Groaning Sound While Swinging Under Load on the IHI 35N

[MikePhua]

The IHI 35N and Its Role in Compact Excavation
The IHI 35N is a compact excavator developed by IHI Construction Machinery Limited, a Japanese manufacturer known for its precision engineering and focus on urban-scale equipment. Introduced in the early 2000s, the 35N was designed to meet the growing demand for nimble, fuel-efficient machines capable of operating in tight spaces without sacrificing lifting power. With an operating weight of approximately 3.5 metric tons and a dig depth of over 10 feet, the 35N became a popular choice for residential contractors, landscapers, and utility crews.
By 2010, IHI had sold tens of thousands of compact excavators globally, with the 35N contributing significantly to its North American market share. Its swing system, powered by a hydraulic motor and planetary gearbox, was engineered for smooth rotation and precise control. However, as with many compact machines, prolonged use under heavy load can reveal vulnerabilities in the swing bearing and hydraulic control systems.
Terminology Annotation

• Swing Box: The assembly that includes the swing motor and gearbox, responsible for rotating the upper structure of the excavator.
  
• Swing Bearing: A large slewing ring that supports the upper frame and allows it to rotate on the undercarriage.
  
• Spool Valve: A cylindrical valve component that shifts to direct hydraulic fluid to different actuators.
  
• Leakdown: A condition where hydraulic cylinders or circuits lose pressure over time, causing unintended movement or drift.
  

Groaning Sound During Heavy Swing Operations
Operators of the IHI 35N have reported a groaning sound when swinging large boulders uphill, particularly under full load. This sound is accompanied by mild vibration and only occurs during high-torque maneuvers. When swinging lighter loads, the machine operates quietly and smoothly.
This groaning is likely the result of the swing motor reaching its torque threshold, combined with minor leakage at the valve plate. The sound resembles that of a hydrostatic transmission under strain—where fluid resistance and mechanical friction produce audible feedback. In compact excavators, this is not uncommon when the swing system is pushed beyond its design envelope.
Potential Causes and Diagnostic Path
Several mechanical and hydraulic factors may contribute to the groaning sound:

• Swing motor operating at maximum torque due to load and incline
  
• Valve plate wear causing internal leakage and pressure drop
  
• Spool valves scoring due to contamination or wear
  
• Swing bearing wear introducing friction and vibration
  

To diagnose the issue:

• Inspect hydraulic fluid for contamination and metal particles
  
• Measure swing motor pressure during operation (compare against factory spec, typically 2,500–3,000 psi)
  
• Check swing bearing for axial play or uneven wear
  
• Listen for noise origin—top (motor/gearbox) vs. bottom (bearing)
  

Hydraulic Leakdown and Internal Valve Wear
In parallel with the groaning issue, some operators have noted hydraulic leakdown—where cylinders slowly drift without external leaks. This suggests internal leakage within control valves or worn seals in the actuator circuits.
Common culprits include:

• Scored spool valves allowing fluid bypass
  
• Worn cylinder seals unable to hold pressure
  
• Contaminants damaging valve seats and O-rings
  

Solutions involve:

• Rebuilding control valves with new spools and seals
  
• Pressure testing individual circuits to isolate leak sources
  
• Installing inline check valves to prevent backflow
  

A Story from the Field
In 2013, a contractor in California used an IHI 35N to clear boulders from a hillside. While swinging uphill with heavy rocks, the machine emitted a groaning sound and slight vibration. Concerned about long-term damage, the operator consulted a local technician who traced the issue to a worn swing bearing and minor leakage in the swing motor valve plate. After replacing the bearing and resealing the motor, the sound disappeared, and the machine resumed full-duty operation. The contractor later added a pressure gauge to the swing circuit for real-time monitoring.
Industry Trends and News
Compact excavators are increasingly equipped with electronic monitoring systems that detect hydraulic anomalies before they become failures. In 2024, several manufacturers introduced swing torque sensors and bearing temperature monitors as standard features. These systems alert operators when components are nearing their load limits, reducing the risk of catastrophic failure.
Meanwhile, aftermarket suppliers have begun offering upgraded swing bearings with improved lubrication channels and hardened raceways, extending service life by up to 40%. These components are especially valuable for machines used in rocky or uneven terrain.
Preventative Maintenance Recommendations
To minimize groaning and leakdown issues:

• Replace hydraulic fluid every 1,000 hours with ISO VG 46 grade
  
• Install magnetic filters to capture fine metal debris
  
• Grease swing bearing weekly with high-pressure lithium-based grease
  
• Inspect valve spools and seats annually for scoring
  
• Monitor swing motor temperature during heavy use
  

Conclusion
The groaning sound during swing operations on the IHI 35N is a mechanical warning that the system is under stress. While not immediately catastrophic, it signals wear in the swing motor, bearing, or control valves. By diagnosing the source and implementing preventative maintenance, operators can extend the life of their machines and maintain safe, efficient performance. As compact excavators evolve, integrating real-time diagnostics and improved component design will further reduce the impact of such issues in the field.