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Komatsu 3D72 Engine

The Komatsu 3D72 is a vertical, water-cooled, 4-stroke, inline 3-cylinder naturally aspirated diesel engine designed primarily for heavy-duty industrial and agricultural applications. Co-developed or cross-referenced with Yanmar design architectures (specifically matching the 3TNA72 series), this engine is commonly utilized in compact utility machinery, agricultural vehicles, and mini-excavators such as the Komatsu PC05 and related industrial equipment. The engine layout features a cast-iron cylinder block with an integrated crankcase, a single-piece cylinder head, and a gear-driven camshaft driving a conventional mechanical valve train. It is designed for high reliability, low vibration, and ease of serviceability in compact engine compartments.

Valve Configuration: Overhead Valve (OHV) pushrod-driven system actuated by a gear-driven camshaft located within the cylinder block. Total Valves: 6 valves total (1 intake valve and 1 exhaust valve per cylinder). Assembly Elements: Includes single-piece cast rocker arm assembly, pushrods, cylindrical valve lifters/tappets, and a stamped steel cylinder head cover. Cylinder Bore: 72.0 mm (2.83 in). Piston Stroke: 72.0 mm (2.83 in). Total Displacement: 0.879 Liters (53.6 cubic inches).

Lubrication System: Full forced-pressure lubrication system fed by a trochoid-type oil pump. Oil Pump Drive: Gear-driven directly from the crankshaft timing gear train. Filtration: Full-flow, spin-on replaceable cartridge oil filter elements coupled with an integrated pressure regulating relief valve. Safety Monitoring: Outfitted with a mechanical diaphragm-type oil pressure switch calibrated to signal low oil pressure faults. Oil Pan: Deep-well stamped steel sheet or cast aluminum oil pan depending on equipment application. Cooling System: Forced liquid cooling circulation. Circulation Pump: Belt-driven centrifugal water pump assembly mounted to the front gear case housing. Thermal Control: Wax-pellet type thermostat assembly situated in the water outlet housing to regulate optimal coolant temperature. Air Movement: Engine-mounted pusher or puller cooling fan driven by a heavy-duty V-belt from the crankshaft pulley.

Fuel System Injection Type: Indirect injection (IDI) utilizes a swirl combustion chamber design or direct injection depending on the sub-variant series. Injection Pump: Inline mechanical Bosch-type injection pump (specifically YPES or YPFR flange-mounted plunger pump series). Governor Assembly: Mechanical centrifugal all-speed governor integrated into the injection pump drive housing to control fuel delivery relative to load demands. Fuel Nozzles: Throttling type or multi-hole fuel injection nozzles preset to a standard opening pressure. Priming and Filtration: Features a mechanical diaphragm fuel feed pump, a spin-on primary fuel filter assembly, and an integrated water separator bowl with a float ring. Cold Start Assist: Electric glow plugs positioned within the cylinder head intake ports, controlled via an automated glow plug timer relay circuit.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 3D72
Engine Type ............... 4-cycle vertical inline 3-cylinder liquid-cooled diesel
Number of Cylinders ............... 3
Cylinder Arrangement ............... In-line
Engine Bore, mm (in) ............... 72.0 (2.83)
Engine Stroke, mm (in) ............... 72.0 (2.83)
Displacement, L (cu.in) ............... 0.879 (53.6)
Rated Engine Power, hp (kW) ............... 18.0-22.0 (13.4-16.4)
Rated Engine Speed, rpm ............... 2700
Peak Torque, Nm (lb-ft) ............... 47.6 (35.1) at 2700 rpm
Low Idle Speed, rpm ............... 800-900
High Idle Speed, rpm ............... 2850-2950
Aspiration Type ............... Naturally Aspirated
Combustion System ............... Swirl Chamber or Direct Injection depending on variant
Compression Ratio ............... 22.0:1-23.0:1
Firing Order ............... 1-3-2
Direction of Rotation ............... Counterclockwise facing flywheel
Cylinder Block Type ............... Monoblock cast iron
Cylinder Head Type ............... Single piece cast iron
Lubrication System ............... Forced pressure circulation by gear pump
Oil Pump Type ............... Trochoid gear driven type
Oil Filter Type ............... Full-flow cartridge spin-on
Cooling System Type ............... Liquid-cooled forced circulation
Water Pump Type ............... Centrifugal belt-driven
Cooling Fan Type ............... Pusher or puller suction type
Air Cleaner Type ............... Dry element dual stage
Starting System ............... Electric motor starter
Glow Plug Type ............... Sheathed rapid heat type
Electrical System, V ............... 12
Alternator Capacity, A ............... 20-40
Starter Motor Power, kW (hp) ............... 1.0-1.2 (1.3-1.6)

