Komatsuengine(no series)

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

Maintenance schedule, common problems & OEM parts breakdown

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

The 6D125-1D (S/N 10001-UP) is a bare six-cylinder diesel engine assembly, not a complete machine. It belongs to Komatsu's 1980s-era 6D125-1 engine family: a naturally aspirated, mechanically governed inline six with 11.04 L displacement and 125 x 150 mm (4.9 x 5.9 in) bore and stroke, rated at roughly 116 kW (155 hp) gross flywheel output at 2200 rpm. An inline injection pump with a flyweight governor meters fuel; there is no turbocharger and no electronic control module anywhere in this build. The wider 6D125-1 family was produced across a long run of suffix-coded variants, each matched to a different Komatsu machine, alongside a turbocharged S-prefixed line rated higher. This naturally aspirated, no-prefix -1D build is documented across more than one candidate host class of the era, including motor graders and crawler dozers, but no single confirmed host machine, weight range, or production-year window applies to this exact serial range.

Across the broader 6D125 nameplate, Komatsu moved from this naturally aspirated mechanical generation to a turbocharged and aftercooled version of the same base architecture, then later to a fully electronically controlled series with an ECM, sensors, and a much higher power band. That progression is why generic parts searches for this engine number blend several genuinely different generations together. In the used and parts market, the plain mechanical 6D125-1D stays relevant precisely because it carries no ECM, no sensors, and no wiring harness to fail: it can be diagnosed and repaired in the field with basic mechanical checks, and its core architecture is shared across a wide family of suffix-coded siblings, which keeps parts interchange and aftermarket support broad even where this exact build's host machine isn't pinned down.

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

Engine

Engine model	6D125-1D, part of the 6D125-1 naturally aspirated inline-six diesel family. Documented candidate host classes for this build era include Komatsu motor graders and crawler dozers; no single host machine is confirmed for this exact serial range.
Configuration note	This engine code is the naturally aspirated build in the 6D125-1 line. A turbocharged, aftercooled version of the same base architecture exists under a separate S-prefixed engine code with a higher power rating; that rating does not apply to this engine.
Rated power (gross)	116 kW (155 HP) at 2200 rpm, flywheel/gross rating.
Displacement	11.04 L (674 cu in).
Bore x stroke	125 mm x 150 mm.
Cylinders	6, inline, 4-stroke, water-cooled diesel.
Emissions tier	Predates EPA/EU emissions-tier certification. Mechanical, pre-electronic diesel design, no ECM and no exhaust aftertreatment.

Weights

Scope	This listing covers the engine only, not a complete machine. Installed/operating weight depends on the host chassis the engine is fitted to.
Dry engine weight	Not consistently documented for this exact engine code across available spec sources. Confirm with the factory shop manual or a dealer parts desk for the exact figure.
Ground pressure	Not applicable. This is an engine assembly, not an undercarriage-equipped machine.

Dimensions

Scope	Transport length/width/height, wheelbase, track gauge, and ground clearance are host-machine dimensions and do not apply to a bare-engine listing.
Engine outline dimensions	Not consistently documented for this exact engine code across available sources. Request the factory engine outline drawing for exact installation dimensions.
Cylinder layout	Inline-six layout, with block length following the standard cylinder spacing of the 6D125-1 family.

Performance

Rated speed	2200 rpm.
Torque rise	Approximately 30% above rated torque on the naturally aspirated rating, per the factory grader engine spec sheet. Improves lugging ability under load before stalling.
Governor	Mechanical, flyweight-type, built into the inline fuel-injection pump. No electronic governor or engine control module.
Aspiration	Naturally aspirated. No turbocharger assembly appears in the parts breakdown for this engine code.
Machine performance figures	Travel speed, drawbar pull, lift/dig/dump figures, and gradeability are host-machine specifications, not engine specifications, and do not apply to this bare-engine listing.

Service capacities (summary)

Engine oil (refill)	Not consistently documented for this exact engine code across available sources. Verify against the factory shop manual for this serial range.
Coolant (engine only)	Not consistently documented for this exact engine code across available sources. Verify against the factory shop manual for this serial range.
Fuel tank	Not applicable. The fuel tank is part of the host machine, not the engine.
Fuel type	Diesel, mechanical inline fuel-injection with flyweight governor.

