Komatsu S6D125-1AG-T(S/N 51975-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu S6D125-1AG-T is a turbocharged, aftercooled diesel engine belonging to the S6D125 series, primarily powering the D65EX-12 bulldozer class. This engine configuration is designated for serial numbers 51975 and up, serving as a direct successor to earlier 6D125 variants in Komatsu's heavy dozer lineup. The D65EX-12 class typically operates in the 50,000 to 55,000 lb weight range, bridging the gap between mid-size and heavy mining dozers. The S6D125-1AG-T provides the necessary torque rise for rugged earthmoving, replacing older naturally aspirated or early turbo models in the D65 series lineage. Configurations vary by regional emissions requirements, but the core architecture remains a six-cylinder, 11-liter displacement unit designed for high durability in continuous duty cycles.
Across the S6D125 generation, Komatsu shifted from mechanical fuel injection to more precise electronic control systems to meet tightening emissions standards while maintaining the rugged simplicity operators rely on. The S6D125-1AG-T represents a mature stage in this evolution, offering improved fuel efficiency and torque characteristics compared to its predecessors. In the used and parts market, this engine matters because it powers a high-volume, long-life machine class. The D65EX-12 and related dozers are common in heavy construction and mining, creating a steady demand for reliable replacement engines and overhaul components. The S6D125 series is known for robust block construction and widely available aftermarket support, making it a cost-effective choice for fleet managers looking to extend machine life without the premium cost of newer Tier 4/Stage V engines.
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 S6D125-1AG-T(S/N 51975-UP) specifications
Engine
| Model | S6D125-1AG-T |
| Series/Generation | Komatsu 125 Series (S6D125-1) |
| Type | 4-stroke, water-cooled, direct injection diesel engine |
| Displacement | 11.04 L (674 cu in) |
| Cylinders | 6 |
| Bore x Stroke | 125 mm x 150 mm (4.92 in x 5.91 in) |
| Compression Ratio | 17:1 |
| Aspiration | Turbocharged and aftercooled |
| Gross Power | varies by configuration/series (typically 260–300 hp / 194–224 kW) |
| Net Power | varies by configuration/series (typically 260–300 hp / 194–224 kW) |
| Torque | varies by configuration/series (typically 920–1100 Nm / 678–811 lb-ft) |
| Emissions Tier | Not documented for this exact serial range — verify with your dealer |
Weights
| Operating Weight | Not documented for this exact serial range — verify with your dealer |
| Shipping Weight | Not documented for this exact serial range — verify with your dealer |
| Ground Pressure | Not documented for this exact serial range — verify with your dealer |
Dimensions
| Transport Length | Not documented for this exact serial range — verify with your dealer |
| Transport Width | Not documented for this exact serial range — verify with your dealer |
| Transport Height | Not documented for this exact serial range — verify with your dealer |
| Track Gauge / Wheelbase | Not documented for this exact serial range — verify with your dealer |
| Ground Clearance | Not documented for this exact serial range — verify with your dealer |
Performance
| Travel Speed | Not documented for this exact serial range — verify with your dealer |
| Gradeability | Not documented for this exact serial range — verify with your dealer |
| Lift/Dig/Dump/Drawbar | Not documented for this exact serial range — verify with your dealer |
Service capacities (summary)
| Fuel Tank | Not documented for this exact serial range — verify with your dealer |
| Hydraulic System | Not documented for this exact serial range — verify with your dealer |
| Engine Oil | Not documented for this exact serial range — verify with your dealer |
| Cooling System | Not documented for this exact serial range — verify with your dealer |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
Komatsu S6D125-1AG-T(S/N 51975-UP) maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
Servicing the S6D125-1AG-T(S/N 51975-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
For the S6D125-1AG-T engine in the D65EX-12 dozer, rely on KOWA fluid analysis to monitor wear metals like iron and copper in the engine oil. Check coolant SCA concentration every 500 hours to prevent liner cavitation in the 11-liter block. Monitor hydraulic oil particle count to protect the high-pressure pumps. Use Komatsu Genuine Lubricants to ensure proper additive packages for the turbocharged aftercooled system. Track fuel dilution levels to detect injector or piston ring wear early. Analyze final drive oil for gear wear indicators to prevent catastrophic undercarriage failure.
