Komatsuengine(no series)

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

Maintenance schedule, common problems & OEM parts breakdown

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

The Komatsu 6D125-1B-PL(S/N 10001-UP) is a naturally aspirated, mechanically governed diesel engine: 6 cylinders inline, roughly 11.0 L displacement, 125 mm x 150 mm bore and stroke, with no turbocharger fitted to this arrangement (the model code carries no "S" prefix). It is documented as a power plant used across Komatsu's articulated-frame A-series motor grader line — the GD605A, GD611A, GD621A, GD623A, GD625A, GD655A and GD663A range — alongside closely related "-1B" suffix arrangements built for the same chassis family. A turbocharged version of the same block architecture offered more power on the same grader platform. Operating weight and dimensions for this exact engine arrangement and serial range are not separately published; confirm against the data plate of the specific unit.

Across the wider 6D125 engine family, the core 11.0 L block architecture stayed fixed while Komatsu retuned governed speed and output by application: this naturally aspirated grader arrangement is rated lower than the turbocharged S6D125/SA6D125 variants used in later, larger Komatsu machines, so published power figures vary by configuration and host machine. In the used and parts market today, these mechanically governed, electronics-free A-series graders are valued for straightforward field rebuilds and for parts commonality across the broader 6D125 engine family used in Komatsu dozers, graders, wheel loaders, and excavators of the same era. Complete running examples are increasingly scarce, so demand leans toward rebuild kits, reconditioned injection pumps, and grader-specific driveline and blade-control wear parts.

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

Engine

Engine family / arrangement	Non-turbocharged 6D125-1 series diesel. The "-1B-PL" suffix identifies a specific factory build/application arrangement within the 6D125-1 family, not a separate generation. No source ties this exact arrangement to one named host machine by name; a closely related non-turbo "-1B" arrangement in this same family is documented on period Komatsu motor graders in the GD605A/GD623A/GD655A/GD663A range.
Aspiration / fuel system	Naturally aspirated, mechanically governed direct-injection diesel; no electronic engine controls. The model code carries no "S" (supercharged/turbo) prefix — that prefix is reserved for the turbocharged builds in this family — so this arrangement is the non-turbo version.
Gross power	About 116 kW (155 hp) at 2200 rpm is the published rating for the naturally aspirated 6D125 engine across this application family (versus about 134 kW / 180 hp for the turbocharged version). Not separately published for this exact arrangement and serial range — confirm against the engine serial plate with your dealer.
Net power	Not documented for this exact arrangement/serial range.
Displacement	11.0 L (11,040 cc)
Cylinders, bore x stroke	6 cylinders, inline; 125 mm x 150 mm (4.92 in x 5.91 in)
Emissions tier	Pre-regulation mechanical diesel; no EPA/EU emissions certification (predates Tier 1/Stage I).

Weights

Operating weight	Not documented for this bare engine arrangement. Installed weight depends on the host machine, which is not confirmed for this exact serial range.
Shipping weight	Not documented for this exact arrangement/serial range — verify with your dealer or the applicable parts book.

Dimensions

Engine block dimensions	Not documented for this exact arrangement/serial range.
Installed dimensions	Not applicable to a bare engine listing. Overall length/width/height are host-machine figures, and no host machine is confirmed for this exact arrangement and serial range.

Performance

Governed engine speed	About 2200 rpm is the typical governed speed for this naturally aspirated arrangement family; not separately confirmed for this exact serial range.
Travel speed / gradeability	Not applicable to a bare engine listing. These are host-machine figures, and no host machine is confirmed for this exact arrangement and serial range.

Service capacities (summary)

Engine oil (crankcase)	Not documented for this exact arrangement/serial range — check the applicable shop manual for the confirmed capacity.
Cooling system	Not documented for this exact arrangement/serial range.
Fuel tank	Not applicable. Fuel tank capacity is a host-machine figure, and no host machine is confirmed for this exact arrangement and serial range.
Hydraulic system	Not applicable. Hydraulic system capacity is a host-machine figure, and no host machine is confirmed for this exact arrangement and serial range.

