Komatsuengine(no series)
Komatsu 6D125-1AB(S/N 10276-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu 6D125-1AB (S/N 10276-UP) is a mechanical, naturally aspirated inline-six diesel engine belonging to the 6D125-1 family, primarily powering the Komatsu D50A-17 crawler dozer and its D50P-17 and D50PL-17 low-ground-pressure swamp variants. This engine places the host machine in the small-to-medium crawler dozer class, with operating weights ranging from 10,850 kg to 17,550 kg (23,920 lb to 38,690 lb) depending on the specific chassis configuration. The D50A-17 series succeeded the D50A-16, which utilized a smaller four-cylinder engine, and was followed by the D50A-18, which carried the same 6D125-1 base engine at a higher rating. Configurations offered across this lineage include the standard A-frame dozer and the wide-track LGP swamp variants, each available with straight or angle blade fitment.
The transition from the D50A-16 to the D50A-17 marked a significant shift to a longer-stroke, smoother-running six-cylinder unit that Komatsu carried across a wide range of dozers, loaders, and other machines of the same era. This design choice gave the -17 series strong parts commonality with sibling models and established a robust, mechanical powertrain with no onboard diagnostics. The engine's simplicity is exactly what keeps the 6D125-1AB relevant in the used and parts market today: rental yards, small contractors, and secondary-market rebuilders favor these pre-electronic engines because they can be serviced and repaired in the field without diagnostic tooling, using widely available common 6D125-family parts. Demand for the D50A-17 platform persists mainly in regions and applications where low-cost, easily-maintained mid-size dozers still do useful work long after newer, electronically-governed generations have taken over frontline fleets.
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 6D125-1AB(S/N 10276-UP) specifications
Engine
| Model | 6D125-1AB (S/N 10276-UP) |
| Configuration | Mechanical, naturally aspirated inline-6 diesel; part of the 6D125-1 family. Distinct from the turbocharged S6D125-1 and later suffix variants (1AF, 1AM, 1AN). |
| Displacement | 11.04 L (673.8 cu in / 11,042 cm3) |
| Cylinders | 6 cylinders in line |
| Bore x Stroke | 125 mm x 150 mm |
| Gross Power | Not documented for this exact serial range in available spec sheets; varies by host machine configuration. |
| Net Power | Not documented for this exact serial range in available spec sheets; varies by host machine configuration. |
| Emissions Tier | Predates emissions-tier certification; no EPA/EU tier rating applies to this engine. |
Weights
| Operating Weight | Not documented for this exact serial range - verify with dealer or shop manual. |
| Shipping Weight | Not documented separately from operating weight in available spec sheets. |
| Ground Pressure | Not documented for this exact serial range - verify with dealer or shop manual. |
Dimensions
| Transport Length/Width/Height | Not documented for this exact serial range - verify with dealer or shop manual. |
| Track Gauge | Not documented for this exact serial range - verify with dealer or shop manual. |
| Ground Clearance | Not documented for this exact serial range - verify with dealer or shop manual. |
Performance
| Travel Speeds | Not documented for this exact serial range - verify with dealer or shop manual. |
| Rated Engine Speed | 1750-1900 rpm depending on governed application. |
| Gradeability | Not documented for this exact serial range - verify with dealer or shop manual. |
Service capacities (summary)
| Engine Oil (crankcase) | Exact factory refill quantity is not published in the accessible factory literature for this serial range; verify against the machine's fuel/coolant/lubricant table or with a Komatsu dealer before servicing. |
| Cooling System | Exact refill quantity not confirmed for this serial range in available factory documentation; radiator is a "D-type" core per the factory specification sheet. Confirm capacity with the periodic maintenance chart before draining/refilling. |