Corrective & Common Repairs
Address S6D125-1AG-T specific issues by inspecting the turbocharger housing for oil leaks common in high-hour dozer applications. Check the fuel injection pump for wear if power drops or black smoke appears. Replace worn piston rings if compression drops, often indicated by excessive blow-by. Inspect the oil cooler element for clogging that causes overheating under heavy load. Verify the integrity of the aftercooler core for coolant leaks that can lead to hydro-lock. Check the alternator brushes and voltage regulator for consistent charging in dusty environments.
Overhaul & Rebuild Points
Plan the S6D125-1AG-T overhaul when compression falls below spec or oil consumption exceeds limits. Replace cylinder liners, pistons, and rings as a set to restore power in the 11-liter block. Inspect the crankshaft for journal wear and replace bearings if clearance exceeds factory limits. Check the camshaft lobes for wear that affects valve timing and performance. Replace the turbocharger if shaft play is excessive or blades are damaged. Rebuild the fuel injection pump and injectors to ensure proper spray pattern and atomization for clean combustion.
Seasonal & Environment Servicing
In cold climates, use low-temperature fuel additives to prevent waxing in the S6D125-1AG-T fuel system. Check the coolant freeze point before winter to protect the aluminum components in the aftercooler. In dusty environments, inspect the air filter restriction indicator more frequently and clean the radiator fins daily to prevent overheating. Use high-temperature grease for undercarriage points in hot conditions to prevent washout. Monitor DEF quality and storage to prevent crystallization in the SCR system during cold starts. Ensure the battery is insulated or heated in extreme cold to maintain cranking power.
S6D125-1AG-T(S/N 51975-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| 07281-00197 | Clamp,(With Pre-Fuel Filter) | Fuel system service | Check fitment → |
| 6221-71-6201 | Fuel Filter Ass'Y | Fuel system service | Check fitment → |
| ND092220-0040 | Filter,Fuel | Fuel system service | Check fitment → |
| 6125-81-7032 | Element Ass'Y,Air Cleaner | Air intake service | Check fitment → |
| 09637-30161 | Plate? Instruction,Air Cleaner (Single Element) | Air intake service | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
S6D125-1AG-T(S/N 51975-UP) fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| CA115 | Engine crankshaft speed sensor failure | Broken sensor, wiring issue, or connector corrosion | Replace the speed sensor and verify the voltage at the pin connector |
| CA111 | Internal engine controller fault | ECM hardware or software failure | Replace or reprogram the ECM |
| CA451 | Common rail pressure sensor feedback value too high | Malfunction in the rail sensor or actual overpressure condition | Diagnose the fuel rail pressure sensor or pump lines |
| CA441 | Battery voltage too low | Weak battery or alternator failure | Replace the alternator or battery; check the voltage regulator |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration and engine load cycle |
| AA10NX | Air cleaner clogging | Dirty or blocked air filter element | Replace the air filter |
| CA122 | Intake air pressure high voltage | Faulty intake pressure sensor or wiring issue | Verify the intake pressure sensor and wiring |
| CA153 | Intake air temperature sensor high voltage | Faulty IAT sensor | Replace or test the IAT sensor |
| CA2311 | IMV solenoid valve failure | Failed IMV solenoid or wire harness issue | Replace the IMV solenoid or inspect the wire harness |
| CA428 | Fuel moisture sensor invalid voltage | Contaminated fuel supply or sensor harness fault | Ensure a clean fuel supply and check the moisture sensor harness |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
S6D125-1AG-T(S/N 51975-UP) attachments & work tools
Motor Grader Blades
The S6D125-1AG engine is explicitly linked to the GD663A-2 motor grader in parts documentation. This class typically utilizes a moldboard blade with a width of approximately 3.7 meters (12 feet) and a capacity of 2.5 cubic meters (3.3 cubic yards), designed for the machine's operating weight class.
Bulldozer Blades
The engine is identified in equipment guides as the powerplant for the D65EX-12 dozer series. Standard configurations for this class include a semi-U or straight blade with a capacity ranging from 5.5 to 6.5 cubic meters (7.2 to 8.5 cubic yards), depending on the specific blade variant (e.g., SU, SE, or S) fitted to the frame.
Excavator Buckets
The S6D125-1 engine series is documented in applications for the PC400-5 and PC400LC-5 excavators. Typical work tool configurations for this size class involve rock or heavy-duty buckets with capacities between 2.5 and 3.5 cubic meters (3.3 to 4.6 cubic yards), requiring high-flow hydraulic circuits to manage the engine's torque output.
Hydraulic Coupler Systems
Komatsu excavators in this engine class generally utilize proprietary quick coupler systems compatible with the machine's hydraulic line configuration. Factory specifications often include guard options for hydraulic hoses and couplers to protect against impact damage in mining or heavy demolition environments.
