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The Komatsu PC50MR-2 and Its Hydraulic Drive System
The Komatsu PC50MR-2 is a compact excavator designed for urban construction, landscaping, and utility work. Introduced in the early 2000s, it features a zero-tail-swing design, a 39 hp diesel engine, and an advanced hydraulic system that powers both the boom and the travel motors. Komatsu, founded in 1921, has sold thousands of PC50MR-2 units globally, and the model remains popular for its maneuverability and reliability in tight spaces.
The travel system on the PC50MR-2 uses two independent hydraulic motors—one for each track—fed by a variable displacement pump. These motors are protected by integrated final drives and relief valves, which regulate pressure and prevent damage during high-load conditions.
Terminology Notes
In one field case, the left track of a PC50MR-2 moved significantly slower than the right, even after checking for seized rollers and confirming equal hydraulic pressure at the pump. The operator suspected a fault in the final drive or travel motor and prepared to disassemble the unit.
Key diagnostic steps included:
One technician in Wales shared that after exhausting all external checks, he disassembled the final drive and found a damaged relief valve spring. Replacing it restored full track speed. Another operator in Alberta noted that his PC50MR-2 had similar symptoms caused by a cracked seal inside the travel motor, which allowed internal leakage.
A mechanic in Oregon emphasized that relief valve settings must be matched between both tracks. He recommended using a pressure gauge to verify valve opening points and adjusting them to factory spec—usually around 4,500 psi for compact excavators.
Preventive Measures and Recommendations
A slow track on a Komatsu PC50MR-2 is often caused by internal issues in the final drive or travel motor, particularly relief valve malfunction or seal degradation. By verifying hydraulic pressure, inspecting valve components, and matching settings across both tracks, operators can restore balanced movement and avoid unnecessary downtime. The PC50MR-2’s compact design demands precision in hydraulic tuning—but with careful diagnostics, it remains a reliable partner in tight job sites.
The Komatsu PC50MR-2 is a compact excavator designed for urban construction, landscaping, and utility work. Introduced in the early 2000s, it features a zero-tail-swing design, a 39 hp diesel engine, and an advanced hydraulic system that powers both the boom and the travel motors. Komatsu, founded in 1921, has sold thousands of PC50MR-2 units globally, and the model remains popular for its maneuverability and reliability in tight spaces.
The travel system on the PC50MR-2 uses two independent hydraulic motors—one for each track—fed by a variable displacement pump. These motors are protected by integrated final drives and relief valves, which regulate pressure and prevent damage during high-load conditions.
Terminology Notes
- Final Drive: A gear reduction unit that multiplies torque from the hydraulic motor to the track sprocket.
- Relief Valve: A pressure-limiting device that opens when hydraulic pressure exceeds a set threshold.
- Travel Motor: A hydraulic motor that powers the movement of each track.
- Flow Divider: A hydraulic component that splits flow evenly between circuits.
In one field case, the left track of a PC50MR-2 moved significantly slower than the right, even after checking for seized rollers and confirming equal hydraulic pressure at the pump. The operator suspected a fault in the final drive or travel motor and prepared to disassemble the unit.
Key diagnostic steps included:
- Verifying roller and sprocket movement
- Checking hydraulic pressure at both travel motor ports
- Inspecting relief valve settings and bypass behavior
- Comparing track speed under load and no-load conditions
- Relief Valve Malfunction: If the relief valve on one final drive opens prematurely, it can bleed pressure and reduce motor output.
- Internal Motor Wear: Worn seals or vanes inside the travel motor can cause reduced torque and slower rotation.
- Contaminated Hydraulic Fluid: Debris or water in the fluid can affect valve response and motor efficiency.
- Flow Imbalance: A faulty flow divider or directional valve may send unequal pressure to each motor.
One technician in Wales shared that after exhausting all external checks, he disassembled the final drive and found a damaged relief valve spring. Replacing it restored full track speed. Another operator in Alberta noted that his PC50MR-2 had similar symptoms caused by a cracked seal inside the travel motor, which allowed internal leakage.
A mechanic in Oregon emphasized that relief valve settings must be matched between both tracks. He recommended using a pressure gauge to verify valve opening points and adjusting them to factory spec—usually around 4,500 psi for compact excavators.
Preventive Measures and Recommendations
- Flush Hydraulic System Annually: Prevent contamination and valve sticking.
- Match Relief Valve Settings: Use calibrated tools to ensure symmetry.
- Inspect Final Drive Oil: Look for metal shavings or water intrusion.
- Use OEM Seals and Springs: Aftermarket parts may alter valve behavior.
- Document Disassembly Steps: Final drives are complex and require precise reassembly.
A slow track on a Komatsu PC50MR-2 is often caused by internal issues in the final drive or travel motor, particularly relief valve malfunction or seal degradation. By verifying hydraulic pressure, inspecting valve components, and matching settings across both tracks, operators can restore balanced movement and avoid unnecessary downtime. The PC50MR-2’s compact design demands precision in hydraulic tuning—but with careful diagnostics, it remains a reliable partner in tight job sites.