| Fuel Tank | Exact tank capacity not confirmed for this serial range in the accessible factory literature. |
| Hydraulic System | Not an engine-level spec; capacity is set by the host machine's hydraulic circuit and not documented specifically against this engine. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
6D125-1AB(S/N 10276-UP) fluids & capacities
| System | Capacity | Recommended fluid |
|---|---|---|
| Engine crankcase (with filter) | Not documented for this exact serial range — verify with your dealer | Komatsu Genuine Diesel Engine Oil, SAE 15W-40 for normal ambient temperatures; SAE 10W-30 is the Komatsu-approved grade for colder climates. Equivalent cross-reference: Chevron Delo 400 series diesel engine oil built to the same Komatsu engine-oil specification. |
| Cooling system | Not reliably documented for this exact serial range. Closely related earlier D-series generations of similar displacement ran roughly 42-63 L (11-17 gal), but this figure is not confirmed as applicable to the 6D125-1A S/N 10001-UP - verify with dealer | Komatsu Super Coolant, supplied as concentrate mixed 50/50 with water (extended-life, all-season, anti-corrosion coolant). No separate winter/summer concentration split is called out beyond the standard 50/50 mix; use a higher concentrate ratio only for extreme cold per Komatsu's coolant freeze-protection chart. |
| Fuel tank | 250-320 L (66-85 gal), varies by dozer model; not a fixed engine-level figure | Automotive diesel fuel (ASTM D975 No. 2-D equivalent) for normal conditions; switch to a lighter No. 1-D-equivalent fuel in cold weather per Komatsu's ambient-temperature fuel guidance. Keep tank topped up at end of shift to reduce condensation. |
| Transmission/powertrain compartments | Not separately published for this serial range. The D50A/P-17 uses a manually shifted spur-gear transmission (5 speeds forward, 4 reverse) with splash-type lubrication, sharing lubrication with the spiral bevel gear shaft and the wet multiple-disc steering clutch/band brake, per the factory specifications section; no standalone capacity figure was accessible. | Komatsu Powertrain & Micro Clutch Oil (drive-train fluid spec): SAE 10W in cold conditions, SAE 30 in normal/warm conditions. Equivalent cross-reference: Chevron Delo TorqForce in matching viscosity grade. |
| Final drives (each) | Not separately published for this serial range. Final drive is a 2-stage spur-gear reduction with splash-type lubrication per the factory specifications section; Komatsu shop literature for this chassis does not show it as an independently drained/filled compartment separate from the power train case in the data reviewed. | Komatsu Powertrain & Micro Clutch Oil, same grade as the power train case (SAE 10W cold / SAE 30 normal), unless the periodic maintenance chart calls out a dedicated final-drive fill point with Komatsu Gear Lubricant (SAE 80W-90 or 85W-140, API GL-5 class) - confirm which applies before servicing. |
| Hydraulic system and tank | No standalone hydraulic tank capacity is published; the hydraulic tank is integrated into the control valve assembly, so there is no separate reservoir on this chassis. | Komatsu hydraulic oil (46AW hydraulic fluid spec), ISO VG 46. Equivalent cross-reference: Chevron Rando HD or Delo TorqForce hydraulic-oil equivalents in ISO 46 grade. A Komatsu biodegradable hydraulic fluid option also exists under the same specification for environmentally sensitive sites. |
| Grease (spec only) | Not applicable (grease points serviced per periodic lubrication schedule, not a fill volume). | Komatsu Lithium-base Grease EP2 (G2-LI), NLGI 2, general-purpose chassis grease for normal temperatures. Equivalent cross-reference: Chevron/Delo Grease ESI EP, NLGI 2. Use a lower-consistency (arctic-grade) NLGI 1 or 0.5 lithium grease in sustained sub-freezing climates per standard Komatsu cold-weather guidance. |
Capacities are refill values from factory literature — always fill to the dipstick/sight gauge, not the number.