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

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

System	Capacity	Recommended fluid
Engine crankcase (with filter)	Not documented in accessible OEM literature for this exact serial range and arrangement — verify against the dealer shop manual or dipstick markings before service	Komatsu Genuine EO (diesel engine oil): SAE 15W-40 for normal/warm ambient use, SAE 10W-30 for cold-weather starts. An API CF-class diesel engine oil is the acceptable equivalent where Komatsu-branded oil is unavailable.
Cooling system	Not documented for this exact arrangement and serial range in accessible OEM literature; verify against the dealer shop manual or radiator markings before service	Komatsu Super Coolant (or Komatsu genuine antifreeze/coolant concentrate) mixed 50/50 with clean water; adjust the antifreeze ratio for regional low-temperature protection
Fuel tank	Not documented for this exact serial range in accessible OEM literature; fuel tank size on 6D125-1-family engines varies by host machine	Automotive No. 2-D diesel fuel (ASTM D975 equivalent); use a winter-grade or blended fuel in cold climates to prevent wax/gelling
Transmission and torque-converter case	Not documented for this exact serial range — capacity depends on the host machine this engine variant is fitted to	Komatsu Genuine TO (Powertrain Oil): SAE 10W in cold conditions, SAE 30 in normal/warm ambient temperatures. The transmission and torque-converter case typically share the same powertrain-oil spec on Komatsu machines of this era.
Final drive case, each side	Not documented for this exact serial range in accessible OEM literature	Komatsu Genuine TO (Powertrain Oil), same SAE 10W (cold) / SAE 30 (normal-warm) grading as the transmission case on most Komatsu machines of this era; confirm whether your host machine specifies a separate final-drive grade
Hydraulic system and tank	Not documented for this exact serial range in accessible OEM literature	Komatsu Genuine HO (hydraulic oil), ISO VG46-equivalent; SAE 10W for cold ambient operation, SAE 30 for normal/warm ambient operation
Axles/differentials	Not documented for this exact serial range	Axle/differential fluid spec depends on the host machine's driveline configuration and is not confirmed for this engine arrangement — check the applicable machine shop manual
Grease (spec only)	Not applicable — service item, not a fill-and-check reservoir	Komatsu Genuine grease, lithium-base NLGI No. 2 multipurpose grease for general pin and bushing points; a molybdenum-disulphide-fortified grease is called out on Komatsu lubrication charts for pivot points under heavy shock load

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

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

Service interval	Tasks
Every 50 h	Check engine oil level on the dipstick before starting and top up with the specified grade if low Check coolant level at the radiator or reserve tank and look for external leaks around hoses and the block Drain water and sediment from the fuel tank sump and the primary fuel/water separator Check the air cleaner restriction indicator and service the element if it has tripped Walk around the engine and check for fuel, oil, and coolant seepage at the oil pan and fittings Grease exposed governor and throttle linkage points if grease fittings are present
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 the fan/alternator belt tension and inspect for cracking Clean or replace the air cleaner element based on condition Check battery electrolyte level and clean the terminals Inspect the oil pan and lubricating-oil piping for seepage and retorque loose hardware
Every 500 h	Check the coolant corrosion resistor element, where fitted, and replace it Check the alternator and starting motor mounting and wiring for wear or looseness Inspect the muffler and exhaust manifold mounting for cracks and leaks Check the water pump shaft for play and leakage at the weep hole Check coolant condition and additive concentration Check the lubricating-oil cooler core for external clogging and clean as needed
Every 1,000 h	Change the powertrain case oil (transmission and final-drive cases) on the host machine Check and adjust idle and full-load governed engine speed against the data-plate rating Check torque on the crankshaft pulley, vibration damper, and flywheel housing mounting bolts Clean the crankcase breather and check for excessive blow-by Check starting motor brushes and commutator for wear Retorque cylinder head cover and intake/exhaust manifold fasteners
Every 2,000 h	Check and adjust valve clearance at the cylinder head; this mechanical engine has no self-adjusting valve gear Check and reset fuel injection pump timing and governor linkage settings Pressure-test fuel injection nozzles and recondition or replace as needed Replace coolant and flush the cooling system Check cylinder compression and log it against the baseline reading Inspect the flywheel ring gear and starter pinion engagement for wear
Every 4,000 h	Pull and inspect cylinder liners, pistons, and rings against factory wear limits Inspect main and connecting-rod bearings for wear and replace as a set if worn Recondition or exchange the mechanical fuel injection pump assembly Inspect the cylinder head for valve seat wear and resurface or replace as needed Replace the water pump assembly as a preventive step at major overhaul Coordinate the engine overhaul with an inspection of the host grader's circle, drawbar, and moldboard wear points

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

Predictive Maintenance & Fluid Analysis

On this naturally aspirated 6D125-1B-PL, oil sampling at every engine-oil change is the earliest warning of injection pump or ring wear since there is no electronic fault logging to flag it first. Track soot loading and wear metals in each sample against a baseline set at commissioning. Pair engine oil analysis with periodic sampling of the hydraulic circuit oil, since the same circuit runs blade lift, tilt, side-shift and circle-rotate functions and water or metal contamination there affects both driveline and blade control together.

