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Komatsu 4D102 Engine

The Komatsu 4D102 is a heavy-duty, industrial-grade four-cylinder, in-line diesel engine widely used across construction, agricultural, and commercial machinery, most notably powering compact Komatsu excavators like the PC60-7 and PC120-6. Built on a durable cast-iron platform structurally co-developed with the Cummins B-series engine family, it features direct fuel injection and a water-cooled architecture. Depending on the application context, the assembly is configured as either naturally aspirated or turbocharged (S4D102) to ensure robust low-end torque, extended service durability, and consistent performance under extreme operating stresses.

The engine employs an overhead valve mechanism actuated via a traditional pushrod and lifter system driven by a gear-timed camshaft located in the cylinder block. It uses a two valves per cylinder configuration (comprising four intake and four exhaust valves in total). Valve clearance adjustments are performed at the rocker arm assembly using conventional adjustment screws and locknuts. Cylinder Bore: Exactly 102 mm (4.02 inches). Piston Stroke: Exactly 120 mm (4.72 inches). Total Piston Displacement: Measured at 3.9 liters (238 cubic inches). Static Compression Ratio: Rated at 16.5:1.

The engine utilizes a mechanical direct fuel injection system for highly atomized combustion inside the piston crown bowl. Supply Flow: Fuel is picked up from the equipment tank by a mechanical fuel transfer pump (feed pump) and pushed through a primary fuel filter water-separator assembly. Injection Control: The clean fuel feeds directly into a timing-gear-driven in-line injection pump assembly (typically Bosch PES-A type or equivalent mechanical design) regulated by a mechanical governor. High-Pressure Delivery: The injection pump increases pressures to precise combustion levels and sequences delivery through high-pressure steel lines to mechanical multi-hole fuel injector nozzles situated vertically in the cylinder head. Excess unburned fuel is routed back via an fuel overflow valve and spill tube assembly directly to the fuel reservoir.

Lubrication is managed via a full-pressure, gear-driven internal system supplied directly by an internal oil pump integrated into the engine front gear housing. Main system features include: Flow Path: The pump draws oil from the structural oil pan through a suction strainer and forces it through a full-flow spin-on cartridge filter assembly. Thermal Management: A built-in plate-type oil cooler element interfaces with the engine block jacket to manage oil viscosity under peak loads. The cooling architecture utilizes a closed-circuit, forced-circulation, liquid-cooled layout. Circulation: A heavy-duty water pump is driven by a gear off the main timing train or via a front accessory belt system, prompting coolant flow directly into the cylinder block liners and up through the cylinder head jackets. Temperature Regulation: A pellet-type thermostat element regulates the path of the coolant.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 4D102
Engine Type ............... 4-cycle inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.02 (102.0)
Engine Stroke, in (mm) ............... 4.72 (120.0)
Displacement, cu.in (L) ............... 239 (3.9)
Rated Engine Power, hp (kW) ............... 79-112 (59-84) at 2200-2500 rpm
Rated Engine Speed, rpm ............... 2200-2500
Peak Torque ............... 207-280 lb-ft (280-380 Nm) at 1400-1600 rpm
Idle Speed ............... 750-850 rpm
Aspiration Type ............... Naturally Aspirated or Turbocharged
Operating Speed ............... 2200 rpm
Compression Ratio ............... 16.5:1-17.5:1
Firing Order ............... 1-3-4-2
Combustion System ............... Direct injection open chamber
Valve Mechanism ............... Overhead valve pushrod actuated
Crankshaft Material ............... Forged steel induction hardened journals
Connecting Rod Material ............... Forged steel H-beam split cap alloy
Cylinder Block Type ............... Cast iron non-parent sleeve
Cylinder Head Type ............... Cast iron single piece monoblock
Lubrication System ............... Full-pressure recirculation
Oil Pump Type ............... Gear-driven internal rotor
Oil Filter Type ............... Full-flow, spin-on cartridge
Cooling System ............... Forced liquid circulation
Water Pump Type ............... Belt-driven, centrifugal impeller
Thermostat Type ............... Pellet bypass dual flow regulatory valve
Air Cleaner Type ............... Dry dual-stage element
Starting System ............... Axial-type electric starter
Electrical System ............... 12V or 24V