Komatsu 6D125-1AB(S/N 10276-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 6D125-1AB(S/N 10276-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
Since the 6D125-1AB lacks onboard diagnostics, prevention relies on scheduled oil and coolant sampling plus disciplined gauge watching. Track engine oil condition for early wear metal in the splash-lubricated steering-clutch case and final drives, as neither system has its own filtration to mask contamination. Monitor the air cleaner dust/clog indicator closely to prevent unfiltered air ingress. Verify water-in-fuel caution lamp function at startup to protect the mechanical injection pump from water damage. Use Komatsu Genuine Diesel Engine Oil, SAE 15W-40 for normal temperatures, or SAE 10W-30 for colder climates. Maintain coolant levels with Komatsu Super Coolant mixed 50/50 with water.
Corrective & Common Repairs
Common repairs for the 6D125-1AB focus on the mechanical fuel system and splash-lubricated drivetrain. Replace the fuel filter cartridge every 500 hours to protect the injection pump and nozzles. Inspect the fan belt tension and condition every 250 hours to prevent overheating. Check battery electrolyte levels and clean terminals to ensure reliable starting. Address leaks at the engine, steering-clutch case, and final drives during daily walk-arounds. If the engine loses compression or shows excessive blow-by, inspect the cylinder liners and piston rings, as overhaul work centers on cylinder liner and piston wear.
Overhaul & Rebuild Points
Overhaul work on the 6D125-1AB centers on cylinder liner and piston wear, injection pump and nozzle recalibration, and steering-clutch relining once linings reach the wear limit. Final drive gear sets and cases warrant inspection at major rebuild given their splash-lubrication and lack of filtration. Replace hydraulic hoses and coolant at the 2,000-hour mark to prevent system degradation. Inspect the exhaust system and electrical wiring for wear and tear at 1,000 hours. Perform a full check of the swing machinery and travel system to ensure structural integrity. Use Komatsu Powertrain & Micro Clutch Oil, SAE 10W in cold conditions or SAE 30 in normal conditions, for the shared splash-lubricated sump.
Seasonal & Environment Servicing
In cold weather, switch to Komatsu Genuine Diesel Engine Oil, SAE 10W-30, and use a lighter No. 1-D-equivalent fuel to prevent gelling. Use a lower-consistency (arctic-grade) NLGI 1 or 0.5 lithium grease in sustained sub-freezing climates for chassis points. For extreme cold, increase the Komatsu Super Coolant concentrate ratio beyond the standard 50/50 mix per the freeze-protection chart. In dusty environments, service the air cleaner element immediately when the dust/clog indicator flags. Keep the fuel tank topped up at the end of each shift to reduce condensation. Clean the fuel tank strainer regularly to ensure proper fuel flow in high-debris conditions.
6D125-1AB(S/N 10276-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| ND092220-0040 | Filter,Fuel | Fuel system service | Check fitment → |
| 09637-30161 | Plate? Instruction,Air Cleaner (Single Element) | Air intake service | Check fitment → |
| 600-181-2300 | Element Ass'Y,Outer | Scheduled service item | Check fitment → |
| 6115-81-7602 | Element Ass'Y | Scheduled service item | Check fitment → |
| 600-181-2500 | Element Ass'Y,Outer | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
6D125-1AB(S/N 10276-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, or corroded connector at the pin connector | Replace the speed sensor and verify voltage at the pin connector |
| CA451 | Common rail pressure sensor feedback value too high | Malfunctioning rail pressure sensor or actual overpressure condition in the fuel system | Diagnose the fuel rail pressure sensor and check pump lines |
| CA122 | Intake air pressure sensor feedback voltage too high | Faulty intake pressure sensor or wiring issue | Verify the intake pressure sensor and wiring integrity |
| CA123 | Intake air pressure sensor feedback voltage too low | Sensor short circuit or airflow restriction in the intake system | Check for a sensor short or inspect for airflow restrictions |
| CA441 | Battery voltage too low | Weak battery, failing alternator, or voltage regulator issue | Replace the alternator or battery and check the voltage regulator |
| CA442 | Battery voltage too high | Faulty voltage regulator or alternator overcharging | Replace the alternator or battery and check the voltage regulator |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration and review engine load cycles |
| AA10NX | Air cleaner clogging | Dirty or blocked air filter element | Replace the air filter element |
| B@BCNS | Engine coolant overheating | Low coolant level, blocked radiator fins, or failed fan belt | Check radiator fins, fan belt, and coolant level |
| CA111 | Internal engine controller fault | Critical failure within the Electronic Control Module (ECM) | Replace or reprogram the ECM |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
6D125-1AB(S/N 10276-UP) attachments & work tools
Motor Grader Attachments
The 6D125-1AB engine powers the Komatsu GD663A-2 motor grader, which utilizes standard grading blades and ripper configurations typical for this machine class. Factory guarding options and blade widths are defined by the GD663A-2 chassis specifications rather than the engine serial number.
