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Komatsu 3D75 Engine

The Komatsu 3D75 is a compact, vertical, 3-cylinder, 4-cycle, water-cooled diesel engine naturally aspirated and designed for utility applications such as mini-excavators (Komatsu PC10-5 and PC20-2) and compact industrial equipment. Developed closely alongside or based on the Yanmar 3TN75 platform,
this series focuses on balancing essential mechanical simplicity with heavy-duty reliability. It utilizes a heavy cast-iron cylinder block and cylinder head configuration to provide a rigid operational assembly suitable for continuous vibration and changing load cycles under stressful field work.

Valve ConfigurationOverhead Valve (OHV) pushrod-driven design with an overhead rocker arm assembly. Actuation: Driven via a gear-train-indexed camshaft located within the cylinder block block casting. Total Displacement: 0.994 liters (994 cc). Cylinder Bore: 75 mm (2.95 inches). Piston Stroke: 75 mm (2.95 inches). Geometry: Square engine configuration (1:1 bore-to-stroke ratio) optimized for operational thermal efficiency and structural balance.

Fuel System: Indirect Injection (IDI) design utilizing a pre-combustion chamber geometry for minimized engine noise and smoothed combustion pressure rise. Injection Pump: Inline, mechanical Bosch-type multi-plunger injection pump indexed to the main timing gear train. Governor: Mechanical all-speed centrifugal flyweight governor regulating fuel metering relative to load. Filtration and Supply: Multi-stage mechanical fuel delivery system encompassing an inline water separator sedimenter and a high-efficiency replaceable spin-on fuel element filter.

Lubrication System Type: Forced pressure feed system driven by a dedicated internal trochoid-type oil pump. Filtration: Full-flow, replaceable spin-on oil filter cartridge alongside a mesh oil pump strainer in the lower pan reservoir. Cooling System Type: Forced liquid, water-cooled cooling circuit. Circulation: Belt-driven centrifugal water pump cycling coolant through a multi-row radiator matrix backed by an engine-driven cooling fan. Temperature Regulation: Monitored via an inline thermal wax pellet bypass thermostat to manage engine stabilization.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 3D75-2
Engine Type ............... 4-cycle inline 3-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 3
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 2.95 (75.0)
Engine Stroke, in (mm) ............... 2.95 (75.0)
Displacement, cu.in (L) ............... 60.6 (0.994)
Rated Engine Power, hp (kW) ............... 15-22 (11.2-16.4)
Rated Engine Speed, rpm ............... 2500-2900
Peak Torque ............... 41-48 lb-ft (56-65 Nm) at 1800-2000 rpm
Idle Speed ............... 800-900 rpm
Aspiration Type ............... Naturally Aspirated
Operating Speed ............... 2500 rpm
Compression Ratio ............... 18.0:1-21.5:1
Firing Order ............... 1-3-2
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron
Lubrication System ............... Full-pressure forced lubrication
Oil Pump Type ............... Trochoid gear-driven pump
Oil Filter Type ............... Full-flow spin-on cartridge
Cooling System ............... Liquid-cooled with radiator assembly
Water Pump Type ............... Belt-driven centrifugal pump
Air Cleaner Type ............... Dry dual-element type
Starting System ............... Electric starter motor
Electrical System ............... 12V DC
Alternator Rating ............... 20A or 40A

Fuel System

Injection Pump Type ............... Inline Bosch-type injection pump
Governor Type ............... Mechanical all-speed centrifugal type
Fuel Injection Nozzle Type ............... Hole-type or throttle multi-hole nozzle config
Injection Opening Pressure, psi (MPa) ............... 2844-2987 (19.6-20.6)
Fuel Transfer Pump Type ............... Mechanical diaphragm type pump assembly
Fuel Filter Type ............... Cartridge spin-on style filter element
Fuel Delivery Lines ............... High-pressure seamless steel tube lines
Fuel Return Line Type ............... Low-pressure rubber compound hose config
Injection Timing Angle ............... 14-16 degrees BTDC
Maximum Fuel System Lift, ft (m) ............... 3.3 (1.0)
Fuel Priming Method ............... Manual priming lever on mechanical lift pump
Fuel Specifications ............... Ultra-low sulfur automotive grade diesel fuel oil

Dimensions and Weight

Overall Length, in (mm) ............... 19.8 (505)
Overall Width, in (mm) ............... 18.5 (470)
Overall Height, in (mm) ............... 22.4 (570)
Dry Weight, lbs (kg) ............... 205 (93)
Wet Weight, lbs (kg) ............... 227 (103)

