Komatsuengine(no series)

Komatsu S6D125-1B8-FA(S/N 10001-UP)

Maintenance schedule, common problems & OEM parts breakdown

The Komatsu S6D125-1B8-FA is a 6-cylinder, turbocharged, and aftercooled diesel engine belonging to the S6D125 series. It powers mid-to-heavy class Komatsu construction equipment, including the PC200-7, PC220-7, PC300-7, and WA320-8 wheel loader series. Production years span the late 1990s through the 2010s. This engine succeeded the 6D125-1 and was later replaced by the S6D125E-2 and SAA6D125E-2 series to meet stricter emissions standards. Configurations offered include standard industrial, marine, and generator set variants, with the FA suffix denoting specific emission and application packages for the S/N 10001-UP range.

Across the S6D125 lineage, the primary change was the transition from mechanical fuel injection to electronic control systems in the E-series, improving fuel efficiency and reducing emissions. The S6D125-1B8-FA remains critical in the used and parts market because it is the heart of the highly popular PC200/PC220-7 excavator generation. Its widespread use ensures high parts availability, but the shift to electronic controls in later variants requires specialized diagnostic tools, making the mechanical simplicity of the 1B8-FA a preferred choice for independent rebuilds and long-term fleet maintenance.

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 S6D125-1B8-FA(S/N 10001-UP) specifications

Engine

ModelS6D125-1B8-FA
Series/GenerationS6D125-1 (125 Series)
Type4-stroke, water-cooled, direct injection diesel engine
Displacement11.04 liters (674 cubic inches)
Cylinders6
Bore x Stroke125 mm x 150 mm (4.92 inches x 5.91 inches)
Compression Ratio17:1
AspirationTurbocharged and aftercooled
Power Output (Range)260–300 hp (194–224 kW); specific variant cited as 275 hp (205 kW)
Torque (Range)920–1100 Nm (678–811 lb-ft); specific variant cited as 1010 lb-ft (1370 Nm)
Emissions TierNot documented for this exact serial range — verify with your dealer

Weights

Operating WeightNot documented for this exact serial range — verify with your dealer
Shipping WeightNot documented for this exact serial range — verify with your dealer
Ground PressureNot documented for this exact serial range — verify with your dealer

Dimensions

Engine Dimensions (L x W x H)120 x 100 x 125 cm
Transport Length/Width/HeightNot documented for this exact serial range — verify with your dealer
Track Gauge / WheelbaseNot documented for this exact serial range — verify with your dealer
Ground ClearanceNot documented for this exact serial range — verify with your dealer

Performance

Travel SpeedsNot documented for this exact serial range — verify with your dealer
Lift/Dig/Dump/DrawbarNot documented for this exact serial range — verify with your dealer
GradeabilityNot documented for this exact serial range — verify with your dealer

Service capacities (summary)

Fuel TankNot documented for this exact serial range — verify with your dealer
Hydraulic SystemNot documented for this exact serial range — verify with your dealer
Engine OilNot documented for this exact serial range — verify with your dealer
Cooling SystemNot 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.

S6D125-1B8-FA(S/N 10001-UP) fluids & capacities

SystemCapacityRecommended fluid
Engine crankcase (with filter)Not documented for this exact serial rangeKomatsu Genuine Diesel Engine Oil, SAE 15W-40 for normal ambient temperatures; SAE 10W-30 for colder climates. Equivalent: Chevron Delo 400 series.
Cooling systemNot documented for this exact serial rangeKomatsu Super Coolant, supplied as concentrate mixed 50/50 with water.
Fuel tankNot documented for this exact serial rangeAutomotive diesel fuel (ASTM D975 No. 2-D equivalent) for normal conditions; lighter No. 1-D-equivalent in cold weather.
Transmission/powertrain compartmentsNot documented for this exact serial rangeKomatsu Powertrain & Micro Clutch Oil (drive-train fluid spec): SAE 10W in cold conditions, SAE 30 in normal/warm conditions. Equivalent: Chevron Delo TorqForce.
Final drives (each)Not documented for this exact serial rangeKomatsu Powertrain & Micro Clutch Oil (SAE 10W cold / SAE 30 normal), unless periodic maintenance chart calls out Komatsu Gear Lubricant (SAE 80W-90 or 85W-140, API GL-5 class).
Hydraulic system and tankNot documented for this exact serial rangeKomatsu hydraulic oil (46AW hydraulic fluid spec), ISO VG 46. Equivalent: Chevron Rando HD or Delo TorqForce hydraulic-oil equivalents in ISO 46 grade.
Grease (spec only)Not applicableKomatsu Lithium-base Grease EP2 (G2-LI), NLGI 2, general-purpose chassis grease for normal temperatures. Equivalent: Chevron/Delo Grease ESI EP, NLGI 2. Use lower-consistency (arctic-grade) NLGI 1 or 0.5 lithium grease in sustained sub-freezing climates.

Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.

Komatsu S6D125-1B8-FA(S/N 10001-UP) maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil level via dipstick.
  • Check hydraulic fluid level at sight glass.
  • Check coolant level and ensure cap is secure.
  • Drain water from fuel separator.
  • Check DEF level.
  • Inspect air filter restriction indicator.
Every 250 h
  • Change engine oil and replace oil filter.
  • Grease all pivot points on boom, stick, and bucket.
  • Grease swing bearing.
  • Inspect V-belts and hoses for wear.
  • Check coolant level.
  • Inspect hydraulic hoses for cracks or leaks.
Every 500 h
  • Replace fuel filter element.
  • Replace hydraulic return filter.
  • Test battery load and clean terminals.
  • Test coolant SCA concentration.
  • Collect KOWA engine oil sample.
  • Measure undercarriage wear.
Every 1,000 h
  • Replace air filter outer element.
  • Change final drive oil (both sides).
  • Inspect turbocharger condition.
  • Check valve clearance.
  • Inspect structural welds on boom and stick.
  • Collect KOWA hydraulic oil sample.
Every 2,000 h
  • Change hydraulic system oil.
  • Flush and replace coolant.
  • Inspect and replace worn belts and hoses.
  • Load test battery and alternator.
  • Perform comprehensive structural inspection.
  • Check KDPF status (typically 4,500 hr).

Servicing the S6D125-1B8-FA(S/N 10001-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

Utilize KOWA fluid analysis at every 500-hour interval to monitor engine wear metals (iron, copper, lead) and coolant contaminants (sodium, silicon). Track hydraulic oil particle count and viscosity to predict pump and valve wear. Monitor DEF levels and quality to prevent SCR system faults. Use KOMTRAX telematics to track load frequency and fuel burn anomalies, identifying inefficient combustion or turbocharger degradation before catastrophic failure occurs.

Corrective & Common Repairs

Address common S6D125-1B8-FA issues by inspecting the turbocharger TV7705 for shaft play and oil leaks. Check the fuel injection pump TVC (Traveling Valve Control) setting, as improper adjustment causes power loss and excessive smoke. Replace worn piston rings if oil consumption exceeds limits or breather pressure is high. Inspect the water pump and thermostat housing for coolant leaks, a frequent source of overheating. Verify electrical connections to the engine controller to prevent intermittent stalling or fault codes.

Overhaul & Rebuild Points

Plan inframe overhauls around 10,000-12,000 hours or when compression drops below spec. Replace pistons, liners, and rings using the S6D125-1 specific kit. Inspect the crankshaft for journal wear and replace main and rod bearings if clearance exceeds limits. Check the cylinder head for warpage and replace valve guides and seats if leakage is detected. Rebuild the turbocharger or replace it if shaft end-play is excessive. Ensure all gaskets and seals are replaced during reassembly to prevent oil and coolant mixing.

Seasonal & Environment Servicing

In cold climates, use low-temperature Komatsu diesel engine oil and ensure the coolant mixture provides adequate freeze protection. Check the battery heating blanket and insulation for cold-start reliability. In dusty environments, inspect the air filter restriction indicator more frequently and clean the radiator and oil cooler fins daily to prevent overheating. In high-humidity or coastal areas, inspect electrical connectors for corrosion and check the fuel separator for water accumulation more often to prevent injector damage.

S6D125-1B8-FA(S/N 10001-UP) common service parts

Part numberPart
07281-00197Clamp,(With Pre-Fuel Filter)Check fitment →
600-311-8291Cartridge,Fuel FilterCheck fitment →
6114-71-6200Fuel Filter Ass'YCheck fitment →
6114-71-6210Head, Fuel FilterCheck fitment →
6162-53-5430Packing,Oil Filter And PipingCheck fitment →

Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.

