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Komatsu 4D105 Engine

The Komatsu 4D105 (and its turbocharged variant, the S4D105) is a heavy-duty, inline 4-cylinder, 4-stroke cycle water-cooled diesel engine widely utilized in Komatsu construction equipment, such as bulldozers (D31, D37, and D40) and excavators. Known for its robust and reliable structural design, the engine relies on a standard overhead valve layout driven by a gear-train camshaft, pushrods, and rocker arms. This engine family features a high-strength cast-iron block with replaceable cylinder liners and is engineered to maintain stable operational efficiency under heavy industrial loads.

The engine employs an Overhead Valve (OHV) actuation system driven by a single camshaft, pushrods, and rocker arms. It is configured with a total of 8 valves (4 intake valves and 4 exhaust valves), assigning 2 valves per cylinder. The cylinder head includes replaceable valve guides and exhaust valve seats to simplify workshop reconditioning. The engine features a cylinder bore of 105 mm (4.13 in) and a piston stroke of 125 mm (4.92 in). Total engine displacement measures 4.33 liters (4330 cc) with a standard firing order configured at 1-2-4-3.

Fuel delivery is managed by a mechanical Bosch PES-A inline fuel injection pump coupled with an integrated RSV centrifugal all-speed mechanical governor to balance engine RPM under variable loading. The fuel system utilizes multi-hole injection nozzles calibrated to an opening injection pressure of 225 kg/cm2. System purity is sustained via a primary feed pump drawing fuel through a replaceable cartridge-type fuel filter before entering the high-pressure gallery.

Engine lubrication is maintained by a forced-feed pressure system powered by a high-efficiency Trochoid oil pump. Oil filtration is managed through a single full-flow cartridge-type oil filter. A built-in pressure regulating valve manages safe system pressure, ensuring continuous delivery of clean lubricant directly to the main bearings, connecting rod journals, and overhead valve mechanism. The cooling loop is an unpressurized or pressurized liquid-forced system circulated by a centrifugal spiral-type water pump. System temperature regulation is handled by a wax-case type thermostat designed with an operating range of 75-90C (167-194F) to manage swift warm-up times and ensure thermal equilibrium during prolonged operation.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 4D105-3
Engine Type ............... 4-cycle inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line vertical
Engine Bore, in (mm) ............... 4.13 (105.0)
Engine Stroke, in (mm) ............... 4.92 (125.0)
Displacement, cu.in (L) ............... 264.2 (4.33)
Rated Engine Power, hp (kW) ............... 49-90 (37-67)
Rated Engine Speed, rpm ............... 2400
Peak Torque, lb-ft (Nm) ............... 163-231 (220-314)
Peak Torque Engine Speed, rpm ............... 1400-1600
Low Idle Speed, rpm ............... 650-700
High Idle Speed, rpm ............... 2600-2650
Aspiration Type ............... Naturally aspirated or turbocharged
Compression Ratio ............... 17.0:1
Firing Order ............... 1-2-4-3
Combustion Chamber Style ............... Direct injection toroidal bowl
Governor Mechanism Type ............... Centrifugal mechanical all-speed type
Direction of Rotation ............... Counterclockwise viewed from flywheel side
Valves Per Cylinder Intake ............... 1
Valves Per Cylinder Exhaust ............... 1
Cylinder Liner Style ............... Dry type thin wall chrome plated cast iron
Camshaft Drive Train ............... Spur gear driven valve gear train
Cylinder Block Construction ............... Cast iron alloy monoblock
Cylinder Head Design ............... Cast iron single piece head
Lubrication System ............... Forced pressure circulation
Oil Pump Type ............... Trochoid type gear driven
Oil Filter Type ............... Full-flow cartridge spin-on
Cooling System ............... Liquid distribution with centrifugal pump
Water Pump Type ............... Belt-driven centrifugal spiral type
Air Cleaner Type ............... Dry element multi-stage filter
Starting System ............... Electric starter motor actuation
Electrical System, V ............... 24
Alternator Capacity, A ............... 25
Starter Motor Rating, hp (kW) ............... 7.0-7.4 (5.2-5.5)