Corrective & Common Repairs

Fuel injection pump and nozzle wear drive most corrective calls on this mechanical engine; rough idle or smoking under load usually traces to nozzle spray pattern rather than the naturally aspirated air side. Starting motor and alternator brush wear are common on high-hour units of this era. On the host grader, circle and moldboard wear — circle gib clearance, moldboard cutting-edge and end-bit wear — is a frequent corrective item given the machine's grading duty cycle. Check governor linkage travel whenever power complaints come in.

Overhaul & Rebuild Points

A major rebuild on the 6D125-1B-PL centers on cylinder liners, pistons, and main/rod bearings once compression trends down from baseline; this naturally aspirated arrangement has no turbocharger to inspect, so overhaul scope stays on the block, head, and injection pump. Recondition or exchange the mechanical injection pump and nozzles as a set rather than piecemeal. On the host grader, plan an inspection of the circle-drawbar-moldboard assembly and articulation joint alongside the engine overhaul, since both wear on a similar hour cycle in heavy grading duty.

Seasonal & Environment Servicing

This engine's mechanical governor and injection pump have no cold-start electronics, so cold-weather starts depend on correct seasonal fuel grade, a block heater where fitted, and the specified lower-viscosity oil grade. In hot, dusty grading conditions, shorten air-cleaner element service intervals and check the cooling system and corrosion resistor more often than the standard chart calls for. Grease the circle, drawbar, and articulation pivot points on a shortened schedule when working in mud or standing water to keep grit from packing the joints.

6D125-1B-PL(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.

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

Code	Meaning	Likely cause	What to do
CHARGE lamp (red, battery symbol)	Alternator is not charging the battery circuit	Broken or slipping fan/alternator belt, faulty alternator, loose or corroded wiring connection	Stop and check belt tension and alternator wiring before continuing; do not keep running on battery power alone
Engine oil pressure lamp (red, oil can symbol)	Engine lube oil pressure has dropped below the safe minimum	Low oil level, clogged oil filter, worn oil pump, internal leak	Shut engine down immediately, check oil level and filter condition before restarting
Engine coolant temperature gauge/lamp (red zone)	Engine coolant temperature has risen above normal operating range	Low coolant, debris-clogged radiator core, failed thermostat, slipping fan belt	Reduce load and idle to cool down, check coolant level and radiator fins once cool; never remove a hot radiator cap
Coolant level lamp (sub-tank low level)	Coolant level in the reserve/sub tank is below the minimum mark	External coolant leak, deteriorated hose or gasket, gradual evaporation loss	Inspect hoses, radiator and water pump for leaks, top up with the correct coolant mix once engine is cool
Torque converter (final drive) oil temperature lamp	Power-train oil temperature is above normal operating range	Low transmission/torque converter oil, clogged oil cooler, sustained lugging or overload	Reduce work load, idle to cool, check oil level and cooler for blockage
Air pressure warning (brake system)	Air or air-over-hydraulic brake system pressure is below the level needed for normal brake operation	Compressor fault, leak in brake lines or fittings, insufficient warm-up time after start-up	Let pressure build at idle before moving the machine; if pressure will not build, inspect lines and compressor before operating
Parking brake lamp	Parking brake is applied	Operator engaged the parking brake lever, or a fault in the brake release circuit	Confirm parking brake lever position and release fully before attempting to move the machine
Preheater (intake air heater) indicator	Cold-start intake air preheat device is active before or during start-up	Normal cold-weather starting aid cycle; stays lit longer than usual if the heater element or relay is faulty	Wait for the indicator to go out before cranking; if preheat time is excessive, check the heater circuit

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

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

Host machine and class

6D125-1B-PL(S/N 10001-Up) is the naturally aspirated grader-duty tier of the 6D125-1B engine family (alongside 1B-P and other 1B suffixes), used across Komatsu's A-series articulated-frame motor grader line - GD605A, GD623A, GD625A, GD655A and GD663A-2 class. This places it in the roughly 13-13.6 t operating weight, 116 kW (155 hp) gross power tier of Komatsu graders; a turbocharged sibling engine offers about 134 kW (180 hp) on the same chassis family. The exact difference between the "P" and "PL" suffix is not documented in available factory literature - treat as a closely related build variant within the same grader family rather than a separate host machine.

