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Kobelco’s Legacy and the SK120 Line
Kobelco Construction Machinery traces its roots back to Kobe Steel, with its first hydraulic excavators dating to the late 1960s. Over the decades, Kobelco gained a reputation for durable hydraulics, efficient fuel use, and thoughtful machine design. The SK series — including the SK120 — has been part of this journey, targeting the 12-ton class of excavators.
According to used‑machine market data, the SK120 has an operating weight around 11,800 kg (~26,000 lb) and a bucket capacity in the range of 0.45 m³, making it a solid mid‑sized excavator with good reach and digging depth. Its traction force has been rated at approximately 102.5 kN, showing it packs a respectable punch in both digging and stability.
Reported Operational Issues of the SK120 MKV
Although many owners praise the MKV (Mark V) version of the SK120 for reliability, several recurring issues have been flagged in field reports:
From the shared owner feedback, a well-inspected MKV SK120 with moderate hours (for example, ~2,500 h on a used unit) can still be around 90–95% healthy, assuming no major structural faults. That’s encouraging for prospective owners of used units.
One owner reported that after cleaning rust flakes out of the fuel tank and replacing the small mesh filter (found inside a banjo bolt), the machine regained full power. That suggests that fuel system maintenance is critical for longevity.
Maintenance and Prevention Strategies
Based on reported issues and typical use patterns, here are several recommendations for SK120 MKV owners:
A farmer in rural Australia bought a 1996 SK120 MKV with roughly 2,500 hours on the meter. Initially, the machine wouldn’t throttle past a mid-range setting. After digging into the issue, he discovered a clogged mesh filter inside a banjo bolt on the fuel line. He cleaned it, replaced a couple of banjo fittings, and suddenly the excavator regained full power — noticeably improving digging speed during dam-cleaning and stump removal. Later, a “Stepper Motor NG” warning popped up. He didn’t have a local Kobelco dealer nearby, so he greased the ball joints himself, and the warning cleared. While he lost the automatic throttle efficiency, he regained consistent control.
Evaluation of Kobelco as a Brand
Kobelco is generally well regarded in the construction and compact excavator space for several reasons:
Conclusion
The Kobelco SK120 MKV is a rugged, capable excavator with a proven platform, but like many older machines, it has some quirks. Fuel contamination, stepper motor/ECU issues, and display failures are among the most commonly reported. With preventive maintenance, especially in the fuel and throttle systems, many of these issues can be managed or avoided. For anyone buying a used MKV model, a careful pre‑purchase inspection focusing on these known problem areas—and access to service manuals like the Kobelco SK120 Mark 5 parts catalog/manual —will go a long way toward ensuring reliable service for years to come.
Kobelco Construction Machinery traces its roots back to Kobe Steel, with its first hydraulic excavators dating to the late 1960s. Over the decades, Kobelco gained a reputation for durable hydraulics, efficient fuel use, and thoughtful machine design. The SK series — including the SK120 — has been part of this journey, targeting the 12-ton class of excavators.
According to used‑machine market data, the SK120 has an operating weight around 11,800 kg (~26,000 lb) and a bucket capacity in the range of 0.45 m³, making it a solid mid‑sized excavator with good reach and digging depth. Its traction force has been rated at approximately 102.5 kN, showing it packs a respectable punch in both digging and stability.
Reported Operational Issues of the SK120 MKV
Although many owners praise the MKV (Mark V) version of the SK120 for reliability, several recurring issues have been flagged in field reports:
- Fuel starvation
One user described a problem where the machine could not rev past a mid‑range throttle notch. After changing a fuel filter, performance improved dramatically. The root cause seemed to be debris in the fuel tank or lines, likely rust flakes or contamination.
- Display (LCD) failures
A common problem cited is the failure of the on‑dash LCD display panel. Because this is a proprietary part, replacement is expensive and difficult, especially for older machines where the display may no longer be stocked.
- Stepper motor / ECU issues
The SK120 MKV uses an electronic throttle system controlled by a stepper motor. Several owners report “STEPPER MOTOR NG” (no good) warnings. According to feedback, when the stepper motor starts to fail (due to wear or grease breakdown), the ECU may disable it, causing low or erratic throttle behavior. In some cases, people bypass this by removing the linkage and installing a manual throttle cable — losing automatic throttle but restoring basic control.
- Linkage wear
Ball joints or linkage bushings, especially in the throttle linkage, may wear out and cause stepper motor binding or erratic behavior. Maintenance experts suggest greasing or replacing worn pins/bushings carefully — ideally one joint at a time — to avoid misaligning the stepper motor.
