Diagnosing Ticking Noise in a Komatsu PC40MR-2

[MikePhua]

Komatsu PC40MR-2 Background and Design
The Komatsu PC40MR-2 is a compact hydraulic excavator introduced in the early 2000s as part of Komatsu’s MR (Minimum Radius) series. Designed for urban construction and utility work, it features a tight tail swing radius and a robust hydraulic system. Powered by a Komatsu 3D88E-5 engine, the machine delivers approximately 40 horsepower and operates with a hydraulic flow of 100 liters per minute at pressures up to 3,000 psi. Its compact design makes it ideal for confined spaces, but it also means components like the hydraulic pump and engine accessories are tightly packed—making noise diagnosis more complex.
Identifying the Source of Ticking Sounds
A persistent ticking noise near the rear of the engine, especially around the hydraulic pump area, can indicate several mechanical or hydraulic issues. In the case of a well-used PC40MR-2, the ticking may emerge after fluid changes or prolonged idle operation.
Potential causes include:

• Hydraulic pump cavitation: When air enters the pump due to low fluid levels or poor bleeding, it causes a ticking or rattling sound as bubbles collapse under pressure.
  
• Loose injector fittings: Diesel injectors that are not fully seated or have worn seals can produce rhythmic ticking, especially at low idle.
  
• Valve lash misadjustment: Incorrect valve clearance can lead to tapping noises, though this is typically more metallic and located higher on the engine.
  
• Worn pump bearings or couplings: The main hydraulic pump is gear-driven and mounted directly to the engine. Worn couplings or bearings can produce a repetitive knock or tick.
  

In one documented case, a mechanic suspected injector noise and attempted bleeding by loosening each injector line at idle. While this is a valid diagnostic step, it did not resolve the issue—suggesting the noise originated elsewhere.
Hydraulic System Bleeding and Fluid Checks
After a hydraulic fluid change, air pockets can remain in the system, especially in older machines with manual bleed procedures. To ensure proper bleeding:

• Run the machine at low idle with all hydraulic functions cycled slowly.
  
• Check fluid level with the boom and arm fully retracted.
  
• Inspect return lines for foam or bubbles, which indicate aeration.
  
• Use OEM-spec fluid, as viscosity mismatches can affect pump behavior and noise.
  

If the pump was recently serviced or replaced, verify that the suction line is sealed and the filter is properly seated. A minor vacuum leak can cause cavitation and ticking.
Engine and Pump Interface Considerations
The Komatsu PC40MR-2 uses a direct-coupled hydraulic pump mounted at the rear of the engine. This interface includes:

• Drive gear or spline coupling
  
• Pump mounting flange
  
• Vibration dampening bushings
  

Wear in any of these components can cause rhythmic ticking, especially under load. A technician in Oregon once traced a similar noise to a worn spline coupling that had developed play over time. Replacing the coupling eliminated the sound and restored smooth operation.
Recommendations for Further Diagnosis
To isolate the issue:

• Use a mechanic’s stethoscope to pinpoint the sound source—compare engine block, pump housing, and injector lines.
  
• Monitor hydraulic pressure at idle and under load—fluctuations may indicate internal leakage or pump inefficiency.
  
• Inspect engine mounts and pump brackets for looseness or fatigue.
  
• Consider infrared thermography to detect abnormal heat buildup in the pump or injector area.
  

If the noise persists and no mechanical damage is found, consider sending a fluid sample for analysis. Contaminants or metal particles may indicate internal wear.
Conclusion
A ticking noise in the Komatsu PC40MR-2 near the hydraulic pump area can stem from cavitation, injector issues, valve lash, or mechanical wear. Systematic diagnosis—starting with fluid checks, injector inspection, and pump coupling evaluation—can narrow down the cause. With proper maintenance and attention to hydraulic integrity, the PC40MR-2 remains a reliable compact excavator capable of handling demanding tasks in tight spaces.