Komatsuengine(no series)

Komatsu 6D125-1AB-EW(S/N 10001-UP)

Maintenance schedule, common problems & OEM parts breakdown

Search live 6D125-1AB-EW(S/N 10001-UP) parts

The 6D125-1AB-EW (S/N 10001-UP) is a bare Komatsu 6D125-1 series engine block, not a complete machine: an 11.05-liter (674 cu in), naturally aspirated, mechanical direct-injection inline-six diesel with a 125 mm x 150 mm bore and stroke, a mechanical inline injection pump, and an integral all-speed governor. No ECM, no electronic sensors. Komatsu fitted this build, one continuous production run starting at serial 10001, across a wide range of hosts: D50A-17, D50P-17, D50PL-17, D53A-17, D53P-17, D58E-1, and D70LE-12 crawler dozers, plus GD600R-3, GD605A-3, GD605A-5, GD605A-5S, GD623A-1, GD625A-1, GD655A-3, and GD663A-2 motor graders. Rated output is documented at 116 kW (155.6 hp) at 2,200 rpm as installed in grader service; output for dozer-host installations of this exact suffix is not separately published. Production runs through the 1980s and into the 1990s, following on from Komatsu's earlier 6D125 block used in dozer service since the mid-1970s.

Within the wider 6D125-1 family, suffix codes like AB, N, M, AF, and EW mark different governor, accessory, and fitment calibrations built for specific host machines rather than separate engine generations; treat each suffix as its own catalog entry, not an interchangeable one. As emissions rules tightened through the 1990s and 2000s, these dozer and grader platforms moved on to the direct-injection 6D125E-2 block and later to the electronically controlled, common-rail SAA6D125E family, with some grader lines eventually shifting to smaller-displacement Tier-compliant engines entirely. That succession is exactly why this engine still turns up in the used and rebuild market: it predates any ECM, sensor network, or aftertreatment, so it stays simple to diagnose by mechanical means and comparatively cheap to rebuild for owners keeping older D-series dozers and GD-series graders running past their original service life.

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-EW(S/N 10001-UP) specifications

Engine

Engine model6D125-1AB-EW, part of the 6D125-1 series — inline-6, 4-stroke, water-cooled diesel, naturally aspirated
Cylinders6, in-line, direct injection
Displacement11.05 L (674 cu in)
Bore x stroke125 mm x 150 mm
Rated power116 kW (155.6 hp) at 2,200 rpm, flywheel rating as installed — gross and net figures not separately published for this configuration
Emissions tierNot published for this serial range; this configuration pre-dates EPA/EU nonroad emissions-tier certification requirements — confirm current regional compliance status with your dealer

Weights

Operating weight (as installed, standard grader configuration)varies by configuration/source: approximately 13,700-14,190 kg (30,200-31,280 lb)
Shipping weightnot published in available spec sheets — verify with dealer

Dimensions (motor grader example — dozer-host dimensions differ)

Overall transport length8.50 m (27.9 ft)
Width over tires2.41 m (7.9 ft)
Height to cab top3.32 m (10.9 ft)
Wheelbase6.00 m (19.7 ft)
Rear ground clearance0.36 m (1.17 ft)
Moldboard (blade) width3.69 m (12.1 ft), class-relevant implement dimension

Performance (motor grader example — dozer-host figures differ)

Travel speed, forward (max)up to 45 km/h (28 mph)
Travel speed, reverse (max)up to 54.9 km/h (34.1 mph)
Turning radius6.71 m (22 ft)

Service capacities (summary)

Fuel tank (motor grader example)285 L (75.3 gal)
Hydraulic systemnot published in available spec sheets — verify with dealer or shop manual
Engine oil (Komatsu EO)not published in available spec sheets — verify with dealer or shop manual
Cooling systemnot published in available spec sheets — verify with dealer or shop manual

Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.