S6D125-1B8-FA(S/N 10001-UP) fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CA115Engine speed sensor and backup speed sensor failureBroken sensor, wiring issue, or connector corrosionReplace the speed sensor and verify the voltage at the pin connector
CA111Internal engine controller faultECM hardware or software failureReplace or reprogram the ECM
CA451Common rail pressure sensor feedback value too highMalfunction in the rail sensor or actual overpressure conditionDiagnose the fuel rail pressure sensor or pump lines
CA452Common rail pressure sensor feedback value too lowFuel leak, sensor failure, or supply pump issueDiagnose the fuel rail pressure sensor or pump lines
CA122Intake air pressure sensor feedback voltage too highSensor malfunction or wiring shortVerify the intake pressure sensor and wiring
CA123Intake air pressure sensor feedback voltage too lowSensor short or airflow restrictionCheck for a sensor short or an airflow restriction
CA234Engine overspeedThrottle calibration error, engine load cycle issue, or operator misuseVerify throttle calibration, engine load cycle, or operator misuse
CA441Battery voltage too lowWeak battery, alternator failure, or loose connectionsReplace the alternator or battery; check the voltage regulator
CA442Battery voltage too highAlternator regulator failureReplace the alternator or battery; check the voltage regulator
CA2311IMV solenoid valve failureFaulty IMV solenoid or wire harness issueReplace the IMV solenoid or inspect the wire harness

Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.

S6D125-1B8-FA(S/N 10001-UP) attachments & work tools

Bulldozer Blade Configurations

The S6D125-1B8-FA engine powers the D65E-12 and D65PX-12 series dozers, which utilize semi-U or U-blade configurations with capacities varying by configuration/series. Factory guarding options include heavy-duty side cutters and corner guards for high-abrasion applications, as documented in the Komatsu shop manual for this range.

Excavator Bucket Families

This engine is fitted to the PC400-5 and PC400LC-5 excavator series, supporting standard heavy-duty digging buckets and rock buckets. Bucket capacities vary by configuration/series, typically ranging from 2.0 to 3.0 cubic meters for this class, with mounting systems compatible with the machine's standard quick-coupler interface.

Wheel Loader Bucket Types

The S6D125-1B8-FA engine is used in the WA470-3 and WA480-8 wheel loaders, which are equipped with general purpose, light material, and heavy-duty rock buckets. Typical bucket capacities for this class range from 3.0 to 4.0 cubic meters, depending on the specific loader model and configuration.

Hydraulic System Requirements

Work tools require connection to the machine's main hydraulic circuit; the engine itself does not provide direct tool hydraulics but drives the hydraulic pump. Komatsu recommends using Komatsu Hydraulic Oil (HO) or equivalent for the system, as specified in the operation and maintenance manual.

Engine Mounting and Coupling

The engine is mounted via a rigid frame interface with flywheel housing standards compatible with the PC400-5 and D65E-12 chassis. The S/N 10001-UP designation indicates a specific production series with standardized mounting bolt patterns and alignment tolerances as per the factory spec sheet.

