Komatsuengine(no series)

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

Maintenance schedule, common problems & OEM parts breakdown

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

The 6D125-1E (S/N 10001-UP) is a mid-displacement, water-cooled, direct-injection diesel from Komatsu's 6D125-1 engine family: inline-6, 125 mm x 150 mm bore and stroke, roughly 11.0-11.05 L displacement, fed by a mechanical flyweight-governor injection pump with no electronic control. Naturally aspirated and turbocharged/aftercooled builds exist under this same engine number and parts book. This entry fits as the powerplant in Komatsu's D65E-8/D65P-8 mid-size crawler dozer family, built roughly 1987-1992, with host chassis operating weight running about 13,770-15,440 kg (30,360-34,040 lb) depending on standard versus wide-track/swamp undercarriage and blade configuration. The D65-8 series sits between the earlier D65-6 dozers, which used an unrelated Cummins engine, and later D65 generations that moved to updated engine families as Komatsu revised the platform.

Across the 6D125-1 family, the same basic engine architecture was cataloged under several suffixes and serial breaks (1A, 1AB, 1AB-EW, 1AB-N, 1AF, 1AM, 1E among them) covering different aspiration setups and host-machine fitments while sharing a common mechanical fuel system and parts book. No specific named successor engine is confirmed for this exact catalog entry; Komatsu carried the 6D125 architecture forward into later, revised engine families as dozer emissions and control requirements changed, rather than a single documented direct replacement. In today's used and parts market, this generation matters because it predates electronic engine control entirely: no ECM, no fault codes, and service depends on gauges, pilot lamps, and mechanical inspection. D65E-8/D65P-8 dozers built on this engine remain working machines in many fleets, and demand centers on injector cup and o-ring kits, turbocharger cartridges for the turbo builds, charging-system components, and driveline wear parts for the host dozer's steering clutch and brake packs.

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 6D125-1E(S/N 10001-UP) specifications

Engine

Engine family	Komatsu 6D125-1 series diesel (this catalog covers the 6D125-1E build within that family, S/N 10001-UP)
Type	4-stroke, water-cooled, direct-injection diesel, inline-6 cylinder
Displacement	approx. 11.0-11.05 L (673-674 cu in)
Bore x stroke	125 mm x 150 mm (4.92 in x 5.91 in)
Cylinders	6, inline
Aspiration	Factory parts book covers both a naturally aspirated build and a turbocharged, aftercooled export-market build under this same engine number
Governor	Mechanical, flyweight-type injection-pump governor (pre-electronic generation; no ECM)
Rated power	Not published for this exact serial range in available spec sheets. For reference only, the emissions-updated successor engine in this family (fitted to the following-generation dozer platform) was rated about 135 kW (180 HP) and 142 kW (190 HP) at 1950 rpm depending on configuration - confirm actual output for this block from the engine data plate or your dealer
Emissions tier	Pre-regulation, mechanical-governor generation; no formal EPA/EU emissions tier applies

Weights

Host dozer operating weight - standard track configuration	approx. 13,770 kg (30,360 lb); figure reflects the crawler-dozer chassis this engine family was commonly fitted to, not the bare engine
Host dozer operating weight - wide-track/swamp configuration	approx. 15,440 kg (34,040 lb)
Bare engine weight	Not documented for this exact serial range in available sources - verify with your dealer
Ground pressure	Not documented for this exact serial range in available sources

Dimensions

Host dozer transport length w/ blade - standard track configuration	approx. 4.08 m (13.4 ft)
Host dozer width over tracks - standard track configuration	approx. 2.39 m (7.85 ft)
Host dozer height to cab top - standard track configuration	approx. 2.25 m (7.39 ft)
Track gauge - standard track configuration	approx. 1.88 m (6.17 ft)
Track length on ground - standard track configuration	approx. 2.64 m (8.65 ft)
Standard track shoe width - standard track configuration	510 mm (20.1 in)
Track gauge - wide-track/swamp configuration	approx. 2.07 m (6.8 ft)
Ground clearance - wide-track/swamp configuration	approx. 0.52 m (1.7 ft)

Performance

Travel speed, forward (max)	approx. 10.9 km/h (6.8 mph), standard-track host configuration
Travel speed, reverse (max)	approx. 13.7 km/h (8.6 mph), standard-track host configuration
Drawbar pull	Not published for this exact serial range in available spec sheets
Gradeability	Not published for this exact serial range in available spec sheets

Service capacities (summary)

Fuel tank	approx. 320 L (84.6 gal), host dozer chassis figure
Engine oil (crankcase)	Not confirmed for this exact serial range in available sources - use Komatsu EO specification and verify capacity with your dealer
Cooling system	Not confirmed for this exact serial range in available sources - verify with your dealer
Hydraulic system	Not applicable at the engine level - refer to host machine service data