Fuel System

Injection Pump Type ............... Bosch Inline PES-A or Bosch VE Distributor
Fuel Feed Pump Type ............... Camshaft-lobe mechanical plunger
Fuel Injection Timing ............... 11.5-14.5 deg before top dead center
Fuel Injector Type ............... Multi-hole nozzle hole-type mechanical
Number of Injector Holes ............... 4 or 5 micro orifices
Injector Opening Pressure, psi (MPa) ............... 3550-3770 (24.5-26.0)
Fuel Filter Type ............... Spin-on water separator element
Fuel Transfer Pump Pressure, psi (kPa) ............... 25-35 (172-241)
Governor Type ............... Mechanical RSVP or electronic control
Fuel Supply Line Outer Diameter, in (mm) ............... 0.315 (8.0)
Fuel Return Line Outer Diameter, in (mm) ............... 0.236 (6.0)
High Pressure Line Inner Diameter, in (mm) ............... 0.078 (2.0)
Injection Plunger Diameter, in (mm) ............... 0.354-0.433 (9.0-11.0)
Injection Plunger Stroke, in (mm) ............... 0.315-0.393 (8.0-10.0)
Fuel Grade Recommendation ............... ASTM D975 No.2-D ultra low sulfur diesel
Fuel Priming Pump Type ............... Hand-operated mechanical thumb plunger
Overflow Valve Cracking Pressure, psi (kPa) ............... 14-18 (96-124)
Maximum Fuel Filter Pressure Drop, psi (kPa) ............... 5.0 (34.5)
Leak-off Line Management ............... Manifolded internal routing to common return
Air Venting Mechanism ............... Manual bleed screw on primary head adapter

Dimensions and Weight

Engine Length, in (mm) ............... 31.1 (790)
Engine Width, in (mm) ............... 28.0 (710)
Engine Height, in (mm) ............... 35.2 (895)
Dry Weight, lbs (kg) ............... 860 (390)
Wet Weight, lbs (kg) ............... 915 (415)

Maintenance Data

Service Information

Compression Pressure Test, psi (MPa) ............... 350-450 (2.41-3.10)
Compression Pressure Between Cylinders, psi (MPa) ............... 35.0 (0.24)
Oil Pressure Bypass Cracking Pressure, psi (kPa) ............... 65.0 (448.0)
Radiator Cap Rating Pressure, psi (kPa) ............... 7.0-10.0 (48.2-68.9)
Coolant Operating Temperature Range, F (C) ............... 160-200 (71-93)
Oil Operating Temperature Range, F (C) ............... 180-240 (82-115)
Oil Pressure at Low Idle, psi (kPa) ............... 10.0 (69.0)
Oil Pressure at Rated Speed, psi (kPa) ............... 30.0-50.0 (207.0-345.0)
Thermostat Opening Temperature, F (C) ............... 180 (82)
Thermostat Full Open Temperature, F (C) ............... 203 (95)
Intake Valve Clearance (Cold), in (mm) ............... 0.0100 (0.254)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0200 (0.508)

Engine Oil and Coolant

Engine Oil Type .................. SAE 5W-30, SAE 15W-40, SAE 10W-30
API Service Classifications ......................... CH-4 or CI-4
Engine Oil Capacity, qt (L) ............... 10.5-12.7 (10.0-12.0)
Coolant Capacity, qt (L) ............... 8.5-10.6 (8.0-10.0)

Service Intervals

Change oil and filter ............... Every 250 hours
Inspect air cleaner ............... Every 250 hours
Replace air cleaner ............... Every 1000 hours
Replace fuel filter ............... Every 500 hours
Valve clearance adjustment ............... Every 1000 hours
Fuel system inspection ............... Every 1000 hours
Change coolant ............... Every 2000 hours
Compression test ............... Every 1000 hours
Clean radiator core ............... Every 250 hours
Inspect belt tension ............... Every 150 hours

