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Komatsu 4D84 Engine

The Komatsu 4D84 is a vertical, in-line, 4-cycle, 4-cylinder liquid-cooled industrial diesel engine. It is widely deployed across a range of compact construction and utility machinery, primarily serving as a reliable power plant for mini-excavators (such as the Komatsu PC40) and skid steers. Engineered for durability and high torque density in restricted spaces, this naturally aspirated engine utilizes heavy-duty components including a rigid, cast-iron cylinder block and an integrated cylinder head setup designed to sustain high mechanical stresses. The engine configuration minimizes vibrations and yields highly efficient combustion characteristics to comply with regional off-road emission profiles.

The cylinder head utilizes an overhead valve configuration driven by a conventional block-mounted camshaft via pushrods and rocker arm assemblies. The layout features two valves per cylinder, split into one intake valve and one exhaust valve per combustion chamber. Valve clearance adjustments are handled manually at the rocker arm set screw, typically mandated at specific workshop service intervals to ensure exact gas exchange metrics. Cylinder Bore: 84 mm. Piston Stroke: 90 mm. Total Displacement: 1.995 liters.

Fuel distribution relies on a direct injection combustion system configured to optimize thermal efficiency and decrease cold-start cranking times. The architecture utilizes an in-line fuel injection pump assembly paired with a mechanical governor that modulates fuel delivery based on load fluctuations. High-pressure steel lines route metered fuel to individual mechanical fuel injection nozzles seated directly over each piston crown. The low-pressure supply layout incorporates an external fuel water separator assembly and a primary spin-on fuel filter to capture contaminants before they enter the high-pressure injection circuit.

Lubrication is managed via a full-pressure, wet-sump system. A trochoid-type oil pump driven directly by the crankshaft forces lubricating oil through a full-flow, spin-on oil filter cartridge. Main oil galleries feed pressurized oil directly to the main bearings, connecting rod journals, camshaft bushings, and upward through the cylinder head to lubricate the rocker arm assembly. A standard dipstick assembly facilitates regular oil level monitoring via the cylinder block flank.

The cooling loop uses forced liquid circulation driven by a heavy-duty, belt-driven centrifugal water pump assembly. A cooling fan draws air across an external radiator matrix while coolant circulation through the block and cylinder head is regulated by a wax-pellet type thermostat. During engine warmup, the thermostat remains closed, diverting fluid through a bypass channel; it opens dynamically at factory-preset operating temperatures to route flow back through the main radiator core.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 4D84
Engine Type ............... 4-cycle inline 4-cylinder water-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line vertical
Combustion Chamber Type ............... Swirl chamber type or direct injection
Engine Bore, in (mm) ............... 3.307 (84.0)
Engine Stroke, in (mm) ............... 3.543 (90.0)
Displacement, cu.in (L) ............... 121.74 (1.995)
Rated Engine Power, hp (kW) ............... 30.1-45.3 (22.4-33.8)
Rated Engine Speed, rpm ............... 2450-3000
Peak Torque, lb-ft (Nm) ............... 93.5 (126.8) at 1800 rpm
Idle Speed, rpm ............... 750-850
Max No-Load Speed, rpm ............... 2650-3200
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 18.0:1-19.5:1
Firing Order ............... 1-3-4-2
Direction of Rotation ............... Counterclockwise viewed from flywheel
Cylinder Block Type ............... High-strength cast iron monoblock
Cylinder Head Type ............... Single-piece cast iron crossflow
Lubrication System ............... Forced pressure circulation lubrication
Oil Pump Type ............... Trochoid gear-driven pump
Oil Filter Type ............... Full-flow cartridge spin-on element
Cooling System ............... Liquid circulation with forced bypass thermostat
Water Pump Type ............... Belt-driven centrifugal impeller pump
Air Cleaner Type ............... Heavy-duty dry dual-element type
Starting System ............... Electric starter motor actuation
Electrical System, V ............... 12V or 24V
Alternator Capacity, A ............... 40A or 55A
Starter Motor Capacity, hp (kW) ............... 2.68 (2.0)