All S6D125-1AG-T(S/N 51975-UP) assemblies by section
Every catalogued assembly group for the Komatsu S6D125-1AG-T(S/N 51975-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Engine
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Air Cleaner
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 4 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Air Intake
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 11 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 4 |
| 01***05 | Bolt, Mount Hose Clip | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Alternator (35a) (Inner Parts)
| 60***60 | Alternator A. (35a),(With Non Hardening Pulley) | 1 |
| KD***57 | Bearing,Ball? Front | 1 |
| KD***80 | Collar | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Alternator Mounting (35a) (With Safety Cover)
| 01***30 | Bolt,(Not Used With Emergency Str.) | 1 |
| 01***20 | Screw | 2 |
| 01***65 | Bolt | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Camfollower Cover
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***00 | Bolt, Mount Back-Up Alarm | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Camshaft
| 01***22 | Bolt | 2 |
| 04***25 | Key, Plain Woodruff | 1 |
| 04***12 | Ring,Snap (For Ripper) | 12 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Cooling Fan
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 6 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 6 |
| 60***51 | Fan,Cooling | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Corrosion Resistor
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 3 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 2 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Crank Pulley
| 01***30 | Screw | 1 |
| 01***35 | Screw | 5 |
| 04***28 | Pin, Dowel - Transmission Case, Pin-Dowel | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Crankshaft(#51975-62861)
| 61***10 | Bearing, Main (Standard) | 7 |
| 61***50 | Bearing, Thrust Assembly (Standard) | 1 |
| 61***10 | Bearing, Main (1.00mm Undersize) | 7 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Cylinder Block
| 01***12 | Bolt,(Without Air Compressor Type) | 2 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 14 |
| 04***14 | Pin, Dowel | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Cylinder Block Gasket Kit(#51976-)
| 07***15 | O-Ring,Relief Valve | 1 |
| 07***20 | O-Ring,Lubricating Oil Piping | 1 |
| 07***25 | O-Ring (K2?K8) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Cylinder Head
| 04***20 | Pin,Dowel (Welded) | 2 |
| 61***30 | Sleeve,Holder | 1 |
| 61***20 | Cotter, Valve | 48 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Cylinder Head Gasket Kit(#51976-)
| 02***43 | O-Ring,Water Manifold | 6 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,Mechanical Pump Piping | 12 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Damper
| 01***25 | Bolt,(Without Rops Guard? Canopy) | 6 |
| 61***00 | Damper Ass'Y | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Engine Mounting
| 01***50 | Bolt,(With Service Valve R.H.) | 2 |
| 01***05 | Bolt, Mount Hose Clip | 4 |
| 01***10 | Bolt, Fan Mounting | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Exhaust Manifold (With Safety Cover)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***50 | Bolt,(With Service Valve R.H.) | 2 |
| 01***70 | Bolt, Mount Bracket And Oil Inlet Tube, Bolt | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fan Drive
| 01***14 | Nut,(For Slag Handling) | 1 |
| 01***60 | Washer,(Without Rops Guard? Canopy) | 1 |
| 04***25 | Ring,Snap (Kit) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fan Guard (1/2)
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***40 | Bolt, Mount Master Brake Cylinder | 2 |
| 01***70 | Bolt, Mount Bracket And Oil Inlet Tube, Bolt | 8 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fan Guard (2/2)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 13 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 2 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 3 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fan Pulley
| 04***69 | V-Belt Set,Fan | 1 |
| 61***20 | Pulley?Non Hardening | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Flywheel
| 01***55 | Bolt | 6 |
| 01***45 | Washer,(For Travel Motor) (Not Show) | 6 |
| 06***08 | Bearing, Ball | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Flywheel Housing
| 01***50 | Bolt | 2 |
| 01***50 | Bolt, Radiator To Frame | 6 |
| 01***60 | Bolt, Hanger Bearing Mounting | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Front Cover
| 01***65 | Bolt,(Except Japan) | 8 |
| 01***75 | Bolt,(For Adjusting) | 4 |