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

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

System	Capacity	Recommended fluid
Engine crankcase (oil pan, with oil filter change)	Exact factory refill quantity is not confirmed for this specific engine/serial range in accessible factory literature. Comparable naturally-aspirated Dash-8-era engines in this same 11-liter inline-six family run roughly in the 25-30 L (6.6-7.9 US gal) range with filter change, but this varies by the host machine's oil pan design. Always fill to the dipstick mark, not to a fixed volume.	Komatsu Genuine Diesel Engine Oil (EO), SAE 15W-40 for temperate service. Komatsu's viscosity-by-climate guidance for this engine generation calls for SAE 10W or 10W-30 below about 0°C (32°F), and straight SAE 30 in sustained heat above about 25°C (77°F).
Cooling system	Exact refill quantity not confirmed for this specific engine/serial range in available factory documentation. Radiator and jacket volume is set by the host chassis, not the bare engine, so it is not published for this job.	Komatsu Super Coolant (ethylene-glycol antifreeze and corrosion-inhibitor concentrate), mixed 50/50 with clean soft water for standard climates. A richer concentrate ratio is used only where the machine's ambient-temperature chart calls for protection well below freezing.
Fuel tank	Not applicable to the engine itself. Fuel tank is a chassis component; its capacity depends on which machine this engine variant was installed in and is not documented for this bare-engine job.	ASTM D975 No. 2-D diesel for normal ambient service. No. 1-D (or a winter-blend No. 2-D/No. 1-D mix) is recommended below freezing to keep the fuel from waxing and plugging the filter.
Transmission / powertrain compartment	Not documented for this bare-engine job. The transmission case belongs to the host machine's chassis, not the engine, and its refill volume was not confirmed for this exact engine/serial range.	Komatsu Powertrain Oil (TO). SAE 10W is used in cold ambient conditions and SAE 30 in standard/warm conditions, consistent with the mechanical powershift transmissions paired with this engine family.
Final drive case (each side)	Not documented for this bare-engine job. Final drives are part of the host machine's undercarriage, not the engine, and their capacity is not confirmed for this exact engine/serial range.	Komatsu Final Drive / Powertrain Oil (TO), SAE 30, matching standard factory fill practice for crawler final drives of this era.
Hydraulic system and tank	Not documented for this bare-engine job. Hydraulic tank size belongs to the host machine's implement/blade circuit, not the engine, and was not confirmed for this exact engine/serial range.	Komatsu Genuine Hydraulic Oil (HO), SAE 10W (or an equivalent anti-wear hydraulic oil), matching standard factory fill practice for this engine generation's host machines.
Grease points (chassis and engine external linkages)	Not a bulk-fill system — applied by grease point and service interval rather than a refill volume.	Komatsu Lithium-base Grease EP2 (G2-LI), NLGI grade 2, the standard general-purpose chassis grease for this equipment generation.

