Komatsu 3D84N-2H(S/N 03157-UP)
Maintenance schedule, common problems & OEM parts breakdown
The Komatsu 3D84N-2H engine is a compact, three-cylinder diesel powerplant manufactured by Komatsu starting in 2017. It is primarily installed in the PC20-7 mini excavator series, a class of compact crawler excavators with operating weights ranging from approximately 2,640 kg (5,821 lb) to 2,980 kg (6,571 lb). The engine delivers 25.6 hp (25.6 horsepower) and is designed for utility, municipal, and light construction applications. This engine replaced earlier 3D84 variants in the PC20-7 lineage and serves as the core power source for the 3D84N-2H serial range (S/N 03157-UP). Configurations vary by regional emissions standards and attachment packages, but the engine architecture remains consistent across the mini excavator class.
Across the 3D84N series generations, the primary changes involve emissions compliance updates and integration with Komatsu’s electronic control systems. The 3D84N-2H (S/N 03157-UP) represents a specific serial break in the production line, distinguishing it from earlier 3D84N-2AA or later 3D84N-2CA variants. In the used and parts market, this engine matters because its compact size and widespread use in the PC20-7 series make it a high-volume component for replacement. Owners seek specific 3D84N-2H parts to maintain the machine’s reliability, as the engine’s vertical, water-cooled design is prone to specific wear patterns in the cylinder head and fuel system that require model-specific knowledge for effective repair.
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 3D84N-2H(S/N 03157-UP) specifications
Engine
| Model | 3D84N-2H |
| Type | Vertical, water-cooled, 4-stroke, 3-cylinder diesel |
| Bore x Stroke | 84 mm x 86 mm (3.31 in x 3.39 in) |
| Displacement | 1.429 L (87.2 cu.in.) |
| Gross Power | 25.6 HP @ 2,500 RPM |
| Max Speed at No Load | 2,675 RPM |
| Min Speed at No Load | 900 RPM |
| Emissions Tier | Not documented for this exact serial range — verify with your dealer |
Weights
| Operating Weight | 2,640 Kg (5,821 lbs) |
| 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 | 4,710 mm (15'5") |
| Transport Width | 1,450 mm (4'9") |
| Transport Height | 2,435 mm (8'0") |
| Track Gauge | Not documented for this exact serial range — verify with your dealer |
| Ground Clearance | Not documented for this exact serial range — verify with your dealer |
| Track Width | 300 mm (1'0") |
| Track Length | 1,940 mm (6'4") |
Performance
| Travel Speed | 2.4 km/h (1.5 mph) |
| Swing Speed | 8.6 rpm |
| Gradeability | Not documented for this exact serial range — verify with your dealer |
| Dig Depth | Not documented for this exact serial range — verify with your dealer |
| Lift Capacity | 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 3D84N-2H(S/N 03157-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 3D84N-2H(S/N 03157-UP) beyond the schedule
Predictive Maintenance & Fluid Analysis
For the 3D84N-2H engine (S/N 03157-UP), implement KOWA fluid analysis at every 500-hour interval. Monitor engine oil for wear metals (iron, copper) and coolant for SCA concentration. Check hydraulic fluid for particle count and water content. Use Komatsu Genuine Lubricants to maintain viscosity and oxidation resistance. Track fuel dilution and soot levels in the oil to predict injector or piston ring wear. Early detection of coolant contamination prevents head gasket failure. Regular sampling identifies pump wear before catastrophic hydraulic failure occurs.
Corrective & Common Repairs
Address common 3D84N-2H issues by inspecting the fuel water separator daily. Replace the fuel filter at 500 hours to prevent injector clogging. Check the air filter restriction indicator; replace the outer element at 1,000 hours if dirty. Inspect the turbocharger for shaft play at 1,000 hours. Monitor for coolant leaks around the cylinder head gasket. Check the battery terminals for corrosion and load test at 500 hours. Replace worn hydraulic hoses if cracks or leaks are visible. Ensure the DEF system functions correctly to avoid fault codes.
