708-1W-00131 708-1W-00042 Excavator Hydraulic Pump Komatsu PC60-7 Main Piston Pump

The main pump of Komatsu PC60-7 is HPV55 variable displacement piston pump. Root causes of frequent failures for this model include contaminated hydraulic fluid, suction-side air ingress, and seized power regulator spool.

1. Sluggish operation, insufficient machine output and low system pressure
   Symptom: Normal operation at no-load; pressure drops rapidly under loaded conditions
   Cause: Internal leakage caused by worn valve plates and piston shoes; seized regulator spool and fatigued failed springs
   External factors: Blocked suction filter, air leakage on suction pipeline, metallic particulates in hydraulic fluid
   Diagnosis: Excessive pump case drain flow indicates internal wear of the pump
2. Abnormal pump noise, high-pitched squealing and severe vibration
   • High-pitched squeal (Cavitation): Inadequate suction or air entrainment in system; milky and foamy hydraulic fluid
   • Metallic tapping noise: Damaged internal bearing and ball joint, misaligned coupling
3. Engine lugging, speed reduction or stall under loaded operation
   Cause: Seized power control spool. The pump stays at large displacement continuously, and its power consumption exceeds the rated output of engine
   Diagnostic: Cut off the control oil supply to regulator. If lugging disappears, the regulator is defective
4. Elevated hydraulic fluid temperature
   Symptom: Fluid temperature rises rapidly after continuous operation, and the movement of actuators slows down gradually
   Cause: Severe internal leakage of pump; blocked case drain circuit leading to elevated case pressure
   Note: Verify the radiator and return filter are free of blockage before inspection
5. Main shaft oil seal leakage
   Cause: Degraded seal; high case pressure; seal lip scratched by misaligned coupling
   Risk: A damaged seal draws in air, inducing cavitation and accelerating pump deterioration
6. Actuator jitter and system pressure fluctuation
   Cause: Air trapped in hydraulic circuit; unstable regulator response; localized scoring on valve plate
7. Pilot pump malfunction
   Symptom: Unstable pilot pressure and abnormal displacement control of main pump
   Cause: Worn pilot gear, seal leakage and internal fluid bypass

1. Inspect hydraulic fluid condition, fluid level, suction filter and suction hose
2. Measure maximum main pump pressure and pilot pressure; cross-reference with service manual specifications
3. Take pump case drain flow readings
4. Disassemble and clean power regulator; inspect spring condition
5. Verify coupling concentricity

• Minor wear: Lap valve plate, renew pistons, piston shoes, ball joint and full seal kit; perform regulator cleaning
• Severe scoring: Fit new or remanufactured complete pump assembly
• Post-repair: Replace all hydraulic filters and thoroughly clean the hydraulic tank