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

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

Service interval	Tasks
Every 10 h	Check engine oil level on the dipstick before starting; top up to the mark without overfilling. Check coolant level in the radiator or sight glass; add coolant mixed to spec if low. Drain water and sediment from the fuel tank and water separator. Inspect the block, injection pump, and hose fittings for fresh oil, fuel, or coolant leaks. Check the air cleaner restriction indicator; service the element if it reads full. Weekly: check drive belt tension and condition, and check battery electrolyte level and terminals.
Every 250 h	Change engine oil and replace the oil filter cartridge. Replace the fuel filter cartridge and bleed air from the fuel system. Check and adjust fan and charging-belt tension. Clean the air cleaner outer element; replace it if damaged or heavily loaded with dust. Lubricate the injection pump governor linkage and external throttle linkage pins. Check exhaust manifold and intake connections for leaks and retighten as needed.
Every 500 h	Check and, if needed, replenish the coolant's corrosion-resistor concentration. Clean radiator and oil-cooler fins of dust, mud, and debris. Check battery electrolyte condition and clean the terminals. Inspect charging and starting wiring for chafing, corrosion, or loose connections. Check muffler and exhaust piping mounting for cracks or looseness.
Every 1,000 h	Check fuel injection timing against the factory setting. Check injection nozzle spray pattern and opening pressure; send out for bench testing if suspect. Clean the crankcase breather and fuel tank breather. Check engine mounting bolts and the crankshaft vibration damper for cracking or looseness. Record a baseline compression or blow-by reading for trend comparison at future services.
Every 2,000 h	Check and adjust intake and exhaust valve clearance. Recheck and recalibrate fuel injection pump timing. Remove the injection nozzles as a set and send them for bench reconditioning. Retorque cylinder head bolts to the factory sequence and specification. Compare current compression or blow-by against the baseline reading, cylinder to cylinder.
Every 4,000 h	Drain and completely replace engine coolant, flushing the cooling system (roughly every 2 years or 4000 hours). Send the injection pump out for full bench calibration or overhaul. Plan a top-end inspection of liners, rings, and wet-liner O-ring seals if oil consumption or oil-analysis trends are climbing. Check main and connecting-rod bearing clearances at any teardown. Base the decision for an inframe or full overhaul on compression and oil-analysis trend data, not a fixed hour number.

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

Predictive Maintenance & Fluid Analysis

This engine carries no ECM and no sensors, so predictive upkeep runs on oil analysis and mechanical trend data instead of fault codes. Pull scheduled oil samples and watch for coolant intrusion, a signature of the wet cylinder liners' rubber O-ring seals starting to fail, plus fuel dilution and wear metals. Track cylinder compression or blow-by cylinder to cylinder over time rather than against one fixed number. Note idle stability trends too: early governor-linkage wear inside the injection pump shows up as idle hunting before it becomes a driveability complaint.

Corrective & Common Repairs

Idle hunting or surging usually traces to worn governor linkage or fatigued springs in the injection pump's flyweight governor, not the pump itself. A power-loss complaint is often a low-pressure fuel-side air leak at the feed line or priming pump, not a bad pump; pressure-test and bleed the fuel side first. Milky oil or a steaming breather points to wet-liner O-ring seepage or a failed head gasket; a pressure test tells them apart. Starting or charging complaints are basic electrical faults, not sensor faults, on a build with no electronic control.

Overhaul & Rebuild Points

Rising oil consumption or blue/white smoke on this naturally aspirated six usually means glazed or worn cylinder liners and rings; confirm with a blow-by check and a cylinder-to-cylinder compression comparison before an inframe overhaul. Because the liners are the wet type, sealed to the block with rubber O-rings, fresh seals are mandatory anytime a liner is pulled. Send the injection pump and nozzles out for bench calibration rather than adjusting them in the field. At teardown, retorque the cylinder head to spec and check crankshaft and rod bearing clearances.

Seasonal & Environment Servicing

Factory build options on this engine include dedicated sandy/dusty-terrain and cold-terrain variants, so match servicing to climate rather than one generic schedule. Switch crankcase oil viscosity by season: a lighter grade below freezing, a heavier one in sustained heat, per the factory chart. Run a winter-blend diesel below freezing to stop fuel waxing and filter plugging, and confirm the coolant's corrosion-resistor concentration before cold or humid seasons. In sandy or dusty conditions, service the air cleaner and radiator/oil-cooler fins more often than standard.

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

Part number	Part	Notes
07281-00197	Clamp,(With Pre-Fuel Filter)	Fuel system service	Check fitment →
ND092220-0040	Filter,Fuel	Fuel system service	Check fitment →
09637-02161	Plate? Instruction,Air Cleaner (Double Element)	Air intake service	Check fitment →
600-181-2500	Element Ass'Y,Outer	Scheduled service item	Check fitment →
6114-80-7101	Element Ass'Y	Scheduled service item	Check fitment →

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

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

Host machine scope

The 6D125-1D(S/N 10001-UP) is a bare engine block, not a standalone machine. Its own parts breakdown carries dozer-related fitment references (straight-tilt dozer, trimming dozer, and several dozer-model callouts), while other research on this same engine code points toward motor-grader applications instead; no single host machine is confirmed for this exact serial range. The work-tool coverage below reflects the dozer-class candidate only — verify the actual host machine with your dealer before ordering blade or ripper components.