Grading moldboard (main work tool)

Main work tool for this class is the hydraulic power-shift moldboard, roughly 3.7 m (12 ft) wide by 0.66 m (26 in) high on the mid-size A-series graders in this engine's host family. It carries a replaceable through-hardened cutting edge and bolt-on end bits rather than a one-piece wear blade. Exact width varies by specific grader model within the class - narrower boards on the lighter GD605A end, wider on the GD663A-2 end.

Scarifier / ripper attachments

Rear-mounted and mid-mounted scarifier/ripper toolbars are documented factory or dealer-fit options for the A-series graders in this engine's host family. They use multi-shank parallel-toolbar designs with forged, replaceable points; shank count and spacing are selected per job rather than fixed to one configuration.

Coupler / mounting system

No quick-attach coupler is used on this machine class. The moldboard rides in a circle mounted to the drawbar (circle-drawbar-moldboard arrangement), rotated and side-shifted hydraulically rather than pin-and-latch quick-coupled. Scarifier/ripper toolbars pin-mount to the rear or mid-frame.

Hydraulic kit / arrangement notes

Blade lift, tilt, side-shift and circle-rotate functions run on the grader's own factory-integrated hydraulic circuit; no separate auxiliary hydraulic kit is documented as needed to run the standard moldboard or scarifier/ripper toolbar on this class. Blade-shock accumulators sit in the lift-cylinder circuit to absorb impact loads when the cutting edge strikes a fixed obstacle.

Factory configuration / guarding options

Articulated front-to-rear frame steering is standard for this A-series grader line, giving independent crab-steer and offset-blade operation. Naturally aspirated (this engine) and turbocharged engine tiers were both factory-offered on the same chassis family; specific cab/ROPS guarding options are not documented for this exact serial range in available sources - confirm with your dealer.

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

Every catalogued assembly group for the Komatsu 6D125-1B-PL(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Cylinder Block : Flywheel And Flywheel Housing

01***40	Bolt,(Dust And Dirt Protection)	2
01***45	Bolt,(For Slag Handling)	2
01***50	Bolt, Radiator To Frame	2
01***70	Bolt - Thrust Plate Mounting	4

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Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Cylinder Block : Front Cover(#10001-34750)

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 : 6d125-1b-Pl(S/N 10001-Up) : Cylinder Block : Front Cover(#34751-)

01***25	Bolt,(Without Auto Priming System)	6
01***60	Screw	1
01***65	Bolt,(Except Japan)	8
01***75	Bolt,(For Adjusting)	6

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

01***20	Bolt,(With Auto Emergency Steering)	6
01***25	Bolt,(For Canvas Canopy?Head Guard)	4
01***14	Nut,Ring	2
01***23	Washer,Lock (K5)	2

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

01***20	Bolt,(With Auto Emergency Steering)	6
01***25	Bolt,(For Canvas Canopy?Head Guard)	8
01***30	Bolt,(For Quick Shift) (Mitsubishi)	4
01***45	Bolt, Mounting Bracket To Radiator (Top)	7

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Cylinder Head

Komatsu : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Cylinder Head : Muffler And Mounting(#10001-27909)

Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Cylinder Head : Muffler And Mounting(#27910-)

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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Engine Kit : Gasket Kit

01***23	Washer,Lock (K5)	3
02***43	O-Ring,Water Manifold	10
07***10	O-Ring,(F4350-62a0 -5 ), O-Ring; Komatsu S/N 22***01 & Abv - Was 07000-02010, O-Ring; Was 07000-02010	1
07***15	O-Ring,(For Low Speed) (D40pf)	1

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Fuel System

Komatsu : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#10001-37407)

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

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Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Coupling)(#37408-)

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

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Komatsu : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#10001-37407)

ND***40	Plug,Screw	1
ND***50	Washer? 0.3mm	0
ND***30	Governor Ass'Y	1
ND***90	Lever Ass'Y,Control	1

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Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)(#37408-)

ND***40	Plate,Thrust	1
ND***40	Plug,Screw	1
ND***70	Adapter Ass'Y	1
ND***10	Adapter	1

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Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#10001-37407)

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

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Komatsu : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)(#37408-)

ND***20	Washer? 1.0mm,Cover Plate	2
ND***90	Seal,Oil	1
ND***40	O-Ring	1
ND***50	Packing,Rubber Plate	1

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

61***11	Injection Pump A	1
61***12	Injection Pump A	1
61***13	Injection Pump A	1
ND***50	Ring,Adjust	1