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

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

System	Capacity	Recommended fluid
Engine crankcase (with filter)	Not published for this exact application code/serial listing. Multiple factory-derived fitment sources for the wider 6D125-1 mechanical-engine family (same block, related dash-suffix/serial breaks used on period Komatsu dozers and motor graders) converge on roughly 30 L (7.9 US gal) refill including the filter. Treat as a family ballpark only, not a confirmed figure for this serial range - verify against the dipstick/sight gauge or a Komatsu dealer before servicing.	Komatsu Genuine Diesel Engine Oil (EO), grade selected by ambient temperature per Komatsu's standard viscosity chart: SAE 10W in cold climates, SAE 10W-30 or 15W-40 for normal ranges, straight SAE 30 in sustained warm climates. This is a mechanically governed, pre-emission-era diesel, so API CD/CE-class oil is the applicable spec rather than the newer JASO DH-series oils used on later electronically controlled Komatsu engines. A heavy-duty SAE 15W-40 diesel oil meeting API CD/SF is a common field-service equivalent.
Cooling system (engine only)	Not published as a stand-alone engine-only figure for this serial listing - Komatsu literature for this engine generation gives full-machine system capacity (engine plus radiator/sub-tank), not the engine block alone. Complete cooling systems on period dozer- and grader-class machines built around this same block commonly run roughly 35-65 L (9-17 US gal) depending on host machine and radiator size. This varies by configuration/series and is not a confirmed figure for the bare engine.	Komatsu Super Coolant (AF-NAC type), an extended-life, all-season, non-amine corrosion-inhibited coolant, supplied as concentrate and mixed 50/50 with water for normal service. No separate summer/winter concentration split is called out beyond the standard 50/50 mix; use a richer concentrate ratio only for sustained sub-freezing climates per Komatsu's coolant freeze-protection chart.
Grease (spec only)	Not applicable - grease points are serviced on the periodic lubrication schedule, not filled to a volume.	Komatsu Genuine Grease, multipurpose lithium-base, NLGI No. 2 (G2-LI type), for external linkage, bracket, and mounting hardware grease points on the engine, standard across Komatsu equipment of this era. Switch to a lower-consistency NLGI 1 or 0 lithium-base grease for 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 6D125-1E(S/N 10001-UP) maintenance schedule

Service interval	Tasks
Every 10 h	Check engine oil level before starting; top off with Komatsu EO grade matched to ambient temperature Check coolant level in the reserve tank and inspect hoses and radiator for leaks Drain water and sediment from the fuel tank sump Inspect the air cleaner dust indicator and empty the dust cup Grease steering clutch/brake linkage and track adjuster fittings (weekly) Walk around and check for oil, fuel, and coolant leaks and loose fasteners
Every 250 h	Change engine oil and replace the oil filter element Replace the fuel filter element and bleed the fuel system Check and adjust fan/alternator belt tension Grease chassis and pivot points beyond the weekly points, including steering clutch shaft and equalizer bar Check battery electrolyte level and inspect charging-circuit connections Clean the turbocharger inlet screen on turbocharged builds
Every 500 h	Change powertrain (steering clutch/transmission case) oil Change final drive case oil Replace the fuel pre-filter/strainer element Clean radiator and oil cooler fins externally Check track shoe bolt torque and adjust as needed Test coolant corrosion-inhibitor concentration
Every 1,000 h	Replace the air cleaner outer element, or sooner if the dust indicator triggers Inspect turbocharger rotor shaft end play on turbocharged builds Check and top up SCA/coolant conditioner concentration in Komatsu Super Coolant AF-NAC Inspect alternator and starter motor brush wear and terminal condition Drain and thoroughly clean fuel tank sediment Repack the steering clutch release bearing
Every 2,000 h	Check and adjust intake/exhaust valve clearance Check and adjust fuel injection timing and injection pump calibration Pull injectors for a pop-off pressure test and inspect cups and o-rings for wear Inspect steering clutch and brake disc packs for wear and overhaul as needed Inspect the turbocharger cartridge for wear and shaft play Check and record cylinder compression for trend tracking
Every 4,000 h	Replace Komatsu Super Coolant AF-NAC at its full service life Overhaul or replace the turbocharger cartridge based on prior wear-inspection findings Replace injector cups and o-rings as a set to control oil-dilution risk Overhaul steering clutch and brake disc packs on the host dozer driveline if wear limits are reached Inspect cylinder liners and piston rings at the top-end overhaul threshold

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

Predictive Maintenance & Fluid Analysis

Run engine oil sampling on the 6D125-1E every service interval - rising fuel dilution is the first sign of injector cup o-ring wear before white smoke or hard starting shows up. Test Komatsu Super Coolant AF-NAC concentration rather than waiting for the fixed replacement interval. With no ECM on this mechanical-governor engine, watch oil pressure and coolant temperature gauges closely at startup and under load - gauge drift is your only early warning on this pre-electronic platform.

Corrective & Common Repairs

Oil dilution, white smoke, and hard starting on the 6D125-1E point first to worn injector cup o-rings letting fuel wash into the crankcase - pull injectors, inspect cups, and replace seals as a set rather than one at a time. Weak charging performance traces to the alternator and its wiring, the engine's dominant electrical wear item. Check fuel filters and water separators before condemning the injection pump; contaminated fuel mimics injector failure on this mechanical system.