Crawler Dozer Attachments
This engine family is associated with the D50A-17 crawler dozer and its D50P-17/D50PL-17 low-ground-pressure variants, which use standard dozer blades and ripper attachments. The operating weight for the standard A-suffix machine is approximately 12,240 kg (27,000 lb), placing it in the small-to-medium crawler dozer class.
Wheel Loader Attachments
The 6D125-1 series is used in the WA1200-3 and WA380-1/WA380-3 wheel loaders, which employ standard loader buckets and quick-coupler systems for this size class. Hydraulic kit arrangements for these loaders require auxiliary hydraulic lines to operate high-flow attachments.
Excavator Attachments
The engine is fitted to the PC400-5 excavator, which uses standard boom/stick configurations and buckets for its class. The PC400-5 series utilizes specific oil cooler elements and hydraulic arrangements distinct from later S6D125E-2 models.
All 6D125-1AB(S/N 10276-UP) assemblies by section
Every catalogued assembly group for the Komatsu 6D125-1AB(S/N 10276-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Accessory
Komatsu : 6d125-1ab(S/N 10276-Up) : Accessory : Air Compressor (Inner Parts)(#10276-40172)
| 61***10 | Air Compressor Ass'Y,(See Fig.0711) | 1 |
| DK***20 | Connecting Rod A | 1 |
| DK***00 | Spring,Delivery Valve | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Accessory : Air Compressor (Inner Parts)(#40173-)
| 61***11 | Air Compressor Ass'Y,(See Fig.0711a) | 1 |
| DK***20 | Connecting Rod A | 1 |
| DK***90 | Washer,Air Compressor | 2 |
Komatsu : 6d125-1ab(S/N 10276-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 |
Cooling System
Komatsu : 6d125-1ab(S/N 10276-Up) : Cooling System : Cooling Fan And Mounting
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 22 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***95 | Bolt,(For 2nd Travel Speed) (Op) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cooling System : Cooling Fan And Mounting (Suction Fan)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 16 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***50 | Bolt,(With Service Valve R.H.) | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cooling System : Corrosion Resistor And Piping(#24453-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 5 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
| 02***25 | Bolt,(Cold Weather Spec.) | 4 |
Komatsu : 6d125-1ab(S/N 10276-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) | 5 |
Cylinder Block
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Camshaft(#20091-)
| 01***22 | Bolt | 2 |
| 04***25 | Key, Plain Woodruff | 1 |
| 04***12 | Ring,Snap (For Ripper) | 12 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Crankshaft(#24453-)
| 01***25 | Bolt,(Without Rops Guard? Canopy) | 6 |
| 01***30 | Screw | 1 |
| 01***35 | Screw | 5 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Cylinder Block Cover(#24453-)
| 07***20 | Clamp, Spring Hose | 1 |
| 07***63 | Hose | 1 |
| 61***90 | O-Ring,Breather | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Cylinder Block(#24453-)
| 01***12 | Bolt,(Without Air Compressor Type) | 1 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 14 |
| 04***14 | Pin, Dowel | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Flywheel And Flywheel Housing(#20091-)
| 01***45 | Bolt,(For Suction? Reversible Fan) | 1 |
| 01***50 | Bolt, Radiator To Frame | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Front Cover And Front Support(#24453-)
| 01***25 | Bolt,(Without Auto Priming System) | 6 |
| 01***60 | Screw | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Oil Pan(#24453-)
| 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 : 6d125-1ab(S/N 10276-Up) : Cylinder Block : Piston And Connecting Rod(#20091-)
| 02***13 | Pin, Dowel | 2 |
| 04***18 | Ring, Snap | 12 |
| 61***32 | Piston Ring Ass'Y | 6 |
Cylinder Head