| 01***16 | Washer,Radio Controlled Slag Handling | 12 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Filter
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 7 |
| 01***05 | Bolt, Mount Hose Clip | 1 |
| 01***20 | Screw | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Coupling) (208ps) (Inner Parts)
| ND***10 | Flange,Coupling | 1 |
| ND***50 | Bolt | 1 |
| ND***40 | Bolt | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Feed Pump) (208ps) (Inner Parts)
| ND***40 | Washer? 1mm,Plate | 1 |
| ND***70 | Washer,Union | 4 |
| ND***10 | Spring, Check Valve | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Governor) (1/2) (208ps) (Inner Parts)
| ND***40 | Plate,Thrust | 1 |
| ND***40 | Plug,Screw | 1 |
| ND***50 | Washer? 0.3mm | 0 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Governor) (2/2) (208ps) (Inner Parts)
| ND***80 | Pin,Stop | 1 |
| ND***70 | Arm,Spring | 1 |
| ND***20 | Washer? 1.0mm,Cover Plate | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Pump) (1/2) (208ps) (Inner Parts)
| 61***80 | Injection Pump A | 1 |
| ND***80 | Bearing,Center | 1 |
| ND***50 | Ring,Adjust | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump (Pump) (2/2) (208ps) (Inner Parts)
| ND***21 | Shim? 2.4mm | 0 |
| ND***91 | Shim? 2.25mm,Element Holder | 0 |
| ND***60 | Element,Pump | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump Drive
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 4 |
| 01***14 | Nut (Itl) | 1 |
| 01***60 | Washer,(Without Rops Guard? Canopy) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump Mounting (208ps)
| 01***75 | Bolt,(See Fig.0142) | 4 |
| 61***10 | Washer,Spring | 4 |
| (6***0) | Injection Pump A.,(See Fig.A4010-B3a2) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Injection Pump Piping(#51976-)
| 01***30 | Bolt | 4 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 4 |
| 01***70 | Bolt, Mount Bracket And Oil Inlet Tube, Bolt | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Fuel Return
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 1 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***08 | Nut,(For Canvas Canopy?Head Guard) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Head Cover
| 01***16 | Washer,Radio Controlled Slag Handling | 24 |
| 61***11 | Cover,Head? No.2?3?4?5?6 | 6 |
| 61***10 | Gasket,Cylinder Head Cover | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Heater Switch
| 01***16 | Bolt, Mount Washer Tank To Bracket, Bolt | 2 |
| 01***55 | Bolt, Mount Tube To Switch Pump | 1 |
| 01***10 | Washer,(For 35a Alternator) | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Idler Gear
| 01***60 | Screw | 1 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 6 |
| 01***30 | Bolt,(With Body Positioner) | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Injection Nozzle
| 01***45 | Bolt, Divider Valve Mounting | 12 |
| 07***65 | O-Ring,Cylinder Block | 6 |
| 07***12 | Gasket,(Without Air Compressor Type) (K2) | 12 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Muffler (With Safety Cover)
| 01***40 | Bolt,(Dust And Dirt Protection) | 4 |
| 01***25 | Bolt - Rear Guard Mounting | 4 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 3 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Name Plate And Caution (English)
| 09***61 | Plate? Instruction,Air Cleaner (Single Element) | 1 |
| 09***01 | Plate? Instruction,(English) (Except Japan) | 1 |
| 60***60 | Plate? Caution,Oil Filter | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Nozzle Holder (Inner Parts)
| 07***12 | Gasket,Mechanical Pump Piping | 2 |
| 61***11 | Holder Ass'Y | 6 |
| ND***90 | Connector,Inlet | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Oil Cooler (7-Element Type)(#51975-73268)
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 12 |
| 01***65 | Bolt - Return Line And Suction Linehose Clamps | 2 |
| 01***80 | Bolt,(With Corrosion Resistor) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Oil Filter
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 3 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
| 01***35 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Oil Levle Gauge
| 01***16 | Bolt (With Air Heater & Conditioner) | 1 |
| 01***06 | Nut,(With Back-Up Alarm) (Op), Nut; Was 01580-10806 | 1 |
| 01***10 | Washer,See Fig. K4010-12a0 | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Oil Pan And Suction Tube
| 01***20 | Bolt,(Large Capacity Type) (Std) | 1 |
| 01***25 | Bolt,(Sandy? Dusty Terrain Spec.) | 1 |
| 01***35 | Bolt, Mounting - Flywheel Housing End | 2 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Oil Pump
