Diagnosing and Resolving Swing Noise Issues in Caterpillar E120B Excavators

[MikePhua]

Introduction: Understanding Swing Noise in the CAT E120B
The swing function on a Caterpillar E120B excavator allows the upper structure to rotate smoothly on the undercarriage. Swing noise is a common concern reported by operators and maintenance personnel, often signaling potential issues with the swing system components. This article provides a detailed examination of swing noise causes, diagnostic approaches, maintenance strategies, and practical repair tips to keep the E120B operating quietly and efficiently.
Components Involved in the Swing Mechanism
The swing system consists of several key components working in unison:

• Swing Motor: A hydraulic motor that powers rotation.
  
• Swing Reducer (Gearbox): Reduces motor speed and increases torque.
  
• Swing Bearing (Slew Ring): A large bearing supporting the upper structure on the undercarriage, enabling rotation.
  
• Swing Brake: Controls the stoppage and holds the swing position.
  
• Hydraulic lines and control valves: Deliver fluid and control swing motion.
  

Any abnormal noise during swing operation usually points to wear or malfunction in these components.
Common Types of Swing Noise
Operators often describe swing noise in several ways:

• Grinding or rattling: Indicative of worn gears or damaged bearing teeth.
  
• Knocking or clunking: Could result from loose bolts, worn pins, or slack in the swing bearing.
  
• Squealing or whining: Often related to hydraulic issues, such as cavitation in the swing motor or pump.
  
• Metal-on-metal scraping: Suggests lack of lubrication or damaged bearing surfaces.
  

Diagnostic Steps for Swing Noise
A systematic diagnostic process includes:

• Visual inspection: Check for oil leaks, loose bolts, or visible damage on the swing bearing and motor.
  
• Listen carefully: Determine noise characteristics and whether it changes with load or speed.
  
• Check swing bearing backlash: Excessive backlash (play) between gear teeth indicates wear.
  
• Hydraulic pressure test: Ensure swing motor receives proper pressure and flow without cavitation.
  
• Lubrication check: Verify grease levels and inspect for contamination in bearing grease.
  
• Torque test: Measure swing motor torque to detect internal wear.
  

Common Causes of Swing Noise

• Wear in swing bearing teeth: Over time, wear or damage to the gear teeth on the swing bearing can cause grinding sounds.
  
• Insufficient lubrication: Lack of grease or contaminated grease in the swing bearing causes metal contact and noise.
  
• Loose or damaged mounting bolts: Can result in clunking noises as parts move under load.
  
• Hydraulic issues: Cavitation or air in hydraulic fluid can produce whining or squealing sounds.
  
• Swing brake wear: A worn or maladjusted brake can cause clicking or clunking when engaging or releasing.
  
• Swing motor internal damage: Worn motor components produce rough sounds during rotation.
  

Maintenance and Repair Recommendations

• Regularly grease the swing bearing per manufacturer specifications to ensure proper lubrication.
  
• Tighten and torque all swing bearing and motor mounting bolts to correct values.
  
• Replace worn or damaged swing bearings to eliminate gear tooth noise.
  
• Flush and replace hydraulic fluid to remove air and contamination.
  
• Inspect and service the swing motor, including checking seals and internal components.
  
• Adjust or replace swing brake pads if noise occurs during engagement.
  
• Schedule periodic inspections of swing system components as part of preventive maintenance.
  

Real-World Case Study
A construction company operating several CAT E120Bs in a high-production environment reported persistent grinding noises during swing operation. Upon inspection, technicians discovered excessive wear in the swing bearing teeth, caused by insufficient lubrication and contaminated grease. After replacing the swing bearing and upgrading to a higher-quality grease with more frequent lubrication intervals, the noise was eliminated. This case highlights the importance of proper lubrication and regular inspection in prolonging swing system life.
Technical Terms Explained

• Swing bearing backlash: The clearance or play between the teeth of the swing ring gear and the pinion gear, measured to assess wear.
  
• Cavitation: The formation and collapse of vapor bubbles in hydraulic fluid, which can cause noise and damage.
  
• Swing brake: A mechanical or hydraulic device that stops and holds the rotation of the upper structure.
  
• Grease contamination: The presence of dirt, water, or metal particles in grease, reducing its lubricating effectiveness.
  
• Torque test: Measurement of the rotational force output of the swing motor to diagnose internal wear or hydraulic issues.
  

Conclusion: Maintaining Quiet and Efficient Swing Operation
Swing noise in the CAT E120B excavator can stem from various mechanical or hydraulic sources. Timely diagnosis, proper lubrication, and maintenance of the swing bearing, motor, and related components are crucial to prevent costly repairs and downtime. Operators and technicians should remain vigilant for early signs of noise and follow recommended service intervals. By investing in routine care and quality parts, the swing system can deliver smooth, quiet, and reliable rotation throughout the excavator’s service life.