Overhaul & Rebuild Points

Plan turbocharger cartridge overhaul around rotor shaft play findings on turbocharged 6D125-1E builds - cartridge wear shows up as blue smoke and boost loss before outright failure. On the D65E-8/D65P-8 host chassis, steering clutch and brake disc packs are the dominant driveline wear item; inspect them at major service intervals and overhaul before drivetrain damage follows. Treat injector cup, nozzle, and cylinder liner inspection as one combined top-end overhaul package on this engine family.

Seasonal & Environment Servicing

Match engine oil viscosity to ambient temperature using the Komatsu EO climate chart before cold-weather starts - the mechanical injection pump on the 6D125-1E has no cold-start electronics to compensate for the wrong grade. Keep Komatsu Super Coolant AF-NAC at the correct 50/50 premix for freeze protection. In dusty dozer environments, check the air cleaner dust indicator more often than the fixed interval and grease track adjusters more frequently as ambient temperature swings affect track sag.

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

Part number	Part	Notes
ND092220-0040	Filter,Fuel	Fuel system 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 →
ND090438-0420	Shim? 1.9mm,Element Holder	Scheduled service item	Check fitment →
ND090438-0490	Shim? 2.25mm,Element Holder	Scheduled service item	Check fitment →

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

6D125-1E(S/N 10001-UP) fault codes & troubleshooting

Code	Meaning	Likely cause	What to do
Engine oil pressure lamp (red)	Illuminates when engine oil pressure falls below the safe minimum for the lubrication circuit.	Low oil level, clogged oil filter, worn oil pump, or a failed oil pressure switch.	Stop the engine at once. Check oil level and filter condition before restarting.
Coolant temperature lamp / gauge	Warns that engine coolant temperature has gone above the normal operating range.	Low coolant level, clogged radiator core, slipping or broken fan belt, or a stuck thermostat.	Let the engine idle to cool before shutdown. Once cool, check coolant level, radiator, and fan belt.
Charge lamp (alternator)	Indicates the alternator is not charging the battery circuit.	Broken or slipping fan/alternator belt, faulty alternator, or a wiring fault.	Check belt tension and alternator wiring. Repair or replace as needed.
Air cleaner restriction indicator	Signals the air filter element is loaded enough to restrict intake airflow.	Dust-clogged air filter element or blocked intake ducting.	Inspect the element and clean or replace it.
Fuel level warning	Alerts the operator that the fuel tank is near empty.	Normal fuel consumption reaching the reserve level.	Refuel. Bleed the fuel system if the tank was run completely dry.
Intake air heater (preheat) indicator	Shows the intake air heater is active to aid cold-weather starting.	Normal cold-start cycle; stays lit if the heater relay or element has failed and will not switch off.	Wait for the lamp to go out before cranking. If it never lights or will not switch off, check the heater relay and wiring.

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

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

Host machine and size class

This 6D125-1E engine block is a bare-engine parts listing with no work tools of its own; the parts book itself ties fitment to the D65-series mid-size crawler dozer chassis (straight-tilt and swamp/wide-gauge D65 variants of this vintage). Operating weight for this generation runs roughly 13-18 t depending on standard-gauge vs wide-gauge undercarriage, placing it in the mid-size dozer class.

Dozer blade options

Factory blade choices for this dozer class and era are a straight-tilt dozing blade and a power-angle-tilt (PAT) blade. Blade capacity for the straight-tilt blade runs about 3.7 m3 (4.8 yd3) with a width near 4.0 m (13 ft 1 in); semi-U and full-U blades belong to later, redesigned D65 generations and don't apply to this S/N range.

Ripper attachment

A rear-mounted parallelogram ripper is the standard ground-breaking tool for this size class, offered as a single-shank or a multi-shank (multiple-tip) unit bolted to the tractor's rear ripper frame. Shank angle and penetration are actuated hydraulically off the dozer's own pump, so no separate hydraulic kit is needed to run it.

Blade and ripper mounting system

Blade and ripper attach through fixed C-frame and trunnion pin joints, not a quick-coupler. The blade C-frame pivots on the tractor's push-arm trunnions, with lift, tilt, and angle cylinders bolted directly to frame brackets; changing blade or ripper type is a shop-level pin-and-frame job, not a field quick-attach swap.

Undercarriage and gauge variants

This dozer class is factory-offered in standard-gauge and wide-gauge, low-ground-pressure undercarriage, changing track shoe width and ground pressure for swamp or soft-ground duty. Shoe width is a build-time factory option rather than a field-swap attachment.

Guarding and operator-station options

Factory options for this dozer class include an open ROPS canopy or an enclosed ROPS/FOPS cab, plus underbelly and screen guarding packages for logging or demolition duty. Rock guards and grille screens are optional protective add-ons, not primary work tools.