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

ND***70	O-Ring	6
ND***71	Rack,Control	1
ND***10	Washer	2
ND***50	Seat,Spring? Lower	6

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Komatsu : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (2/2)(#10001-11755)

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 : 6d125-1b-Pl(S/N 10001-Up) : Fuel System : Fuel Injection Pump And Piping (2/2)(#11755-)

01***30	Bolt	1
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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(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 : 6d125-1b-Pl(S/N 10001-Up) : Lubricating Oil System : P.T.O. Lubricating Oil Piping

01***25	Bolt,(For Canvas Canopy?Head Guard)	2
07***12	Gasket,(Without Air Compressor Type) (K2)	22
61***60	Bolt,Joint	6
61***70	Bolt,Joint	5

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Frequently asked questions

What engine does the Komatsu 6D125-1B-PL(S/N 10001-UP) use?

This listing is the engine itself: a naturally aspirated, mechanically governed 6D125-1 diesel with 6 cylinders inline, about 11.0 L displacement, and 125 mm x 150 mm bore and stroke. There is no turbocharger in this arrangement (the code carries no "S" prefix). The naturally aspirated rating documented for this engine family in grader applications is about 116 kW (155 hp) at 2200 rpm, versus roughly 134 kW (180 hp) for the turbocharged version of the same block on the same chassis family; the exact rating for this precise arrangement and serial range is not separately published, so confirm against the engine data plate.

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

This is a bare engine catalog entry, so weight depends on the host machine it is installed in. The best-documented application for this naturally aspirated "-1B" arrangement is Komatsu's articulated A-series motor grader line; no arrangement-specific or serial-specific operating weight figure is published for this exact engine listing. Confirm the exact figure against your unit's data plate.

What replaced the 6D125-1B-PL(S/N 10001-UP) engine?

Within its own family, this naturally aspirated "-1B" arrangement was one of several 6D125-1 configurations Komatsu offered on the same grader chassis family, while turbocharged S6D125/SA6D125 variants of the same block architecture powered larger, later Komatsu machines. No single documented one-for-one successor engine exists for this exact arrangement; check current Komatsu literature for the modern equivalent class.

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

What machine is this 6D125-1B-PL engine built for, and does that change what to expect from it?

This is the naturally aspirated, mechanically governed six-cylinder Komatsu engine documented across the company's articulated A-series motor grader line. It runs an inline mechanical injection pump with a flyweight governor, no ECM, no fault codes. Diagnosis is done with gauges and a wrench, not a laptop. The tradeoff owners report is access: getting to any one component on this era of machine often means pulling several other things out of the way first.

Oil looks milky or smells like fuel or coolant. Where do owners say to start looking?

Cross-contamination on this block traces back to the water pump, the head gasket, or the cylinder liner seals. Check the water pump weep hole first; a plugged weep hole hides a bad seal and lets coolant migrate into the oil instead of dripping outside. Diesel-smelling oil with no coolant loss points to a leaking injector washing fuel down a cylinder wall rather than a head problem. Before condemning rings or liners for high oil consumption, check for a blocked piston-cooling oiler jet; one plugged oiler can take a cylinder out quickly and gets mistaken for ring wear. Have your dealer verify head gasket and liner seal condition before committing to an inframe.

Charge light stays on, or the machine will not crank even with a known-good battery. What is the usual cause?

Charging systems of this vintage route a third alternator wire into a starter safety relay, and that circuit is the usual suspect. If the alternator's internal diode trio starts leaking voltage back to that terminal, the safety relay gets fooled into thinking the engine is already running, blocking the starter, or the charge light stays lit with the key on and the engine off. Before replacing a starter or battery, check voltage at that relay terminal with the key on and engine off; more than a couple volts there points to a bad diode trio in the alternator.

What should a buyer check before purchasing a used 6D125-1B-PL machine?

Cold-start it and watch the exhaust past normal warm-up haze; persistent white or blue smoke, or heavy blow-by at the breather, signals ring or liner wear on an engine with no codes to help narrow it down. Pull a dipstick check for milky or diesel-smelling oil and look at the radiator for oil residue; either points to an internal leak worth a dealer inspection before buying. Cycle the moldboard through lift, tilt, side-shift and circle-rotate and listen for chatter or slow response, which points to hydraulic pump or cylinder wear. Walk the circle and drawbar for slop and check articulation-joint play, since both are common wear points on machines of this era. Have your dealer verify compression, blow-by, and hydraulic system pressures against factory spec before final purchase.

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

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