6D125-1AB-EW(S/N 10001-UP) fluids & capacities

SystemCapacityRecommended fluid
Engine crankcase (with oil filter)Not published for this exact catalog entry. This mechanical 6D125-1 family typically refills in roughly the mid-20 liter range (about 6-7 US gal) with filter change, but confirm the exact figure against the host machine's periodic maintenance chart before servicing.Komatsu Genuine diesel engine oil, SAE 15W-40 for normal ambient temperatures (current Komatsu counter spec: 15W-40 low-ash CK-4 diesel engine oil); SAE 10W-30 is the Komatsu-approved grade for colder climates. An equivalent-grade diesel engine oil from another major brand meeting the same API/JASO classification is acceptable.
Cooling system (engine coolant)No fixed engine-only figure confirmed for this catalog entry. Combined engine-plus-radiator capacity on the dozer and motor-grader chassis built around this engine family runs roughly 35-50 liters (9-13 US gal) depending on the host machine's radiator package, so treat this as varying by configuration and verify against the host machine's maintenance chart.Komatsu Supercoolant, a pre-mixed, all-season, anti-corrosion antifreeze concentrate. Hold the mix at the concentration specified for the expected ambient range; do not dilute below the minimum freeze-protection ratio in cold climates.
Fuel systemNo engine-level tank. Tank size is set by the host chassis and typically runs from roughly 150 liters up to 300-plus liters (40 to 80-plus US gal) across the dozer and motor-grader models that used this engine family.Automotive-grade No. 2-D diesel fuel (ASTM D975-equivalent) for normal operating temperatures; switch to a lighter No. 1-D winter blend, or a No.1/No.2 blend, in cold weather to prevent fuel waxing.
Grease (accessory-drive and mounting-point fittings)Spec only, no fixed refill quantity; apply per the grease-point schedule in the host machine's maintenance chart.Komatsu Genuine multipurpose grease, lithium-based EP NLGI #2 (Komatsu G2-LI equivalent), for accessory-drive bearings and any grease-fitted mounting points on the engine.
Transmission, hydraulic system, final drives, axlesNot applicable to this catalog entry.This entry documents a bare Komatsu diesel engine block used across several different dozer and motor-grader chassis, each with its own transmission, hydraulic, final-drive, and axle systems. Those capacities and fluid specs are chassis-specific — check the operation & maintenance manual for the exact host machine.

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

Komatsu 6D125-1AB-EW(S/N 10001-UP) maintenance schedule

Service intervalTasks
Every 50 h
  • Check engine oil level before starting and top off as needed.
  • Check coolant level and inspect hoses and the corrosion-resistor canister for external leaks.
  • Drain water and sediment from the fuel tank sump.
  • Listen for a hunting or surging idle and inspect governor linkage free play if noted.
  • Check the air cleaner service indicator and service the element if flagged.
  • Check fan belt tension and condition.
Every 250 h
  • Change engine oil and replace the oil filter.
  • Replace or service the coolant corrosion-resistor spin-on element.
  • Inspect battery condition, electrolyte level, and terminal connections, and test the glow-plug bank.
  • Grease accessory-drive and mounting-point fittings per the lubrication chart.
  • Clean or replace the primary fuel filter element.
Every 500 h
  • Replace fuel filter elements.
  • Inspect the radiator core and hoses for cracking, chafing, or fouling.
  • Check engine mounting bolts and cooling-shroud fasteners for tightness.
  • Drain and inspect the fuel tank water separator.
  • Check charging-circuit wiring and connections for corrosion or looseness.
Every 1,000 h
  • Check and adjust valve clearance to factory specification; it is hand-set on this engine, not self-adjusting.
  • Service or replace the air cleaner element.
  • Inspect and clean the crankcase breather and note any startup vapor or pressure.
  • Check engine mount rubber for cracking or softening.
  • Pull the oil filler cap at idle and check for excess crankcase pressure as an early blow-by flag.
Every 2,000 h
  • Replace engine coolant and confirm corrosion-inhibitor concentration.
  • Check injection pump timing and governor linkage adjustment; have a dealer verify on a test bench if drift is suspected.
  • Pop-test fuel injectors for spray pattern and opening pressure and recondition as needed.
  • Inspect the fuel tank interior and clean if contaminated.
  • Run a compression check and note any cylinder-to-cylinder variation.
Every 4,000 h
  • Overhaul or exchange the injection pump and injectors as a matched, calibrated set.
  • Replace the water pump and thermostat.
  • Check for coolant-in-oil contamination, a milky or aerated look on the dipstick, and address head gasket or liner-seal wear if found.
  • Perform a top-end inspection of valve seats, guides, and injector sleeves.
  • Flush and pressure-test the cooling system.
Every 8,000 h
  • Plan an inframe overhaul: replace pistons, rings, and liners as a matched, correctly specified set rather than mixed combinations.
  • Verify piston-cooling oiler jets are clear before reassembly; a plugged jet is a known cause of early piston failure.
  • Recondition or replace main and rod bearings to factory clearance, following the correct torque sequence on reassembly.
  • Recheck and recalibrate the full fuel system as a matched set.
  • Reassess engine mounts, drive couplings, and cooling components for full-life replacement.

Servicing the 6D125-1AB-EW(S/N 10001-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

No ECM means there are no fault codes here, so scheduled oil sampling is the main early-warning tool on this mechanical injection block. Watch for a milky, aerated look on the dipstick or filler cap, a sign of coolant working into the crankcase past a head gasket or liner seal. Check the crankcase breather for vapor or pressure on startup, an early flag for ring-and-liner blow-by. Track injection pump timing and governor linkage condition at scheduled intervals rather than waiting for a hunting idle to show up.

