than the original to maintain consistency.
**2.2 Reassembly of the Reverse Support**
After cleaning the inner and outer races, steel balls, cages, and sealing components, the outer race was placed on the inner race, ensuring the raceways were aligned. Steel balls and cages were inserted through the radial holes until fully filled. The plug was then installed, and the taper pin was secured. A sealant was applied to the sealing device and groove to ensure a tight seal.
Once reassembled, the reverse bearing was tested for any binding or stiffness. If found, adjustments were made to ensure smooth movement. Finally, the outer race was refilled with grease, and the raceway and pinion were also lubricated.
The upper part of the excavator was lifted with a crane, and the lower end of the reverse support was aligned with the outer seat. Bolts were positioned using round steel matching the Bolt hole diameter, and the bolts were installed symmetrically in three groups. After tightening all bolts, a torque wrench was used to apply 650 N·m of torque. The final step involved replacing the engine and ensuring normal operation resumed.
**Related Bearing Knowledge** - Rolling Bearing Basics Summary - Double Outer (Inner) Ring Double Row Angular Contact Ball Bearing [Contact Angle 40°] - How to Properly Seal Rolling Bearings - Bearing Installation (Positioning) - Bearing Steel Metallurgical Skills This article is linked to http:// Please indicate the bearing network: http:// Previous: “TIMKEN Imported Bearings Smooth Protection†Next: What is an Air Bearing?
Repair and Adjustment of the Reverse Rotation Support in a Hydraulic Excavator
Source: China Bearing Network | Time: 2014-03-29
| /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089'; |
**Related Bearing Knowledge** - Rolling Bearing Basics Summary - Double Outer (Inner) Ring Double Row Angular Contact Ball Bearing [Contact Angle 40°] - How to Properly Seal Rolling Bearings - Bearing Installation (Positioning) - Bearing Steel Metallurgical Skills This article is linked to http:// Please indicate the bearing network: http:// Previous: “TIMKEN Imported Bearings Smooth Protection†Next: What is an Air Bearing?
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