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Air Cleaner And Mounting (Highaltitude Spec.)(#24453-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 8 |
| 01***08 | Nut,(For Straight Tilt Dozer) (D65p) | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Air Cleaner And Mounting(#24453-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***08 | Nut,(For Straight Tilt Dozer) (D65p) | 6 |
| 01***16 | Washer,Radio Controlled Slag Handling | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Air Intake Manifold And Connection
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 14 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 5 |
| 01***60 | Bolt, Mount Tube To Switch Pump | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Air Intake Manifold And Connection (High Altitude Spec.)
| 01***10 | Bolt,(With Auto Emergency Steering) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 14 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 5 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Cylinder Head(#10276-24780)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Cylinder Head(#24781-)
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Exhaust Manifold And Mounting
| 01***80 | Bolt, Mount Strainer Flange | 18 |
| 07***08 | Plug,(Without Auto Priming System) | 1 |
| 61***20 | Spacer,(For Shipping) | 18 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Exhaust Manifold And Turbocharger (High Altitude Spec.)
| 01***80 | Bolt, Mount Strainer Flange | 2 |
| 01***00 | Bolt (M10-1.50x100) | 16 |
| 01***45 | Screw | 4 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Muffler And Mounting
| 01***25 | Bolt,(Sandy? Dusty Terrain Spec.) | 4 |
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***30 | Bolt, Mount Pump | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Muffler And Mounting (High Altitude Spec.)(#24453-)
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***55 | Bolt,(For Suction? Reversible Fan) | 4 |
| 01***30 | Bolt,Radio Controlled Slag Handling | 4 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Rocker Arm And Housing
| 01***08 | Nut,R.H. Thread | 12 |
| 01***16 | Washer,Radio Controlled Slag Handling | 40 |
| 61***10 | Housing, Rocker Lever | 6 |
Komatsu : 6d125-1ab(S/N 10276-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 : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Turbocharger (High Altitude Spec.) (Inner Parts)
| 61***00 | Turbocharger Ass'Y,(Tv7705) | 1 |
| GA***85 | V-Band Ass'Y | 1 |
| GA***85 | V-Band | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Cylinder Head : Water Manifold And Thermostat(#24453-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***12 | Washer, Gasket,(Without Thermo Sensor) (K1) | 1 |
| 07***08 | Plug,(Without Auto Priming System) | 1 |
Electrical System
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator (25a) (Inner Parts)(#24453-)
| 60***40 | Alternator A. (25a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator (35a) (Inner Parts)(#20091-)
| 60***60 | Alternator A. (35a),(With Non Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator (35a) (With Hardening Pulley) (Inner Parts)
| 60***20 | Alternator A. (35a),(With Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator (50a) (Inner Parts)
| 60***30 | Alternator A. (50a),(With Non Hardening Pulley) | 1 |
| SD***X0 | Pulley,Non Hardening | 1 |
| SD***X0 | Coil Assembly | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator (50a) (With Hardening Pulley) (Inner Parts)
| 60***60 | Alternator A. (50a),(With Hardening Pulley) | 1 |
| SD***X0 | Coil Assembly | 1 |
| SD***X0 | Washer | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator And Mounting (25a)(#24453-)
| 01***90 | Bolt, Fan Mounting | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator And Mounting (35a) (With Hardening Pulley)
| 01***90 | Bolt, Fan Mounting | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator And Mounting (35a)(#20091-)