Corrective & Common Repairs

Most reported fixes trace to the mechanical fuel system before the injection pump itself: a low-pressure feed-line air leak, a dirty primary filter, or a sticking throttle/governor linkage, check those first. Hunting or surging idle usually points to worn governor linkage bushings or fatigued flyweight-governor springs, not the pump. Because this block crosses D50 through D70-class dozers and GD600 through GD663-class graders, mounts, fan drives, and cooling shrouds differ by host, so confirm the exact chassis before ordering hardware. Corroded charging-circuit wiring and connections are the most common electrical complaint.

Overhaul & Rebuild Points

Ring and liner wear driving oil consumption is the most reported long-term issue, and rebuild shops flag matched-set ring-and-liner selection as critical since mismatched combinations have failed within months. Piston-cooling oiler jets are a known weak point; a single plugged jet can take a piston out fast, so flush and verify oil galleries during teardown. Follow the factory torque sequence on cylinder head and main/rod bearing caps exactly, skipped or incorrect sequence is called out repeatedly as a root cause of head-gasket leaks and premature bearing wear.

Seasonal & Environment Servicing

Cold-start reliability leans on glow plugs or an ether aid, so a partial glow-plug-bank failure is a common cause of hard cold starts; test the bank rather than assuming the batteries are at fault. Drain fuel-tank sediment and water more often in humid or wet-season work, especially on graders in wet cut sections. Confirm coolant corrosion-inhibitor concentration each season; wet cylinder liners on this block are sensitive to cavitation erosion if the inhibitor depletes. Watch for radiator-core fouling on dozer hosts working dry, dusty sites.

6D125-1AB-EW(S/N 10001-UP) common service parts

Part numberPart
ND092220-0040Filter,FuelCheck fitment →
09019-08035Wrench,Filter (For Add. Fuel Filter)Check fitment →
09637-02161Plate? Instruction,Air Cleaner (Double Element)Check fitment →
09637-90263Plate? Instruction,Air Cleaner Element MainteCheck fitment →
09637-30161Plate? Instruction,Air Cleaner (Single Element)Check fitment →

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

6D125-1AB-EW(S/N 10001-UP) attachments & work tools

Identity / Scope

This is a bare Komatsu 6D125-1 series engine block, not a complete machine, so no ground-engaging work tools, buckets, or quick-couplers apply. Parts catalogs cross-reference this arrangement most consistently to a late-1980s wheel loader engine option and, less consistently, to several motor-grader engine options that share the base 6D125 block; confirm the exact host chassis against your own unit's serial plate before ordering engine-mount hardware.

Flywheel & PTO Housing

Uses an SAE-pattern flywheel with a bolt-on flywheel housing that mates to the host machine's torque converter or drivetrain input. Housing pattern and size are set by the chassis the engine is installed in, not a field-selectable option on the engine itself.

Cooling Fan & Drive

Belt-driven cooling fan on a dedicated fan pulley, sized and positioned to match the radiator package of the host machine (wheel loader and motor grader cooling packages differ). Fan diameter and pulley ratio are matched at the factory and are not a customer-selectable option.

Fuel Injection & Governor

Mechanical (Denso-type) in-line injection pump with an integral all-speed mechanical governor, typical of mobile off-highway duty rather than a fixed constant-speed genset governor. Turbocharger-related piping is documented for this arrangement, so treat it as a turbocharged build even though the base name lacks an "S" prefix; verify against the engine tag.

Charging & Starting

24V DC electrical system with a belt-driven alternator and a gear-reduction starter motor. Output ratings (commonly in the 30-40A alternator and roughly 11kW starter range across this engine family) vary by configuration/series and host electrical load, so confirm against the engine nameplate rather than assuming one figure.

High-Altitude Arrangement

A factory high-altitude kit is documented for this engine: turbocharger oil-piping with a safety cover paired with a matching high-altitude-spec air-cleaner element, intended for sustained operation at elevation where standard aspiration would run lean or over-boosted.

Coolant Corrosion Resistor

An inline corrosion-resistor (coolant conditioner) canister is fitted to protect the wet-sleeve cylinder liners from cavitation erosion. It is a factory-standard accessory on this engine family, serviced as a spin-on element rather than an optional add-on.