Fuel System

Fuel Injection Pump Type ............... Yanmar YPES or YPFR inline type
Feed Pump Type ............... Mechanical diaphragm type
Fuel Injection Nozzle Type ............... Throttle or hole type
Fuel Injection Pressure, MPa (psi) ............... 19.61 (2844)
Fuel Injection Timing, deg btdc ............... 14.0-16.0 BTDC
Fuel Filter Type ............... Spin-on element with water separator
Water Separator Capacity, L (fl.oz) ............... 0.2 (6.7)
Fuel Delivery Pressure, MPa (psi) ............... 0.02-0.03 (2.9-4.3)
Governor Type ............... Mechanical all-speed centrifugal
Governor Linkage ............... Mechanical spring loaded control lever
Plunger Diameter, mm (in) ............... 5.5 (0.21)
Plunger Stroke, mm (in) ............... 6.0 (0.24)
Injection Pipe Inner Diameter, mm (in) ............... 1.5 (0.059)
Injection Pipe Outer Diameter, mm (in) ............... 6.0 (0.236)
Fuel Leak-off System ............... Return pipe to fuel tank
Maximum Fuel Consumption, g/kWh (lb/hph) ............... 250 (0.41)
Stop Solenoid Type ............... Electric engine stop motor
Fuel Transfer Line Inner Diameter, mm (in) ............... 8.0 (0.315)

Dimensions and Weight

Overall Length, mm (in) ............... 485 (19.1)
Overall Width, mm (in) ............... 435 (17.1)
Overall Height, mm (in) ............... 525 (20.7)
Dry Weight, kg (lbs) ............... 85 (188)
Wet Weight, kg (lbs) ............... 92 (203)

Maintenance Data

Service Information

Compression Pressure, Standard, MPa (psi) ............... 2.94-3.24 (426-469)
Compression Pressure, Limit, MPa (psi) ............... 2.45 (355)
Compression Pressure Between Cylinders, MPa (psi) ............... 0.20-0.29 (29-42)
Oil Pressure at Rated Speed, MPa (psi) ............... 0.29-0.39 (42-56)
Oil Pressure at Idle Speed, MPa (psi) ............... 0.05-0.08 (7.1-11.4)
Lubricating Oil Temperature, C (F) ............... 80-100 (176-212)
Thermostat Opening Temperature, C (F) ............... 71 (160)
Thermostat Full Open Temperature, C (F) ............... 85 (185)
V-Belt Tension Deflection, mm (in) ............... 10.0-15.0 (0.39-0.59)
Intake Valve Clearance, Cold , mm (in) ............... 0.200 (0.0079)
Exhaust Valve Clearance, Cold, mm (in) ............... 0.200 (0.0079)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W-30, or 15W-40
API Service Classifications ......................... CD or higher
Engine Oil Capacity, Upper Level, L (qt) ............... 2.8 (2.96)
Engine Oil Capacity, Lower Level, L (qt) ............... 1.8 (1.90)
Cooling System Fluid Capacity, L (qt) ............... 3.5 (3.70)