| 01***90 | Bolt, Fan Mounting | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Alternator And Mounting (50a)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***30 | Bolt | 1 |
| 01***23 | Washer,(A)(W/After Cooler)(S6d155-4b) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Heater Switch
| 60***70 | Switch,Air Intake Heater | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Starting Motor (11kw) (Inner Parts)(#24453-)
| 60***31 | Starting Motor Ass'Y,(11kw) | 1 |
| SD***00 | Metal | 1 |
| SD***60 | O-Ring | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Electrical System : Starting Motor And Mounting (7.5kw? 11kw)(#24453-)
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***40 | Bolt,(With Center Guard) | 3 |
| 60***20 | Clip,(Large Capacity Type) | 1 |
Engine Kit
Komatsu : 6d125-1ab(S/N 10276-Up) : Engine Kit : Air Compressor Gasket Kit(#24453-)
| 07***25 | O-Ring,Injection Pump Mounting | 1 |
| 07***12 | Gasket,(Without Air Compressor Type) (K2) | 4 |
| 07***12 | Gasket,(Without Air Compressor Type) (K1) | 8 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Engine Kit : Cylinder Block Gasket Kit(#24453-)
| 07***20 | O-Ring,Relief Valve | 1 |
| 07***30 | Ring, Seal - Between Sections | 1 |
| 07***20 | O-Ring,Lubricating Oil Piping | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Engine Kit : Cylinder Head Gasket Kit(#24453-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***34 | O-Ring,(F2320-62a0 -7 ) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Engine Kit : Water Pump Gasket Kit
| 07***15 | O-Ring,(For Low Speed) (D40pf) | 1 |
| 61***61 | Gasket (K2?K6) | 1 |
| 61***10 | Seal,Water (K6) | 1 |
Fuel System
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Filter And Piping(#24453-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 2 |
| 01***16 | Washer,(With Water Separator) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Coupling) (High Altitude Spec.) (Inner Parts)
| ND***50 | Bolt | 1 |
| ND***40 | Bolt | 2 |
| ND***61 | Bolt | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Coupling) (Inner Parts)(#24453-)
| ND***30 | Block,Coupling | 1 |
| ND***50 | Bolt | 1 |
| ND***50 | Coupling,Cross | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Feed Pump) (High Altitude Spec.) (Inner Parts)
| ND***61 | Feed Pump Ass'Y | 1 |
| ND***40 | Washer? 1mm,Plate | 1 |
| ND***70 | Washer,Union | 4 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Feed Pump) (Inner Parts)(#24453-)
| ND***40 | Washer? 1mm,Plate | 1 |
| ND***70 | Washer,Union | 4 |
| ND***10 | Spring, Check Valve | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2) (High Altitude Spec.) (Inner Parts)
| ND***40 | Plate,Thrust | 1 |
| ND***10 | Governor Ass'Y | 1 |
| ND***40 | Plug,Screw | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2) (Inner Parts)(#24453-)
| ND***40 | Plate,Thrust | 1 |
| ND***40 | Plug,Screw | 1 |
| ND***80 | Gasket | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2) (High Altitude Spec.) (Inner Parts)
| ND***80 | Pin,Stop | 1 |
| ND***20 | Washer? 1.0mm,Cover Plate | 2 |
| ND***30 | Lever,Adjusting | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2) (Inner Parts)(#24453-)
| ND***20 | Washer? 1.0mm,Cover Plate | 2 |
| ND***30 | Lever,Adjusting | 1 |
| ND***70 | Packing,Rubber Plate | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2) (High Altitude Spec.) (Inner Parts)
| 61***10 | Injection Pump A | 1 |
| 61***11 | Injection Pump Ass'Y | 1 |
| ND***50 | Ring,Adjust | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2) (Inner Parts)(#24453-)
| 61***10 | Injection Pump A | 1 |
| ND***50 | Ring,Adjust | 1 |
| ND***80 | O-Ring | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2) (High Altitude Spec.) (Inner Parts)
| ND***70 | O-Ring | 6 |
| ND***71 | Rack,Control | 1 |
| ND***50 | Seat,Spring? Lower | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2) (Inner Parts)(#24453-)