All 6D125-1AB-EW(S/N 10001-UP) assemblies by section

Every catalogued assembly group for the Komatsu 6D125-1AB-EW(S/N 10001-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Engine
Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Cleaner (High Altitude Spec.)(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)8
01***40Bolt (Op)2
01***08Nut,(For Straight Tilt Dozer) (D65p)6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Cleaner (With Screen Cap)(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***40Bolt (Op)1
01***08Nut,(For Straight Tilt Dozer) (D65p)6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Compressor (Inner Parts)(#47990-)
61***11Air Compressor Ass'Y,(See Fig.0711a)1
61***12Air Compressor Ass'Y,(See Fig.0711a)1
DK***20Connecting Rod A1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Compressor Gasket Kit(#47990-)
07***25O-Ring,Injection Pump Mounting1
07***25O-Ring (K2?K8)1
07***12Gasket,(Without Air Compressor Type) (K2)4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Compressor Mounting(#47990-)
01***40Bolt4
01***14Nut (Itl)1
01***16Washer,Radio Controlled Slag Handling4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Intake (High Altitude Spec.)(#47990-)
01***30Bolt,(With Body Positioner)16
01***55Bolt,(See Service News)5
01***10Bolt,(With Joy Stick Steering)8
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Air Intake(#47990-)
01***30Bolt,(With Body Positioner)16
01***55Bolt,(See Service News)6
01***10Bolt,(With Joy Stick Steering)8
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Alternator (35a) (Inner Parts)(#47990-)
60***60Alternator A. (35a),(With Non Hardening Pulley)1
KD***57Bearing,Ball? Front1
KD***80Collar1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Alternator (50a) (Inner Parts)(#47990-)
60***30Alternator A. (50a),(With Non Hardening Pulley)1
SD***X0Pulley,Non Hardening1
SD***X0Coil Assembly1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Alternator Mounting (35a)(#47990-)
01***90Bolt, Fan Mounting1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Alternator Mounting (50a)(#47990-)
01***30Bolt,(With Body Positioner)1
01***30Bolt1
01***23Washer,(A)(W/After Cooler)(S6d155-4b)2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Camfollower Cover(#47990-)
07***20Clamp, Spring Hose1
07***63Hose1
61***90O-Ring,Breather1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Camshaft(#47990-)
01***22Capscrew2
04***25Key, Plain Woodruff1
04***12Ring,Snap (For Ripper)12
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cooling Fan (Noise Supression Sepc. For Ec)(#47990-)
01***30Bolt,(With Body Positioner)6
01***50Bolt,(Spark Arrester Spec.)6
60***50Fan,Suction1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cooling Fan(#47990-)
01***30Bolt,(With Body Positioner)12
60***50Fan,(S6d105-1yy? S6d105-1zz)1
61***40Spacer1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Corrosion Resistor(#47990-)
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 : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Crank Pulley (Non Hardening Pulley)(#47990-)
01***30Screw1
01***35Screw5
04***28Pin, Dowel - Transmission Case, Pin-Dowel1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Crankshaft(#47990-63162)
61***10Bearing, Main (Standard)7
61***50Bearing, Thrust Assembly (Standard)1
61***10Bearing, Main (1.00mm Undersize)7
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Crankshaft(#63163-68350)
61***10Bearing, Main (Standard)7
61***50Bearing, Thrust Assembly (Standard)1
61***10Bearing, Main (1.00mm Undersize)7
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Crankshaft(#68351-)
61***10Bearing, Main (Standard)7
61***50Bearing, Thrust Assembly (Standard)1
61***10Bearing, Main (1.00mm Undersize)7
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Block (High Altitude Spec.)(#47990-)
01***12Bolt,(Without Air Compressor Type)2
01***45Washer,(For Travel Motor) (Not Show)14
04***14Pin, Dowel2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Block Gasket Kit(#47990-)
06***03Seal,Bearing (K2)2
07***20O-Ring,Relief Valve1
07***15O-Ring,(For Low Speed) (D40pf)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Block(#47990-)
01***12Bolt,(Without Air Compressor Type)2
01***45Washer,(For Travel Motor) (Not Show)14
04***14Pin, Dowel2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Head Gasket Kit(#47990-)
02***43O-Ring,Water Manifold6
07***60O-Ring,(For Pc750?800?1800) (A2610)1
07***65O-Ring,Cylinder Block6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Head(#47990-68353)
01***20Bolt (M10-1.75x120)6
04***20Pin,Dowel (Welded)2
61***30Sleeve,Holder1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Cylinder Head(#68354-)
01***20Bolt (M10-1.75x120)6
04***20Pin,Dowel (Welded)2
61***30Sleeve,Holder1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Damper(#47990-)
01***25Bolt,(Without Rops Guard? Canopy)6
61***00Damper Ass'Y1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Engine Mounting(#47990-)
61***20Support,Front1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Exhaust Manifold (High Altitude Spec.)(#47990-)
01***80Screw18
07***08Plug,(Without Auto Priming System)1
61***20Spacer,(For Shipping)18
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Exhaust Manifold(#47990-)
01***80Screw18
07***08Plug,(Without Auto Priming System)1
61***20Spacer,(For Shipping)18
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fan Drive(#47990-)
Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fan Pulley(#47990-)
01***30Bolt,(With Body Positioner)6
04***65V-Belt Set,(For 35a? 50a Alternator)1
61***10Pulley?Non Hardening1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Flywheel Housing(#47990-)
01***50Bolt, Radiator To Frame6
01***60Bolt, Hanger Bearing Mounting2
01***45Bolt,(With Water Separator Type)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Flywheel(#47990-)
01***45Screw6
01***45Washer,(For Travel Motor) (Not Show)6
61***41Gear, Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Front Cover(#47990-)
01***20Bolt,(For Mono Lever Steering)2
01***70Bolt - Bracket And Oil Inlet Tubemounting11
01***75Bolt (M10-1.50x75)6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Filter(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***16Washer,Radio Controlled Slag Handling2