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, mm (in) ............... 72.000-72.030 (2.8346-2.8358)
Cylinder Bore Wear Limit, mm (in) ............... 72.200 (2.8425)
Cylinder Roundness Limit, mm (in) ............... 0.010 (0.0004)
Cylinder Taper Limit, mm (in) ............... 0.010 (0.0004)
Connecting Rod Small End Bushing I.D, mm (in) ............... 22.020-22.035 (0.8669-0.8675)
Connecting Rod Small End Clearance, mm (in) ............... 0.010-0.035 (0.0004-0.0014)
Crankshaft Main Journal Outer Diameter, mm (in) ............... 47.950-47.965 (1.8878-1.8884)
Crankshaft Main Bearing Clearance, mm (in) ............... 0.035-0.068 (0.0014-0.0027)
Crankpin Outer Diameter, mm (in) ............... 41.950-41.965 (1.6516-1.6522)
Crankpin Bearing Oil Clearance, mm (in) ............... 0.035-0.065 (0.0014-0.0026)
Crankshaft End Play, mm (in) ............... 0.110-0.210 (0.0043-0.0083)
Piston Outer Diameter, mm (in) ............... 71.940-71.970 (2.8323-2.8335)
Piston to Cylinder Clearance, mm (in) ............... 0.045-0.075 (0.0018-0.0030)
Piston Pin Outer Diameter, mm (in) ............... 22.000-22.010 (0.8661-0.8665)
Piston Pin Boss Inner Diameter, mm (in) ............... 22.005-22.015 (0.8663-0.8667)
Piston Pin to Boss Clearance, mm (in) ............... 0.000-0.010 (0.0000-0.0004)
Top Ring Side Clearance, mm (in) ............... 0.060-0.095 (0.0024-0.0037)
Second Ring Side Clearance, mm (in) ............... 0.050-0.085 (0.0020-0.0033)
Oil Ring Side Clearance, mm (in) ............... 0.030-0.065 (0.0012-0.0026)
Top Ring End Gap, mm (in) ............... 0.200-0.350 (0.0079-0.0138)
Second Ring End Gap, mm (in) ............... 0.150-0.300 (0.0059-0.0118)
Oil Ring End Gap, mm (in) ............... 0.150-0.350 (0.0059-0.0138)
Intake Valve Guide Inner Diameter, mm (in) ............... 7.000-7.015 (0.2756-0.2762)
Intake Valve Stem Outer Diameter, mm (in) ............... 6.960-6.975 (0.2740-0.2746)
Intake Valve to Guide Clearance, mm (in) ............... 0.025-0.055 (0.0010-0.0022)
Exhaust Valve Guide Inner Diameter, mm (in) ............... 7.000-7.015 (0.2756-0.2762)
Exhaust Valve Stem Outer Diameter, mm (in) ............... 6.945-6.960 (0.2734-0.2740)
Exhaust Valve to Guide Clearance, mm (in) ............... 0.040-0.070 (0.0016-0.0028)
Intake Valve Sinkage Depth, mm (in) ............... 0.400-0.600 (0.0157-0.0236)
Exhaust Valve Sinkage Depth, mm (in) ............... 0.400-0.600 (0.0157-0.0236)
Valve Spring Free Length, mm (in) ............... 37.800 (1.4882)
Camshaft Journal Outer Diameter (Front), mm (in) ............... 39.940-39.960 (1.5724-1.5732)
Camshaft Journal Outer Diameter (Center), mm (in) ............... 39.910-39.930 (1.5713-1.5720)
Camshaft Journal Outer Diameter (Rear), mm (in) ............... 39.940-39.960 (1.5724-1.5732)
Camshaft Bearing Clearance Limit, mm (in) ............... 0.120 (0.0047)
Cam Lobe Height (Intake), mm (in) ............... 34.050-34.150 (1.3405-1.3445)
Cam Lobe Height (Exhaust), mm (in) ............... 34.050-34.150 (1.3405-1.3445)
Tappet Outer Diameter, mm (in) ............... 21.950-21.970 (0.8642-0.8650)
Tappet Guide Hole Inner Diameter, mm (in) ............... 22.000-22.020 (0.8661-0.8669)
Tappet Guide Clearance, mm (in) ............... 0.030-0.070 (0.0012-0.0028)
Rocker Arm Shaft Outer Diameter, mm (in) ............... 11.970-11.990 (0.4713-0.4720)
Rocker Arm Bushing Inner Diameter, mm (in) ............... 12.000-12.020 (0.4724-0.4732)
Rocker Arm Bushing to Shaft Clearance, mm (in) ............... 0.010-0.050 (0.0004-0.0020)
Idler Gear Shaft Outer Diameter, mm (in) ............... 37.960-37.980 (1.4945-1.4953)
Idler Gear Bushing Inner Diameter, mm (in) ............... 38.000-38.025 (1.4961-1.4970)
Idler Gear Bushing to Shaft Clearance, mm (in) ............... 0.020-0.065 (0.0008-0.0026)

