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Komatsu 3D84 Engine

The Komatsu 3D84 is an industrial-grade, 3-cylinder, vertical 4-cycle, water-cooled diesel engine designed for high efficiency and durability in compact construction machinery. Co-developed alongside Yanmar's TN/TNE platform, this naturally aspirated inline engine is widely utilized in compact excavators like the Komatsu PC30 and mini wheel loaders. It is engineered to deliver reliable torque at low operational speeds while complying with historical tier-emission regulations through robust mechanical control systems.

The engine employs an overhead valve (OHV) layout actuated by a camshaft, pushrods, and adjustable rocker arms. It features 2 valves per cylinder (1 intake and 1 exhaust valve), providing a total configuration of 6 valves for the entire engine block. Valve clearance maintenance is manually adjusted at the rocker arm set screws. Cylinder Bore: 84 mm. Piston Stroke: 90 mm. Total Displacement: 1.5 liters.

The fuel architecture relies on a mechanical inline multi-plunger fuel injection pump (typically an MP-series pump) timed directly to the engine gear train. Fuel is drawn from the tank by a mechanical feed pump, then pushed through a fuel filter housing equipped with an integrated water separator. High-pressure fuel lines deliver metered fuel to fuel injection nozzles that spray directly into the combustion chambers. Engine speeds are managed via an attached mechanical all-speed governor.

Lubrication is managed via a forced-feed lubrication system pressurized by a crankshaft-driven trochoid oil pump. Oil is routed under pressure from the oil pan through a full-flow, spin-on cartridge filter. Main oil galleries distribute lubricant directly to the crankshaft main bearings, connecting rod bearings, camshaft journals, and upward through the cylinder head to lubricate the rocker arm assembly. An electrical oil pressure switch monitors system pressure.

The engine uses a forced-circulation liquid cooling system. Coolant is circulated through the internal jackets of the cylinder block and head by a belt-driven, centrifugal water pump. System temperature is regulated by a wax-pellet type thermostat that restricts flow to the radiator during warm-up and fully opens to allow dissipation once standard operating temperatures are achieved.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 3D84
Engine Type ............... 4-cycle inline 3-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 3
Cylinder Arrangement ............... In-line
Engine Bore, mm (in) ............... 84.00 (3.31)
Engine Stroke, mm (in) ............... 90.00 (3.54)
Displacement, L (cu.in) ............... 1.496 (91.30)
Rated Engine Power, kW (hp) ............... 27.90-28.50 (37.40-38.20)
Rated Engine Speed, rpm ............... 2700-3000
Maximum No-Load Speed, rpm ............... 2900-3150
Minimum No-Load Speed, rpm ............... 750-850
Peak Torque, Nm (lb-ft) ............... 88.0-98.0 (64.9-72.3) at 1600-1800 rpm
Idle Speed, rpm ............... 800-850
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 18.0:1-19.0:1
Firing Order ............... 1-3-2
Combustion Chamber ............... Direct injection toroidal crown design
Rotation Direction ............... Counterclockwise from flywheel view
Cylinder Block Type ............... Monoblock cast iron
Cylinder Head Type ............... One-piece cast iron crossflow design
Lubrication System ............... Forced pressure circulation by trochoid pump
Oil Pump Type ............... Gear-driven trochoid rotor type
Oil Filter Type ............... Full-flow cartridge spin-on paper element
Cooling System ............... Liquid-cooled with forced centrifugal circulation
Water Pump Type ............... Belt-driven centrifugal type
Thermostat Type ............... Wax pellet type with bypass valve
Air Cleaner Type ............... Dry dual-element heavy-duty design
Starting System ............... Axial-type electric starter motor
Electrical System, V ............... 12
Alternator Capacity, A ............... 40-55

Fuel System

Fuel Injection Pump Type ............... Bosch inline MP distributor type or YPES pump
Governor Control System ............... Centrifugal mechanical linkage layout
Governor Type ............... Mechanical all-speed centrifugal flyweight type
Fuel Feed Pump Type ............... Mechanical diaphragm type
Fuel Feed Pump Pressure, kPa (psi) ............... 20.0-30.0 (2.9-4.3)
Fuel Injection Nozzle Type ............... Multi-hole mini nozzle design
Number of Injection Nozzle Holes ............... 4 or 5 holes
Injection Nozzle Hole Diameter, mm (in) ............... 0.20-0.25 (0.0078-0.0098)
Injection Valve Opening Pressure (Std), MPa (psi) ............... 19.6-20.6 (2842-2987)
Injection Valve Opening Pressure (Limit), MPa (psi) ............... 18.5 (2683)
Fuel Filter Assembly Type ............... Spin-on element with sedimentator ring
Water Separator Device ............... Integrated float sensor bottom draining mechanism
Fuel Spill Timing Angle, deg BTDC ............... 14.0-16.0
High Pressure Fuel Pipe Outer Diameter, mm (in) ............... 6.00 (0.236)
High Pressure Fuel Pipe Inner Diameter, mm (in) ............... 1.50 (0.059)
Fuel Injection Pipe Length, mm (in) ............... 400.00 (15.74)
Maximum Fuel Inlet Temperature, C (F) ............... 50.00 (122.00)