Fuel System

Fuel Injection Pump Model ............... Bosch PES-A type inline plunger pump
Fuel Feed Pump Type ............... Mechanical piston type transfer pump
Governor Model Designation ............... RSV mechanical centrifugal governor
Fuel Injection Nozzle Holder ............... Multi-hole standard nozzle body assembly
Injection Opening Pressure, psi (kg/cm2) ............... 3200 (225)
Fuel Filter Configuration ............... Spin-on dual element cartridge assembly
Fuel System Delivery Line Type ............... High-pressure seamless steel tube lines
Injection Timing Angle, deg BTDC ............... 14-16
Plunger Diameter, in (mm) ............... 0.35 (9.0)
Plunger Stroke length, in (mm) ............... 0.39 (10.0)
Delivery Valve Relieving Volume, cu.in (cu.mm) ............... 0.0024 (40.0)
Number of Nozzle Holes ............... 4
Nozzle Hole Diameter, in (mm) ............... 0.011 (0.28)
Nozzle Spray Angle, deg ............... 150
Fuel Transfer Pump Pressure, psi (kg/cm2) ............... 28.4-42.6 (2.0-3.0)
Overflow Valve Cracking Pressure, psi (kg/cm2) ............... 21.3 (1.5)
Fuel Tank Vent Valve Pressure, psi (kg/cm2) ............... 0.71 (0.05)
Fuel Injection Pipe Outer Diameter, in (mm) ............... 0.24 (6.0)
Fuel Injection Pipe Inner Diameter, in (mm) ............... 0.08 (2.0)
Maximum Fuel Inlet Temperature, F (C) ............... 140 (60)
Fuel Leak-off Line Path ............... Return circuit connected directly to filter housing
Prime Pump Displacement Per Stroke, cu.in (cc) ............... 0.24 (4.0)
Maximum Fuel Suction Lift, ft (m) ............... 3.3 (1.0)
Injection Pump Lubrication ............... Splash flow shared with engine block oil sump

Dimensions and Weight

Overall Length, in (mm) ............... 38.8 (985)
Overall Width, in (mm) ............... 27.6 (700)
Overall Height, in (mm) ............... 54.1 (1375)
Dry Weight, lbs (kg) ............... 1191 (540)
Wet Weight, lbs (kg) ............... 1257 (570)

Maintenance Data

Service Information

Compression Pressure, Standard, psi (kg/cm2) ............... 426 (30.0)
Compression Pressure, Limit, psi (kg/cm2) ............... 313 (22.0)
Oil Pressure at Low Idle, psi (kg/cm2) ............... 14.2 (1.0)
Oil Pressure at Rated Speed, psi (kg/cm2) ............... 42.6-56.9 (3.0-4.0)
Oil Pressure Valve Opening, psi (kg/cm2) ............... 64.0 (4.5)
Radiator Cap Pressure, psi (kg/cm2) ............... 7.1-12.8 (0.5-0.9)
Thermostat Full Open Temperature, F (C) ............... 194 (90)
Thermostat Initial Crack Temperature, F (C) ............... 167 (75)
Thermostat Operational Range, F (C) ............... 167-194 (75-90)
Fan Belt Deflection Under 22 lbs force, in (mm) ............... 0.39-0.59 (10.0-15.0)
Intake Valve Clearance Cold state, in (mm) ............... 0.012 (0.30)
Exhaust Valve Clearance Cold state, in (mm) ............... 0.014 (0.35)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 15W-40, SAE 10W-30
API Service Classifications ......................... CD or CE
Engine Oil Capacity, Sump Only, qt (L) ............... 10.6 (10.0)
Engine Oil Capacity, System Total, qt (L) ............... 12.7 (12.0)
Cooling System Fluid Capacity, qt (L) ............... 14.8 (14.0)

