Komatsuengine(no series)

Komatsu S6D155-4-R(S/N 10014-UP)

Maintenance schedule, common problems & OEM parts breakdown

The Komatsu S6D155-4-R engine powers the D155A-1 and D155A-2 crawler dozer series, a heavy-duty earthmoving class designed for large-scale construction and land clearing. Production years span approximately 1989 to 1995, with the S6D155-4-R specifically covering serial number 10014 and up. The engine delivers 320 hp gross power and displaces 1175 cu in (19.2 L). It is a turbocharged diesel unit used in dozers with operating weights around 59,350 lb (26,943 kg). The D155A series succeeded earlier D155 models and was later replaced by the D155C-1 and D155W-1 series. Configurations included standard dozer, low ground pressure (LGP), and specialized variants for high-altitude or specific terrain applications.

Across the S6D155-4 series generations, key changes involved updates to the engine control system, emissions compliance packages, and serial number breaks that altered component compatibility. The S6D155-4-R (S/N 10014-UP) represents a specific build phase distinct from earlier S6D155-4 units (Eng. No. 20001-24804) and later S6D155-4S units (Eng. No. 52707-Up). This machine matters in the used and parts market because its widespread use in heavy dozers created a large installed base, driving demand for reliable aftermarket components like cylinder heads, injectors, and turbochargers. The transition to the S6D155-4S and subsequent SA6D155-4 engines introduced changes in fuel injection and emissions systems, making accurate serial identification critical for parts buyers and mechanics maintaining these legacy heavy machines.

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 S6D155-4-R(S/N 10014-UP) specifications

Engine

ModelS6D155-4
ConfigurationTurbocharged, 4-cylinder in-line
Displacement12.840 L (783.5 cu in)
Bore155.0 mm (6.10 in)
Stroke170.0 mm (6.69 in)
Gross Power320 hp (239 kW) @ 1850 rpm
Net Power Range210-240 hp (156-178 kW) @ 1850 rpm

Weights

Operating Weight (D155A-1 Crawler Dozer)59,350 lb (26,920 kg)
Engine Weight (Approximate)2,050 kg (4,519 lb)

Dimensions

Transport Length (D155A-1)13.6 ft (4.15 m)
Transport Width (D155A-1)62.6 in (1.59 m)
Transport Height (D155A-1)13.7 yd (12.5 m)
Track Shoe Width (D155A-1)22.1 in (561 mm)
Ground Pressure (D155A-1)11 psi (76 kPa)
Engine Length (Approximate)1,456 mm (57.3 in)
Engine Width (Approximate)1,125 mm (44.3 in)
Engine Height (Approximate)1,910 mm (75.2 in)

Performance

Travel Speed (Low)7.4 mph (11.9 km/h)
Travel Speed (High)8.6 mph (13.8 km/h)
Blade Capacity (D155A-1)13.7 yd³ (10.5 m³)
Transmission TypePlanetary gear

Service capacities (summary)

Fuel Tank Capacity (D155A-1)158.6 gal (600 L)
Hydraulic System Capacity (D155A-1)43.6 gal (165 L)

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

Komatsu S6D155-4-R(S/N 10014-UP) maintenance schedule

Service intervalTasks
Every 10 h
  • Check engine oil level and condition
  • Check hydraulic fluid level at sight glass
  • Check coolant level and ensure cap is secure
  • Drain water from fuel separator
  • Check DEF level on Tier 4 machines
  • Inspect air filter restriction indicator
Every 250 h
  • Change engine oil and filter
  • Grease all points including boom, stick, bucket, and swing bearing
  • Check fluid levels
  • Inspect air filter outer element
  • Inspect belts and hoses for wear
  • Perform visual walk-around inspection
Every 500 h
  • Replace fuel filter
  • Replace hydraulic return filter
  • Service battery and test alternator
  • Test coolant SCA concentration
  • Collect KOWA engine oil sample
  • Perform detailed undercarriage visual inspection
Every 1,000 h
  • Collect KOWA hydraulic oil sample
  • Change final drive oil on both sides
  • Inspect turbocharger
  • Check valve adjustment clearances
  • Inspect structural welds on boom and stick
  • Measure undercarriage wear
Every 2,000 h
  • Change hydraulic system oil
  • Flush and replace coolant
  • Perform transmission service
  • Conduct comprehensive component evaluation
  • Inspect KDPF system
  • Replace worn belts and hoses