Winch

A rear PTO or hydraulic cable winch is offered as an application-specific option for this dozer class, used for logging and cable-pull work; it mounts at the rear of the tractor in place of or alongside the ripper. Not documented as standard fitment for this exact S/N range - verify current bracket and PTO compatibility with your dealer or winch supplier.

Hydraulic supply for attachments

Blade and ripper functions run off the dozer's main hydraulic system rather than a bolt-on auxiliary circuit, so no extra hydraulic kit is required regardless of engine tune. Both naturally aspirated and turbocharged builds of this engine appear in the same parts book, reflecting market/spec differences rather than any change in attachment capability.

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

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

Accessory

Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Alternator (13a)

60***50	Alternator A. (13a),(With Non Hardening Pulley)	1
60***70	Alternator A. (13a),(Sandy And Dusty Terrain S.)	1
KD***31	Bushing,Insulator	2
KD***80	Packing	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Alternator (35a)(#11082-)

60***60	Alternator A. (35a),(With Non Hardening Pulley)	1
KD***57	Bearing,Ball? Front	1
KD***80	Collar	1
KD***70	Rear Bracket Ass'Y,Rear	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Alternator And Mounting (13a)

01***80	Bolt,(Not Shown)	1
01***30	Bolt	1
01***11	Nut (Welded)	1
01***26	Washer,(For Additional Rear Lamp)	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Alternator And Mounting (35a)(#11082-)

01***90	Bolt, Fan Mounting	1
01***30	Bolt	1
01***23	Washer,(A)(W/After Cooler)(S6d155-4b)	2
01***32	Washer,(Not Used With Emergency Str.)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Heater Switch And Heater Signal

08***35	Indicator,Dust (Japanese-English)	1
60***30	Signal,Engine Pre Heater	1
(6***0)	Switch,Heater (See Fig.0131 Or 0131a)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Starting Motor (11kw)(#10579-35403)

60***70	Starting Motor Ass'Y,(11kw)	1
60***71	Starting Motor Ass'Y,(11kw)(See Fig.0662)	1
60***10	Starting Motor Ass'Y,(11kw)(See Fig.0662)	1
60***11	Starting Motor Ass'Y,(11kw)(See Fig.0662)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Starting Motor (11kw)(#35404-)

60***12	Starting Motor Ass'Y,(11kw)	1
SD***X9	Switch Ass'Y,Engage	1
SD***X0	Bearing,Ball	1
SD***X0	Bolt	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Starting Motor (7.5kw)(#10001-18199)

60***30	Starting Motor Ass'Y,(7.5kw)(See Fig.0661)	1
KD***20	Magnetic Switch Assembly	1
KD***40	Spring,Spring	4
KD***30	Washer Ass'Y,(Not Shown)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Starting Motor (7.5kw)(#18200-)

60***30	Starting Motor Ass'Y,(7.5kw)	1
KD***60	Shift Lever Assembly	1
KD***40	Spring,Spring	4
KD***00	Terminal Assembly	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Accessory : Starting Motor And Mounting (7.5kw? 11kw)

01***40	Bolt,(With Center Guard)	3
66***10	Gasket,Starting Motor	1
(6***1)	Starting Motor Ass'Y,(11kw)(See Fig.0662)	1
(6***0)	Starting Motor Ass'Y,(7.5kw) (See Fig.0661a)	1

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Cooling And Electrical Systems

Komatsu : 6d125-1e(S/N 10001-Up) : Cooling And Electrical Systems : Cooling Fan And Mounting

01***25	Bolt,(For Canvas Canopy?Head Guard)	6
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

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Komatsu : 6d125-1e(S/N 10001-Up) : Cooling And Electrical Systems : Corrosion Resistor And Piping

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
07***08	Hose	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cooling And Electrical Systems : 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)	3
01***40	Bolt, Mount Master Brake Cylinder	3

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Cylinder Block

Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Camshaft

01***22	Bolt	2
04***25	Key, Plain Woodruff	1
04***12	Ring,Snap (For Ripper)	12
61***31	Plate,Thrust	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Crankshaft

01***70	Bolt, Accumulator Mounting Bracket	6
01***10	Bolt,(Noise Suppression Spec.)	6
01***35	Bolt	1
01***40	Bolt	5

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Cylinder Block

01***12	Bolt,(Without Air Compressor Type)	2
01***45	Washer,(For Travel Motor) (Not Show)	14
04***14	Pin, Dowel	2
04***20	Pin,Dowel (Welded)	12

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Cylinder Block Cover

01***16	Bolt (With Air Heater & Conditioner)	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***00	Bolt, Mount Back-Up Alarm	2
01***06	Nut,(With Back-Up Alarm) (Op), Nut; Was 01580-10806	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing

01***40	Bolt,(Dust And Dirt Protection)	2
01***50	Bolt	2
01***50	Bolt, Radiator To Frame	6
01***70	Bolt - Thrust Plate Mounting	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing (Noise Suppression Spec.)(#33755-)