Service Intervals

Change oil and filter ............... Every 250 hours
Inspect air cleaner ............... Every 100 hours
Replace air cleaner ............... Every 1000 hours
Replace fuel filter ............... Every 500 hours
Valve clearance adjustment ............... Every 500 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 Liner Inside Diameter, in (mm) ............... 4.134 (105.000)
Cylinder Liner Out-of-Roundness, in (mm) ............... 0.0008 (0.020)
Cylinder Liner Taper Max, in (mm) ............... 0.0012 (0.030)
Cylinder Block Top Surface Flatness, in (mm) ............... 0.002 (0.05)
Cylinder Head Bottom Surface Flatness, in (mm) ............... 0.003 (0.08)
Main Journal Outer Diameter, in (mm) ............... 3.150 (80.0)
Crankpin Journal Outer Diameter, in (mm) ............... 2.559 (65.0)
Main Journal Bearing Clearance, in (mm) ............... 0.0024-0.0043 (0.060-0.110)
Crankpin Bearing Clearance, in (mm) ............... 0.0020-0.0039 (0.050-0.100)
Crankshaft Thrust Washer Thickness, in (mm) ............... 0.091-0.093 (2.31-2.36)
Main Bearing Shell Thickness, in (mm) ............... 0.098 (2.500)
Connecting Rod Bearing Shell Thickness, in (mm) ............... 0.079 (2.000)
Connecting Rod Big End Bore I.D, in (mm) ............... 2.756 (70.0)
Connecting Rod Small End Bushing I.D, in (mm) ............... 1.418 (36.015)
Piston Skirt Outer Diameter, in (mm) ............... 4.131 (104.93)
Piston to Cylinder Liner Clearance, in (mm) ............... 0.0028-0.0043 (0.070-0.110)
Piston Pin Bore Inner Diameter, in (mm) ............... 1.417 (36.0)
Piston Pin To Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0004 (0.000-0.010)
Piston Pin To Small End Bushing Clearance, in (mm) ............... 0.0010-0.0020 (0.025-0.050)
Top Ring End Gap, in (mm) ............... 0.012-0.018 (0.30-0.45)
Second Ring End Gap, in (mm) ............... 0.010-0.016 (0.25-0.40)
Oil Ring End Gap, in (mm) ............... 0.010-0.016 (0.25-0.40)
Top Ring Groove Side Clearance, in (mm) ............... 0.0028-0.0045 (0.070-0.115)
Second Ring Groove Side Clearance, in (mm) ............... 0.0020-0.0035 (0.050-0.090)
Oil Ring Groove Side Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Intake Valve Stem To Guide Clearance, in (mm) ............... 0.0012-0.0026 (0.030-0.065)
Exhaust Valve Stem To Guide Clearance, in (mm) ............... 0.0020-0.0033 (0.050-0.085)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.352 (8.940)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.351 (8.910)
Intake Valve Seat Width, in (mm) ............... 0.055-0.071 (1.40-1.80)
Exhaust Valve Seat Width, in (mm) ............... 0.067-0.083 (1.70-2.10)
Valve Guide Inner Diameter, in (mm) ............... 0.354 (9.000)
Valve Face Angle, deg ............... 45
Valve Seat Angle, deg ............... 45
Valve Head Sinkage, in (mm) ............... 0.028-0.043 (0.70-1.10)
Valve Spring Free Length, in (mm) ............... 1.929 (49.00)
Camshaft Journal Outer Diameter, in (mm) ............... 1.969 (50.0)
Camshaft Journal Bushing Clearance, in (mm) ............... 0.0020-0.0047 (0.050-0.120)
Camshaft End Play, in (mm) ............... 0.0020-0.0071 (0.050-0.180)
Cam Lobe Height (Intake), in (mm) ............... 0.28 (7.1)
Cam Lobe Height (Exhaust), in (mm) ............... 0.29 (7.4)
Rocker Arm Shaft To Bushing Clearance, in (mm) ............... 0.0004-0.0024 (0.010-0.060)
Idler Gear Shaft To Bushing Clearance, in (mm) ............... 0.0010-0.0030 (0.025-0.075)