| 01***25 | Bolt,(Rear Attachment Less) | 4 |
| 01***25 | Bolt,(For Canvas Canopy?Head Guard) | 3 |
| 01***35 | Bolt,(F4320-52a0 -5 ) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Piston
| 02***13 | Pin, Dowel | 2 |
| 04***18 | Ring, Snap | 12 |
| 61***33 | Piston Ring Ass'Y | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Rocker Arm
| 01***08 | Nut,R.H. Thread | 12 |
| 01***32 | Washer,(With Auto Emergency Steering) | 40 |
| 61***10 | Housing, Rocker Lever | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Safety Guard (Fuel Injection Pump Drive)
| 01***20 | Bolt,(For Mono Lever Steering) | 2 |
| 61***50 | Cover, Safety | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Starting Motor (7.5kw) (Inner Parts)
| 60***10 | Starting Motor Ass'Y,(7.5kw) | 1 |
| KD***60 | Shift Lever Assembly | 1 |
| KD***40 | Spring,Spring | 4 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Starting Motor Mounting (7.5kw)
| 01***40 | Bolt,(With Center Guard) | 3 |
| 08***19 | Band,(Without Air Conditioner) | 1 |
| 08***10 | Connector, Clip | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Thermostat Housing
| 01***16 | Washer,Radio Controlled Slag Handling | 1 |
| 08***10 | Connector, Clip | 1 |
| 60***10 | Thermostat,(Cold Terrain Spec.) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Turbocharger (Inner Parts)
| 61***00 | Turbocharger Ass'Y,(T04e08) | 1 |
| GA***22 | Housing Ass'Y,Center Housing | 1 |
| GA***01 | Bolt | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Turbocharger Oil Piping (With Safety Cover)
| 01***30 | Bolt,(For Mechanical Governor) | 2 |
| 01***16 | Bolt, Battery To Frame Ground Wire Attaching | 2 |
| 01***20 | Bolt,(For Quick Shift) (Mitsubishi) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Water Drain Valve
| 61***12 | Valve,Water Drain | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Water Manifold
| 02***43 | O-Ring,Water Manifold | 6 |
| 61***11 | Manifold,Water | 2 |
| 61***20 | Manifold,Water | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Water Pump
| 01***30 | Bolt,(For France Noise Suppression) | 2 |
| 01***16 | Bolt (With Air Heater & Conditioner) | 6 |
| 01***30 | Bolt,(For Quick Shift) (Mitsubishi) | 6 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Water Pump Gasket Kit
| 07***15 | O-Ring,Scavenge Pump | 1 |
| 61***10 | Seal,Water (K6) | 1 |
| 61***20 | Seal? Water (K6) | 1 |
Komatsu : S6d125-1ag-T(S/N 51975-Up) : Engine : Water Temperature Sensor
| 07***15 | Plug,(Used When Without Heater) | 1 |
| 07***08 | Plug,(Without Oil Pressure Switch) | 1 |
| 61***10 | Nipple | 2 |
S6D125-1AG-T(S/N 51975-UP) serial number reference
The engine serial number is stamped on the left side of the engine block near the injection pump, or on a metal data plate affixed to the block or valve cover. The machine PIN plate is typically riveted to the right-hand side of the cab on the lower frame (excavators) or on the front frame casting (dozers).
| Prefix | Identifies | Notes |
|---|---|---|
| D65EX-12 | Crawler Dozer | Komatsu D65EX-12 Bulldozer. Engine: S6D125-1AG. Serial range: 51975-UP. Source: published references Equipment Guide. |
Frequently asked questions
What is the engine model for the Komatsu D65EX-12 dozer?
The Komatsu D65EX-12 dozer uses the S6D125-1AG-T engine for serial numbers 51975 and up. This is a turbocharged, aftercooled diesel engine with an 11-liter displacement.
What is the operating weight of the Komatsu D65EX-12?
The operating weight of the Komatsu D65EX-12 dozer varies by configuration, typically ranging from 50,000 to 55,000 lb (22,680 to 24,948 kg).
What replaced the Komatsu D65EX-12?
The D65EX-12 was succeeded by the D65EX-20 series dozers, which feature updated emissions-compliant engines and modernized hydraulic systems to meet current environmental standards.
What S6D125-1AG-T(S/N 51975-UP) owners discuss
How does the S6D125-1AG-T engine's torque curve and pump flow setup differ from the L10 variant?
What are the typical undercarriage and wear patterns for machines equipped with the S6D125-1AG-T engine?
What are the known engine quirks and reliability characteristics of the S6D125-1AG-T series?
What are the common electrical and sensor issues reported for this engine series?
What are the typical hydraulic behaviors and troubleshooting patterns for machines with this engine?
What should be checked when buying a used machine with the S6D125-1AG-T engine (S/N 51975-Up)?
How does the S6D125-1AG-T engine compare to the S6D102E variants in terms of application and reliability?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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