Komatsuengine(no series)
Komatsu S6D125-1KK(S/N 26750-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu S6D125-1KK (S/N 26750-UP) is a 6-cylinder, turbocharged, aftercooled diesel engine belonging to the S6D125 series, manufactured since 2017. With a displacement of 11 liters, it delivers power outputs ranging from 155 HP (116 kW) to 237 HP (177 kW) depending on the specific application and configuration. This engine powers mid-to-heavy class Komatsu construction equipment, including the D65EX-12 crawler dozer, PC400-5/7 excavators, and WA470-3 wheel loaders. Operating weights for the host machines typically range from 20,000 kg to 40,000 kg. The S6D125 series succeeded earlier 6D125 variants and serves as a robust powertrain for rugged earthmoving and mining duties, offering high torque at low speeds.
Across the S6D125 generation, Komatsu refined the engine's torque rise and fuel efficiency while maintaining the durability of its wet cylinder liner design. The S6D125-1KK variant specifically addresses the needs of high-duty cycles found in dozers and large excavators. In the used and parts market, this engine remains critical due to the extensive installed base of PC400, D65, and WA470 series machines. Its mechanical simplicity and lack of complex electronic emissions controls in earlier iterations make it a preferred choice for rebuilds and long-term fleet maintenance, ensuring continued availability of genuine and aftermarket components.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Komatsu S6D125-1KK(S/N 26750-UP) specifications
Engine
| Model | S6D125-1KK |
| Displacement | 11 L (671.8 cu in) |
| Cylinders | 6 |
| Aspiration | Turbocharged and aftercooled |
| Power Output | 134 kW (180 HP) or 116 kW (155 HP) depending on configuration |
| Torque | 1,370 N·m (1,010 lb·ft) |
| Emissions Tier | Not documented for this exact serial range — verify with your dealer |
Weights
| Operating Weight | Not documented for this exact serial range — verify with your dealer |
| Shipping Weight | Not documented for this exact serial range — verify with your dealer |
| Ground Pressure | Not documented for this exact serial range — verify with your dealer |
Dimensions
| Transport Length | Not documented for this exact serial range — verify with your dealer |
| Transport Width | Not documented for this exact serial range — verify with your dealer |
| Transport Height | Not documented for this exact serial range — verify with your dealer |
| Track Gauge | Not documented for this exact serial range — verify with your dealer |
| Ground Clearance | Not documented for this exact serial range — verify with your dealer |
Performance
| Travel Speed | Not documented for this exact serial range — verify with your dealer |
| Gradeability | Not documented for this exact serial range — verify with your dealer |
| Digging/Dumping Force | Not documented for this exact serial range — verify with your dealer |
Service capacities (summary)
| Fuel Tank | Not documented for this exact serial range — verify with your dealer |
| Hydraulic System | Not documented for this exact serial range — verify with your dealer |
| Engine Oil | Not documented for this exact serial range — verify with your dealer |
| Cooling System | Not documented for this exact serial range — verify with your dealer |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
Komatsu S6D125-1KK(S/N 26750-UP) maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
Servicing the S6D125-1KK(S/N 26750-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
Monitor KOWA oil analysis results at every 500-hour interval to detect early wear metals like iron and copper from the S6D125-1KK's wet liners and bearings. Check coolant SCA concentration regularly to prevent cavitation pitting in the cylinder liners. Track hydraulic oil particle counts and viscosity changes to anticipate pump and valve wear. Use KOMTRAX telematics to monitor engine load frequency and fuel consumption trends, identifying inefficiencies before they cause component failure. Early detection of coolant contamination or fuel dilution in the oil prevents catastrophic liner and bearing damage.
Corrective & Common Repairs
Address oil leaks from the S6D125-1KK breather by inspecting piston rings and crankcase ventilation systems for blockage or wear. Replace worn turbocharger seals if excessive oil consumption or blue smoke is observed. Fix coolant leaks by replacing thermostat housing gaskets or water pump seals. Repair hydraulic hose leaks promptly to maintain system pressure and prevent contamination. Replace fuel filters and drain the water separator to protect the injection pump from water and particulate damage. Check electrical connections for corrosion to prevent intermittent starting or sensor faults.