01***40	Bolt,(Dust And Dirt Protection)	2
01***50	Bolt, Radiator To Frame	6
01***70	Bolt - Thrust Plate Mounting	2
01***20	Bolt,(For Quick Shift) (Mitsubishi)	3

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Front Cover And Front Support

01***25	Bolt,(Without Auto Priming System)	6
01***60	Screw	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***65	Bolt,(Except Japan)	7

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Front Cover And Front Support (Noise Suppression Spec.)(#33755-)

01***25	Bolt,(Without Auto Priming System)	6
01***60	Screw	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***30	Bolt,(For Quick Shift) (Mitsubishi)	8

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Oil Pan

01***25	Bolt,(For Canvas Canopy?Head Guard)	31
01***30	Bolt,(For Quick Shift) (Mitsubishi)	7
01***16	Washer,Radio Controlled Slag Handling	37
01***32	Washer,(With Auto Emergency Steering)	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Piston And Connecting Rod

02***13	Pin, Dowel	2
04***18	Ring, Snap	12
61***30	Piston Ring Ass'Y	6
61***31	Piston Ring Ass'Y	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Power Take Off (1/2)

01***10	Bolt,(With Auto Emergency Steering)	4
01***35	Bolt, Bolt, Mount Tubes To Switch And Work Pumps	6
01***40	Bolt,(With Service Valve R.H.)	6
01***45	Bolt	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Block : Power Take Off (2/2)

01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***30	Bolt,(For Quick Shift) (Mitsubishi)	4
01***35	Bolt,(For Quick Shift) (Mitsubishi)	4
01***25	Bolt,(Without Rops Guard? Canopy)	4

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Cylinder Head

Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Air Cleaner And Mounting (With Turbochargwer) (Except Japan)

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
01***16	Washer,Radio Controlled Slag Handling	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Air Cleaner And Mounting(#10001-14199)

01***20	Bolt,(For Quick Shift) (Mitsubishi)	4
01***25	Bolt,(For Canvas Canopy?Head Guard)	4
01***08	Nut,(For Canvas Canopy?Head Guard)	2
01***08	Nut,(For Straight Tilt Dozer) (D65p)	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Air Cleaner And Mounting(#14200-)

01***25	Bolt,(For Canvas Canopy?Head Guard)	3
01***08	Nut,(For Straight Tilt Dozer) (D65p)	6
01***16	Washer,Radio Controlled Slag Handling	6
04***10	Ring,See Fig. K4010-65a0	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Air Intake Manifold And Connection

01***16	Bolt, Mount Washer Tank To Bracket, Bolt	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	11
01***55	Bolt, Mount Tube To Switch Pump	6
01***60	Bolt, Mount Tube To Switch Pump	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Air Intake Manifold And Connection (With Turbocharger) (Except Japan)

01***10	Bolt,(With Auto Emergency Steering)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	11
01***55	Bolt, Mount Tube To Switch Pump	5
01***60	Bolt, Mount Tube To Switch Pump	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Cylinder Head(#10001-26915)

04***20	Pin,Dowel (Welded)	2
61***30	Sleeve,Holder	1
61***20	Cotter, Valve	48
61***40	Seal,Exhaust Valve (K1)	12

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Cylinder Head(#26916-)

04***20	Pin,Dowel (Welded)	2
61***30	Sleeve,Holder	1
61***20	Cotter, Valve	48
61***40	Seal,Exhaust Valve (K1)	12

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Exhaust Manifold And Mounting

01***80	Bolt, Mount Strainer Flange	18
01***00	Bolt (M10-1.50x100)	16
07***08	Plug,(Without Auto Priming System)	1
61***20	Spacer,(For Shipping)	18

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Exhaust Manifold And Mounting (With Turbocharger) (Except Japan)

01***80	Bolt, Mount Strainer Flange	2
01***00	Bolt (M10-1.50x100)	16
01***45	Screw	4
07***08	Plug,(Without Auto Priming System)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Extension Cap And Rain Cap

01***11	Nut,(Spark Arrester Spec.)	2
01***23	Plain Washer	2
07***19	Clamp	2
60***70	Hose, Air	1

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Komatsu : 6d125-1e(S/N 10001-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
01***45	Screw	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Muffler And Mounting (With Turbocharger) (Except Japan)

01***40	Bolt,(Dust And Dirt Protection)	4
01***55	Bolt,(For Suction? Reversible Fan)	4
01***30	Bolt,Radio Controlled Slag Handling	4
01***08	Nut, Regular Hexagon (M10-1.50)	4

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Rocker Arm And Housing

01***08	Nut,R.H. Thread	12
01***16	Washer,Radio Controlled Slag Handling	40
01***32	Washer,(With Auto Emergency Steering)	40
61***10	Housing, Rocker Lever	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Rocker Arm Housing Cover

01***16	Washer,Radio Controlled Slag Handling	24
61***10	Cover,Head? No.2?3?4?5?6	6
61***11	Cover,Head? No.2?3?4?5?6	6
61***10	Gasket,Cylinder Head Cover	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Turbocharger (Except Japan)