Dimensions and Weight

Overall Length, mm (in) ............... 535 (21.1)
Overall Width, mm (in) ............... 495 (19.5)
Overall Height, mm (in) ............... 610 (24.0)
Dry Weight, kg (lbs) ............... 145 (320)
Wet Weight, kg (lbs) ............... 154 (340)

Maintenance Data

Service Information

Standard Cylinder Compression Pressure, MPa (psi) ............... 2.94 (426.40)
Minimum Cylinder Compression Pressure, MPa (psi) ............... 2.45 (355.30)
Cylinder-to-Cylinder Compression Variation, MPa (psi) ............... 0.20-0.30 (29.00-43.50)
Oil Operating Pressure at Rated Speed, MPa (psi) ............... 0.29-0.39 (42.10-56.50)
Oil Operating Pressure at Idle Speed, MPa (psi) ............... 0.06 (8.70)
Relief Valve Opening Pressure, MPa (psi) ............... 0.34-0.44 (49.30-63.80)
Radiator Cap Opening Pressure, kPa (psi) ............... 88.20 (12.79)
Thermostat Opening Temperature, C (F) ............... 71.0 (159.8)
Thermostat Full Open Temperature, C (F) ............... 85.0 (185.0)
Standard Coolant Temperature Range, C (F) ............... 75.0-85.0 (167.0-185.0)
Maximum Coolant Temperature Limit, C (F) ............... 95.0 (203.0)
Drive Belt Deflection Under 10 kg Force, mm (in) ............... 10.0-14.0 (0.39-0.55)
Intake Valve Clearance (Cold), mm (in) ............... 0.20 (0.0078)
Exhaust Valve Clearance (Cold), mm (in) ............... 0.20 (0.0078)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 10W, SAE 10W-30
API Service Classifications ......................... CD, CE, CF-4, or CG-4
Engine Oil Capacity, Maximum Level, L (qt) ............... 5.50 (5.81)
Engine Oil Capacity, Minimum Level, L (qt) ............... 3.80 (4.01)
Cooling System Capacity, Engine Only, L (qt) ............... 2.10 (2.21)
Cooling Capacity with Radiator, L (qt) ............... 4.80 (5.07)