Tightening Torques

Cylinder Head Bolts (Stage One), Nm (lb-ft) ............... 30.0 (22.1)
Cylinder Head Bolts (Stage Two), Nm (lb-ft) ............... 55.0 (40.6)
Cylinder Head Bolts (Final Stage), Nm (lb-ft) ............... 73.6-83.4 (54.3-61.5)
Connecting Rod Cap Bolts, Nm (lb-ft) ............... 22.6-27.5 (16.7-20.3)
Main Bearing Cap Bolts, Nm (lb-ft) ............... 53.9-58.8 (39.8-43.4)
Flywheel Bolts, Nm (lb-ft) ............... 58.8-63.7 (43.4-47.0)
Flywheel Housing Bolts, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Crankshaft V-Belt Pulley Nut, Nm (lb-ft) ............... 83.4-93.2 (61.5-68.7)
Camshaft Thrust Metal Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Rocker Shaft Support Bolts, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Cylinder Head Cover Nuts, Nm (lb-ft) ............... 6.9-8.8 (5.1-6.5)
Oil Pan Drain Plug, Nm (lb-ft) ............... 39.2-49.0 (28.9-36.1)
Oil Pan Mounting Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Fuel Injection Pump Drive Gear Nut, Nm (lb-ft) ............... 58.8-68.6 (43.4-50.6)
Fuel Injection Pump Mounting Nuts, Nm (lb-ft) ............... 22.6-27.5 (16.7-20.3)
Fuel Injection High Pressure Pipe Nuts, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Fuel Injection Nozzle Holder Assembly, Nm (lb-ft) ............... 49.0-58.8 (36.1-43.4)
Fuel Nozzle Retention Nut, Nm (lb-ft) ............... 39.2-44.1 (28.9-32.5)
Glow Plugs, Nm (lb-ft) ............... 14.7-19.6 (10.8-14.5)
Oil Pressure Switch Sensor, Nm (lb-ft) ............... 14.7-19.6 (10.8-14.5)
Water Temperature Sensor Thermostat, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Intake Manifold Flange Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Exhaust Manifold Flange Nuts, Nm (lb-ft) ............... 22.6-27.5 (16.7-20.3)
Starter Motor Mounting Bolts, Nm (lb-ft) ............... 39.2-49.0 (28.9-36.1)
Alternator Mounting Bracket Bolts, Nm (lb-ft) ............... 39.2-49.0 (28.9-36.1)
Alternator Adjusting Link Pivot Bolt, Nm (lb-ft) ............... 19.6-24.5 (14.5-18.1)
Water Pump Mounting Fasteners, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Cooling Fan Drive Pulley Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Gear Case Front Cover Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Idler Shaft Retaining Plate Bolts, Nm (lb-ft) ............... 22.6-27.5 (16.7-20.3)
Lubricating Oil Delivery Internal Pipe Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Lubricating Oil Pump Assembly Bolts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Breather Valve Cover Assembly Screws, Nm (lb-ft) ............... 3.9-4.9 (2.9-3.6)
Fuel Feed Pump Flange Nuts, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Exhaust Pipe Silencer Muffler Nuts, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Flywheel Inspection Port Blind Plug, Nm (lb-ft) ............... 14.7-19.6 (10.8-14.5)
Engine Bed Grounding Strap Cable Bolt, Nm (lb-ft) ............... 19.6-24.5 (14.5-18.1)
Engine Lifting Bracket Eye Hooks, Nm (lb-ft) ............... 24.5-29.4 (18.1-21.7)
Air Intake Duct Connection Hose Clamps, Nm (lb-ft) ............... 3.5-4.5 (2.6-3.3)
Radiator Soft Hose Clamp Fasteners, Nm (lb-ft) ............... 4.0-5.0 (3.0-3.7)
Thermostat Housing Cover Fasteners, Nm (lb-ft) ............... 9.8-11.8 (7.2-8.7)
Fuel Return Spill Pipe Joint Screw, Nm (lb-ft) ............... 7.8-9.8 (5.8-7.2)
Fuel Injection Pump Air Bleed Screw, Nm (lb-ft) ............... 4.9-6.9 (3.6-5.1)
Fuel Filter Bracket Support Frame Bolts, Nm (lb-ft) ............... 19.6-24.5 (14.5-18.1)
Main Oil Gallery End Blind Taper Plugs, Nm (lb-ft) ............... 19.6-24.5 (14.5-18.1)
Cylinder Block Water Drain Cock Fitting, Nm (lb-ft) ............... 14.7-19.6 (10.8-14.5)

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