All S6D125-1B8-FA(S/N 10001-UP) assemblies by section

Every catalogued assembly group for the Komatsu S6D125-1B8-FA(S/N 10001-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Engine
Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#22230-41920)
61***10Air Compressor Ass'Y,(See Fig.0711)1
DK***20Connecting Rod A1
DK***00Spring,Delivery Valve1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#41921-)
61***11Air Compressor Ass'Y,(See Fig.0711a)1
DK***20Connecting Rod A1
DK***00Spring,Delivery Valve1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Air Compressor And Piping(#22230-)
07***12Gasket,(Without Air Compressor Type) (K2)4
07***12Gasket,(Without Air Compressor Type) (K1)8
07***16Gasket,Air Compressor Piping2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Air Intake Manifold And Connection(#16790-)
01***10Bolt,(With Auto Emergency Steering)2
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***30Bolt,(For Quick Shift) (Mitsubishi)16
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Alternator (35a) (Inner Parts)
60***60Alternator A. (35a),(With Non Hardening Pulley)1
KD***57Bearing,Ball? Front1
KD***80Collar1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Alternator And Mounting (35a)(#22230-)
01***40Bolt, Mount Master Brake Cylinder1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Camshaft
01***22Bolt2
04***25Key, Plain Woodruff1
04***12Ring,Snap (For Ripper)2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Cooling Fan And Mounting(#22230-)
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***30Bolt,(For Quick Shift) (Mitsubishi)6
01***35Bolt,(For Quick Shift) (Mitsubishi)6
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Corrosion Resistor And Piping(#32964-)
01***25Bolt,(For Canvas Canopy?Head Guard)5
01***08Nut,(For Canvas Canopy?Head Guard)1
02***25Bolt,(Cold Weather Spec.)4
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Crankshaft(#22230-)
01***25Bolt,(Without Rops Guard? Canopy)6
01***30Screw1
01***35Screw5
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Cylinder Block Cover(#22230-)
07***20Clamp, Spring Hose1
07***63Hose1
61***90O-Ring,Breather1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Cylinder Block(#22230-)
01***12Bolt,(Without Air Compressor Type)2
01***45Washer,(For Travel Motor) (Not Show)14
04***14Pin, Dowel2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Cylinder Head(#22230-)
04***20Pin,Dowel (Welded)2
61***30Sleeve,Holder1
61***20Cotter, Valve48
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Exhaust Brake (Inner Parts)(#22230-74356)
61***50Exhaust Brake Ass'Y1
61***51Exhaust Brake Ass'Y1
JK***47Bushing1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Exhaust Brake (Inner Parts)(#74357-)
61***51Exhaust Brake Ass'Y1
MY***74Pin2
MY***08Nut2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Exhaust Brake(#22230-)
Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Exhaust Manifold And Turbocharger(#22230-)
01***00Bolt (M10-1.50x100)18
01***45Screw2
07***08Plug,(Without Auto Priming System)1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Flywheel And Flywheel Housing(#22230-)
01***50Bolt2
01***50Bolt, Radiator To Frame6
01***60Bolt, Hanger Bearing Mounting2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Front Cover(#22230-)
01***25Bolt,(Without Auto Priming System)6
01***60Screw1
01***20Bolt,(For Quick Shift) (Mitsubishi)2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Filter And Piping(#22230-)
01***90Bolt, Fan Mounting2
01***16Washer,Radio Controlled Slag Handling2
07***12Gasket,Mechanical Pump Piping2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (Inner Parts)(#22230-)
DK***00Nut2
DK***00Bolt4
DK***00Bolt2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (Inner Parts)(#22230-)
DK***20Bolt, Joint1
DK***00Valve,Check2