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 4.0157-4.0173 (102.000-102.040)
Cylinder Bore Maximum Wear Limit, in (mm) ............... 4.0208 (102.130)
Cylinder Maximum Out-of-Round, in (mm) ............... 0.0015 (0.038)
Connecting Rod Small End Bushing I.D, in (mm) ............... 1.6925-1.6935 (42.990-43.015)
Main Journal Outside Diameter, in (mm) ............... 3.2665-3.2677 (82.973-83.003)
Crankpin Journal Outside Diameter, in (mm) ............... 2.7154-2.7165 (68.972-69.002)
Main Bearing Clearance, in (mm) ............... 0.0016-0.0047 (0.041-0.119)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0015-0.0045 (0.038-0.114)
Crankshaft End Play, in (mm) ............... 0.0043-0.0130 (0.110-0.330)
Thrust Bearing Journal Width, in (mm) ............... 1.4567-1.4591 (37.000-37.060)
Connecting Rod Side End Play, in (mm) ............... 0.0039-0.0118 (0.100-0.300)
Main Bearing Cap Housing Bore I.D, in (mm) ............... 3.4646-3.4658 (88.001-88.031)
Con Rod Big End Housing Bore I.D, in (mm) ............... 2.8736-2.8744 (72.989-73.010)
Piston Skirt Outside Diameter, in (mm) ............... 4.0102-4.0118 (101.860-101.900)
Piston-to-Cylinder Bore Clearance, in (mm) ............... 0.0039-0.0071 (0.100-0.180)
Piston Pin Diameter, in (mm) ............... 1.5746-1.5749 (39.994-40.003)
Piston Pin Bushing Inner Diameter, in (mm) ............... 1.5755-1.5761 (40.018-40.033)
Piston Pin to Bushing Clearance, in (mm) ............... 0.0006-0.0015 (0.015-0.039)
Top Ring Groove Width, in (mm) ............... Keystone style structure geometric profile
Second Ring Groove Width, in (mm) ............... 0.0957-0.0972 (2.430-2.470)
Oil Ring Groove Width, in (mm) ............... 0.1583-0.1594 (4.020-4.050)
Top Ring Side Clearance, in (mm) ............... 0.0020-0.0043 (0.050-0.110)
Second Ring Side Clearance, in (mm) ............... 0.0016-0.0035 (0.040-0.090)
Oil Ring Side Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Top Ring End Gap, in (mm) ............... 0.0118-0.0216 (0.300-0.550)
Second Ring End Gap, in (mm) ............... 0.0256-0.0374 (0.650-0.950)
Oil Ring End Gap, in (mm) ............... 0.0098-0.0216 (0.250-0.550)
Cylinder Head Deck Flatness, in (mm) ............... 0.0020 (0.050)
Cylinder Block Top Surface Flatness, in (mm) ............... 0.0020 (0.050)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.3126-0.3138 (7.941-7.971)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.3114-0.3126 (7.911-7.941)
Intake Valve Guide Inner Diameter, in (mm) ............... 0.3150-0.3165 (8.000-8.039)
Exhaust Valve Guide Inner Diameter, in (mm) ............... 0.3150-0.3165 (8.000-8.039)
Intake Valve Stem-to-Guide Clearance, in (mm) ............... 0.0011-0.0039 (0.029-0.098)
Exhaust Valve Stem-to-Guide Clearance, in (mm) ............... 0.0023-0.0050 (0.059-0.128)
Valve Head Recess, in (mm) ............... 0.0591 (1.500)
Intake Valve Face Angle, deg ............... 30
Intake Valve Seat Angle, deg ............... 30
Exhaust Valve Face Angle, deg ............... 45
Exhaust Valve Seat Angle, deg ............... 45
Valve Spring Free Length, in (mm) ............... 1.8799 (47.75)
Camshaft Journal Outer Diameter, in (mm) ............... 2.1236-2.1248 (53.940-53.970)
Camshaft Bushing Inner Diameter, in (mm) ............... 2.1264-2.1287 (54.010-54.070)
Camshaft Journal-to-Bushing Clearance, in (mm) ............... 0.0016-0.0051 (0.040-0.130)
Camshaft Axial End Play, in (mm) ............... 0.0047-0.0134 (0.120-0.340)
Cam Lobe Height (Intake), in (mm) ............... 1.8346-1.8488 (46.600-46.960)
Cam Lobe Height (Exhaust), in (mm) ............... 1.8213-1.8354 (46.260-46.620)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.7469-0.7480 (18.971-19.000)
Rocker Arm Bushing Inner Diameter, in (mm) ............... 0.7490-0.7505 (19.025-19.063)
Rocker Arm Bushing to Shaft Clearance, in (mm) ............... 0.0010-0.0036 (0.025-0.092)
Tappet Stem Outer Diameter, in (mm) ............... 0.6276-0.6287 (15.941-15.970)
Tappet Guide Inner Diameter, in (mm) ............... 0.6300-0.6315 (16.000-16.039)
Tappet Stem to Guide Bore Clearance, in (mm) ............... 0.0012-0.0039 (0.030-0.098)