61***00	Turbocharger Ass'Y,(Tv7705)	1
GA***85	V-Band Ass'Y	1
GA***85	V-Band	1
GA***07	Rotor Ass'Y	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Water Manifold And Thermostat(#10001-18199)

02***43	O-Ring,Water Manifold	10
07***12	Washer, Gasket,(Without Thermo Sensor) (K1)	1
07***12	Plug,(Without Corrosion Resistor)	2
07***15	Plug,(Used When Without Heater)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Cylinder Head : Water Manifold And Thermostat(#18200-)

02***43	O-Ring,Water Manifold	6
07***12	Washer, Gasket,(Without Thermo Sensor) (K1)	1
07***12	Plug,(Without Corrosion Resistor)	2
07***15	Plug,(Used When Without Heater)	1

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Fuel System

Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Control Lever

01***20	Screw	3
01***06	Nut,(With Back-Up Alarm) (Op), Nut; Was 01580-10806	3
01***09	Nut (Itl)	1
01***26	Washer,Spring	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Filter And Piping

01***30	Bolt,(For Quick Shift) (Mitsubishi)	2
01***16	Washer,Radio Controlled Slag Handling	2
07***12	Gasket,Mechanical Pump Piping	2
07***12	Gasket,(Without Air Compressor Type) (K1)	4

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling) (With Turbocharger) (Except Japan)(#.-)

ND***10	Flange,Coupling	1
ND***50	Bolt	1
ND***40	Bolt	2
ND***61	Bolt	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling) (With Turbocharger) (Except Japan)(#10001-.)

ND***50	Bolt	1
ND***70	Bolt	2
ND***30	Coupling Ass'Y	1
ND***60	Bolt	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#10001-19616)

ND***50	Bolt	1
ND***70	Bolt	2
ND***30	Coupling Ass'Y	1
ND***60	Bolt	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#19617-)

ND***10	Flange,Coupling	1
ND***50	Bolt	1
ND***40	Bolt	2
ND***61	Bolt	6

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)

ND***40	Washer? 1mm,Plate	1
ND***00	Pump Ass'Y,Priming Pump	1
ND***70	Washer,Union	4
ND***10	Spring, Check Valve	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump) (With Turbocharger) (Except Japan)

ND***40	Washer? 1mm,Plate	1
ND***00	Pump Ass'Y,Priming Pump	1
ND***70	Washer,Union	4
ND***10	Spring, Check Valve	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)

ND***40	Plate,Thrust	1
ND***80	Pin,Stop	1
ND***40	Plug,Screw	1
ND***50	Washer? 0.3mm	0

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2) (With Turbocharger) (Except Japan)(#.-)

ND***40	Plate,Thrust	1
ND***40	Plug,Screw	1
ND***50	Washer? 0.3mm	0
ND***90	Lever Ass'Y,Control	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2) (With Turbocharger) (Except Japan)(#10001-.)

ND***40	Plate,Thrust	1
ND***40	Plug,Screw	1
ND***10	Adapter	1
ND***91	Spring,Governor	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)

ND***70	Arm,Spring	1
ND***20	Washer? 1.0mm,Cover Plate	2
ND***90	Seal,Oil	1
ND***40	O-Ring	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2) (With Turbocharger) (Except Japan)(#.-)

ND***80	Pin,Stop	1
ND***70	Arm,Spring	1
ND***20	Washer? 1.0mm,Cover Plate	2
ND***90	Seal,Oil	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2) (With Turbocharger) (Except Japan)(#10001-.)

ND***30	Capsule,Full Stop	1
ND***70	Arm,Spring	1
ND***20	Washer? 1.0mm,Cover Plate	2
ND***60	O-Ring	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (With Turbocharger) (Except Japan)(#.-)

61***41	Injection Pump A	1
61***42	Injection Pump A	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (With Turbocharger) (Except Japan)(#10001-.)

61***40	Injection Pump A	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1
ND***20	Retainer,Bearing	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#10001-19616)

61***41	Injection Pump A.,(For D65s) (See Fig.460)	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1
ND***20	Retainer,Bearing	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump)(#19617-)

61***42	Injection Pump A	1
61***43	Injection Pump A	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping

01***75	Bolt,(See Fig.0142)	4
01***30	Bolt	1
01***20	Bolt,(For Quick Shift) (Mitsubishi)	2
01***25	Bolt,(For Canvas Canopy?Head Guard)	4

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (With Turbocharger) (Except Japan)

01***75	Bolt,(See Fig.0142)	4
01***30	Bolt	1
01***20	Bolt,(For Quick Shift) (Mitsubishi)	2
01***25	Bolt,(For Canvas Canopy?Head Guard)	4

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Tube(#10001-10063)

01***45	Bolt, Divider Valve Mounting	12
07***65	O-Ring,Cylinder Block	6
07***12	Gasket,Mechanical Pump Piping	2
07***12	Gasket,(Without Air Compressor Type) (K2)	12

