Bleeding Swing Motor

[MikePhua]

Understanding Swing Motor Air Removal
On hydraulic excavators—especially mid-sized models—the swing motor enables the upper structure to rotate smoothly. After servicing or changing the hydraulic fluid inside the swing motor’s casing, it’s vital to expel trapped air. If not addressed, these air pockets can compromise lubrication, increase heat, and ultimately damage internal bearings.
Procedure Overview
Drawing from manufacturer-recommended maintenance routines, the general air-bleeding process includes:

• Start the engine at low idle.
  
• Loosen the bleeder plug or disconnect the hose at the “S” port.
  
• Observe for oil seepage—this indicates air has been expelled.
  
• If no oil appears, shut down the engine, fill the motor casing with hydraulic fluid, then repeat.
  
• Once oil flows freely, reattach or seal the port securely.
  
• Slowly swing the upper structure at least twice (left and right) to purge residual air.
  

These steps align with standard procedures across multiple Komatsu excavator models .
Terminology note: The “S port” refers to a designated discharge or vent connection on the swing motor, often used specifically for this bleeding procedure.
Filling Gaps With Practical Insights
Beyond the manual, some technicians share that gently tapping the swing housing or manually aiding movement helps coax out stubborn air. It’s also wise to monitor hydraulic temperature during this process—if temperature rises sharply, there may still be air trapped, reducing cooling efficiency and risking wear.
Preventive Tips

• Always bleed hydraulic systems after fluid replacement—this avoids cavitation and premature part failure.
  
• Use clean hydraulic fluid and maintain proper oil specification.
  
• Include the air-bleed step in regular service intervals—not just after repairs.
  
• Monitor for smooth swing action and absence of chatter or binding afterward.
  

Compact Story: A Smoother Swing Saves a Career
A service technician once shared how they were called to a rough-running excavator. The swing action was jerky, and the operator feared costly repairs. A quick bleed at low idle, with a slow swing left and right, restored silky rotation instantly. The operator was thrilled—and the tech joked that sometimes, the simplest step avoids the biggest breakdown.
Komatsu and the PC128UU Line in Perspective
Komatsu, founded in 1921 and rooted in early 20th-century mining equipment work, grew into one of the world’s leading construction equipment manufacturers . The PC128UU excavator, part of Komatsu’s compact lineup, reflects decades of engineering refinement. While exact global sales figures for this model aren’t publicly available, the PC128 series enjoys popularity due to its maneuverability, reliability, and versatility in tight urban or job-site environments.
Company Insights
Komatsu’s expansion since the post-war era—marked by its global footprint and reputation for innovation—underpins how models like the PC128UU benefit from rigorous engineering, wide dealer support, and well-documented maintenance protocols .
Summary of Key Steps and Recommendations

• Bleeding Steps:
  • Run engine at low idle.
    
  • Loosen bleeder/hose at the S port.
    
  • Look for oil flow.
    
  • If none, stop engine, add fluid, retry.
    
  • Reattach port once oil flows.
    
  • Swing upper structure slowly multiple times.
    
• Benefits:
  • Prevents air-induced cavitation.
    
  • Protects bearings and hydraulic components.
    
  • Ensures smoother and more predictable operation.
    
• Extra Suggestions:
  • Monitor hydraulic temperature.
    
  • Tap housing gently to mobilize trapped air.
    
  • Make it standard practice in scheduled maintenance.
    

By combining practical technique, a bit of human touch, and company context, this article aims to guide excavator owners and technicians toward effective swing motor maintenance—keeping machines running smoothly and reliably.