Overhaul & Rebuild Points
Plan for an inframe overhaul of the S6D125-1KK around 10,000 to 12,000 hours, focusing on piston rings, liners, and bearings. Replace the turbocharger if shaft play exceeds limits or efficiency drops significantly. Rebuild the hydraulic pump and final drives when wear metals spike in oil analysis or performance declines. Inspect the cylinder head for warping or cracked valves during major service. Replace all gaskets and seals during overhaul to ensure proper compression and fluid containment. Verify valve clearance and injector nozzle spray patterns to restore rated power and fuel efficiency.
Seasonal & Environment Servicing
In cold climates, check coolant concentration and battery capacity before winter to ensure reliable starts for the S6D125-1KK. Use appropriate grade engine oil to prevent thickening and poor circulation. In hot, dusty environments, shorten air cleaner service intervals and keep the radiator core clear of debris to prevent overheating. Inspect undercarriage components more frequently in abrasive conditions to extend track and roller life. Adjust hydraulic system pressure settings if operating in extreme temperatures to maintain optimal performance. Store the machine in a sheltered area if possible to protect sensitive electronic components from moisture and dust.
S6D125-1KK(S/N 26750-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 07281-00197 | Clamp,(With Pre-Fuel Filter) | Fuel system service | Check fitment → |
| 08036-01414 | Clip,(For Add.Filter)(Except Japan) | Scheduled service item | Check fitment → |
| 600-181-1600 | Kit, Element Assembly | Scheduled service item | Check fitment → |
| 600-181-1660 | Element Assembly, Primary Filter | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
S6D125-1KK(S/N 26750-UP) fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CA115 | Engine crankshaft speed sensor and backup speed sensor failure | Faulty speed sensor, broken wiring harness, or corroded connector at the pin connector | Replace the speed sensor and verify voltage at the pin connector |
| CA111 | Internal engine controller fault | Electronic Control Module (ECM) internal malfunction | Replace or reprogram the ECM |
| CA451 | Common rail pressure sensor feedback value too high | Malfunction in the rail pressure sensor or actual overpressure condition | Diagnose the fuel rail pressure sensor or check pump lines |
| CA452 | Common rail pressure sensor feedback value too low | Fuel rail pressure sensor error or low pressure condition | Diagnose the fuel rail pressure sensor or check pump lines |
| CA122 | Intake air pressure sensor feedback voltage too high | Intake pressure sensor malfunction or wiring issue | Verify the intake pressure sensor and wiring |
| CA123 | Intake air pressure sensor feedback voltage too low | Sensor short or airflow restriction | Check for a sensor short or an airflow restriction |
| CA153 | Intake air temperature sensor feedback voltage too high | Intake air temperature (IAT) sensor error | Replace or test the IAT sensor |
| CA154 | Intake air temperature sensor feedback voltage too low | Intake air temperature (IAT) sensor error | Replace or test the IAT sensor |
| CA234 | Engine overspeed | Throttle calibration issue, engine load cycle problem, or operator misuse | Verify throttle calibration, engine load cycle, or operator misuse |
| CA441 | Battery voltage too low | Weak battery or alternator failure | Replace the alternator or battery; check the voltage regulator |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
S6D125-1KK(S/N 26750-UP) attachments & work tools
Crawler Dozer Blades
The S6D125-1 engine powers the D65EX-12 and D65PX-12 dozer series. These machines utilize standard dozer blades with capacities ranging from 2.5 cubic yards to over 60 cubic yards depending on the specific dozer model variant. Factory configurations include enclosed cabs and advanced telematics via Komtrax for performance monitoring.
Crawler Excavator Buckets
Excavators such as the PC300-3, PC400-3, PC400-5, and PC400LC-5 utilize this engine family. Typical bucket capacities for this class range up to 4.5 m³. Hydraulic kit arrangements vary by generation, with later models like the PC400LC-8 requiring specific solenoid valve setups distinct from earlier mechanical pump configurations.