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 (Std), mm (in) ............... 84.000-84.030 (3.3070-3.3082)
Cylinder Bore Inside Diameter (Wear Limit), mm (in) ............... 84.200 (3.3149)
Cylinder Block Top Surface Flatness Distortion, mm (in) ............... 0.050 or less (0.0019)
Main Journal Outside Diameter, mm (in) ............... 49.952-49.962 (1.9666-1.9670)
Main Bearing Clearance, mm (in) ............... 0.038-0.068 (0.0014-0.0026)
Main Bearing Shell Thickness, mm (in) ............... 1.995-2.005 (0.0785-0.0789)
Crankpin Outside Diameter, mm (in) ............... 43.952-43.962 (1.7303-1.7307)
Connecting Rod Small End Bushing I.D, mm (in) ............... 26.025-26.038 (1.0246-1.0251)
Piston Pin-to-Small End Bushing Clearance, mm (in) ............... 0.025-0.047 (0.0009-0.0018)
Connecting Rod Big End Bore Inside Diameter, mm (in) ............... 47.000-47.015 (1.8503-1.8509)
Connecting Rod Big End Side Clearance, mm (in) ............... 0.150-0.350 (0.0059-0.0137)
Con Rod Bearing Clearance, mm (in) ............... 0.038-0.068 (0.0014-0.0026)
Crankshaft End Play, mm (in) ............... 0.110-0.210 (0.0043-0.0082)
Piston Skirt Outside Diameter, mm (in) ............... 22.00 (0.866) from bottom edge
Piston-to-Cylinder Bore Clearance , mm (in) ............... 0.045-0.065 (0.0017-0.0025)
Piston Pin Bore Inside Diameter, mm (in) ............... 26.000-26.009 (1.0236-1.0239)
Piston Pin Outside Diameter, mm (in) ............... 25.991-26.000 (1.0232-1.0236)
Piston Pin-to-Piston Pin Bore Clearance, mm (in) ............... 0.000-0.018 (0.0000-0.0007)
Top Ring Groove Side Clearance, mm (in) ............... 0.070-0.110 (0.0027-0.0043)
Second Ring Groove Side Clearance, mm (in) ............... 0.040-0.080 (0.0015-0.0031)
Oil Ring Groove Side Clearance, mm (in) ............... 0.020-0.060 (0.0007-0.0023)
Top Piston Ring End Gap, mm (in) ............... 0.200-0.350 (0.0078-0.0137)
Second Piston Ring End Gap, mm (in) ............... 0.200-0.400 (0.0078-0.0157)
Oil Piston Ring End Gap, mm (in) ............... 0.200-0.400 (0.0078-0.0157)
Cylinder Head Bottom Surface Flatness Warpage, mm (in) ............... 0.050 or less (0.0019)
Intake Valve Lift, mm (in) ............... 9.50 (0.374)
Exhaust Valve Lift, mm (in) ............... 9.80 (0.385)
Intake Valve Stem Outside Diameter, mm (in) ............... 6.955-6.970 (0.2738-0.2744)
Exhaust Valve Stem Outside Diameter, mm (in) ............... 6.945-6.960 (0.2734-0.2740)
Intake Valve Guide Inside Diameter, mm (in) ............... 7.000-7.015 (0.2755-0.2761)
Exhaust Valve Guide Inside Diameter, mm (in) ............... 7.000-7.015 (0.2755-0.2761)
Intake Valve Stem-to-Guide Clearance, mm (in) ............... 0.030-0.060 (0.0011-0.0023)
Exhaust Valve Stem-to-Guide Clearance, mm (in) ............... 0.040-0.070 (0.0015-0.0027)
Intake Valve Margin Thickness, mm (in) ............... 1.000-1.200 (0.0393-0.0472)
Exhaust Valve Margin Thickness, mm (in) ............... 1.000-1.200 (0.0393-0.0472)
Intake Valve Head Sinking Depth, mm (in) ............... 0.300-0.500 (0.0118-0.0196)
Exhaust Valve Head Sinking Depth, mm (in) ............... 0.300-0.500 (0.0118-0.0196)
Intake Valve Seat Angle, deg ............... 45
Exhaust Valve Seat Angle, deg ............... 45
Intake Valve Seat Contact Width, mm (in) ............... 1.000-1.400 (0.0393-0.0551)
Exhaust Valve Seat Contact Width, mm (in) ............... 1.000-1.400 (0.0393-0.0551)
Valve Spring Free Length, mm (in) ............... 37.80 (1.488)
Camshaft Main Journal Outside Diameter, mm (in) ............... 44.925-44.950 (1.7687-1.7696)
Camshaft Bearing Inside Bushing Diameter, mm (in) ............... 45.000-45.075 (1.7716-1.7746)
Camshaft Journal Clearance, mm (in) ............... 0.050-0.150 (0.0019-0.0059)
Cam Lobe Height (Intake), mm (in) ............... 33.600-33.800 (1.3228-1.3307)
Cam Lobe Height (Exhaust), mm (in) ............... 33.900-34.100 (1.3346-1.3425)
Camshaft Axial Thrust End Play, mm (in) ............... 0.050-0.150 (0.0019-0.0059)
Rocker Arm Shaft Outside Diameter, mm (in) ............... 11.965-11.980 (0.4710-0.4716)
Rocker Arm Bushing Inside Diameter, mm (in) ............... 12.000-12.020 (0.4724-0.4732)
Rocker Arm Bushing-to-Shaft Clearance, mm (in) ............... 0.020-0.055 (0.0007-0.0021)
Tappet Lifter Body Outside Diameter, mm (in) ............... 11.960-11.975 (0.4708-0.4714)
Tappet Guide Bore Block Inside Diameter, mm (in) ............... 12.000-12.018 (0.4724-0.4731)
Tappet-to-Bore Clearance, mm (in) ............... 0.025-0.058 (0.0009-0.0022)
Crankshaft Timing Gear to Camshaft Idler Gear Backlash, mm (in) ............... 0.060-0.120 (0.0023-0.0047)
Camshaft Timing Gear to Camshaft Idler Gear Backlash, mm (in) ............... 0.060-0.120 (0.0023-0.0047)
Idler Gear Shaft Outside Diameter, mm (in) ............... 36.950-36.975 (1.4547-1.4557)
Idler Gear Bushing Inside Diameter, mm (in) ............... 37.000-37.025 (1.4566-1.4576)
Idler Gear Bushing-to-Shaft Clearance, mm (in) ............... 0.025-0.075 (0.0009-0.0029)