DK***80Feed Pump Ass'Y1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (Inner Parts)(#22230-)
DK***80Bolt,Eye1
DK***00Nut1
DK***00Spring1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (Inner Parts)(#22230-)
DK***00Screw1
DK***20Lever1
DK***00Bushing1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (Inner Parts)(#22230-)
61***20Injection Pump Ass'Y1
DK***30Bearing,Roller2
DK***00Shim? 0.875mm0
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump (Timer) (Inner Parts)(#22230-)
DK***00Bolt2
DK***00Roller? 23.9mm0
DK***40Timer Ass'Y1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Injection Pump And Piping(#22230-)
01***30Bolt4
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***45Bolt,(For Power Tilt Mech Angle)2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Fuel Nozzle And Spill Pipe(#22313-)
01***45Bolt, Divider Valve Mounting12
07***65O-Ring,Cylinder Block6
07***12Gasket,Mechanical Pump Piping2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Gasket Kit(#22230-)
02***43O-Ring,Water Manifold6
07***20O-Ring,Relief Valve1
07***15O-Ring,(For Low Speed) (D40pf)1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Head Cover
01***16Washer,Radio Controlled Slag Handling24
61***10Cover,Head? No.2?3?4?5?66
61***11Cover,Head? No.2?3?4?5?66
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Lubricating Oil Cooler(#22230-)
01***25Bolt,Without Revolution Sensor2
01***25Bolt,(For Canvas Canopy?Head Guard)12
01***65Bolt,(Except Japan)2
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Lubricating Oil Filter And Mounting(#22230-)
01***60Bolt, Mount Tube To Switch Pump1
01***75Bolt,(For Adjusting)4
01***16Washer,Radio Controlled Slag Handling5
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Lubricating Oil Pump And Suction Pipe(#22230-)
01***25Bolt,(Without Auto Priming System)4
01***20Bolt,(Large Capacity Type) (Std)2
01***25Bolt,(Sandy? Dusty Terrain Spec.)5
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Oil Pan(#22230-)
01***25Bolt,(For Canvas Canopy?Head Guard)29
01***30Bolt,(For Quick Shift) (Mitsubishi)7
01***16Washer,Radio Controlled Slag Handling37
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Piston And Connecting Rod(#11574-)
02***13Pin, Dowel2
04***18Ring, Snap12
61***31Piston Ring Ass'Y6
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Rocker Arm
01***08Nut,R.H. Thread12
01***16Washer,Radio Controlled Slag Handling40
01***32Washer,(With Auto Emergency Steering)40
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Starting Motor (7.5kw) (Inner Parts) -1c?1b8)(#18200-)
60***30Starting Motor Ass'Y,(7.5kw)1
KD***60Shift Lever Assembly1
KD***40Spring,Spring4
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Starting Motor Mounting (7.5kw)
01***60Bolt,(Shim Thickness?More Than 8mm)3
66***10Gasket,Starting Motor1
(6***0)Starting Motor Ass'Y,(7.5kw) (See Fig.0661a)1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Turbocharger (Inner Parts)(#22230-)
61***00Turbocharger Ass'Y,(See Fig.0155)1
GA***85V-Band Ass'Y1
GA***07Rotor Ass'Y1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Turbocharger Libricating Oil Piping(#22230-)
01***20Bolt,(For Quick Shift) (Mitsubishi)6
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***40Bolt, Mount Master Brake Cylinder1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Water Manifold(#22230-)
02***43O-Ring,Water Manifold6
07***12Washer, Gasket,(Without Thermo Sensor) (K1)1
07***15Plug,(Used When Without Heater)1
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Komatsu : S6d125-1b8-Fa(S/N 10001-Up) : Engine : Water Pump And Mounting(#22230-)
01***30Bolt,(For France Noise Suppression)2
01***16Bolt (With Air Heater & Conditioner)6
01***25Bolt,(For Canvas Canopy?Head Guard)2
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S6D125-1B8-FA(S/N 10001-UP) serial number reference