Maintenance Data

Service Information

Maximum Allowable Cylinder Pressure, psi (MPa) ............... 1813 (12.5)
Oil Pressure at Low Idle, psi (MPa) ............... 14 (0.10)
Oil Pressure at Rated Speed, psi (MPa) ............... 43-57 (0.30-0.39)
Oil Safety Valve Relief Pressure, psi (MPa) ............... 64 (0.44)
Thermostat Initial Opening Temperature, F (C) ............... 160 (71)
Thermostat Full Open Temperature, F (C) ............... 185 (85)
Maximum Coolant Operating Temperature, F (C) ............... 221 (105)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W-30, or 15W-40
API Service Classifications ......................... CD or higher
Engine Oil Capacity with Filter, qt (L) ............... 3.6 (3.4)
Cooling System Capacity, qt (L) ............... 4.2 (4.0)

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 Bore Inner Diameter, in (mm) ............... 2.9527-2.9537 (75.000-75.025)
Cylinder Bore Maximum Taper, in (mm) ............... 0.0004 (0.010)
Crankshaft Main Journal Diameter, in (mm) ............... 1.9665-1.9671 (49.950-49.965)
Crankpin Journal Diameter, in (mm) ............... 1.7303-1.7309 (43.950-43.965)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0015-0.0035 (0.038-0.090)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0015-0.0033 (0.038-0.085)
Crankshaft End Play, in (mm) ............... 0.0043-0.0083 (0.110-0.210)
Connecting Rod Side Axial Play, in (mm) ............... 0.0039-0.0098 (0.100-0.250)
Piston Skirt Outer Diameter, in (mm) ............... 2.9492-2.9504 (74.910-74.940)
Piston to Cylinder Wall Clearances, in (mm) ............... 0.0024-0.0045 (0.060-0.115)
Piston Pin Bore Outer Diameter, in (mm) ............... 0.8661-0.8665 (22.000-22.010)
Piston Pin Journal Outer Diameter, in (mm) ............... 0.8659-0.8661 (21.995-22.000)
Top Ring Groove Clearance, in (mm) ............... 0.0024-0.0039 (0.060-0.100)
Second Ring Groove Clearance, in (mm) ............... 0.0020-0.0035 (0.050-0.090)
Oil Ring Groove Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Top Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.200-0.400)
Second Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.200-0.400)
Oil Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.200-0.400)
Cylinder Head Flatness Distortion Maximum, in (mm) ............... 0.0020 (0.050)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.2740-0.2746 (6.960-0.975)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.2736-0.2742 (6.950-6.965)
Intake Valve Guide to Stem Clearance, in (mm) ............... 0.0010-0.0024 (0.025-0.060)
Exhaust Valve Guide to Stem Clearance, in (mm) ............... 0.0014-0.0028 (0.035-0.070)
Intake Valve Sinkage Depth, in (mm) ............... 0.0276-0.0354 (0.700-0.900)
Exhaust Valve Sinkage Depth, in (mm) ............... 0.0276-0.0354 (0.700-0.900)
Valve Seat Angle ............... 45 degrees
Valve Spring Free Length, in (mm) ............... 1.6535 (42.000)
Camshaft Journal Outer Diameter, in (mm) ............... 1.5724-1.5732 (39.940-39.960)
Camshaft Bearing Clearance, in (mm) ............... 0.0016-0.0039 (0.040-0.100)
Cam Lobe Height (Intake), in (mm) ............... 1.3366-1.3406 (33.950-34.050)
Cam Lobe Height (Exhaust), in (mm) ............... 1.3366-1.3406 (33.950-34.050)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.4717-0.4724 (11.980-12.000)
Rocker Arm Bushing Inner Diameter, in (mm) ............... 0.4728-0.4736 (12.010-12.030)
Rocker Arm Bushing to Shaft Clearance, in (mm) ............... 0.0004-0.0020 (0.010-0.050)
Tappet Lifter Body Outer Diameter, in (mm) ............... 0.8642-0.8650 (21.950-21.970)
Tappet Guide Bore Inner Diameter, in (mm) ............... 0.8661-0.8669 (22.000-22.021)
Tappet to Block Guide Bore Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.071)
Idler Gear Bushing Inner Diameter, in (mm) ............... 1.4567-1.4577 (37.000-37.025)
Idler Gear Shaft Outer Diameter, in (mm) ............... 1.4547-1.4557 (36.950-36.975)
Idler Gear Bushing to Shaft Clearance, in (mm) ............... 0.0010-0.0030 (0.025-0.075)