Wheel Loader Buckets
Wheel loaders including the WA380-1, WA470-3, and WA1200-3 are equipped with this engine series. Bucket sizes vary by configuration, generally supporting high-volume earthmoving tasks. These machines rely on Komatsu TO or HO hydraulic oils for their transmission and hydraulic systems.
Motor Grader Blades
The GD663A-2 motor grader uses the S6D125-1 engine to deliver 116 kW (155 HP) or 134 kW (180 HP) depending on the specific tuning. Torque rise increases by 30% in the 155 HP version and 13% in the 180 HP version to handle heavy grading loads. Blade capacities are matched to the 11-liter displacement for consistent power delivery.
All S6D125-1KK(S/N 26750-UP) assemblies by section
Every catalogued assembly group for the Komatsu S6D125-1KK(S/N 26750-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Accessory
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor (Inner Parts)(#26750-41984)
| 61***10 | Air Compressor Ass'Y,(See Fig.0711) | 1 |
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor (Inner Parts)(#41985-)
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| 61***12 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor And Piping
| 07***12 | Gasket,(Without Air Compressor Type) (K2) | 4 |
| 07***12 | Gasket,(Without Air Compressor Type) (K1) | 8 |
| 07***16 | Gasket,Air Compressor Piping | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor And Piping(S6d125-1kk #26750-)
| 07***12 | Gasket,(Without Air Compressor Type) (K2) | 4 |
| 07***12 | Gasket,(Without Air Compressor Type) (K1) | 8 |
| 07***16 | Gasket,Air Compressor Piping | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor(1z #21431-41874)(1kk #26750-41984)(#26750-41984)
Komatsu : S6d125-1kk(S/N 26750-Up) : Accessory : Air Compressor(S6d125-1z #41875-)(S6d125-Kk #41985-)(#41985-)
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| 61***12 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
Cooling System
Komatsu : S6d125-1kk(S/N 26750-Up) : Cooling System : Cooling Fan And Mounting
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 10 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***80 | Bolt,(Not Shown) | 6 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cooling System : Cooling Fan And Mounting(S6d125-1kk #26750-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 10 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***80 | Bolt,(Not Shown) | 6 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cooling System : Corrosion Resistor And Piping
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cooling System : Water Pump And Mounting
| 01***30 | Bolt,(For France Noise Suppression) | 2 |
| 01***16 | Bolt (With Air Heater & Conditioner) | 6 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
Cylinder Block
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Camshaft
| 01***22 | Bolt | 2 |
| 04***25 | Key, Plain Woodruff | 1 |
| 04***12 | Ring,Snap (For Ripper) | 12 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Crankshaft
| 01***25 | Bolt,(Without Rops Guard? Canopy) | 6 |
| 01***30 | Screw | 1 |
| 01***35 | Screw | 5 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Cylinder Block
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 14 |
| 04***14 | Pin, Dowel | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Cylinder Block (Cold Terrain Spec.)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Cylinder Block Cover
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Cylinder Block(Cold Terrain Spec.)(S6d125-1kk #26750-)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Flywheel And Flywheel Housing
| 01***50 | Bolt, Radiator To Frame | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Flywheel And Flywheel Housing(S6d125-1kk #26750-)
| 01***50 | Bolt, Radiator To Frame | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Front Cover And Gear
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***60 | Screw | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Front Cover And Gear(S6d125-1kk #26750-)
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***60 | Screw | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Oil Pan
| 01***12 | Bolt, Bolt,(No Need To Quick Shift) | 3 |
| 01***12 | Bolt,(With Cylinder Cover) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Oil Pan (Cold Terrain Spec.)