Overhaul & Rebuild Points
Plan the 3D84N-2H engine overhaul around 4,000 to 5,000 hours. Inspect cylinder liners for wear and measure piston clearance. Check the crankshaft main and rod bearings for clearance. Replace the valve guides and seats if leakage is detected. Inspect the camshaft lobes for wear. Rebuild the fuel injection pump if pressure drops. Replace the turbocharger if shaft play exceeds limits. Inspect the cylinder block for cracks. Use a complete overhaul kit for the 3D84N-2H to ensure proper fitment and performance restoration.
Seasonal & Environment Servicing
In cold climates, use low-temperature fuel and coolant with appropriate antifreeze concentration. Check the battery charge level frequently in cold weather. In dusty environments, inspect the air filter more often and clean the radiator fins daily. In high-humidity areas, check for water accumulation in the fuel separator. Use Komatsu Super Coolant AF-NAC for corrosion protection. Adjust track tension for soft ground to reduce undercarriage wear. Inspect the hydraulic system for seal degradation in extreme temperatures.
3D84N-2H(S/N 03157-UP) common service parts
| Part number | Part | Notes | |
|---|---|---|---|
| YM129100-55650 | Element,Fuel Filter | Fuel system service | Check fitment → |
| YM129100-55621 | Fuel Filter Ass'Y | Fuel system service | Check fitment → |
| YM102103-55520 | O-Ring,(For Fuel Filter) | Fuel system service | Check fitment → |
| YM121120-12900 | Element | Scheduled service item | Check fitment → |
| YM129150-35152 | Filter Element | Scheduled service item | Check fitment → |
Always confirm against your machine's serial number — cross-check any part in Heavy Parts AI before ordering.
3D84N-2H(S/N 03157-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 voltage at the pin connector |
| CA111 | Internal engine controller fault | ECM hardware 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 | Alternator or battery failure; voltage regulator issue | Replace the alternator or battery; check the voltage regulator |
| CA122 | Intake air pressure high voltage | Sensor malfunction or wiring issue | Verify the intake pressure sensor and wiring |
| CA123 | Intake air pressure low voltage | Sensor short or airflow restriction | Check for a sensor short or an airflow restriction |
| CA234 | Engine overspeed | Throttle calibration error, engine load cycle issue, or operator misuse | Verify throttle calibration, engine load cycle, or operator misuse |
| CA153 | Intake air temperature sensor feedback voltage too high | Sensor failure | Replace or test the IAT sensor |
| AA10NX | Air cleaner clogging | Dirty or blocked air filter element | Replace the air filter |
| CA553 | Fuel pressure high | Fuel pump regulator (IMV/PCV) malfunction | Evaluate fuel pump regulator (IMV/PCV) |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
3D84N-2H(S/N 03157-UP) attachments & work tools
Standard Digging Buckets
Typical widths for this mini-excavator class range from 305 mm to 610 mm (12 to 24 in). Capacities generally fall between 0.02 m³ and 0.04 m³ (0.03 to 0.05 cu yd), selected based on the specific boom and stick configuration of the host machine.
Trenching Buckets
Narrow-width buckets are available for utility work, typically 152 mm to 305 mm (6 to 12 in) wide. These tools require the standard quick-attach coupler system and are designed for the hydraulic flow rates available in the PC20-7 class.
Hydraulic Breakers
Light-duty breakers compatible with this engine class require a dedicated high-flow hydraulic kit. Mounting uses the standard quick-attach coupler, but the machine's hydraulic system must be equipped with a pilot-operated flow control valve to prevent overheating.
Hydraulic Thumb Attachments
Mechanical or hydraulic thumbs are available for rock and debris handling. Hydraulic versions require an additional auxiliary hydraulic circuit and a dedicated flow control valve installed in the machine's hydraulic system.
Coupler Systems
The machine utilizes a standard quick-attach coupler system for rapid tool changes. This system is compatible with the full range of Komatsu mini-excavator buckets and attachments, allowing for interchangeable use without manual pinning.
Factory Guarding Options
Factory-installed guarding options include the Falling Object Protective Structure (FOPS) and Falling Object Guard (FOG) for the operator's cab. These structures are integrated into the cab frame and meet standard safety requirements for the machine's size class.