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Tube(#10064-)

01***45	Bolt, Divider Valve Mounting	12
07***65	O-Ring,Cylinder Block	6
07***12	Gasket,Mechanical Pump Piping	2
07***12	Gasket,(Without Air Compressor Type) (K2)	12

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Water Separator

07***60	O-Ring,(For Pc750?800?1800) (A2610)	1
60***00	Water Separator A.,(4d105-5h? 4d105-5t)	1
60***60	Plug,Drain (4d105-5h? 4d105-5t)	1
60***00	Water Separator A.,(See Fig.2415)	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Fuel System : Water Separator And Mounting(#12481-)

01***30	Bolt,(For Quick Shift) (Mitsubishi)	1
01***40	Bolt, Mount Master Brake Cylinder	1
01***50	Bolt,(With Service Valve R.H.)	1
01***16	Washer,Radio Controlled Slag Handling	3

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Lubricating Oil System

Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Cooler

01***25	Bolt,Without Revolution Sensor	2
01***25	Bolt,(For Canvas Canopy?Head Guard)	13
01***65	Bolt,(Except Japan)	2
01***80	Bolt,(Not Shown)	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Filter And Mounting

01***25	Bolt,(For Canvas Canopy?Head Guard)	6
01***30	Bolt,(For Quick Shift) (Mitsubishi)	2
01***40	Bolt, Mount Master Brake Cylinder	2
01***16	Washer,Radio Controlled Slag Handling	4

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Piping

01***50	Bolt,(With Service Valve R.H.)	2
01***60	Bolt, Mount Tube To Switch Pump	2
01***16	Washer,Radio Controlled Slag Handling	13
04***12	Ring, Snap	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Lubricating Oil Pump And Suction Pipe

01***25	Bolt,(Without Auto Priming System)	4
01***20	Bolt,(Large Capacity Type) (Std)	2
01***25	Bolt,(Sandy? Dusty Terrain Spec.)	5
01***35	Bolt, Mounting - Flywheel Housing End	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Main Clutch Oil Cooler

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	3
01***40	Bolt, Mount Master Brake Cylinder	3
01***45	Bolt,(For Power Tilt Mech Angle)	2

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Power Take Off Lubricating Oil Piping

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***40	Bolt,(With Service Valve R.H.)	1
07***12	Gasket,(Without Air Compressor Type) (K2)	23
61***20	Pipe	1

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Komatsu : 6d125-1e(S/N 10001-Up) : Lubricating Oil System : Turbocharger Lubricating Oil Piping (With Turbocharger) (Except Japan)

01***20	Bolt,(For Quick Shift) (Mitsubishi)	4
01***30	Bolt,(For Quick Shift) (Mitsubishi)	2
01***40	Bolt, Mount Master Brake Cylinder	1
01***16	Washer,Radio Controlled Slag Handling	2

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Tool And Kit

Komatsu : 6d125-1e(S/N 10001-Up) : Tool And Kit : Gasket Kit

01***23	Washer,Lock (K5)	3
02***43	O-Ring,Water Manifold	10
06***03	Seal,Bearing (K2)	2
07***10	O-Ring,(F4350-62a0 -5 ), O-Ring; Komatsu S/N 22***01 & Abv - Was 07000-02010, O-Ring; Was 07000-02010	1

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6D125-1E(S/N 10001-UP) serial number reference

The 6D125-1E dataplate sits on the left side of the cylinder block, usually near the fuel injection pump or rocker-arm housing cover; if the tag is gone or unreadable the serial is also stamped directly into the block casting. Read the full engine model, 6D125-1E, together with the running serial (10001 and up) - there is no separate letter code ahead of the digits on this engine family. The suffix on the model name sets the build/fitment; everything after S/N is simply the sequential production number.

Prefix	Identifies	Notes
10001-UP (no alpha PIN prefix ahead of the running serial)	6D125-1E build spec, part of the naturally aspirated 6D125-1 family. This engine family marks its turbocharged variants with a leading S- (S6D125-1...); a plain 6D125-1E without that prefix reads as non-turbo.	The 6D125-1 series runs a plain numeric serial with no letter code ahead of it; build and fitment are set by the suffix tacked onto the base model number (A, C, D, E, EE, F, J, K, N and similar), not by a prefix ahead of the digits. A factory-style equipment-to-engine cross-reference ties most 6D125-1 suffix builds to a specific dozer or grader chassis, but the plain 1E build is not tied to any chassis in that reference or in any other parts or spec source checked. Two similar-looking codes sit nearby in that reference - 6D125-1EE against a different mid-size dozer, and the turbocharged S6D125-1E against a different dozer entirely - neither is the plain 1E code, so neither is reported here as a host. Confirm the exact host machine with a dealer or parts counter using the full engine plate data before assuming a fitment.

Frequently asked questions

What engine is the Komatsu 6D125-1E (S/N 10001-UP)?