| 01***12 | Bolt, Bolt,(No Need To Quick Shift) | 3 |
| 01***12 | Bolt,(With Cylinder Cover) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Oil Pan(Cold Terrain Spec.)(S6d125-1kk #26750-)
| 01***12 | Bolt, Bolt,(No Need To Quick Shift) | 3 |
| 01***12 | Bolt,(With Cylinder Cover) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Oil Pan(S6d125-1kk #26750-)
| 01***12 | Bolt, Bolt,(No Need To Quick Shift) | 3 |
| 01***12 | Bolt,(With Cylinder Cover) | 1 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Block : Piston And Connecting Rod
| 02***13 | Pin, Dowel | 2 |
| 04***18 | Ring, Snap | 12 |
| 61***32 | Piston Ring Ass'Y | 6 |
Cylinder Head
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Air Cleaner And Mounting
| 01***40 | Bolt,(Dust And Dirt Protection) | 2 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Air Cleaner And Mounting(S6d125-1kk #26750-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 2 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Air Intake Manifold And Connection
| 01***10 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 13 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Air Intake Manifold And Connection(S6d125-1kk #26750-)
| 01***10 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 13 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Cylinder Head
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Cylinder Head(S6d125-1kk #26750-)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Exhaust Manifold And Turbocharger
| 01***00 | Bolt (M10-1.50x100) | 18 |
| 01***45 | Screw | 4 |
| 07***08 | Plug,(Without Auto Priming System) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Muffler And Mounting
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 8 |
| 01***45 | Bolt | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Muffler And Mounting(S6d125-1kk #26750-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 8 |
| 01***45 | Bolt | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Rocker Arm And Housing
| 01***95 | Bolt,(For 2nd Travel Speed) (Op) | 2 |
| 01***08 | Nut,R.H. Thread | 12 |
| 01***16 | Washer,Radio Controlled Slag Handling | 42 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Rocker Arm Housing Cover
| 01***16 | Washer,Radio Controlled Slag Handling | 24 |
| 61***11 | Cover,Head? No.2?3?4?5?6 | 6 |
| 61***10 | Gasket,Cylinder Head Cover | 6 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Turbocharger
| 61***10 | Turbocharger Ass'Y,(Ta4532) | 1 |
| GA***60 | V-Band | 1 |
| GA***52 | Center Housing A | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Cylinder Head : Water Manifold And Thermostat
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***12 | Washer, Gasket,(Without Thermo Sensor) (K1) | 1 |
| 07***15 | Plug,(Used When Without Heater) | 1 |
Electrical System
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator (25a) (With Hardening Pulley) (Inner Parts)
| 60***40 | Alternator A. (25a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator (35a) (With Non Hardening Pulley) (Inner Parts)
| 60***60 | Alternator A. (35a),(With Non Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator (50a) (With Hardening Pulley) (Inner Parts)
| 60***90 | Alternator A. (50a),(With Hardening Pulley) | 1 |
| SD***X0 | Washer | 1 |
| SD***X0 | Fan | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator And Mounting (25a? 35a? 50a)
| 01***90 | Bolt, Fan Mounting | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator And Mounting(25a?35a?50a)(S6d125-1kk #26750-)
| 01***90 | Bolt, Fan Mounting | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator(25a)(With Hardening Pulley)(S6d125-1kk #26750-)
| 60***40 | Alternator A. (25a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator(35a)(With Non Hardening Pulley)(1kk #26750-)
| 60***60 | Alternator A. (35a),(With Non Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Alternator(50a)(With Hardening Pulley)(S6d125-1kk #26750-)
| 60***90 | Alternator A. (50a),(With Hardening Pulley) | 1 |
| SD***X0 | Washer | 1 |
| SD***X0 | Fan | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Solenoid Switch
| 17***20 | Relay,Engine Stop Solenoid | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor (11kw) (Inner Parts)(#26750-34667)
| 60***20 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| 60***21 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| SD***09 | Metal | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor (11kw) (Inner Parts)(#34668-)
| 60***22 | Starting Motor Ass'Y,(11kw) | 1 |
| SD***X9 | Switch Ass'Y,Engage | 1 |
| SD***X0 | Bearing,Ball | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor (7.5kw) (Inner Parts)
| 60***80 | Starting Motor Ass'Y,(7.5kw) | 1 |
| KD***60 | Shift Lever Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor And Mounting (7.5kw?11kw)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***40 | Bolt,(With Center Guard) | 3 |