Dozer blade (moldboard)

Hosts in this class are offered with straight-tilt, angle, semi-U, and full-U moldboards. Semi-U blades on the larger D65-class hosts run up to roughly 5.6 cubic m (7.3 cu yd); smaller hosts in the range carry proportionally smaller blades. Power-angle-tilt (PAT) hydraulic blade control is more common toward the lighter end of the class, with straight-tilt (hydraulic tilt only) more typical on the heavier hosts.

Ripper

A rear-mounted parallelogram ripper, in single-shank or multi-shank form, is the standard work tool for this dozer class. The ripper beam rides a parallelogram linkage driven by one or more hydraulic cylinders, holding a near-constant tip angle through the penetration stroke. Single-shank rippers suit hard, frozen, or rocky ground; multi-shank rippers trade digging force for wider coverage in easier ripping conditions.

Blade and ripper mounting

Blades pin-mount to C-frame push arms with hydraulic lift/tilt cylinders, and rippers pin-mount to a rear-frame parallelogram beam. Neither uses a quick-coupler system; swapping between blade or ripper configurations is a pin-and-cylinder shop job, not a field quick-change, and requires the matching hydraulic circuit already plumbed for that tool.

Cab and canopy

Factory cab options span an open ROPS canopy or an enclosed ROPS cab with air conditioning, matching the usual spread for this equipment class. Canopy and head-guard mounting hardware appear directly in this engine's own parts breakdown, confirming the canopy/cab option is tied to this exact engine fitment rather than assumed from the wider class.

Guarding and screens

Rear and side screens, sweeps, and a rock/debris guard package are offered for this equipment class to protect the radiator, rear frame, and undercarriage in brush-clearing or quarry duty. A cooling-system corrosion resistor is also a factory-fit option documented on this exact engine, intended for humid or tropical duty rather than mechanical impact guarding.

Terrain and climate factory specs

This engine's own parts breakdown includes dedicated sandy-and-dusty-terrain and cold-terrain build variants — added sealing and filtration for the former, additional cold-start and corrosion-resistor hardware for the latter. These are factory climate-oriented build specs on the engine itself, not swappable work tools.

Winch

Some hosts in this dozer class offer a rear-mounted drawbar winch as an alternative to the ripper, mainly for logging or land-clearing work. Availability varies by the specific host model and isn't confirmed for every variant in the range — verify with your dealer for the exact host machine.

Trim/finish-grade build variant

This engine's parts breakdown lists a separate 'trimming dozer' oil-pan and air-cleaner variant alongside the standard build, pointing to a factory finish-grading configuration option noted in this engine's own parts records for whichever dozer-class host it may serve. The exact operational difference isn't documented outside the parts catalog for this exact serial range — verify with your dealer for the specific host machine.

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

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

Cooling System

Komatsu : 6d125-1d(S/N 10001-Up) : Cooling System : Cooling Fan And Mounting

01***25	Bolt,(For Canvas Canopy?Head Guard)	6
01***30	Bolt,(For Quick Shift) (Mitsubishi)	10
01***40	Bolt, Mount Master Brake Cylinder	8
01***95	Bolt,(For 2nd Travel Speed) (Op)	4

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Komatsu : 6d125-1d(S/N 10001-Up) : Cooling System : Corrosion Resistor And Piping

01***20	Bolt,(For Quick Shift) (Mitsubishi)	1
01***30	Bolt,(For Quick Shift) (Mitsubishi)	4
01***08	Nut,(For Canvas Canopy?Head Guard)	1
01***16	Washer,Radio Controlled Slag Handling	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Cooling System : Water Pump And Mounting

01***30	Bolt,(For France Noise Suppression)	2
01***16	Bolt (With Air Heater & Conditioner)	6
01***30	Bolt,(For Quick Shift) (Mitsubishi)	5
01***35	Bolt,(For Quick Shift) (Mitsubishi)	1