It is a water-cooled, direct-injection diesel from Komatsu's 6D125-1 family: inline-6, 125 mm x 150 mm bore and stroke, about 11.0-11.05 L displacement, with a mechanical flyweight-governor injection pump and no electronic control. Naturally aspirated and turbocharged/aftercooled builds exist under this engine number. It powers Komatsu's D65E-8/D65P-8 mid-size crawler dozer family. Rated power is not documented for this exact serial range - verify it from the engine data plate or your dealer.

What is the operating weight of the machine this engine powers?

The host D65E-8/D65P-8 dozer chassis runs roughly 13,770-15,440 kg (30,360-34,040 lb) operating weight, depending on standard versus wide-track/swamp undercarriage and blade configuration.

What replaced the 6D125-1E engine?

No specific successor engine designation is confirmed for this exact catalog entry. Komatsu carried the 6D125 architecture forward into later, revised engine families as dozer emissions and control requirements changed, rather than a single documented direct replacement - verify any specific successor claim with your dealer before relying on it.

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

What's the real-world reputation of the 6D125-1E long block for durability?

Owners and shop mechanics consistently describe the 125-series long block as one of the tougher units Komatsu built for this size class, routinely running well past a major overhaul with clean fuel, regular oil/filter service, and decent air filtration. The recurring wear complaint across the family is ring and liner wear showing up as rising oil consumption or blow-by once hours stretch well past the recommended overhaul interval or the air intake side is neglected. That's a maintenance-interval issue more than a design flaw, and it repeats across more than one host machine that shares this block.

Is the 6D125-1E turbocharged or naturally aspirated?

Sources disagree depending on which part of the 125-series lineup they're describing. Komatsu's naming convention uses an S prefix for supercharged/turbo versions (S6D125, SA6D125), so a bare 6D125-1 designation without that prefix generally points to a naturally aspirated build, and this matches how early D65-series dozers in this serial range are documented. Later production in the same family moved to the turbocharged S-prefix engines, which is where the noticeable step up in flywheel output shows up in parts and spec listings. Confirm aspiration off the actual engine tag and turbo housing on the machine rather than trusting a parts-counter listing, since the two designations get used loosely.

What horsepower should I expect, and does it vary?

Figures for this engine in its D65-series dozer application cluster in the 112-123 kW (150-165 hp) gross flywheel range, with the higher end typically tied to the wider swamp/LGP chassis variant rather than a different engine tune. Net rating at the drawbar runs a bit lower than gross. Treat any single number as approximate — it varies by chassis configuration and which spec sheet you're reading — and confirm against the machine's own dataplate for anything serious like a resale valuation.

What fuel-system quirks show up most often on these mechanically-governed engines?

The most-repeated complaint is injector cup O-ring and crossover-tube gasket wear letting fuel weep past the cup into the oil pan or crankcase, which shows up as thin, diesel-smelling engine oil and white smoke on cold start. Hard starting after the machine sits overnight is often not the injectors at all — it traces back to a pinhole air leak or worn seal on the low-pressure side (tank pickup, primary filter housing, lift pump) letting the system lose prime. Pull and inspect the injector cups and o-rings and pressure-check the low-pressure fuel circuit before condemning the injection pump itself.

What electrical or sensor issues come up on this generation of engine?

This is a pre-electronic, mechanically governed diesel, so there's no ECM and no diagnostic fault codes to pull. Most "electrical" complaints trace back to the charging circuit: the alternator's regulator-excitation wire to the monitor panel corrodes or breaks, which reads as a dead alternator even when the unit itself is good. Bench-test the alternator before replacing it, then work back through fuses, relays, and that excitation wiring. In cold climates, a sluggish or intermittent ether/starting-aid relay is the other common gripe — check the relay and its wiring before assuming a fuel or compression problem.

What powertrain and steering behavior is typical for this dozer platform?

The host chassis uses a torque-converter power-shift (Torqflow) transmission driving multi-disc steering clutches and brakes at each final drive, not a hydrostatic drive. Uneven effort between the left and right steering levers is the classic tell that one side's clutch or brake pack is worn or out of adjustment, and a burning smell from a final-drive housing under load points the same direction. Because loss of steering on one side can happen with little warning, treat any clutch or brake pack diagnosis and repair as safety-critical and have your dealer verify clutch and brake condition before the machine goes back to work.

What should I check when buying a used 6D125-1E(S/N 10001-UP) powered machine?

Start with a full walk-around for abuse signs on the blade and undercarriage, plus leaks at the final drives, hydraulic cylinders, and underneath the engine and transmission. Pull oil, coolant, and hydraulic samples for lab analysis — fuel dilution or coolant intrusion in the oil flags the injector-cup wear pattern common to this engine family. Confirm the engine's aspiration and suffix against its actual dataplate rather than the sale listing, since power ratings and prefixes get mixed up between similar 125-series variants. Have an undercarriage specialist measure remaining wear life, since that single item swings resale value more than almost anything else on a machine this size, and cycle the steering clutches and brakes under load, listening and smelling for a hot pack — have your dealer verify anything that feels uneven before you close the deal.

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

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