| 60***20 | Clip,(Large Capacity Type) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor And Mounting(7.5kw?11kw)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***40 | Bolt,(With Center Guard) | 3 |
| 60***20 | Clip,(Large Capacity Type) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor(11kw)(1z #21431-30750)(1kk #26750-34667)(#26750-34667)
| 60***20 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| 60***21 | Starting Motor Ass'Y,(11kw)(See Fig.0662a) | 1 |
| SD***09 | Metal | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor(11kw)(S6d125-1z #30751-)(S6d125-1zz #34668-)(#34668-)
| 60***22 | Starting Motor Ass'Y,(11kw) | 1 |
| SD***X9 | Switch Ass'Y,Engage | 1 |
| SD***X0 | Bearing,Ball | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Electrical System : Starting Motor(7.5kw)
| 60***80 | Starting Motor Ass'Y,(7.5kw) | 1 |
| KD***60 | Shift Lever Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Fuel System
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Engine Stop Motor And Mounting
| 01***25 | Bolt,(For Automatic) | 3 |
| 01***20 | Bolt,(With Auto Emergency Steering) | 4 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Engine Stop Motor And Mounting(S6d125-1kk #26750-)
| 01***25 | Bolt,(For Automatic) | 3 |
| 01***20 | Bolt,(With Auto Emergency Steering) | 4 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Filter And Piping (1 Filter Type)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Filter And Piping (2 Filter Type)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 6 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Filter And Piping(1 Filter Type)(S6d125-1kk #26750-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Filter And Piping(2 Filter Type)(S6d125-1kk#26750-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 6 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump (Coupling) (Inner Parts)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***00 | Coupling,Cross | 1 |
| DK***00 | Nut | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump (Feed Pump) (Inner Parts)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***20 | Bolt, Joint | 1 |
| DK***00 | Valve,Check | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump (Governor 1/2) (Inner Parts)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***00 | Screw | 1 |
| DK***20 | Flyweight Ass'Y | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump (Governor 2/2) (Inner Parts)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***20 | Capsule,Spring | 1 |
| DK***00 | Spring | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump (Pump) (Inner Parts)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| 61***54 | Injection Pump Ass'Y | 1 |
| DK***30 | Bearing,Roller | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump And Piping
| 01***30 | Bolt | 4 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 2 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump And Piping(S6d125-1kk #26750-)
| 01***30 | Bolt | 4 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 2 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 4 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump(Coupling)(S6d125-1kk #26750-)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***00 | Coupling,Cross | 1 |
| DK***00 | Nut | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump(Feed Pump)(S6d125-1kk #26750-)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***20 | Bolt, Joint | 1 |
| DK***00 | Valve,Check | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump(Governor 1/2)(S6d125-1kk #26750-)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***00 | Screw | 1 |
| DK***20 | Flyweight Ass'Y | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump(Governor 2/2)(S6d125-1kk #26750-)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| DK***20 | Capsule,Spring | 1 |
| DK***00 | Spring | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Injection Pump(Pump)(S6d125-1kk #26750-)
| 61***53 | Injection Pump A.,(See Fig.0452) | 1 |
| 61***54 | Injection Pump Ass'Y | 1 |
| DK***30 | Bearing,Roller | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Fuel Nozzle And Spill Tube
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Water Separator And Piping (1 Fuel Filter Type)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 3 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***55 | Bolt | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Water Separator And Piping (2 Fuel Filter Type)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
| 07***12 | Gasket,Mechanical Pump Piping | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Water Separator And Piping(1 Fuel Filter Type)(1kk #26750-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 3 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***55 | Bolt | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Fuel System : Water Separator And Piping(2 Fuel Filter Type)(1kk #26750-)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