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Cylinder Block

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

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

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

01***50	Bolt,(For Strengthened Cover)	6
01***15	Bolt	1
01***20	Bolt	5
04***28	Pin, Dowel - Transmission Case, Pin-Dowel	1

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

01***20	Bolt,(For Quick Shift) (Mitsubishi)	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***08	Nut,(For Canvas Canopy?Head Guard)	1
01***16	Washer,Radio Controlled Slag Handling	2

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

01***40	Bolt,(Dust And Dirt Protection)	2
01***50	Bolt, Radiator To Frame	6
01***65	Bolt - Battery Box	2
01***40	Bolt,R.H. Outside And L.H. Inside, Bolt	8

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

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)	8

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

01***25	Bolt,(For Canvas Canopy?Head Guard)	29
01***30	Bolt,(For Quick Shift) (Mitsubishi)	7
01***16	Washer,Radio Controlled Slag Handling	36
01***32	Washer,(With Auto Emergency Steering)	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Cylinder Block : Oil Pan (For Trimming Dozer)

01***25	Bolt,(For Canvas Canopy?Head Guard)	29
01***30	Bolt,(For Quick Shift) (Mitsubishi)	7
01***16	Washer,Radio Controlled Slag Handling	35
01***32	Washer,(With Auto Emergency Steering)	1

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

02***13	Pin, Dowel	2
04***18	Ring, Snap	2
61***10	Piston Ass'Y	6
61***11	Piston Ass'Y	6

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Cylinder Head

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

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	2
01***40	Bolt, Mount Master Brake Cylinder	1
01***08	Nut,(For Straight Tilt Dozer) (D65p)	6

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Komatsu : 6d125-1d(S/N 10001-Up) : Cylinder Head : Air Cleaner And Mounting (For Trimming Dozer)

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	2
01***08	Nut,(For Straight Tilt Dozer) (D65p)	6
01***16	Washer,Radio Controlled Slag Handling	6

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Komatsu : 6d125-1d(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)	15
01***55	Bolt, Mount Tube To Switch Pump	6
01***60	Bolt, Mount Tube To Switch Pump	1

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Komatsu : 6d125-1d(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	8
61***40	Seal,Exhaust Valve (K1)	2

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

04***20	Pin,Dowel (Welded)	2
61***30	Sleeve,Holder	1
61***20	Cotter, Valve	8
61***40	Seal,Exhaust Valve (K1)	2

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

01***80	Bolt, Mount Strainer Flange	18
01***00	Bolt (M10-1.50x100)	18
07***08	Plug,(Without Auto Priming System)	2
61***20	Spacer,(For Shipping)	18

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Komatsu : 6d125-1d(S/N 10001-Up) : Cylinder Head : Muffler And Mounting(#10001-11478)

01***25	Bolt,(Sandy? Dusty Terrain Spec.)	4
01***40	Bolt,(Dust And Dirt Protection)	4
01***35	Bolt,(For Quick Shift) (Mitsubishi)	1
01***30	Bolt, Mount Pump	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Cylinder Head : Muffler And Mounting(#11479-)

01***25	Bolt,(Sandy? Dusty Terrain Spec.)	4
01***40	Bolt,(Dust And Dirt Protection)	4
01***35	Bolt,(For Quick Shift) (Mitsubishi)	1
01***30	Bolt, Mount Pump	2

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

01***08	Nut, Regular Hexagon (M10-1.50)	6
01***08	Nut,R.H. Thread	6
01***16	Washer,Radio Controlled Slag Handling	40
01***32	Washer,(With Auto Emergency Steering)	40

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

01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***08	Nut,(For Canvas Canopy?Head Guard)	1
01***16	Washer,Radio Controlled Slag Handling	25
07***50	Cap,Oil Filler	1

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

02***43	O-Ring,Water Manifold	10
07***12	Washer, Gasket,(Without Thermo Sensor) (K1)	1
07***08	Plug,(Without Auto Priming System)	1
07***12	Plug,(Without Corrosion Resistor)	2

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Electrical System

Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Alternator (13a)

60***50	Alternator A. (13a)	1
KD***31	Bushing,Insulator	2
KD***80	Packing	1
KD***72	Slip Ring Ass'Y	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Alternator (13a) (Sandy Dusty Spec.)