Tightening Torques

Cylinder Head Bolts (Step 1), lb-ft (Nm) ............... 66 (90)
Cylinder Head Bolts (Step 2), lb-ft (Nm) ............... 88 (120)
Cylinder Head Bolts (Step 3), lb-ft (Nm) ............... 100 (136)
Main Bearing Cap Early Bolts (Step 1), lb-ft (Nm) ............... 44 (60)
Main Bearing Cap Early Bolts (Step 2), lb-ft (Nm) ............... 66 (90)
Main Bearing Cap Early Bolts (Step 3), lb-ft (Nm) ............... 131 (178)
Main Bearing Cap Late Bolts (Step 1), lb-ft (Nm) ............... 44 (60)
Main Bearing Cap Late Bolts (Step 2), lb-ft (Nm) ............... 66 (90)
Connecting Rod Cap (Step 1), lb-ft (Nm) ............... 22 (30)
Connecting Rod Cap (Step 2), lb-ft (Nm) ............... 44 (60)
Flywheel Mounting Capscrews, lb-ft (Nm) ............... 101 (137)
Flywheel Housing Bolts to Block, lb-ft (Nm) ............... 57 (77)
Crankshaft Damper Pulley Bolt, lb-ft (Nm) ............... 148 (200)
Camshaft Thrust Flange Bolts, lb-ft (Nm) ............... 18 (24)
Camshaft Gear Center Driven Bolt, lb-ft (Nm) ............... 57 (77)
Rocker Arm Support Capscrews, lb-ft (Nm) ............... 18 (24)
Valve Adjustment Screw Nut, lb-ft (Nm) ............... 18 (24)
Intake Manifold Flange Bolts, lb-ft (Nm) ............... 18 (24)
Exhaust Manifold Flange Nut, lb-ft (Nm) ............... 33 (45)
Turbocharger Mounting Nuts, lb-ft (Nm) ............... 33 (45)
Oil Pan Drain Plug, lb-ft (Nm) ............... 60 (81)
Oil Pan Frame Mounting Screws, lb-ft (Nm) ............... 18 (24)
Oil Pump Fasteners, lb-ft (Nm) ............... 18 (24)
Water Pump Body Mounting Screws, lb-ft (Nm) ............... 18 (24)
Front Gear Housing Case to Block Bolts, lb-ft (Nm) ............... 18 (24)
Front Timing Gear Cover Face Bolts, lb-ft (Nm) ............... 18 (24)
Fuel Injection Pump Drive Gear Nut, lb-ft (Nm) ............... 48 (65)
Fuel Injection Pump Flange Mounting Nut, lb-ft (Nm) ............... 18 (24)
Fuel Injector Hold Down Clamp Bolt, lb-ft (Nm) ............... 26 (35)
Fuel High Pressure Line Union Nut, lb-ft (Nm) ............... 22 (30)
Fuel Low Pressure Banjo Connector Bolts, lb-ft (Nm) ............... 18 (24)
Fuel Filter Adapter Base Bracket Studs, lb-ft (Nm) ............... 24 (32)
Oil Cooler Core Flange Bolts, lb-ft (Nm) ............... 18 (24)
Oil Pressure Regulator Plug, lb-ft (Nm) ............... 59 (80)
Compressor Cylinder Drive Gear Nut, lb-ft (Nm) ............... 111 (150)