Servicing the S6D155-4-R(S/N 10014-UP) beyond the schedule

Predictive Maintenance & Fluid Analysis

Use KOWA fluid analysis to monitor engine wear metals and hydraulic contamination. Check coolant SCA levels at 500-hour intervals to prevent liner cavitation. Monitor DEF levels daily on Tier 4 variants. Track fuel dilution and soot levels in engine oil to determine optimal drain intervals. Use KOMTRAX telematics to track load frequency and fault codes for proactive service scheduling. Inspect air filter restriction indicators before every shift to ensure proper airflow and prevent turbocharger damage.

Corrective & Common Repairs

Address common S6D155-4-R issues by inspecting fuel injector sleeves and O-rings for leaks. Replace worn turbocharger KTR130-11F bearings if boost pressure drops. Check floating seals on the engine block for oil leaks. Inspect the cylinder head gasket for coolant loss or compression leaks. Replace worn timing case gaskets and oil pan gaskets during routine service. Verify electrical connections for engine speed sensors to prevent fault codes like E10 or E11.

Overhaul & Rebuild Points

Plan inframe overhauls based on KOWA results and compression tests. Replace piston rings, liners, and main bearings when wear exceeds limits. Inspect the crankshaft for journal wear and replace if out of spec. Rebuild the turbocharger if shaft play is detected. Replace all gaskets and seals during cylinder head removal. Use genuine Komatsu or OEM-equivalent gasket kits for accurate torque specifications and sealing.

Seasonal & Environment Servicing

In cold climates, use low-temperature grade engine oil and ensure DEF fluid is protected from freezing. Check battery charge and insulation regularly. In hot environments, clean radiator and oil cooler fins daily to prevent overheating. Inspect coolant hoses for softening or cracking. Use high-temperature grade hydraulic oil if ambient temperatures exceed standard operating ranges. Adjust fuel injection timing if operating at high altitudes to maintain power output.

S6D155-4-R(S/N 10014-UP) common service parts

Part numberPart
07281-00197Clamp,(With Pre-Fuel Filter)Check fitment →
600-311-8282Cartridge,Fuel FilterCheck fitment →
600-311-8283Cartridge,Fuel FilterCheck fitment →
600-311-8331Cartridge,Fuel FilterCheck fitment →
6127-71-6701Fuel Filter Ass'YCheck fitment →

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

S6D155-4-R(S/N 10014-UP) fault codes & troubleshooting

CodeMeaningLikely causeWhat to do
CA115Engine crankshaft speed sensor failureBroken sensor, wiring issue, or connector corrosionReplace the speed sensor and verify voltage at the pin connector
CA111Internal engine controller faultECM internal abnormalityReplace or reprogram the ECM
CA451Common rail pressure sensor feedback value too highMalfunction in the rail sensor or actual overpressure conditionDiagnose the fuel rail pressure sensor or pump lines
CA234Engine overspeedThrottle calibration error, engine load cycle issue, or operator misuseVerify throttle calibration and engine load cycle
CA441Battery voltage too lowAlternator failure, battery degradation, or voltage regulator issueReplace the alternator or battery; check the voltage regulator
CA442Battery voltage too highAlternator overcharging or voltage regulator failureReplace the alternator or battery; check the voltage regulator
AA10NXAir cleaner cloggingDirty or blocked air filter elementReplace the air filter
CA122Intake air pressure high voltageSensor malfunction or wiring issueVerify the intake pressure sensor and wiring
CA123Intake air pressure low voltageSensor short or airflow restrictionCheck for a sensor short or an airflow restriction
CA153Intake air temperature sensor error (high voltage)Sensor malfunctionReplace or test the IAT sensor

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

S6D155-4-R(S/N 10014-UP) attachments & work tools

Crawler Dozer Blade

The Komatsu D155A-1 and D155A-2 dozers equipped with the S6D155-4 engine utilize a semi-U or U-blade configuration. Factory specifications list a blade capacity of 13.7 cubic yards (10.5 cubic meters) with a blade height of 62.6 inches (1.59 meters). The blade width is 13.6 feet (4.15 meters), designed for heavy-duty land clearing and earthmoving tasks.