Tightening Torques

Cylinder Head Bolts (Stage One), lb-ft (Nm) ............... 22 (30)
Cylinder Head Bolts (Stage Two), lb-ft (Nm) ............... 44 (60)
Cylinder Head Bolts (Final Stage), lb-ft (Nm) ............... 54-61 (73-83)
Main Bearing Cap Support Stud Bolts, lb-ft (Nm) ............... 58-65 (78-88)
Connecting Rod Cap Hardened Joint Bolts, lb-ft (Nm) ............... 33-38 (45-51)
Flywheel Retaining Mounting Bolts, lb-ft (Nm) ............... 61-68 (83-92)
Flywheel Housing Shell Outer Mounting Bolts, lb-ft (Nm) ............... 18-24 (25-33)
Crankshaft Front Pulley Dampener Center Bolt, lb-ft (Nm) ............... 83-94 (113-127)
Camshaft Thrust Plate Positioning Hex Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Camshaft Timing Gear Center Hub Attachment Bolt, lb-ft (Nm) ............... 58-65 (78-88)
Idler Gear Support Shaft Assembly Stub Bolts, lb-ft (Nm) ............... 18-24 (25-33)
Rocker Arm Shaft Support Bracket Retaining Nut Studs, lb-ft (Nm) ............... 22-29 (30-39)
Valve Cover Overhead Rocker Cap Sealing Nut, lb-ft (Nm) ............... 7-10 (9-14)
Oil Pan Perimeter Lower Sheet Flange Bolts, lb-ft (Nm) ............... 7-10 (9-14)
Oil Pan Bottom Central Hex Oil Drain Plug, lb-ft (Nm) ............... 36-43 (49-59)
Fuel Injection Pump Drive Gear Attachment Nut, lb-ft (Nm) ............... 43-51 (59-69)
Fuel Injection Pump Flange Mounting Block Nuts, lb-ft (Nm) ............... 14-19 (20-26)
Fuel Injection High Pressure Line Union Nut Joints, lb-ft (Nm) ............... 18-22 (25-30)
Fuel Injector Assembly Hold-Down Nozzle Bolt, lb-ft (Nm) ............... 22-26 (30-35)
Fuel Leak-Off Return Rail Low Pressure Screws, lb-ft (Nm) ............... 7-11 (10-15)
Exhaust Manifold Heat Resisting Block Flange Nuts, lb-ft (Nm) ............... 18-24 (25-33)
Intake Manifold Induction Air Duct Channel Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Water Pump Assembly Casting Body Block Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Thermostat Housing Top Cover Water Flange Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Oil Cooler Plate Heat Exchanger Core Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Oil Pump Assembly Trochoid Housing Plate Screws, lb-ft (Nm) ............... 6-9 (8-12)
Oil Pressure Regulator Spring Valve Relief Plug, lb-ft (Nm) ............... 29-36 (39-49)
Starter Motor Heavy Mounting Face Flange Bolts, lb-ft (Nm) ............... 36-43 (49-59)
Alternator Pivot Mount Bracket Support Adjust Bolt, lb-ft (Nm) ............... 14-19 (20-26)
Glow Plug Pre-Heating Head Elements, lb-ft (Nm) ............... 11-15 (15-20)
Coolant Temperature Sensor Gauge Sender Plug, lb-ft (Nm) ............... 14-18 (19-25)
Oil Pressure Monitoring Warning Light Switch Sensor, lb-ft (Nm) ............... 11-14 (15-19)
Front Timing Gear Case Cover Outer Shell Bolts, lb-ft (Nm) ............... 14-19 (20-26)
Rear Oil Seal Retainer Case Housing Flange Bolts, lb-ft (Nm) ............... 7-10 (9-14)
Air Cleaner Housing Support Frame Holding Brackets, lb-ft (Nm) ............... 14-19 (20-26)
Radiator Core Support Frame Isolation Nuts, lb-ft (Nm) ............... 22-29 (30-39)
Exhaust Pipe Muffler Outlet Flange Nut Clamps, lb-ft (Nm) ............... 25-33 (34-45)
Fuel Tank Drain Plug Bottom Sump Port Nut, lb-ft (Nm) ............... 18-25 (25-34)
Fan Blade Assembly Water Pump Hub Mounting Bolts, lb-ft (Nm) ............... 7-10 (9-14)

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