60***70	Alternator A. (13a),(Sandy And Dusty Terrain S.)	1
KD***31	Bushing,Insulator	2
KD***72	Slip Ring Ass'Y	1
KD***90	Wire,Read	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Alternator And Mounting

01***55	Bolt, Mount Tube To Switch Pump	1
01***25	Bolt	1
01***11	Nut (Welded)	1
01***26	Washer,(For Additional Rear Lamp)	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Alternator And Mounting (For Anti-Corrosive Alternator)

01***55	Bolt, Mount Tube To Switch Pump	1
01***25	Bolt	1
01***11	Nut (Welded)	1
01***26	Washer,(For Additional Rear Lamp)	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Heater Switch And Heater Signal

60***70	Switch,Air Intake Heater	1
60***30	Signal,Engine Pre Heater	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Starting Motor (7.5kw) (1/2)

60***70	Starting Motor A.,(7.5kw) (See Fig.A6210-B4a4)	1
KD***20	Armature Ass'Y	1
KD***51	Switch Ass'Y,Safety Relay	1
KD***50	Rear Bracket Ass'Y	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Starting Motor (7.5kw) (2/2)

KD***60	Plunger Ass'Y	1
KD***30	Holder	1
KD***20	Screw	2
KD***01	Washer,(Not Shown)	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : 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***50	Brush Assembly	4

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : 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 : 6d125-1d(S/N 10001-Up) : Electrical System : Starting Motor And Mounting

01***60	Bolt,(Shim Thickness?More Than 8mm)	3
66***10	Gasket,Starting Motor	1
(6***0)	Starting Motor Ass'Y,(7.5kw) (See Fig.0661a)	1
(6***0)	Starting Motor Ass'Y,(7.5kw) (See Fig.0661)	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Electrical System : Starting Motor And Mounting (For Trimming Dozer)

01***40	Bolt,(With Center Guard)	3
60***20	Clip,(Large Capacity Type)	1
66***10	Gasket,Starting Motor	1
(6***0)	Starting Motor Ass'Y,(7.5kw) (See Fig.A6210-B4a4)	1

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Engine Kit

Komatsu : 6d125-1d(S/N 10001-Up) : Engine Kit : Gasket Kit

02***43	O-Ring,Water Manifold	10
07***15	O-Ring,(For Low Speed) (D40pf)	1
07***25	O-Ring,Injection Pump Mounting	1
07***30	Ring, Seal - Between Sections	1

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Fuel System

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

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	4
01***35	Bolt,(For Quick Shift) (Mitsubishi)	2
01***16	Washer,Radio Controlled Slag Handling	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#10001-11478)

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

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#11479-)

ND***30	Block,Coupling	2
ND***10	Flange,Coupling	1
ND***50	Bolt	1
ND***50	Coupling,Cross	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#10001-11478)

ND***40	Washer? 1mm,Plate	1
ND***00	Pump Ass'Y,Priming Pump	1
ND***70	Washer,Union	4
ND***10	Piston? 21.988mm,Blue	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Feed Pump)(#11479-)

ND***40	Washer? 1mm,Plate	1
ND***70	Washer,Union	4
ND***10	Spring, Check Valve	2
ND***10	Pin,Roller	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#10001-11478)

ND***40	Plug,Screw	1
ND***50	Washer? 0.3mm	0
ND***90	Lever Ass'Y,Control	1
ND***20	Screw,Adjusting	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#11479-)

ND***40	Plate,Thrust	1
ND***80	Pin,Stop	1
ND***40	Plug,Screw	1
ND***10	Adapter	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#10001-11478)

ND***20	Washer? 1.0mm,Cover Plate	2
ND***60	O-Ring	2
ND***70	Packing,Rubber Plate	1
ND***10	Seal,Oil	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#11479-)