Crawler Dozer Ripper

Single-shank or multi-shank ripper attachments are available for the D155A series dozers to break hard rock or compacted soil. The ripper shank length is specified at 22.1 inches (0.56 meters). Mounting points are integrated into the rear frame structure, requiring specific hydraulic lines for depth control and lift functions.

Excavator Bucket

The S6D155-4 engine powers the PC650-5 and PC800-6 excavator classes, which utilize heavy-duty digging buckets. Typical bucket capacities for these machine classes range from 4.0 to 6.0 cubic meters (5.2 to 7.8 cubic yards) depending on material density. The attachment interface uses a standard pin-on coupler system requiring hydraulic quick-attach lines for auxiliary circuits.

Wheel Loader Bucket

The WA350-1 wheel loader, powered by the S6D155-4 engine, is fitted with a general-purpose or rock bucket. Bucket capacities typically range from 3.0 to 4.0 cubic meters (3.9 to 5.2 cubic yards). The loader arm uses a Z-bar linkage with pin-on bucket attachment, requiring dual hydraulic cylinders for tilt and curl functions.

Hydraulic Coupler System

Work tools for the associated excavator and loader classes utilize a pin-on coupler system with integrated hydraulic quick-attach lines. The mounting geometry follows standard Komatsu excavator and loader interface specifications for the respective machine class. Auxiliary hydraulic flow is routed through the quick-attach hoses to operate tool functions such as tilt or rotation.

Factory Guarding Options

Dozer configurations for the D155A series include factory-installed front grille guards and rear guard assemblies to protect the engine and radiator from debris. Cab guards (ROPS/FOPS) are standard on the operator station to meet safety regulations for falling object and rollover protection. Undercarriage guards are available as optional factory configurations for high-abrasion environments.

All S6D155-4-R(S/N 10014-UP) assemblies by section

Every catalogued assembly group for the Komatsu S6D155-4-R(S/N 10014-UP). Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.