Fuel System

Fuel Injection Pump Type ............... Bosch VE distributor inline distribution plunger
Fuel Feed Pump Type ............... Mechanical diaphragm type pump
Fuel Injection Nozzle Type ............... Hole nozzle or throttle pin type nozzle
Fuel Injection Timing, deg ............... 12-16 BTDC
Fuel Injection Pressure, psi (MPa) ............... 1783-1929 (12.3-13.3)
Second Stage Injection Pressure, psi (MPa) ............... 2320-2465 (16.0-17.0)
Fuel Filter Type ............... Spin-on cartridge type with internal water separator
Fuel Transfer Pump Delivery Pressure, psi (MPa) ............... 2.9-4.3 (0.02-0.03)
Fuel Return Line Maximum Backpressure, inHg (kPa) ............... 3.0 (10.0)
Recommended Fuel Grade ............... Diesel oil ISO 8217 DMA or BS 2869 A1
Minimum Cetane Rating ............... 45
Governor Type ............... Mechanical all-speed centrifugal governor
Maximum Fuel Inlet Temperature, deg F (deg C) ............... 140 (60)
Maximum Fuel Filter Pressure Drop, psi (MPa) ............... 2.9 (0.02)
Injection Nozzle Spray Angle, deg ............... 4 or 5 hole multi-directional spray

Dimensions and Weight

Overall Length, in (mm) ............... 24.8 (630)
Overall Width, in (mm) ............... 19.6 (500)
Overall Height, in (mm) ............... 25.4 (645)
Dry Weight, lbs (kg) ............... 397 (180)
Wet Weight, lbs (kg) ............... 430 (195)

Maintenance Data

Service Information

Compression Pressure (Standard), psi (MPa) ............... 412-441 (2.84-3.04)
Compression Pressure (Minimum), psi (MPa) ............... 341 (2.35)
Maximum Cylinder Pressure Difference, psi (MPa) ............... 29-43 (0.20-0.30)
Oil Pressure at Rated Speed, psi (MPa) ............... 42.6-56.8 (0.29-0.39)
Oil Pressure at Idle Speed, psi (MPa) ............... 9.9 (0.068)
Oil Pressure Relief Valve Setting, psi (MPa) ............... 56.8-71.1 (0.39-0.49)
Thermostat Opening Temperature (Initial), F (C) ............... 160 (71)
Thermostat Opening Temperature (Full Open), F (C) ............... 185 (85)
Standard Operating Temperature, F (C) ............... 167-194 (75-90)
Maximum Coolant Temperature, F (C) ............... 203 (95)
V-Belt Deflection, Force applied 22 lbs, in (mm) ............... 0.39-0.59 (10.0-15.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0059-0.0098 (0.150-0.250)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0059-0.0098 (0.150-0.250)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 20W-20, SAE 10W-30
API Service Classifications ......................... CD, CE, CF-4
Engine Oil Capacity (Total), qt (L) ............... 5.81-7.92 (5.5-7.5)
Engine Oil Capacity (High Level), qt (L) ............... 7.08 (6.7)
Engine Oil Capacity (Low Level), qt (L) ............... 4.22 (4.0)
Cooling System Capacity (Engine Block), qt (L) ............... 4.43 (4.2)
Cooling System Capacity with Radiator, qt (L) ............... 9.51 (9.0)