07***12Gasket,Mechanical Pump Piping2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
ND***50Bolt1
ND***40Bolt2
ND***61Bolt6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***50Bolt1
ND***40Bolt2
ND***61Bolt6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (With Electrical Governor) (Inner Parts)(#47990-)
ND***30Block,Coupling1
ND***50Bolt1
ND***50Coupling,Cross1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Coupling) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***30Block,Coupling1
ND***50Bolt1
ND***50Coupling,Cross1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
ND***61Feed Pump Ass'Y1
ND***40Washer? 1mm,Plate1
ND***70Washer,Union4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***61Feed Pump Ass'Y1
ND***40Washer? 1mm,Plate1
ND***70Washer,Union4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (With Electrical Governor) (Inner Parts)(#47990-)
ND***40Washer? 1mm,Plate1
ND***70Washer,Union4
ND***10Spring, Check Valve2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Feed Pump) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***40Washer? 1mm,Plate1
ND***70Washer,Union4
ND***10Spring, Check Valve2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***40Plate,Thrust1
ND***40Plug,Screw1
ND***50Washer? 0.3mm0
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (With Electrical Governor) (Inner Parts)(#47990-)
ND***40Plate,Thrust1
ND***40Plug,Screw1
ND***80Gasket1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***40Plate,Thrust1
ND***40Plug,Screw1
ND***80Gasket1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
ND***20Washer? 1.0mm,Cover Plate2
ND***20Bushing,Bearing1
ND***70O-Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***80Pin,Stop1
ND***20Washer? 1.0mm,Cover Plate2
ND***30Lever,Adjusting1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (With Electrical Governor) (Inner Parts)(#47990-)
ND***20Washer? 1.0mm,Cover Plate2
ND***20Bushing,Bearing1
ND***70O-Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***20Washer? 1.0mm,Cover Plate2
ND***30Lever,Adjusting1
ND***90Seal,Oil1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (1/2) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
61***12Injection Pump Ass'Y1
ND***80Bearing,Center1
ND***50Ring,Adjust1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (1/2) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
61***11Injection Pump Ass'Y1
ND***50Ring,Adjust1
ND***80O-Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (1/2) (With Electrical Governor) (Inner Parts)(#47990-)
61***12Injection Pump Ass'Y1
ND***50Ring,Adjust1
ND***80O-Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (1/2) (With Mechanical Governor) (Inner Parts)(#47990-)
61***11Injection Pump Ass'Y1
ND***50Ring,Adjust1
ND***80O-Ring1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (2/2) (High Altitude Spec.) (With Electrical Governor) (Inner Parts)(#47990-)
ND***21Shim? 2.4mm0
ND***91Shim? 2.25mm,Element Holder0
ND***60Element,Pump6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (2/2) (High Altitude Spec.) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***70O-Ring6
ND***71Rack,Control1
ND***50Seat,Spring? Lower6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (2/2) (With Electrical Governor) (Inner Parts)(#47990-)
ND***30Sleeve,Control6
ND***20Shim? 0.3mm0
ND***70O-Ring6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump (Pump) (2/2) (With Mechanical Governor) (Inner Parts)(#47990-)
ND***30Sleeve,Control6
ND***20Shim? 0.3mm0
ND***70O-Ring6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Mounting (High Altitude Spec.) (With Electrical Governor)(#47990-)
01***75Capscrew4
61***10Washer,Spring4
(6***2)Injection Pump Ass'Y,(See Fig.A4010-B3c5)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Mounting (High Altitude Spec.) (With Mechanical Governor)(#47990-)
01***75Capscrew4
61***10Washer,Spring4
(6***1)Injection Pump Ass'Y,(See Fig.A4010-B3b8)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Mounting (With Electrical Governor)(#47990-)
01***75Capscrew4
61***10Washer,Spring4
(6***2)Injection Pump Ass'Y,(See Fig.A4010-B3c4)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Mounting (With Mechanical Governor)(#47990-)
01***75Capscrew4
61***10Washer,Spring4
(6***1)Injection Pump Ass'Y,(See Fig.A4010-B3b7)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Piping (High Altitude Spec.)(#47990-)
01***30Screw4
01***45Bolt,(With Water Separator Type)2
01***55Bolt,(See Service News)4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Injection Pump Piping(#47990-)
01***30Bolt4
01***45Bolt,(With Water Separator Type)2
01***55Bolt,(See Service News)4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Fuel Return(#47990-)
07***80Tube,Spill1
07***85Clip1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Head Cover(#47990-)
01***16Washer,Radio Controlled Slag Handling24
61***11Cover,Head? No.2?3?4?5?66
61***10Gasket,Cylinder Head Cover6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Heater Switch(#47990-)
08***19Cap, At Heater Relay Terminals1
60***70Switch,Air Intake Heater1
66***40Wire? 170mm1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Idler Gear(#47990-)
01***60Screw1
01***25Bolt,(For Canvas Canopy?Head Guard)6
01***30Bolt,(With Body Positioner)6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Injection Nozzle(#47990-)
01***45Bolt, Mount Divider Valve12
07***65O-Ring,Cylinder Block6
07***12Gasket,Mechanical Pump Piping2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Muffler (High Altitude Spec.)(#47990-)
01***30Bolt,(With Body Positioner)1
01***40Bolt (Op)4
01***55Screw4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Muffler(#47990-)
01***40Bolt (Op)4
01***45Bolt,(With Water Separator Type)1
01***25Bolt,Joint4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Arabic)(#47990-)
09***61Plate? Instruction,Air Cleaner (Double Element)1
09***63Plate? Instruction,(For Arabic)1
09***05Plate? Instruction,(Arabic)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Chinese)(#47990-)
09***61Plate? Instruction,(Chinese) (Not Shown)1
09***63Plate? Instruction,Air Cleaner Element Mainte1