Cooling And Electrical System
Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Alternator And Mounting (Starting Motor Spec.)(#56577-)
01***25Bolt,(Rear Attachment Less)4
01***40Bolt (Op)2
01***45Bolt,(With Water Separator Type)3
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Alterno\Ator (Starting Motor Spec.)(#56577-)
60***40Alternator A. (50a)1
SD***01Cord Ass'Y1
SD***00Bearing,Ball1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Cooling Fan And Fan Drive(#30551-)
01***20Bolt, Wiring Harness Mounting Bracket7
01***35Bolt,(F4320-52a0 -5 )2
01***30Bolt,(Not Used When Towing Winch)3
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Corrosion Resistor And Piping (Starting Motor Spec.)(#56577-)
01***20Bolt, Wiring Harness Mounting Bracket1
01***30Bolt,(With Body Positioner)8
01***25Washer,Spring?(Sandy And Dusty Spec.)1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Starting Motor (Starting Motor Spec.)(#56577-)
60***41Starting Motor Ass'Y,(Extreme Cold Terrain Spec.)1
KD***82Screw,Dish8
KD***60Field Coil Ass'Y1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Statring Motor And Mounting(#56577-)
01***45Capscrew - M163
01***25Bolt,(Without Rops Guard? Canopy)2
01***25Bolt2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cooling And Electrical System : Water Pump And Piping(#30551-)
01***15Bolt6
01***16Bolt - Box Mounting6
01***20Bolt, Wiring Harness Mounting Bracket4
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Cylinder Block
Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Alternator Drive(#30557-)
01***16Bolt - Box Mounting6
01***40Bolt,For Weight Adjusting Bolt3
01***10Nut,Lock1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Camshaft And Tappet(#30551-)
01***20Bolt,(For Mono Lever Steering)2
04***35Key1
61***30Plug, No. 41
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Crankshaft And Vibration Damper(#30551-)
01***25Bolt - Rear Guard Mounting6
01***45Bolt,Nylock1
01***36Washer,Radio Controlled Slag Handling6
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Cylinder Block (1/2)(#30551-)
01***18Bolt6
01***25Bolt,(For Canvas Canopy?Head Guard)4
01***35Bolt,(F4320-52a0 -5 )3
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Cylinder Block (2/2)(#30551-)
01***25Bolt - Rear Guard Mounting1
01***35Bolt - Torque Converter Totransmission Mounting2
01***25Bolt,(Rear Attachment Less)8
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Flywheel And Flywheel Housing(#30551-)
01***45Bolt, Mount Bracket4
01***45Bolt8
01***55Bolt7
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Gear Case And Front Support(#30551-)
01***12Bolt,(Without R.P.C.U.)2
01***40Bolt,(Not Used With Cab)2
01***55Screw4
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Heater (Starting Motor Spec.)(#56577-)
01***16Bolt,(Sandy And Dusty Spec.)1
01***95Bolt,(For Reversible Fan)1
01***30Bolt - M8 X 30lg5
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Oil Pan(#30551-)
01***30Bolt,(For France Noise Suppression)11
01***35Bolt, Mounting - Flywheel Housing End36
01***20Bolt, Wiring Harness Mounting Bracket1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Pistion And Connecting Rod(#30551-)
61***20Ring,Snap2
61***30Piston Ass'Y,(Service Parts)6
61***40Piston,(Service Parts)1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Block : Power Take Off(#30551-)
01***30Bolt,Radio Controlled Slag Handling12
01***40Bolt,(Dust And Dirt Protection)2
01***20Bolt,(For Mono Lever Steering)6
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Cylinder Head
Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Air Cleaner And Pre-Cleaner(#30551-)
01***45Screw1
01***30Bolt4
01***08Nut, Regular Hexagon (M10-1.50)1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Air Intake Manifold And Connection(#30551-)
01***35Bolt4
01***45Hexagon Bolt4
01***30Bolt - M8 X 30lg4
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Compression Release(#30551-)
01***30Bolt - M8 X 30lg1
01***25Washer,Spring?(Sandy And Dusty Spec.)1
04***20Key1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Cylinder Head(#30551-)
01***30Bolt,(With Body Positioner)6
01***30Washer,Spring(Sandy?Dusty Terrain S.)6
07***20Plug2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Exhaust Manifold And Muffler(#30551-)
01***40Bolt,(Dust And Dirt Protection)1
01***25Bolt - Rear Guard Mounting1
01***90Bolt1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Fuel Nozzle And Spill Pipe(#30551-)
01***40Bolt (Op)12
07***12Gasket,Mechanical Pump Piping14
61***12Pipe,Fuel Supply6
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Rocker Arm And Housing(#30551-)
01***10Bolt, Mount Filler Tube2
01***05Capscrew22