ND***20	Washer? 1.0mm,Cover Plate	2
ND***40	O-Ring	1
ND***10	Seal,Oil	1
ND***50	Packing,Rubber Plate	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)(#10001-11478)

61***21	Injection Pump A	1
61***22	Injection Pump A	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)(#11479-)

61***20	Injection Pump A	1
ND***50	Ring,Adjust	1
ND***80	O-Ring	1
ND***40	Shim? 0.16mm	0

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)(#10001-11478)

ND***70	O-Ring	6
ND***50	Seat,Spring? Lower	6
ND***11	Spring,Plunger	6
ND***20	Shim? 1.9mm,Element Holder	0

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)(#11479-)

ND***30	Sleeve,Control	6
ND***20	Shim? 0.3mm	0
ND***70	O-Ring	6
ND***20	Bolt,With Washer	3

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (1/2)

01***75	Bolt,(See Fig.0142)	4
01***25	Bolt,(For Canvas Canopy?Head Guard)	4
01***45	Bolt,(For Power Tilt Mech Angle)	2
01***70	Bolt, Mount Bracket And Oil Inlet Tube, Bolt	2

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (2/2)(#10001-11478)

01***30	Bolt	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***55	Bolt, Mount Tube To Switch Pump	4
01***19	Washer,Spring (With Extinguisher) (D31p)	1

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (2/2)(#11479-)

01***30	Bolt	4
01***20	Bolt,(For Quick Shift) (Mitsubishi)	1
01***25	Bolt,(For Canvas Canopy?Head Guard)	1
01***55	Bolt, Mount Tube To Switch Pump	4

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Komatsu : 6d125-1d(S/N 10001-Up) : Fuel System : Fuel Nozzle And Spill Pipe

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

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Lubricating Oil System

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

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
01***30	Bolt,(For Quick Shift) (Mitsubishi)	4
01***35	Bolt,(For Quick Shift) (Mitsubishi)	2
01***16	Washer,Radio Controlled Slag Handling	4

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

01***16	Bolt, Battery To Frame Ground Wire Attaching	1
01***35	Bolt,(For Quick Shift) (Mitsubishi)	2
01***50	Bolt,(With Service Valve R.H.)	2
01***85	Bolt,(For 2nd Travel Speed) (Op)	1

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Komatsu : 6d125-1d(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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6D125-1D(S/N 10001-UP) serial number reference

The 6D125-1D 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 stamped directly into the block casting. Read the full engine model, 6D125-1D, 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 3-character alpha PIN prefix)	6D125-1D build spec, part of the naturally aspirated 6D125-1 family. No S- prefix on this model code; per this engine family's own convention an S- prefix marks the turbocharged variant, so a plain 6D125-1D reads as non-turbo.	The 6D125-1 series carries a plain numeric running serial with no letter code ahead of it. Build/fitment is set by the suffix on the base model number (A, C, D, DD, EE, F, J, K, N, Q, R, Z and similar), not by a prefix ahead of the serial digits. Some suffix builds in this family tie to a specific dozer or grader chassis - for example the 1C build to the D53A-17/D53P-17 dozer, the 1DD build to the D58E-1/D58E-1B dozer, the 1F build to the D60A-8/D60P-8/D60S-8 dozer - but the plain 1D build shows no confirmed chassis tie in any parts or spec source checked; scattered aftermarket fitment lists bundle it in with several other suffix codes at once (a sign of generic cross-fit copy, not a factory pairing) and one grader-model tie found only in an AI search summary could not be confirmed against a primary source. 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 6D125-1D (S/N 10001-UP)?

It is Komatsu's own 6D125-1D: a naturally aspirated, mechanically governed inline-six diesel of 11.04 L displacement, with 125 x 150 mm (4.9 x 5.9 in) bore and stroke. Gross flywheel output is about 116 kW (155 hp) at 2200 rpm. Fuel is metered by an inline injection pump with a flyweight governor; there is no turbocharger and no electronic control module on this build.

What is the operating weight of the 6D125-1D (S/N 10001-UP)?