| ND***30 | Sleeve,Control | 6 |
| ND***20 | Shim? 0.3mm | 0 |
| ND***70 | O-Ring | 6 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump And Piping (High Altitude Spec.)(#24453-)
| 01***75 | Bolt,(See Fig.0142) | 4 |
| 01***30 | Bolt | 4 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Injection Pump And Piping(#24453-)
| 01***75 | Bolt,(See Fig.0142) | 4 |
| 01***30 | Bolt | 4 |
| 01***45 | Bolt,(For Power Tilt Mech Angle) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Fuel Nozzle And Spill Pipe
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Fuel System : Water Separator And Mounting
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
Lubricating Oil System
Komatsu : 6d125-1ab(S/N 10276-Up) : Lubricating Oil System : Lubricating Oil Cooler(#24453-)
| 01***25 | Bolt,Without Revolution Sensor | 2 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 13 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Lubricating Oil System : Lubricating Oil Filter And Mounting(#24453-)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 4 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Lubricating Oil System : Lubricating Oil Piping(#20091-)
| 01***60 | Bolt, Mount Tube To Switch Pump | 2 |
| 01***16 | Washer,Radio Controlled Slag Handling | 7 |
| 04***12 | Ring, Snap | 1 |
Komatsu : 6d125-1ab(S/N 10276-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe(#24453-)
| 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 : 6d125-1ab(S/N 10276-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping (High Altitude Spec.)
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 5 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
6D125-1AB(S/N 10276-UP) serial number reference
The engine data plate is located on the left side of the engine block, typically on or near the valve cover. If the tag is missing or unreadable, the serial number is also stamped directly into the block casting. Read the alphanumeric code stamped on the plate or block to identify the engine model and serial range.
| Prefix | Identifies | Notes |
|---|---|---|
| No alpha prefix | 6D125-1AB | The 6D125-1AB engine serial range (10276-UP) uses a sequential numeric serial starting at 10276. No alpha prefix precedes the running serial for this engine family in available documentation; the letter/number suffix (AB) identifies the build/fitment configuration, while the digits that follow are the sequential production serial. Verify with your dealer if your specific unit has an undocumented prefix. |
Frequently asked questions
What is the engine model for the Komatsu 6D125-1AB (S/N 10276-UP)?
The 6D125-1AB (S/N 10276-UP) is a mechanical, naturally aspirated inline-six diesel engine from the 6D125-1 family, powering the Komatsu D50A-17 crawler dozer and its D50P-17/D50PL-17 LGP swamp variants.
What is the operating weight range for machines using this engine?
Operating weight ranges from 10,850 kg to 17,550 kg (23,920 lb to 38,690 lb), varying by dozer model and configuration (standard, LGP, swamp).
What replaced the D50A-17 series?
The D50A-17 series was followed by the D50A-18, which carried the same 6D125-1 base engine at a higher rating.
What 6D125-1AB(S/N 10276-UP) owners discuss
What is the power output and configuration of the 6D125-1AB(S/N 10276-UP) engine?
The 6D125-1AB(S/N 10276-UP) is a naturally aspirated, inline-six diesel engine. It is part of the 6D125-1 family, which is a mechanical, pre-electronic design. Gross power for this engine family ranges from 92 kW to 123 kW (124 hp to 165 hp) at 1750-1900 rpm, depending on the specific host machine configuration. The engine features a 125 mm bore and 150 mm stroke, with a total displacement of 11.04 L (673.8 cu in). It predates modern emissions-tier certification and relies on mechanical fuel injection rather than electronic controls, making it serviceable without diagnostic tooling.