01***25Washer,Spring?(Sandy And Dusty Spec.)1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Rocker Arm Housing Cover(#30551-)
01***22Capscrew3
01***40Screw, Hex Socket2
01***25Bolt,(For Canvas Canopy?Head Guard)2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Turbocharger(#30551-)
01***30Screw4
04***50Screw2
07***95O-Ring (Kit)2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Cylinder Head : Water Manifold And Thermostat(#30551-)
01***30Bolt,(With Body Positioner)4
01***35Bolt,(F4320-52a0 -5 )8
01***80Bolt,(With Corrosion Resistor)2
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Engine Kit
Komatsu : S6d155-4-R(S/N 10014-Up) : Engine Kit : Gasket Kit(#56577-)
01***21Washer3
01***12Washer,Lock (K2)4
01***08Washer (K2)1
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Fuel System
Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Accessory Parts(#57335-)
61***20Lamp,Aps1
78***00Controller Unit A1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Auto Priming System(#57335-)
01***30Screw2
01***12Bolt - Front Cover Mounting2
01***25Bolt,(Rear Attachment Less)1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Automatic Timer(#30551-)
61***32Automatic Timer A1
DK***00Washer1
DK***00Flyweight2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Feed Pump(#35072-)
02***04Plug,(For Shipping)1
61***53Injection Pump Ass'Y1
61***32Joint,Fuel1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Fuel Fitler(#30551-)
01***35Bolt,(F4320-52a0 -5 )4
01***08Nut, Regular Hexagon (M10-1.50)4
01***30Washer,Spring(Sandy?Dusty Terrain S.)4
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Fuel Injection Pump And Piping(#30551-)
01***40Capscrew3
01***45Hexagon Bolt1
01***12Bolt - M8 - 1.25 X 124
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Fuel Injection Pump Drive Service Meter(#30551-)
01***30Bolt,(Not Used When Towing Winch)6
01***35Bolt, Mount Ground Driven Steering Pump1
01***30Bolt,(Cold Weather Spec.)6
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Fuel Injection Pump(#35072-)
61***53Injection Pump Ass'Y1
DK***30Bearing,Roller2
DK***30Washer12
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Governor(#35072-)
61***53Injection Pump Ass'Y1
DK***00Gear1
DK***70Seal,Oil1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Hand Primer(#30551-)
66***20Body1
66***30Nut,Lock3
66***40Washer1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Name Plate And Caution Plate(#57335-)
61***21Plate,Auto Primming System2
61***60Plate? Operating,Auto Primming System1
61***91Plate? Caution,Auto Primming System1
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Komatsu : S6d155-4-R(S/N 10014-Up) : Fuel System : Nozzle And Holder(#30551-)
07***12Gasket,Mechanical Pump Piping2
61***04Nozzle Holder Ass'Y6
61***33Nozzle,Fuel1
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Lubricating Oil System
Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Bypass Filter (Starting Motor Spec.)(#56577-)
01***75Bolt - Tube Mounting2
01***15Bolt2
01***36Washer,Radio Controlled Slag Handling4
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Camshaft Lubricating Oil Piping(#30551-)
07***10Connector,Pipe6
61***40Nozzle,Oil12
61***12Pipe,Oil2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Lubricating Oil Cooler(#30551-)
01***20Bolt,(For Mono Lever Steering)2
01***30Bolt,(With Body Positioner)2
01***35Bolt,(F4320-52a0 -5 )19
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Lubricating Oil Filter Bracket(#30551-)
01***70Bolt - Bracket And Oil Inlet Tubemounting2
01***40Bolt,For Weight Adjusting Bolt3
01***80Bolt,For Weight Adjusting Bolt2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Lubricating Oil Filter(#30551-)
01***40Bolt,For Weight Adjusting Bolt5
01***85Bolt,(Used With Pin Puller)3
01***36Washer,Radio Controlled Slag Handling8
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Lubricating Oil Pump(#30551-)
01***20Bolt,(Large Capacity Type) (Std)2
01***20Bolt,(For Mono Lever Steering)2
01***25Bolt,(For Canvas Canopy?Head Guard)2
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Oil Strainer And Piping(#30551-)
01***14Screw2
01***22Capscrew3
01***25Bolt,(For Canvas Canopy?Head Guard)5
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : P.T.O. Lubricating Oil Piping(#30551-)
01***22Capscrew1
01***30Bolt,(With Body Positioner)3
01***30Washer,Spring(Sandy?Dusty Terrain S.)4
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Komatsu : S6d155-4-R(S/N 10014-Up) : Lubricating Oil System : Tubrocharger Lubricaiting Oil Piping(#30551-)
01***10Bolt1
01***35Bolt,(For Fix Position)2
01***35Bolt,(F4320-52a0 -5 )2
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S6D155-4-R(S/N 10014-UP) serial number reference