Compressor Mounting Flange Case Bolts, lb-ft (Nm) ............... 57 (77)
Water Inlet Tube Connection Flange Screws, lb-ft (Nm) ............... 18 (24)
Water Outlet Thermostat Housing Fasteners, lb-ft (Nm) ............... 18 (24)
Fan Hub Mounting Base Support Bolts, lb-ft (Nm) ............... 33 (45)
Alternator Pivot Mount Support Bolt, lb-ft (Nm) ............... 57 (77)
Alternator Tension Link Adjuster Lock Screw, lb-ft (Nm) ............... 18 (24)
Starter Motor Mounting Flange Socket Bolts, lb-ft (Nm) ............... 33 (45)
Crankcase Breather Baffle Cover Screws, lb-ft (Nm) ............... 7 (10)
Oil Pressure Sensor Sender Switch Housing, lb-ft (Nm) ............... 11 (15)
Coolant Temperature Sensor Plug, lb-ft (Nm) ............... 14 (19)
Glow Plug Preheater Element, lb-ft (Nm) ............... 18 (24)
Flywheel Housing Access Port Cover, lb-ft (Nm) ............... 7 (10)
Oil Suction Tube Screen Pickup Flange, lb-ft (Nm) ............... 18 (24)
Oil Suction Tube Supporting Pillow Block, lb-ft (Nm) ............... 18 (24)
Rear Crankshaft Oil Seal Retainer Fasteners, lb-ft (Nm) ............... 8 (11)
Cylinder Block Oil Gallery Main Core Plugs, lb-ft (Nm) ............... 44 (60)
Cylinder Block Coolant Side Drain Cock, lb-ft (Nm) ............... 18 (24)
Turbocharger Oil Supply Feed Pipe Flange, lb-ft (Nm) ............... 18 (24)
Turbocharger Oil Return Drain Tube Flange, lb-ft (Nm) ............... 18 (24)
Exhaust Elbow Adaptor V-Band T-Bolt Clamp, lb-ft (Nm) ............... 8 (11)
Intake Crossover Tube Support Bracket Clamps, lb-ft (Nm) ............... 18 (24)
Fuel Injection Pump Bleed Screw Plug Valve, lb-ft (Nm) ............... 7 (10)
Fuel Injector Leak-off Return Line Banjo, lb-ft (Nm) ............... 7 (10)
Governor Housing Cover Plate Fasteners, lb-ft (Nm) ............... 7 (10)
Aneroid Boost Control Capsule Sensing Line, lb-ft (Nm) ............... 11 (15)
Engine Lifting Bracket Heavy Eyelet Bolts, lb-ft (Nm) ............... 57 (77)
Front Crankshaft Hub Wear Sleeve Ring, lb-ft (Nm) ............... 8 (11)
Dipstick Tube Adapter Compression Nut, lb-ft (Nm) ............... 11 (15)
Crankcase Inspection Side Plate Cover Gasket, lb-ft (Nm) ............... 18 (24)
Hydraulic Accessory Pump Drive Flange Coupling, lb-ft (Nm) ............... 48 (65)
Safety Shield Guard Fan Belt Cover Bolts, lb-ft (Nm) ............... 7 (10)

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