| 07***12 | Gasket,Mechanical Pump Piping | 1 |
Kit
Komatsu : S6d125-1kk(S/N 26750-Up) : Kit : Gasket Kit
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***20 | O-Ring,Relief Valve | 1 |
| 07***15 | O-Ring,(For Low Speed) (D40pf) | 1 |
Lubricating Oil System
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Cooler
| 01***25 | Bolt,Without Revolution Sensor | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 12 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Filter And Mounting
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 3 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***32 | Washer,(With Auto Emergency Steering) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Filter And Mounting(S6d125-1kk #26750-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 3 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***32 | Washer,(With Auto Emergency Steering) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Piping
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***50 | Bolt,(With Service Valve R.H.) | 4 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Piping(S6d125-1kk #26750-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 1 |
| 01***50 | Bolt,(With Service Valve R.H.) | 4 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe
| 01***25 | Bolt,(Without Auto Priming System) | 4 |
| 01***20 | Bolt,(Large Capacity Type) (Std) | 2 |
| 01***25 | Bolt,(Sandy? Dusty Terrain Spec.) | 5 |
Komatsu : S6d125-1kk(S/N 26750-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping
| 01***20 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Mechanical Governor) | 2 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 2 |
Tool And Kit
Komatsu : S6d125-1kk(S/N 26750-Up) : Tool And Kit : Gasket Kit(S6d125-1kk #26750-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***20 | O-Ring,Relief Valve | 1 |
| 07***15 | O-Ring,(For Low Speed) (D40pf) | 1 |
S6D125-1KK(S/N 26750-UP) serial number reference
The engine serial number is stamped on the engine block, typically on the left side near the injection pump or on a metal data plate affixed to the engine. The prefix is the first part of the engine model code (e.g., S6D125-1KK) found on the engine identification plate, which identifies the engine family and generation.
| Prefix | Identifies | Notes |
|---|---|---|
| S6D125-1KK | Engine Model | Komatsu S6D125-1KK engine family. Serial range S/N 26750-UP. Factory spec sheet and parts catalog for this specific engine designation. |
Frequently asked questions
What type of engine is the Komatsu S6D125-1KK?
It is a 6-cylinder, turbocharged, aftercooled diesel engine with an 11-liter displacement, part of the S6D125 series manufactured since 2017.
What is the operating weight range for machines using this engine?
Operating weights vary by configuration and series, typically ranging from 20,000 kg to 40,000 kg for host machines like the D65EX-12 dozer and PC400 excavator.
What replaced the Komatsu S6D125-1KK?
The S6D125 series is part of Komatsu's ongoing engine lineage, with newer variants like the S6D125E-2 and SAA6D125E-2 succeeding earlier models to meet evolving emissions standards and performance requirements.
What S6D125-1KK(S/N 26750-UP) owners discuss
What are the known powertrain and hydraulic behaviors associated with the Komatsu S6D125-1KK engine series?
The S6D125-1KK is a turbocharged and aftercooled diesel engine designed for heavy-duty applications. It delivers high torque at low engine speeds, which supports efficient operation in construction and mining environments. The engine is often paired with Komatsu’s hydraulic systems, which are known for smooth operation and fuel efficiency. However, the hydraulic pump and engine are closely linked; if the hydraulic pump fails, the engine may suffer damage shortly thereafter due to the high loads placed on it. Pump flow settings vary by engine model, with the S6D125 typically set to a mid-range value between minimum and maximum, unlike other series that may be set near the maximum. The engine is robust and reliable with proper maintenance, but contamination or extended service intervals can accelerate wear on fuel delivery components and injectors. Power output varies by configuration, generally ranging from 155 HP to 275 HP (116 kW to 205 kW) depending on the specific machine application and emissions package. Torque rise increases by 30% in the 155 HP variant and 13% in the 180 HP variant compared to baseline models. Fuel consumption at rated power is approximately 70 liters per hour (18.5 gallons per hour). Displacement is 11 liters with a 6-cylinder configuration. Wet cylinder liners are used, requiring careful management of supplemental coolant additive to prevent cavitation pitting.
What undercarriage or wear patterns are typical for machines powered by this engine series?