The PIN plate is typically riveted to the right-hand side of the cab on the lower frame, just behind the front idler or beneath the operator's window. Read the 17-character ISO PIN; the first three characters (KMT) identify Komatsu, while positions 4–8 encode the model family and configuration, and position 10 indicates the model year.

PrefixIdentifies
S6D155-4-REngine Model

Frequently asked questions

What is the engine model for the Komatsu D155A-1 dozer?

The Komatsu D155A-1 dozer uses the S6D155-4 turbocharged diesel engine, producing 320 hp gross power.

What is the operating weight of the Komatsu D155A-1?

The operating weight of the Komatsu D155A-1 is approximately 59,350 lb (26,943 kg), varying by configuration and attachments.

What replaced the Komatsu D155A-1 series?

The D155A-1 series was succeeded by the D155C-1 and D155W-1 crawler dozer models, which featured updated engines and emissions systems.

What S6D155-4-R(S/N 10014-UP) owners discuss

What is the net horsepower rating for the Komatsu S6D155-4 engine in the D155A-1 dozer configuration?
320 hp (238.7 kW). This rating applies to the turbocharged S6D155-4 engine installed in the D155A-1 crawler dozer. Values vary by configuration/series depending on the specific machine application (dozer, excavator, or generator set). Have your dealer verify the exact rating for your specific serial range and emissions package.
What are the common hydraulic behaviors and failure patterns associated with the Komatsu S6D155-4 engine platform?
Operators report that hydraulic pump failures often precede engine wear, with a common consensus that if the main pump fails, the engine is likely near the end of its service life. Early dash-6 machines in this lineage experienced main control valve issues. A key diagnostic pattern is that if all hydraulic functions (boom, arm, bucket, swing, travel) become slow simultaneously, the issue is likely shared (hydraulic oil, filters, or engine speed) rather than a single cylinder. Weakness that appears only when hot indicates internal leakage due to viscosity loss.
What undercarriage and wear patterns are typical for machines powered by the S6D155-4, such as the D155A series?
The D155A-1 dozer has an operating weight of 59,350 lb (26,942 kg). Common wear items include final drives and travel motors. A specific community note is that Komatsu final drives require special tools for splitting. Track tension and undercarriage wear are critical; machines that pull to one side should be checked for mechanical resistance (mud/debris) before diagnosing travel motors. The line is noted for wearing out complete machines simultaneously rather than gradual component failure.
What electrical and sensor issues are frequently reported for Komatsu equipment using this engine series?
Komatsu machines rely heavily on electronic control systems. Common reports include intermittent starting, dashboard failures, and random shutdowns triggered by a single faulty sensor or unstable power supply. Multiple fault codes often point to battery state, chassis grounds, or connector integrity rather than individual component failure. Owners should check battery load and voltage drop under starter load, as voltage can appear acceptable until the starter is engaged.
What are the known engine quirks and maintenance priorities for the S6D155-4 series?
The S6D155-4 is a 6-cylinder, 4-stroke, water-cooled, turbocharged diesel engine. Key maintenance priorities include the cooling package (radiator, hydraulic oil cooler, charge-air cooler) which is prone to packing with fine debris between heat exchangers. Engine performance issues often stem from airflow restriction or fuel delivery components. The engine control system (Chapter 14 of the shop manual) has undergone significant revisions, with updates continuing into the 2020s. Fuel quality and water separation are critical to prevent injector wear.
What fluids are specified for the Komatsu S6D155-4 engine and associated systems?
Komatsu specifies Komatsu Genuine fluids for optimal protection. Recommended fluids include Komatsu EO (Engine Oil), Komatsu TO (Transmission Oil), Komatsu AXO (Axle Oil), and Komatsu HO (Hydraulic Oil). Super-coolant AF-NAC is specified for the cooling system. Chevron Delo and other OEM-approved equivalents are also commonly used. Always verify the specific viscosity grade and specification level in the Operation and Maintenance Manual for your ambient temperature and duty cycle.
What should be checked when buying a used machine with the S6D155-4 engine (S/N 10014-UP)?
Verify the exact engine build (e.g., Build 14A) and serial number against the parts book, as configurations vary significantly between serial ranges. Check for signs of hydraulic pump failure, as this often correlates with engine wear. Inspect the cooling package for packed debris between the radiator, oil cooler, and charge-air cooler. Test all hydraulic functions cold and hot to identify viscosity-related leakage. Check for intermittent electrical faults, dashboard errors, and random shutdowns. Verify the condition of the final drives and travel motors, ensuring no grinding noises or pulling tendencies. Have your dealer verify the engine's current compression and turbocharger condition.

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

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