Tightening Torques

Cylinder Head Bolts (Initial Pass), Nm (lb-ft) ............... 30.00-35.00 (22.10-25.80)
Cylinder Head Bolts (Final Pass), Nm (lb-ft) ............... 76.40-80.40 (56.30-59.20)
Connecting Rod Cap Bolts, Nm (lb-ft) ............... 44.00-49.00 (32.40-36.10)
Main Bearing Cap Bolts, Nm (lb-ft) ............... 78.00-83.00 (57.50-61.20)
Flywheel Bolts, Nm (lb-ft) ............... 80.00-85.00 (59.00-62.60)
Crankshaft Pulley Front Damper Bolt, Nm (lb-ft) ............... 115.00-125.00 (84.80-92.10)
Camshaft Thrust Plate Bolts, Nm (lb-ft) ............... 9.80-11.80 (7.20-8.70)
Camshaft Timing Drive Gear Nut, Nm (lb-ft) ............... 80.00-90.00 (59.00-66.30)
Idler Gear Shaft Core Bracket Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Flywheel Housing Metal Case M8 Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Flywheel Housing Metal Case M10 Bolts, Nm (lb-ft) ............... 45.00-55.00 (33.10-40.50)
Timing Gear Case Cover Housing Base Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Rocker Arm Shaft Support Bracket Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Valve Clearance Adjusting Lock Screw Nut, Nm (lb-ft) ............... 9.80-11.80 (7.20-8.70)
Cylinder Head Valve Cover Holding Cap Nuts, Nm (lb-ft) ............... 7.00-9.80 (5.10-7.20)
Oil Pan Sump Attachment Holding Screws and Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Oil Pan Sump Bottom Fluid Oil Drain Plug, Nm (lb-ft) ............... 50.00-60.00 (36.80-44.20)
Fuel Injection Pump Drive Assembly Gear Nut, Nm (lb-ft) ............... 60.00-70.00 (44.20-51.60)
Fuel Injection Pump Flange Block Mounting Nuts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Fuel Injection Pump Rear Alignment Support Bolt, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Fuel Injection Valve Nozzle Assembly Holding Retainer Nut, Nm (lb-ft) ............... 39.20-44.10 (28.90-32.50)
High Pressure Fuel Line Injection Pipe Flare Nut, Nm (lb-ft) ............... 24.50-29.40 (18.00-21.60)
Fuel Return Rail Overflow Bolt Connector, Nm (lb-ft) ............... 7.80-9.80 (5.70-7.20)
Fuel Feed Supply Attachment Mounting Nuts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Intake Manifold Attachment Face Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Exhaust Manifold Attachment Face Nuts, Nm (lb-ft) ............... 25.00-30.00 (18.40-22.10)
Water Pump Assembly Shell Housing Bolts M8, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Thermostat Case Cover Attachment Bolts, Nm (lb-ft) ............... 23.00-28.00 (16.90-20.60)
Oil Main Pressure Switch Unit Threaded Connector, Nm (lb-ft) ............... 15.00-20.00 (11.00-14.70)
Starter Motor Unit Main Flange Mounting Bolts, Nm (lb-ft) ............... 45.00-55.00 (33.10-40.50)
Alternator Charging Unit Support Bottom Long Bolt, Nm (lb-ft) ............... 35.00-45.00 (25.80-33.10)
Alternator Tensioner Slotted Adjusting Brace Bolt, Nm (lb-ft) ............... 19.00-24.00 (14.00-17.70)
Glow Plug Preheater Units Cylinder Head, Nm (lb-ft) ............... 15.00-20.00 (11.00-14.70)
Glow Plug Core Upper Current Brass Small Nuts, Nm (lb-ft) ............... 1.50-2.50 (1.10-1.80)
Engine Mounting Bracket Iron Core Bolts, Nm (lb-ft) ............... 45.00-55.00 (33.10-40.50)
Oil Pump Assembly Rotor Cover Plate Screws, Nm (lb-ft) ............... 7.00-9.80 (5.10-7.20)
Oil Pressure Relief Control Valve Cap, Nm (lb-ft) ............... 40.00-50.00 (29.50-36.80)
Cooling Fan Plastic Component Screws, Nm (lb-ft) ............... 8.00-11.00 (5.90-8.10)

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