Machines equipped with the S6D125-1KK engine, such as the PC400-5 excavator or D65 dozer, experience significant wear on bushings, bearings, and track pads due to heavy loading and continuous operation. Worn bushings can lead to increased noise and vibration, while degraded bearings may cause premature failure of the tracks. The undercarriage is subject to rapid wear in dusty or abrasive environments, necessitating frequent inspection of track tension, roller condition, and track-chain integrity. If a machine pulls to one side during travel, check for mud or debris packed into the undercarriage, uneven track tension, or worn rollers before diagnosing hydraulic issues. The line is generally designed to wear out complete machines all at once, contributing to lower resale values if major components like the hydraulic pump or engine fail. Regular maintenance of the undercarriage is critical to avoid costly repairs and ensure stable operation.
What are the common engine quirks per the S6D125-1KK series?
The S6D125-1KK engine uses wet cylinder liners that are in direct contact with the coolant. Keeping supplemental coolant additive topped up is critical; letting the additive deplete allows the liners to pit from cavitation, which can eventually lead to coolant leaking into the crankcase. This may manifest as steam coming off the breather on startup or milky oil. The engine is naturally aspirated in some configurations or turbocharged in others, but it lacks electronic cold-start assist beyond glow plugs or ether aids, making coolant concentration and battery capacity checks vital in cold conditions. In hot, dusty environments, air cleaner service intervals should be shortened, and the radiator core must be kept clear of debris to prevent overheating. The engine is known for durability, but contamination, extended service intervals, and low-quality fuel can accelerate wear on internal components. Hardened liners are matched to the rings, and using OEM parts is recommended to avoid issues.
What are the common electrical or sensor issues reported for this engine?
Komatsu excavators and dozers with the S6D125-1KK engine rely heavily on electronic control systems, meaning a single faulty sensor or unstable power supply can trigger multiple warning signals. Owners often report intermittent starting, dashboard failure, or machines that randomly shut down. Common electrical issues include faulty batteries, poor engine and chassis grounds, and damaged connectors. A battery may show acceptable voltage until the starter is loaded, so load and voltage-drop tests are recommended before replacing the starter. Intermittent fault codes often point to battery, grounds, or connector issues rather than component failure. The engine’s electronic control module monitors pressure sensors, valves, circuits, and actuators, and fault codes are used to diagnose these systems. Ensuring stable power supply and clean connections is essential to prevent erratic behavior.
What should be checked when buying a used machine with the S6D125-1KK engine?
When buying a used machine with the S6D125-1KK engine, check the following: 1. Engine oil condition and coolant level for signs of contamination or leakage into the crankcase. 2. Supplemental coolant additive levels to ensure liners are protected from cavitation. 3. Hydraulic oil level, condition, and filter status, as well as engine RPM under load. 4. Air filter condition and intake hoses for restrictions or damage. 5. Fuel filters and water separator for contamination. 6. Battery state of charge and terminal condition. 7. Undercarriage wear, track tension, and roller condition. 8. Hydraulic function performance both cold and hot to identify internal leakage. 9. Fault codes and warning messages on the display. 10. Cooling system components, including radiator, hydraulic oil cooler, and charge-air cooler, for debris or blockage. Verify the exact serial range and configuration, as specs can vary by machine model and emissions package. Consult official OEM service manuals for precise operating specs and safety protocols.
What are the recommended fluid specifications for this engine?
For the S6D125-1KK engine, use Komatsu Genuine Diesel Engine Oil that meets Komatsu Engineering Standards. For the cooling system, use Super Coolant AF-NAC. Hydraulic oil should meet Komatsu HO specification. Axle oil should meet Komatsu AXO specification. Powertrain oil should meet Komatsu TO specification. Always verify fluid specifications against the machine’s operation and maintenance manual, as requirements may vary by configuration and regional standards. Use of non-compliant fluids can lead to accelerated wear and component failure.
What is a safety-critical fix related to the S6D125-1KK engine that requires dealer verification?
If coolant is found in the crankcase or oil appears milky, this indicates a potential failure of the cylinder liner seals or gasket, allowing coolant to leak into the engine. This is a safety-critical issue that can lead to catastrophic engine failure. Have your dealer verify the extent of the damage and perform the necessary repairs. Do not operate the machine until the issue is resolved. Have your dealer verify.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Need a specific S6D125-1KK(S/N 26750-UP) part?
Search live OEM part data, check fitment, and cross-reference alternatives with Heavy Parts AI.