All 3D84N-2H(S/N 03157-UP) assemblies by section
Every catalogued assembly group for the Komatsu 3D84N-2H(S/N 03157-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Cooling System
Komatsu : 3d84n-2h(S/N 03157-Up) : Cooling System : Water Pump And Cooling Fan
| YM***20 | Gasket,Water Pump | 1 |
| YM***02 | Screw | 4 |
| YM***30 | Cover | 1 |
Cylinder Block
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Camshaft And Tappet
| YM***01 | Gear Ass'Y,Camshaft | 1 |
| YM***11 | Camshaft | 1 |
| YM***50 | Bearing, Thrust | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Crankshaft
| YM***60 | Parallel Pin | 1 |
| YM***00 | Gear,Crank | 1 |
| YM***01 | Ball,Steel | 3 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Cylinder Block
| YM***00 | Gauge, Oil Level | 1 |
| YM***20 | Plug,Drain(Without Oil Cooler Type) | 1 |
| YM***20 | Screw | 8 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Flywheel And Flywheel Housing
| YM***02 | Screw | 6 |
| YM***02 | Screw | 4 |
| YM***80 | Parallel Pin | 4 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Front Cover
| YM***02 | Bolt Plated | 2 |
| YM***10 | Washer,Seal | 5 |
| YM***51 | Cap, Lub. Oil Supply | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Oil Pan
| YM***50 | O-Ring | 1 |
| YM***02 | Screw | 4 |
| YM***40 | O-Ring,Drain Plug | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Block : Piston And Connecting Rod
| YM***00 | Screw | 2 |
| YM***00 | Crank Pin Metal A. (Std) | 1 |
| YM***00 | Piston Ring Ass'Y | 1 |
Cylinder Head
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Air Cleaner And Mounting
| YM***41 | Buffle | 1 |
| YM***10 | Cap | 1 |
| YM***30 | Pan,Dust | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Air Intake Manifold And Connection
| YM***01 | Heater,Intake Air | 1 |
| YM***00 | Manifold,Air Intake | 1 |
| YM***52 | Screw | 4 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Cylinder Head
| YM***80 | Retainer, Spring | 6 |
| YM***40 | Seal,Valve? Exhaust (Kit) | 3 |
| YM***10 | Valve,Exhaust | 3 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Cylinder Head Cover
| YM***20 | Cover, Breather | 1 |
| YM***51 | Cap, Lub. Oil Supply | 1 |
| YM***00 | Clip,Breather Hose | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Exhaust Manifold And Muffler
| YM***00 | Manifold,Exhaust | 1 |
| YM***22 | Stud | 4 |
| YM***00 | Gasket,Muffler | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Cylinder Head : Rocker Arm
| YM***02 | Screw | 6 |
| YM***80 | Spring | 3 |
| YM***00 | Plug | 2 |
Electrical System
Komatsu : 3d84n-2h(S/N 03157-Up) : Electrical System : Alternator (20a)
| YM***00 | Stator Ass'Y | 1 |
| YM***10 | Bearing,Ball | 1 |
| YM***02 | Alternator A. (20a) | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Electrical System : Alternator And Mounting (20a)
| YM***30 | Plate,Adjust | 1 |
| YM***70 | Stud | 1 |
| YM***02 | Nut | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Electrical System : Safety Relay? Current Limiter And Charge Indicator
| YM***21 | Indicator, Charging | 1 |
| YM***11 | Limiter, Current | 1 |
| YM***00 | Relay, Safety | 2 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Electrical System : Starting Motor (1.8kw)
| YM***40 | Bolt,Through | 2 |
| YM***50 | Pinion Ass'Y,Pinion | 1 |
| YM***30 | Coil Ass'Y,Field | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Electrical System : Starting Motor And Mounting (1.8kw)
| YM***52 | Bolt Plated | 2 |
| (Y***0) | Starting Motor Ass'Y,(1.8kw) (See Fig.0662) | 1 |
Fuel System
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Engine Stop Motor And Mounting
| YM***80 | Ring,Snap | 1 |
| YM***00 | Pin,Cotter | 1 |
| YM***90 | Washer | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Filter And Piping
| YM***70 | Union | 1 |
| YM***00 | O-Ring (Kit) | 1 |