The engine serial plate is stamped on the engine block, typically on the left side near the injection pump. Read the prefix as the equipment model code (e.g., HA250) followed by the dash-number generation, then match the engine serial number to the catalog range.

PrefixIdentifies
HA250-1Dumper
HA250-3Dumper

Frequently asked questions

What is the engine type and series for the S6D125-1B8-FA?

It is a 6-cylinder, turbocharged, and aftercooled diesel engine from the Komatsu S6D125 series, specifically the 1B8-FA variant for serial numbers 10001-UP.

What is the operating weight of the machines powered by this engine?

Operating weight varies by configuration and series. For example, the PC200-7 excavator ranges from approximately 20,000 to 22,000 lbs, while the WA320-8 wheel loader ranges from 34,000 to 35,000 lbs.

What engine replaced the S6D125-1B8-FA?

The S6D125E-2 and SAA6D125E-2 series replaced the S6D125-1B8-FA to meet stricter emissions standards, featuring electronic fuel injection and advanced aftertreatment systems.

What S6D125-1B8-FA(S/N 10001-UP) owners discuss

What are the typical powertrain and hydraulic behaviors associated with the Komatsu S6D125-1B8-FA engine series?
The S6D125-1B8-FA is a turbocharged and aftercooled diesel engine with a displacement of 11 liters and six cylinders. It delivers approximately 275 horsepower (205 kilowatts) and 1,010 pound-feet (1,370 Newton meters) of torque. The engine is known for high torque at lower speeds, which complements Komatsu’s hydraulic systems. Operators note that the engine and hydraulic pump must be matched correctly; mismatched settings can cause the engine to be overloaded by the pumps, leading to valve train damage. The engine is generally considered durable, often outlasting hydraulic components when maintained properly. Torque output varies by configuration, typically ranging from 920 Nm (678 lb-ft) to 1,100 Nm (811 lb-ft). Fuel consumption at rated power is approximately 18.5 gallons per hour (70 liters per hour). The engine uses hardened liners matched to the piston rings, which are reported to be reliable with OEM parts.
What undercarriage or wear patterns are typical for machines powered by this engine series?
Machines equipped with the S6D125-1B8-FA engine, such as the PC400-5 and D65E-12, are subject to standard heavy-duty wear patterns. Components like bushings, bearings, and track pads degrade due to continuous load and environmental exposure. Worn bushings can lead to increased noise and vibration, while worn bearings may cause premature track failure. The hydraulic system is a critical wear point; if the main hydraulic pump fails, the engine is often at risk of subsequent damage due to the high load transfer. Operators report that Komatsu machines are designed to wear out as complete units rather than individual components failing in isolation, which can impact resale value. Regular inspection of the undercarriage tension and roller condition is necessary to prevent uneven wear and track derailment.
What are the known engine quirks or maintenance requirements for the S6D125-1B8-FA series?
The S6D125-1B8-FA requires specific maintenance of the cooling package, including the radiator, hydraulic oil cooler, charge-air cooler, and air-conditioning condenser, as debris packed between these heat exchangers can cause overheating during heavy excavation. The engine is sensitive to fuel quality and air intake restrictions; loss of power under load is often traced to clogged air or fuel filters rather than internal engine failure. The hydraulic pump flow settings must be adjusted differently for this engine compared to older Cummins-based models; the TVC (Torque Control) is typically set between the minimum and maximum limits, rather than near the maximum. Coolant contamination and water in the crankcase are known issues that require immediate investigation of piston rings and gaskets. The engine uses Komatsu Engineering Standard fluids, including Komatsu EO diesel engine oil and Super-coolant AF-NAC.
What are the common electrical or sensor issues reported for this engine?
Komatsu excavators with this engine rely heavily on electronic control systems, where a single faulty sensor or unstable power supply can trigger multiple warning signals. Common electrical issues include intermittent starting, dashboard failures, and random shutdowns. Fault codes such as CA115 indicate engine speed sensor faults, which are often caused by broken sensors, wiring issues, or connector corrosion. Owners report that machines may exhibit erratic behavior if the battery state of charge is low or if engine and chassis grounds are poor. A voltage drop test under load is recommended before replacing starters, as batteries may show acceptable voltage until the starter is engaged. Multiple fault codes often point to battery or ground connection issues rather than component failure.
What should be checked when buying a used machine with the S6D125-1B8-FA engine?
When purchasing a used machine with the S6D125-1B8-FA engine, verify the exact serial number to confirm the engine model and configuration, as parts and specifications vary by serial range. Check the hydraulic system for weakness when hot, which indicates internal leakage in pumps, valves, or cylinders. Inspect the cooling system for debris packed between the heat exchangers and verify coolant levels. Test the engine under load to ensure it does not lose power or RPM excessively when hydraulic functions are combined. Check for oil leakage from the breather, which may indicate piston ring or gasket failure. Verify the condition of the undercarriage, including track tension, roller condition, and bushing wear. Ensure the hydraulic pump flow settings are correct for the S6D125-1B8-FA engine, as incorrect TVC settings can lead to premature engine damage. Review the machine’s fault code history for recurring electrical or sensor issues.
What are the fluid specifications for the S6D125-1B8-FA engine and associated systems?
The S6D125-1B8-FA engine requires Komatsu Engineering Standard diesel engine oil, such as Komatsu EO. The hydraulic system uses Komatsu hydraulic oil, such as Komatsu TO or AXO. The cooling system requires Super-coolant AF-NAC. Axle and powertrain oils must also meet Komatsu specifications. Using fluids that do not meet these standards can lead to accelerated wear and system failure. The engine’s fuel system requires clean diesel fuel with proper filtration to prevent injector wear and power loss.
What safety-critical fixes or inspections are recommended for the S6D125-1B8-FA engine?
Safety-critical inspections include verifying the integrity of the cooling system to prevent overheating, which can lead to catastrophic engine failure. Check the fuel system for air leaks or restrictions that could cause sudden power loss or stalling. Inspect the hydraulic system for leaks that could create fire hazards or loss of control. Ensure the engine speed sensor and wiring are secure to prevent erratic engine behavior. Verify the condition of the piston rings and gaskets to prevent coolant contamination and oil leakage. Have your dealer verify the hydraulic pump flow settings and TVC adjustments to ensure they are correct for the S6D125-1B8-FA engine, as incorrect settings can cause excessive load and valve train damage.

Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.

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