09***06Plate? Instruction1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (English)(#47990-71494)
09***61Plate? Instruction,Air Cleaner (Single Element)1
09***63Plate? Instruction,Air Cleaner (Single Element)1
09***05Plate? Caution,(Not Shown)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (English)(#71495-)
09***08Plate? Instruction,Air Cleaner1
61***20Plate? Name,Engine (Limited Supply)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (French)(#47990-)
09***61Plate? Instruction,Air Cleaner (French)1
09***06Plate? Instruction,(French)1
09***07Plate? Instruction,Air Cleaner1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (German)(#47990-)
09***61Plate? Instruction,(German-English) (Not Shown)1
09***63Plate? Instruction,Air Cleaner Element Mainte1
09***05Plate? Instruction,(German)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Greek)(#47990-)
09***61Plate? Instruction,(Greek-English)1
09***63Plate? Instruction,Air Cleaner1
09***05Plate? Instruction,(Greek)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Indonesian)(#47990-)
09***61Plate? Instruction,(Indonesian-English)(Not Shown1
09***63Plate? Instruction,(For Indonesia)1
09***05Plate? Instruction,(Indonesian)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Italian)(#47990-)
09***61Plate? Instruction,(Italian-English) (Not Shown)1
09***63Plate? Instruction,(For Italian)1
09***05Plate? Instruction,(Italian)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Persian)(#47990-)
09***61Plate? Instruction,(Persian-English) (Not Shown)1
09***63Plate? Instruction,(For Persian)1
09***05Plate? Instruction,(Persian)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Portuguese)(#47990-)
09***61Plate? Instruction,(Portuguese-English)(Not Shown1
09***63Plate? Instruction,Air Cleaner Instruction1
09***05Plate? Instruction1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Name Plate And Caution (Spanish)(#47990-)
09***61Plate? Instruction,(Spanish-English) (Not Shown)1
09***63Plate? Instruction,(Spanish) (Not Shown)1
09***05Plate? Instruction,(Spanish)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Nozzle Holder (Inner Parts)(#47990-)
07***12Gasket,Mechanical Pump Piping2
61***11Holder Ass'Y6
ND***90Connector,Inlet1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Adapter(#47990-)
01***60Bolt,(F4320-52a0 -5- )3
01***30Bolt2
01***16Washer,Radio Controlled Slag Handling8
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Cooler (3-Element Type)(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)13
01***65Bolt - Return Line And Suction Linehose Clamps2
01***80Bolt,(With Corrosion Resistor)2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Filter(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***35Bolt,(F4320-52a0 -5 )2
01***16Washer,Radio Controlled Slag Handling4
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Gauge(#47990-)
61***60Gauge,Oil Level1
61***40Guide1
61***20Collar1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Pan And Suction Tube(#47990-)
01***12Bolt, Bolt,(No Need To Quick Shift)3
01***12Bolt - M8 - 1.25 X 121
01***16Bolt, Battery To Frame Ground Wire Attaching1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Oil Pump(#47990-)
01***25Bolt,(Rear Attachment Less)4
01***25Bolt,(For Canvas Canopy?Head Guard)3
01***35Bolt,(F4320-52a0 -5 )1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Piston(#47990-)
02***13Pin, Dowel2
04***18Ring, Snap12
61***33Piston Ring Ass'Y6
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Rocker Arm(#47990-)
01***75Screw40
01***08Nut,R.H. Thread2
01***32Washer,(With Auto Emergency Steering)40
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Spare Parts(#47990-)
04***65V-Belt Set,(For 35a? 50a Alternator)1
07***12Gasket,Mechanical Pump Piping1
09***35Wrench,Filter (For Add. Fuel Filter)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Starting Motor (11kw) (Inner Parts)(#47990-)
60***32Starting Motor Ass'Y,(11kw)1
SD***X9Switch Ass'Y,Engage1
SD***X0Bearing,Ball1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Starting Motor Mounting (11kw)(#47990-)
01***40Bolt,(With Center Guard)3
01***16Bolt, Battery To Frame Ground Wire Attaching1
08***19Band,(Without Air Conditioner)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Stop Motor(#47990-)
60***40Motor Ass'Y,Engine Stop1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Thermostat Housing(#47990-)
01***50Bolt4
01***65Screw2
60***20Thermostat,(Cold Terrain Spec.)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Thermostat Housing(#51975-)
01***16Washer,Radio Controlled Slag Handling1
08***10Connector, Clip1
60***10Thermostat,(Cold Terrain Spec.)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Turbocharger (High Altitude Spec.) (Inner Parts)(#47990-)
61***00Turbocharger Ass'Y,(Tv7705)1
GA***85V-Band Ass'Y1
GA***07Rotor Ass'Y1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Turbocharger Oil Piping (High Altitude Spec.)(#47990-)
01***20Bolt,(For Mono Lever Steering)5
01***30Bolt,(With Body Positioner)2
01***40Bolt (Op)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Drain Valve(#47990-)
61***12Valve,Water Drain1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Manifold(#47990-)
01***65Screw10
02***43O-Ring,Water Manifold6
61***11Manifold,Water2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Pump Gasket Kit(#47990-)
07***15O-Ring,(For Low Speed) (D40pf)1
07***15O-Ring,Scavenge Pump1
07***12Gasket,(Without Air Compressor Type) (K1)1
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Pump(#47990-)
01***16Bolt - Seat And Tether Belt Mounting6
01***30Bolt,(With Body Positioner)4
01***35Bolt,(F4320-52a0 -5 )2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Separator Mounting(#47990-)
01***25Bolt,(For Canvas Canopy?Head Guard)2
01***30Bolt,(With Body Positioner)2
01***08Nut,(For Canvas Canopy?Head Guard)2
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Komatsu : 6d125-1ab-Ew(S/N 10001-Up) : Engine : Water Temperature Sensor(#47990-)
07***12Washer, Gasket,(Without Thermo Sensor) (K1)1
07***15Plug,(Used When Without Heater)1
07***08Plug,(Without Oil Pressure Switch)1
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6D125-1AB-EW(S/N 10001-UP) serial number reference

