Common Faults and Solutions for SANY SY65 and SY75C Mini Excavators

[MikePhua]

The SANY SY65 and SY75C mini excavators are commonly used on construction sites, and operators and service personnel often encounter certain issues. These problems often arise from the differences between mini excavators and larger ones, and typically include concerns such as swing bearing clearance, boom drift, minor black smoke, and oil pressure warnings. Below are explanations and solutions for the most frequently asked questions regarding these models:
1. Large Swing Bearing Clearance

• Phenomenon: When the swing brake is released, the bucket still exhibits some swing, usually for about three times. The customer perceives this as an issue with the swing bearing clearance. Additionally, when quickly returning the swing lever to the neutral position, a noise is heard, which is mistakenly believed to be abnormal swing noise.
  
• Cause Analysis: Unlike larger excavators, mini excavators do not have an anti-swing mechanism in the swing motor. The swing is controlled by the hydraulic system, and due to inertia during the braking process, the working arm may swing slightly, which is normal. If a mechanical brake were used, it could damage the swing motor. The noise heard when quickly returning the swing lever is due to the gaps in all gears in the swing reducer. When the lever is returned to neutral, the hydraulic motor brakes, shifting the gear contact surface, causing the metallic collision sound, which is also normal.
  
• Solution: Assure the customer that this behavior is within normal operating parameters and does not require any immediate action.
  

2. Boom Drift

• Phenomenon: Boom drift occurs when the boom, arm, or bucket cylinders move while the excavator is stationary.
  
• Cause Analysis: This phenomenon is caused by the gravity acting on the work equipment when the main valve is in the neutral position. This pressure is transmitted to the main valve, and due to the necessary gap in the valve spool, leakage occurs, leading to the boom drift. The operator’s manual specifies that the bucket must be placed on the ground when not in operation to avoid this issue. For more severe drift (e.g., if the bucket drops more than 95mm within 5 minutes when the oil temperature is around 45°C), this could indicate a fault in the main valve, which may need cleaning.
  
• Solution: Clean the main valve if necessary and ensure the bucket is grounded when the machine is idle.
  

3. Minor Black Smoke

• Phenomenon: A small amount of black smoke appears from the exhaust pipe during engine startup or under heavy load.
  
• Cause Analysis and Solutions:
  
  1. The black smoke may be caused by sudden changes in load, which lead to a temporary decrease in fuel combustion efficiency.
     
  2. The diesel fuel may contain heavy molecules that do not burn completely, causing black smoke. Using high-quality light diesel fuel is recommended.
     
  3. If the engine has previously used poor-quality diesel, it may have caused carbon build-up on the injectors, leading to black smoke. Using better quality fuel for a period of time will often reduce the smoke, or a fuel additive may be used to speed up the process. If the problem persists, cleaning the injectors or adjusting the hydraulic pump may be necessary.
     
• Solution: Educate the customer on the importance of using quality diesel fuel and regular maintenance to prevent such issues.
  

4. Occasional Oil Pressure Warning

• Phenomenon: The oil pressure warning light occasionally appears on the display when the engine starts, but disappears after a few seconds.
  
• Cause Analysis and Solutions: The excavator has a two-stage oil pressure alarm system. If the warning light comes on for only a few seconds, it is usually not a cause for concern, and the machine can continue to operate. However, it is important to check the oil system, including the oil level, filter, and cleanliness of the oil. If the warning persists for a longer time, the machine should be stopped immediately, and further inspection should be conducted.
  

5. Delay When Lifting the Pilot Lock

• Phenomenon: When the pilot lock is lifted, there is a delay of a few seconds before the excavator starts operating.
  
• Cause Analysis: This delay is a design feature of mini excavators to prevent accidental operation when the pilot lock is lifted. It ensures that if the operator touches the control lever while the lock is lifted, the machine will not perform unintended actions, thereby preventing accidents.
  
• Solution: This is a normal safety feature and does not require adjustment.
  

6. Occasional Stopping of the Arm Cylinder

• Phenomenon: The arm cylinder may occasionally stop or move slowly when performing compound movements, especially when the arm is near the ground.
  
• Cause Analysis: To minimize fuel consumption, the return oil back pressure is set low in the design. When the engine operates at a low RPM, the system flow decreases, and the return oil back pressure becomes even lower. This can lead to air suction in the arm cylinder, causing it to stop or move slowly. The recommended solution is to ensure that the engine speed does not drop below 1600 RPM during operation.
  
• Solution: If this does not resolve the issue, removing and adjusting the return oil one-way valve screws may help, but this will increase fuel consumption.
  

7. Lack of Power When Using Swing to Level Ground

• Phenomenon: When using the swing function to level the ground, the excavator feels weak and unable to move the earth effectively.
  
• Cause Analysis: The manual specifically states that swing leveling should not be used on mini excavators. This is because the swing reducer and swing bearing are gear-driven and hardened, which makes them vulnerable to impact during swing leveling. Using the swing function in this way could damage the gears, which is why the mini excavators are designed with reduced swing torque, leading to a lack of power for this operation.
  
• Solution: Avoid using the swing function to level ground to prevent damage to the gears.
  

8. Large Diesel Waste During Initial Filter Replacement

• Phenomenon: During the replacement of the initial fuel filter, significant diesel waste occurs as the filter is installed with a poor fit.
  
• Cause Analysis and Solutions: In the design of mini excavators, the initial fuel filter is located at the bottom shell. This design causes some difficulty during installation, leading to diesel waste. A more efficient design has been implemented to prevent this issue in newer models.
  

9. Lack of Power on Steep Hills

• Phenomenon: The mini excavator struggles to climb steep slopes in high gear, often failing to make it up.
  
• Cause Analysis: Mini excavators do not have an automatic high-low gear switching system. Therefore, when climbing steep slopes, the machine cannot automatically switch to low gear for better traction, resulting in insufficient power. To resolve this, it is recommended to manually switch to low gear when tackling steeper inclines.
  
• Solution: Ensure to switch to low gear when climbing steep slopes to prevent damage to the travel motor.
  

10. Track Noise During Movement

• Phenomenon: While the excavator is moving, there is noticeable jumping and noise from the tracks.
  
• Cause Analysis: The excavator uses tracks, and due to their segmented nature, when the drive wheel, which is gear-shaped, interacts with the track, it causes vibration and noise. This is known as the "polygon effect," where the speed of the machine fluctuates depending on the contact point of the track with the ground.
  
• Solution: This is a normal occurrence. Adjusting the track tension can help reduce vibration and noise, but it cannot be completely eliminated.
  

Conclusion
The SY65 and SY75C mini excavators are robust and reliable machines, but like all equipment, they may experience some common issues. Understanding the root causes of these problems and addressing them appropriately can help operators maintain optimal performance and extend the lifespan of the machinery. Regular maintenance, proper operation, and adherence to the manufacturer’s guidelines will go a long way in ensuring smooth and efficient operation.