| YM***51 | Check Valve Ass'Y,Joint | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Injection Pump (Governor) (1/2)
| YM***02 | Lever Ass'Y,Stop | 1 |
| YM***10 | Pin,Stop Lever | 1 |
| YM***00 | O-Ring (Kit) | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Injection Pump (Governor) (2/2)
| YM***01 | Weight Assembly., Governor | 1 |
| YM***90 | Shaft,Governor Lever | 1 |
| YM***50 | Angleich Ass'Y | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Injection Pump (Pump) (1/2)
| YM***90 | Injection Pump Ass'Y | 1 |
| YM***50 | Kit, Shim | 1 |
| YM***10 | Plate? Caution | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Injection Pump (Pump) (2/2)
| YM***70 | Retainer, Spring | 3 |
| YM***00 | Plunger Ass'Y | 3 |
| YM***02 | Screw | 2 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Injection Pump And Piping
| YM***20 | Retainer, Pipe | 1 |
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***30 | Bolt | 2 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Fuel Nozzle And Spill Pipe
| YM***20 | Spring | 1 |
| YM***00 | Fuel Injection Nozzle, Assembly | 1 |
| YM***80 | Seat,Nozzle (Kit) | 3 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Fuel System : Water Separator
| YM***00 | Gasket | 2 |
| YM***00 | O-Ring (Kit) | 1 |
| YM***50 | Plug,Air | 2 |
Lubricating Oil System
Komatsu : 3d84n-2h(S/N 03157-Up) : Lubricating Oil System : Lubricating Oil Filter
| YM***50 | Nut | 1 |
| YM***02 | Bolt Plated | 3 |
| YM***50 | Cartridge,Engine | 1 |
Komatsu : 3d84n-2h(S/N 03157-Up) : Lubricating Oil System : Lubricating Oil Pump And Piping
| YM***50 | Oil Pressure Transmitter | 1 |
| YM***40 | Gasket,Inlet Pipe | 1 |
| YM***20 | Bolt,Joint (Cylinder Head Side) | 1 |
Tool And Engine Kit
Komatsu : 3d84n-2h(S/N 03157-Up) : Tool And Engine Kit : Gasket Kit
| YM***60 | O-Ring,Fuel Injection Pump | 1 |
| YM***20 | Gasket,Water Pump | 1 |
| YM***10 | Gasket (Kit) | 1 |
Frequently asked questions
What engine does the Komatsu 3D84N-2H (S/N 03157-UP) use?
The Komatsu 3D84N-2H (S/N 03157-UP) uses a Komatsu 3D84N-2H diesel engine. It is a vertical, water-cooled, 4-stroke, 3-cylinder engine with a displacement of 1,496 cc. It delivers 25.6 hp (25.6 horsepower) and is commonly found in the PC20-7 mini excavator series.
What is the operating weight of the machine equipped with this engine?
The operating weight varies by configuration. For the PC20-7 mini excavator, the operating weight ranges from approximately 2,640 kg (5,821 lb) to 2,980 kg (6,571 lb). Specific weight depends on the attachment package, counterweight, and regional specifications.
What replaced the Komatsu 3D84N-2H engine?
The Komatsu 3D84N-2H engine is part of the 3D84N series, which has been succeeded by newer engine models in subsequent excavator generations (such as the PC20-8 and later). Specific successor engine designations vary by machine model and regional emissions requirements. Consult the Komatsu dealer for the exact replacement engine for your specific serial number and machine model.
What 3D84N-2H(S/N 03157-UP) owners discuss
What is the specific engine configuration and power output for the Komatsu 3D84N-2H(S/N 03157-UP)?
What are the common hydraulic behaviors and failure patterns associated with this machine type?
What undercarriage and wear patterns are typical for Komatsu excavators in this class?
What are the common electrical and sensor issues reported for Komatsu excavators?
What should be checked when buying a used Komatsu 3D84N-2H(S/N 03157-UP)?
What are the recommended fluid specifications for this engine and hydraulic system?
How does the Komatsu 3D84N-2H engine compare to competitors in terms of reliability and maintenance?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
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