The engine serial data plate is riveted to the block, normally on the left side near the fuel-injection pump or on the flywheel housing; on the host dozer or grader it can also be cross-read from the machine's own chassis PIN plate under the engine-option line. This engine family does not use a 3-letter alpha PIN prefix like Komatsu machine chassis do - the build code sits in the model designation itself (the "-1AB-EW" suffix marks the fitment/configuration), and the plate shows a plain running serial number, with "S/N 10001-UP" marking where that configuration's production run begins.

PrefixIdentifies
10001-UP6D125-1AB-EW base build (single continuous run)

Frequently asked questions

What engine powers the Komatsu 6D125-1AB-EW (S/N 10001-UP)?

It is the engine itself: a Komatsu 6D125-1 series block, 11.05 L (674 cu in), naturally aspirated inline-six diesel with mechanical direct injection, a 125 mm x 150 mm bore and stroke, and a mechanical all-speed governor. No ECM, no turbocharger on this build. Rated output is documented at 116 kW (155.6 hp) at 2,200 rpm as installed in grader service; figures for dozer-host installations of this exact suffix are not separately published.

What's the operating weight of the 6D125-1AB-EW?

The engine has no operating weight of its own; it is a power block fitted across multiple dozer and grader chassis. As installed in one common grader host, operating weight runs roughly 13,700-14,190 kg (30,200-31,280 lb); other dozer and grader hosts in this family will run lighter or heavier. Check your specific machine's nameplate for the exact figure.