What are the typical undercarriage and wear patterns for machines powered by this engine series?
Machines equipped with this engine series, such as the D50A-17 dozer, typically exhibit wear on the sprockets, track links, and rollers consistent with their age and duty cycle. Owners and mechanics emphasize checking the undercarriage wear percentage as a primary maintenance indicator. Additionally, because the powertrain uses a splash-lubricated system without dedicated filtration for the steering clutch and final drives, contamination from wear metals is a known issue. The steering clutch linings and brake bands require periodic relining once they reach their wear limits. Final drive gear sets and cases also warrant inspection during major rebuilds due to the lack of filtration in the splash-lubrication system.
What are the common engine quirks or maintenance needs for the 6D125-1 series?
The 6D125-1 series is known for its robust, mechanical design, which allows for field repairs without complex diagnostics. However, common maintenance needs include monitoring oil pressure, coolant temperature, and torque-converter oil temperature via gauges and caution lamps, as there are no onboard fault codes. Overhaul work typically centers on cylinder liner and piston wear, as well as recalibrating the injection pump and nozzles. Owners also note the importance of checking the turbocharger compressor wheel for 'sandblasting' or dust damage, which indicates excessive air filtration issues. The engine uses hardened liners matched to the piston rings, and OEM parts are generally reliable for these components.
What electrical or sensor issues are associated with this engine?
The 6D125-1AB(S/N 10276-UP) engine is a mechanical, pre-electronic unit and does not have onboard diagnostics or electronic sensors for engine management. Monitoring relies entirely on analog gauges and caution lamps for oil pressure, coolant temperature, and water-in-fuel status. The absence of electronic fault codes means that prevention and diagnosis depend on scheduled oil and coolant sampling, disciplined gauge watching, and physical inspection of components like the starter motor and alternator mounting. There are no known specific electrical sensor failures because the engine lacks electronic engine control sensors.
What should be checked when buying a used machine with the 6D125-1AB(S/N 10276-UP) engine?
When purchasing a used machine with this engine, first confirm that the engine and machine serial numbers align with documented history, as mismatched running gear is a known risk on older Komatsu equipment. Beyond serial verification, inspect the undercarriage wear percentage on sprockets, links, and rollers. Test the steering clutch and brake operation in both directions under load. Check hydraulic pump output and look for blade/tilt cylinder drift. Inspect the coolant for an oil sheen and the oil for milkiness or a coolant smell. Perform compression or blow-by tests across all cylinders to assess engine health. Verify the condition of the turbocharger compressor wheel for dust damage.
What fluids and capacities are specified for this engine and its associated systems?
Engine crankcase oil capacity is not explicitly published for this exact serial range in accessible literature; verify with the shop manual or dealer. Recommended fluid is Komatsu Genuine Diesel Engine Oil, SAE 15W-40 for normal temperatures or SAE 10W-30 for cold climates. The cooling system uses Komatsu Super Coolant mixed 50/50 with water. The powertrain case (transmission, bevel gear shaft, steering clutch/brake) uses Komatsu Powertrain & Micro Clutch Oil, SAE 10W in cold conditions or SAE 30 in normal conditions. Final drives may use Komatsu Gear Lubricant (SAE 80W-90 or 85W-140, API GL-5) if specified by the maintenance chart. Hydraulic system fluid is Komatsu hydraulic oil (46AW, ISO VG 46).
What is the safety-critical fix for the steering clutch and brake system?
The steering clutch linings and brake bands must be relined once they reach their wear limit to maintain safe machine operation. Failure to do so can result in loss of steering control. Have your dealer verify the lining thickness and brake band adjustment before operation.
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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