The SANY SY65 and SY75C compact excavators often raise a few common questions among operators and service personnel in China. Most of these are due to differences between compact and mid-size excavators. Below is an explanation of frequent concerns and recommended solutions.

1. Large Swing Bearing Clearance

Issue:
Users sometimes notice that when swing braking stops, the bucket still oscillates slightly (typically about 3 swings). Some believe this means excessive swing bearing clearance. Also, when the swing joystick snaps back to neutral quickly, there may be a metallic sound, which is mistaken for abnormal noise.

Explanation:
Unlike larger models, compact excavators usually don’t have a swing anti-sway device. Braking relies on hydraulic resistance, so some residual swing due to inertia is normal. Using mechanical brakes would damage the swing motor.
The click heard when the joystick returns to neutral comes from gear clearance inside the swing reducer; as the motor brakes, the gear contact shifts sides, producing a metal contact noise. This is normal and not harmful.

2. Boom or Arm Drift (Drop)

Issue:
When the excavator is stationary, the boom, arm, or bucket cylinders may move slightly, causing a slow drop.

Explanation:
When the main control valve is in neutral, the weight of the work equipment creates hydraulic pressure. Due to necessary spool clearance inside the valve, slight internal leakage occurs, causing slow cylinder movement. That’s why the manual specifies that the bucket should always rest on the ground when not working.
If the drop is severe (e.g., bucket teeth drop more than 95 mm within 5 minutes at around 45 °C oil temperature), the main valve may be sticking and should be cleaned.

3. Slight Black Smoke

Issue:
A light black exhaust is visible against light when starting the engine or under heavy load.

Explanation & Solution:

  • This is common due to sudden fuel injection changes under varying loads, leading to incomplete combustion.
  • Poor-quality diesel with more heavy molecules can worsen smoke; good-quality diesel is recommended.
  • If the engine previously used low-grade diesel, slight injector carbon deposits may cause smoke. Switching to better diesel and adding fuel cleaner can help; if needed, clean the injectors or adjust the hydraulic main pump output.

Note:
Manufacturer warranties usually exclude issues like injection pump wear, injector carbon build-up, or cylinder scoring. Operators should be advised to use quality fuel and perform regular maintenance.

4. Occasional Low Oil Pressure Warning

Issue:
Sometimes, when starting the engine, a low oil pressure warning appears briefly but disappears within seconds.

Explanation & Solution:
The excavator uses a two-stage oil pressure alert system. A brief warning is acceptable, but the oil level, filter, and oil cleanliness should be checked. Topping up the oil often solves it. If the warning lasts unusually long, shut down immediately for inspection.

5. Operation Delay After Releasing Pilot Lock

Issue:
After releasing the pilot lock, there is a few-second delay before the excavator responds.

Explanation:
This intentional delay in the control program prevents accidental movement if the operator bumps the control lever while unlocking. It’s a safety feature.

6. Stick Cylinder Hesitation

Issue:
During combined operations, the stick cylinder sometimes hesitates or slows down when nearly vertical to the ground.

Explanation & Solution:
To achieve minimal fuel consumption, return line back pressure is set low. At low engine RPMs, system flow is reduced, and back pressure drops further, occasionally causing cavitation, which leads to hesitation.
Operators should keep engine speed above 1600 rpm. Alternatively, slightly tightening two return check valve screws (by 1–2 turns) can help but will slightly increase fuel consumption. Operators should be informed accordingly.

7. Weak Swing When Leveling Ground

Issue:
When using swing motion to level ground, the machine feels underpowered.

Explanation:
The swing reducer and bearing use gear transmission with hardened surfaces. Using swing to level ground causes impact loads that can damage these gears. To protect the drivetrain, swing torque is intentionally limited, resulting in weak swing force for this purpose. The operator manual advises against using swing to level ground.

8. Diesel Wastage When Replacing Fuel Pre-Filter

Issue:
When replacing the fuel pre-filter, limited space can cause awkward installation and diesel spillage.

Explanation & Solution:
The design intends for the pre-filter and lower casing to be installed together as one piece, providing sufficient space and avoiding fuel loss. This method is described in the updated technical documentation.

9. Weak Climbing Power

Issue:
When driving up steep slopes in high gear, the excavator sometimes can’t climb.

Explanation & Solution:
These compact models do not have automatic travel speed switching. In high gear, traction is limited on steep inclines. Operators should manually switch to low gear for climbing. Even machines with auto switching should use low gear for prolonged climbs to avoid damaging the travel motor’s variable displacement mechanism.

10. Track Noise During Travel

Issue:
While traveling, the upper track may bounce slightly and make noise.

Explanation & Solution:
This is caused by the polygon effect due to track pitch length and sprocket gear teeth. When the entire track is flat, the drive radius is smallest; when angled, it increases slightly, causing minor speed fluctuations and vibration. Mud buildup and tension changes can amplify this. Adjusting track tension can reduce noise and vibration but may not eliminate it completely. This is normal for tracked equipment.

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