Tightening Torques

Cylinder Head Bolts (1-Step), lb-ft (Nm) ............... 147.5 (200.0)
Cylinder Head Bolts (2-Step), lb-ft (Nm) ............... 236.0 (320.0)
Cylinder Head Bolts (3-Step), lb-ft (Nm) ............... 295.0 (400.0)
Main Bearing Cap Bolts (1-Step), lb-ft (Nm) ............... 66.4 (90.0)
Main Bearing Cap Bolts (2-Step), lb-ft (Nm) ............... 101.1 (137.0)
Main Bearing Cap Bolts (3-Step), lb-ft (Nm) ............... 144.6 (196.0)
Connecting Rod Cap Bolts (1-Step), lb-ft (Nm) ............... 44.3 (60.0)
Connecting Rod Cap Bolts (2-Step), lb-ft (Nm) ............... 81.1 (110.0)
Flywheel Retaining Mounting Bolts, lb-ft (Nm) ............... 132.8 (180.0)
Crankshaft Pulley Vibration Damper Bolt, lb-ft (Nm) ............... 258.1 (350.0)
Camshaft Thrust Plate Fasteners, lb-ft (Nm) ............... 18.4 (25.0)
Camshaft Timing Gear Center Nut, lb-ft (Nm) ............... 110.6 (150.0)
Idler Gear Shaft Block Bolts, lb-ft (Nm) ............... 51.6 (70.0)
Rocker Arm Shaft Support Fasteners, lb-ft (Nm) ............... 29.5 (40.0)
Cylinder Head Cover Cap Screws, lb-ft (Nm) ............... 7.4 (10.0)
Intake Manifold Assembly Mounting Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Exhaust Manifold Assembly Mounting Bolts, lb-ft (Nm) ............... 29.5 (40.0)
Oil Sump Pan Flange Hex Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Oil Sump Drain Plug, lb-ft (Nm) ............... 59.0 (80.0)
Oil Pump Assembly Housing Fasteners, lb-ft (Nm) ............... 22.1 (30.0)
Oil Pump Body To Block Bolts, lb-ft (Nm) ............... 29.5 (40.0)
Water Pump Drive Pulley Mounting Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Water Pump Body To Front Cover Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Thermostat Housing Top Cover Shell Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Fuel Injection Pump Mounting Fasteners, lb-ft (Nm) ............... 18.4 (25.0)
Fuel Injection Pump Drive Gear Nut, lb-ft (Nm) ............... 59.0 (80.0)
Fuel Injection Pipe Union Coupling Nuts, lb-ft (Nm) ............... 22.1 (30.0)
Fuel Injector Assembly Clamp Nuts, lb-ft (Nm) ............... 25.8 (35.0)
Fuel Leak-off Line Banjo Fitting Bolts, lb-ft (Nm) ............... 8.9 (12.0)
Fuel Filter Bracket Support Fasteners, lb-ft (Nm) ............... 29.5 (40.0)
Starter Motor Mounting Flange Hex Bolts, lb-ft (Nm) ............... 110.6 (150.0)
Alternator Pivot Support Bracket Frame Bolt, lb-ft (Nm) ............... 36.9 (50.0)
Alternator Tension Adjuster Arm Bracket Bolt, lb-ft (Nm) ............... 18.4 (25.0)
Compressor Drive Gear End Nut, lb-ft (Nm) ............... 73.8 (100.0)
Compressor Main Assembly Flange Bolts, lb-ft (Nm) ............... 36.9 (50.0)
Oil Cooler Housing Core Cover Shell Fasteners, lb-ft (Nm) ............... 18.4 (25.0)
Flywheel Housing Core To Block Bolts, lb-ft (Nm) ............... 66.4 (90.0)
Front Timing Gear Case Cover Screws, lb-ft (Nm) ............... 18.4 (25.0)
Oil Pressure Switch Sensor Unit, lb-ft (Nm) ............... 14.8 (20.0)
Coolant Temperature Sender Sensor Unit, lb-ft (Nm) ............... 22.1 (30.0)
Glow Plug Assembly, lb-ft (Nm) ............... 18.4 (25.0)
Exhaust Pipe Connecting Flange Nuts, lb-ft (Nm) ............... 44.3 (60.0)
Turbocharger Turbine Flange To Manifold Studs, lb-ft (Nm) ............... 33.2 (45.0)
Turbocharger Compressor Housing V-band Clamp, lb-ft (Nm) ............... 5.9 (8.0)
Turbocharger Turbine Housing V-band Core Clamp, lb-ft (Nm) ............... 10.3 (14.0)
Oil Feed Tube Union Fitting Turbocharger Core, lb-ft (Nm) ............... 16.2 (22.0)
Oil Drain Tube Flange Hex Screws, lb-ft (Nm) ............... 18.4 (25.0)
Breather Assembly Deflector Plate Cap Fasteners, lb-ft (Nm) ............... 7.4 (10.0)
Crankcase Hole Side Cover Bolts, lb-ft (Nm) ............... 18.4 (25.0)
Main Oil Gallery End Sealing Plug, lb-ft (Nm) ............... 44.3 (60.0)
Cylinder Head Water Bypass Tube Unions Block, lb-ft (Nm) ............... 29.5 (40.0)
Injection Pump Delivery Valve Holder Retainers, lb-ft (Nm) ............... 33.2 (45.0)
Injection Pump Governor Rear Cover Plate Screws, lb-ft (Nm) ............... 3.7 (5.0)
Fuel Feed Pump Mounting Flange Nuts, lb-ft (Nm) ............... 11.1 (15.0)
Nozzle Tip Cap Nut Outer Sleeve, lb-ft (Nm) ............... 59.0 (80.0)

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