What replaced the Komatsu 6D125-1AB-EW?

As emissions rules tightened, Komatsu moved these dozer and grader platforms on to the direct-injection 6D125E-2 block, then to the electronically controlled, common-rail SAA6D125E family; some later grader lines eventually shifted to smaller-displacement Tier-compliant engines entirely. Which one applies depends on the exact host chassis and production era you are tracing.

What 6D125-1AB-EW(S/N 10001-UP) owners discuss

What usually causes a reported power loss on this engine's mechanical fuel system, and is the injection pump really to blame?
Rarely the pump itself. Techs report chasing a power complaint straight into a full injection pump teardown, only to find a small air leak on the low-pressure fuel transfer/feed line, a dirty primary filter, or a sticking throttle/governor linkage. Check the simple items first (feed-line fittings, filters, linkage free play) before condemning the pump. This engine runs a fully mechanical inline injection pump and governor with no ECM, so there's no fault code to point you at the cause; it's diagnosed by elimination. Have your dealer verify pump timing before any pump work is done.
Why do owners report a hunting or surging idle on this engine?
Most often a worn governor linkage or weak/fatigued governor springs inside the mechanical flyweight governor. Linkage bushings wear from years of vibration and let the throttle arm float, which shows up as a rhythmic idle hunt rather than a steady idle. It's a linkage-and-spring wear item more than an injection pump fault. Because the same governor also limits engine overspeed, have your dealer verify governor operation before putting the machine back to work.
What internal wear patterns show up over the life of this engine?
Ring and liner wear driving oil consumption and crankcase-breather blow-by is the most reported long-term issue. In one rebuild, rings and liners failed within 6-8 months, traced to mixing non-matched ring and liner combinations instead of a matched, correctly-specified set. Piston cooling oilers are another known weak point: a single plugged oiler jet can take a piston out fairly quickly, so oil quality and change interval are treated as real factors in piston and liner life on this engine, not just a paperwork item.
This engine code covers naturally aspirated and turbocharged versions across different Komatsu machines. Does that matter for parts and expected behavior?
Yes. The 6D125 engine family shares the same core architecture (125 mm bore, inline six, roughly 11 L displacement) across generations, but aspiration, injection calibration, and power output vary a lot by configuration and series. Naturally aspirated, mechanically governed versions used in this era run well under half the output of later turbocharged variants used in bigger machines, which can reach roughly 228-235 kW (306-315 hp). Confirm aspiration, generation, and rated output off your engine's own dataplate rather than assuming one spec sheet or parts list applies across the whole 6D125 family.
What crankcase or coolant cross-contamination issues do owners report, and how do they catch it early?
Coolant getting into the crankcase oil is a recurring complaint, usually from a failed head gasket or liner O-ring seal. The tell operators mention is steam or vapor from the crankcase breather on restart, plus a milky look to the oil on the dipstick or filler cap. Owners and techs also point to precise torque sequence on cylinder head bolts and main/rod bearing caps as the preventive fix; skipping the sequence or getting torque wrong is called out repeatedly as a root cause of head-gasket leaks and premature bearing wear. Have your dealer verify head and liner-seal condition rather than just topping off oil and moving on.
This engine has no electronic controls. What electrical issues actually come up with owners?
Because the fuel system and governor are fully mechanical, there's no engine sensor network to throw a fault. The electrical complaints owners raise are accessory-circuit issues: alternator output dropping off, and corroded or loose wiring-harness and ground connections causing voltage drop or a no-charge condition. Cold-start reliability is the other recurring theme, since these engines rely on glow plugs or an ether aid rather than any electronic pre-heat strategy; a partially failed glow plug bank (some plugs working, some not) is a commonly reported cause of hard cold starts. Clean and re-seat corroded terminals and confirm charging voltage under load before chasing a starting complaint into the engine itself.
What should a buyer check on a used 6D125-1AB-EW before purchase?
Do a cold start and watch it closely. A healthy engine fires promptly and clears smoke almost immediately, so lingering blue smoke (oil), white smoke (coolant or poor injection), or heavy black smoke (fuel/air imbalance) are all flags. Pull the oil filler cap while it idles; a strong plume of vapor or pressure out of the filler points to ring and liner blow-by. Check the dipstick and filler cap for a milky, aerated look that signals coolant-in-oil contamination. Listen for a hunting or surging idle, which points to governor linkage wear. Ask for records of valve lash adjustment and injection pump service, since valve clearance on this engine is set by hand on a schedule rather than self-adjusting. Confirm the engine's exact suffix and serial range on the dataplate matches what the seller advertises, since parts and calibration are specific to each variant in this family. A compression test and a proper pre-purchase inspection are worth the cost; have your dealer verify compression and governor condition before you commit.

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

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