- Pump control issues
In one reported example, a machine’s controller was failing to “up-stroke” one of the hydraulic pumps. This resulted in noticeably reduced speed for the bucket and a track. After wiring inspections and verifying the controller, the operator suspected faulty internal signal output, pointing to possible ECU or linkage problems.
- Stepper motor: A small, precise motor that moves in incremental “steps” to open or close the throttle or control linkage.
- ECU (Electronic Control Unit): The onboard computer that controls engine parameters, hydraulics, and other systems.
- Linkage bushings: Bearings or sleeves between pivot points to allow smooth movement; worn bushings can cause binding or play.
- Throttle linkage: The mechanical or mechanical-electronic system that links the throttle pedal or lever to the engine’s throttle mechanism.
From the shared owner feedback, a well-inspected MKV SK120 with moderate hours (for example, ~2,500 h on a used unit) can still be around 90–95% healthy, assuming no major structural faults. That’s encouraging for prospective owners of used units.
One owner reported that after cleaning rust flakes out of the fuel tank and replacing the small mesh filter (found inside a banjo bolt), the machine regained full power. That suggests that fuel system maintenance is critical for longevity.
Maintenance and Prevention Strategies
Based on reported issues and typical use patterns, here are several recommendations for SK120 MKV owners:
- Fuel system checks
- Inspect and clean the fuel tank periodically for rust, debris, or contamination.
- Clean or replace inline mesh filters, especially those located at banjo bolts or under low-pressure lines.
- Use quality diesel and water‑separating filters to reduce particulate issues.
- Inspect and clean the fuel tank periodically for rust, debris, or contamination.
- Throttle and stepper motor upkeep
- Grease ball joints and linkage pins regularly to reduce wear.
- Check for play or shaft slop in the stepper motor; if excessive, consider replacing motor or linkage components.
- When replacing linkage bushings or ball joints, do so one end at a time to avoid disturbing calibration.
- Grease ball joints and linkage pins regularly to reduce wear.
- ECU and wiring vigilance
- Inspect electrical connections to the stepper motor and ECU regularly.
- If “Stepper Motor NG” warnings appear, check the stepper linkage first before jumping to a full ECU swap.
- Consider keeping a manual throttle cable as a backup in case ECU‑driven throttle fails.
- Inspect electrical connections to the stepper motor and ECU regularly.
- Display panel backup
- Because the LCD panel is reported to be a common failure and expensive to replace, consider sourcing used or refurbished units.
- As a workaround, keep a digital camera or phone to photograph warning codes when the panel is functioning, so you can diagnose issues later if it fails.
- Because the LCD panel is reported to be a common failure and expensive to replace, consider sourcing used or refurbished units.
- Hydraulic pump control
- If pump control is sluggish or uneven, trace wiring to the controller and test signal continuity.
- Use a service manual (such as Kobelco SK120‑V service and repair manual) to verify correct output and settings.
- Inspect for hydraulic pressure issues, as underperforming pump output may not always be an electrical problem.
- If pump control is sluggish or uneven, trace wiring to the controller and test signal continuity.
A farmer in rural Australia bought a 1996 SK120 MKV with roughly 2,500 hours on the meter. Initially, the machine wouldn’t throttle past a mid-range setting. After digging into the issue, he discovered a clogged mesh filter inside a banjo bolt on the fuel line. He cleaned it, replaced a couple of banjo fittings, and suddenly the excavator regained full power — noticeably improving digging speed during dam-cleaning and stump removal. Later, a “Stepper Motor NG” warning popped up. He didn’t have a local Kobelco dealer nearby, so he greased the ball joints himself, and the warning cleared. While he lost the automatic throttle efficiency, he regained consistent control.
Evaluation of Kobelco as a Brand
Kobelco is generally well regarded in the construction and compact excavator space for several reasons:
- Engineering heritage: Rooted in Kobe Steel and backed by decades of excavator innovation.
- Parts support: While some components (like custom LCDs or stepper‑motor ECUs) are becoming rare, the core hydraulic and structural parts remain well supported.
- Global presence: Kobelco’s global network ensures access to service and parts in many markets, especially for machines in the 10–20 ton range.
Conclusion
The Kobelco SK120 MKV is a rugged, capable excavator with a proven platform, but like many older machines, it has some quirks. Fuel contamination, stepper motor/ECU issues, and display failures are among the most commonly reported. With preventive maintenance, especially in the fuel and throttle systems, many of these issues can be managed or avoided. For anyone buying a used MKV model, a careful pre‑purchase inspection focusing on these known problem areas—and access to service manuals like the Kobelco SK120 Mark 5 parts catalog/manual —will go a long way toward ensuring reliable service for years to come.