None is published, because this is a bare engine assembly, not a complete machine. Operating weight depends entirely on the host chassis it is installed in, and that host is not confirmed for this exact serial range. Even the engine's own dry weight is not consistently documented across factory sources for this specific build; check with a dealer parts desk if you need that figure.

What replaced the 6D125-1D (S/N 10001-UP)?

No single documented successor ties directly to this exact naturally aspirated, no-prefix build. Komatsu carried the wider 6D125 nameplate forward through a turbocharged and aftercooled generation and eventually into a fully electronically controlled series, but no factory source pairs one specific one-for-one replacement code with this exact serial range.

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

The engine hunts or surges at idle. What's the usual cause on this mechanical 6D125-1?

Idle hunting or surging on this mechanically governed engine is most often worn governor linkage or fatigued governor springs inside the injection pump's flyweight governor, not a fuel-quality or air-intake problem. Check linkage free play and spring tension before assuming the pump itself needs an overhaul.

A power-loss complaint led to a full injection pump rebuild, and the engine still feels weak. What gets missed?

Owners chasing a power-loss complaint into a full inline injection pump overhaul frequently find the real fault was a small air leak on the low-pressure fuel transfer or feed line, not the pump or governor. Pressure-test and bleed the low-pressure fuel side, and check the priming pump and fittings, before pulling the injection pump.

Oil looks milky or the breather is putting out steam. What's typically behind it on this engine?

This engine uses wet cylinder liners sealed to the block with rubber O-rings. Hardened or worn O-rings let coolant seep into the oil pan, showing up as milky oil, steam or vapor from the breather, and unexplained coolant loss. A cracked head or failed head gasket gives similar symptoms, so oil analysis plus a cooling-system pressure test is used to tell the two apart. Coolant-contaminated oil can mask bearing damage that isn't obvious from the dipstick alone — have your dealer verify bearing condition before returning the engine to service.

What wears out first when owners report high oil consumption or persistent smoke on this engine family?

Complaints of rising oil consumption and blue or white smoke on these mechanical, naturally aspirated sixes usually trace to worn or glazed cylinder liners and rings, occasionally described as a liner starting to work loose in its bore. Blow-by volume together with a warm compression or cylinder leak-down comparison (cylinder to cylinder, not against one fixed number) is the usual way owners confirm this before committing to an inframe overhaul.

Are there electrical or sensor problems reported for this engine?

This is a mechanically governed engine with an inline injection pump and no electronic controls, so there's no ECM and no fault codes to chase. Reported electrical issues are limited to the basic cranking and charging circuit: a worn starter solenoid or starting safety relay (on many Komatsu machines this relay reads an alternator signal so the starter can't engage while the engine is already running), and, where cold-start assist is fitted, weak or failed glow plugs causing slow or hard starts. Treat any wiring or starting-circuit repair as basic electrical troubleshooting, not sensor diagnostics.

Does duty cycle change what fails first on the 6D125-1 family, or is wear consistent regardless of the host machine?

Reported wear patterns track duty cycle more than the engine itself, and the exact machine this engine powers can vary by configuration. In sustained heavy-load, dusty applications, radiator or oil-cooler fouling and cylinder liner glazing tend to show up first. In lighter, continuous-duty applications, the governor linkage and low-pressure fuel system are more often the first things to wear or start leaking air before any bottom-end issue appears. Treat these as general tendencies for the mechanical 6D125-1 family rather than a guarantee for any one application.

What should a buyer check before purchasing a used 6D125-1D(S/N 10001-UP)?

Pull an oil sample for lab analysis first — look for coolant intrusion, fuel dilution, and wear metals. Run a warm compression or cylinder leak-down test and compare cylinder to cylinder rather than against one fixed number, since acceptable readings vary by configuration and hours. Check the breather for oil or steam discharge, look for oil sheen in the coolant, and confirm oil pressure holds steady at idle and at rated speed. Ask for service history, especially any prior head or injection-pump work, and get the specific host machine and application confirmed — have your dealer verify overall engine condition and any recent repair work before finalizing the purchase.

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

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