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 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 Inner Diameter, in (mm) ............... 3.3070-3.3082 (84.000-84.030)
Cylinder Head Surface Flatness Distortion, in (mm) ............... 0.0019 (0.05)
Cylinder Bore Roundness, in (mm) ............... 0.0003 (0.01)
Cylinder Bore Taper Max, in (mm) ............... 0.0003 (0.01)
Connecting Rod Small End Bushing I.D, in (mm) ............... 1.0240-1.0247 (26.012-26.032)
Main Journal Outer Diameter, in (mm) ............... 2.1220-2.1228 (53.900-53.920)
Crankpin Journal Outer Diameter, in (mm) ............... 1.8858-1.8866 (47.900-47.920)
Main Journal Bearing Clearance, in (mm) ............... 0.0015-0.0035 (0.040-0.090)
Crankpin Bearing Clearance, in (mm) ............... 0.0015-0.0031 (0.040-0.080)
Crankshaft Side End Play, in (mm) ............... 0.0043-0.0090 (0.110-0.230)
Connecting Rod Side Axial Clearance, in (mm) ............... 0.0078-0.0157 (0.200-0.400)
Crankpin Big End Shell Housing I.D, in (mm) ............... 2.0078-2.0086 (51.000-51.020)
Piston Skirt Outer Diameter, in (mm) ............... 3.3043-3.3055 (83.930-83.960)
Piston to Cylinder Wall Clearance, in (mm) ............... 0.0027-0.0039 (0.070-0.100)
Piston Pin Bore Inner Diameter, in (mm) ............... 1.0236-1.0240 (26.000-26.009)
Piston Pin Outer Diameter, in (mm) ............... 1.0233-1.0236 (25.992-26.000)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0006 (0.000-0.017)
Piston Pin to Small End Bushing Clearance, in (mm) ............... 0.0004-0.0015 (0.012-0.040)
Top Ring Groove Width, in (mm) ............... 0.0027-0.0043 (0.070-0.110)
Second Ring Groove Width, in (mm) ............... 0.0015-0.0031 (0.040-0.080)
Oil Ring Groove Width, in (mm) ............... 0.0007-0.0023 (0.020-0.060)
Top Ring End Gap, in (mm) ............... 0.0078-0.0157 (0.200-0.400)
Second Ring End Gap, in (mm) ............... 0.0078-0.0157 (0.200-0.400)
Oil Ring End Gap, in (mm) ............... 0.0078-0.0157 (0.200-0.400)
Intake Valve Stem Outer Diameter, in (mm) ............... 0.2736-0.2742 (6.950-6.965)
Exhaust Valve Stem Outer Diameter, in (mm) ............... 0.2732-0.2738 (6.940-6.955)
Intake Valve Guide Inner Diameter, in (mm) ............... 0.2755-0.2761 (7.000-7.015)
Exhaust Valve Guide Inner Diameter, in (mm) ............... 0.2755-0.2761 (7.000-7.015)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0013-0.0025 (0.035-0.065)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0017-0.0029 (0.045-0.075)
Intake Valve Sinkage Depth, in (mm) ............... 0.0157-0.0236 (0.400-0.600)
Exhaust Valve Sinkage Depth, in (mm) ............... 0.0157-0.0236 (0.400-0.600)
Valve Seat Angle, deg ............... 90 or 120
Valve Spring Free Length, in (mm) ............... 1.6535 (42.000)
Camshaft Journal Outer Diameter (No 1), in (mm) ............... 1.6515-1.6523 (41.950-41.970)
Camshaft Journal Outer Diameter (No 2), in (mm) ............... 1.6503-1.6511 (41.920-41.940)
Camshaft Journal Outer Diameter (No 3), in (mm) ............... 1.6492-1.6500 (41.890-41.910)
Camshaft Journal Bearing Clearance, in (mm) ............... 0.0019-0.0039 (0.050-0.100)
Cam Lobes Height (Intake), in (mm) ............... 1.3405-1.3444 (34.050-34.150)
Cam Lobes Height (Exhaust), in (mm) ............... 1.3405-1.3444 (34.050-34.150)
Camshaft Side End Play, in (mm) ............... 0.0019-0.0059 (0.050-0.150)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.6279-0.6289 (15.950-15.975)
Rocker Arm Bushing Inner Diameter, in (mm) ............... 0.6299-0.6306 (16.000-16.018)
Rocker Arm Bushing to Shaft Clearance, in (mm) ............... 0.0009-0.0026 (0.025-0.068)
Tappet Lifter Outer Diameter, in (mm) ............... 0.4704-0.4712 (11.950-11.970)
Tappet Lifter Bore Inner Diameter, in (mm) ............... 0.4724-0.4731 (12.000-12.018)
Tappet to Block Bore Clearance, in (mm) ............... 0.0011-0.0026 (0.030-0.068)
Timing Idle Gear Shaft Outer Diameter, in (mm) ............... 1.3366-1.3377 (33.950-33.980)
Timing Idle Gear Bushing Inner Diameter, in (mm) ............... 1.3385-1.3395 (34.000-34.025)
Timing Idle Gear Shaft to Bushing Clearance, in (mm) ............... 0.0007-0.0029 (0.020-0.075)

Tightening Torques

Cylinder Head Bolts (First Step), lb-ft (Nm) ............... 39.7 (53.9)
Cylinder Head Bolts (Final Step), lb-ft (Nm) ............... 79.5 (107.8)
Crankshaft Main Bearing Cap Bolts, lb-ft (Nm) ............... 83.1 (112.7)
Connecting Rod Big End Cap Bolts, lb-ft (Nm) ............... 39.7 (53.9)
Crankshaft Damper Pulley Bolt, lb-ft (Nm) ............... 86.7 (117.6)
Camshaft Thrust Lock Plate Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Flywheel Mounting Bolts Fasteners, lb-ft (Nm) ............... 61.4 (83.3)
Flywheel Housing Shell Bolts, lb-ft (Nm) ............... 21.6 (29.4)
Timing Gear Protection Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Timing Gear Cover Screws, lb-ft (Nm) ............... 8.6 (11.7)
Timing Camshaft Drive Gear Lock Nut, lb-ft (Nm) ............... 61.4 (83.3)
Timing Idler Gear Mounting Bolt, lb-ft (Nm) ............... 21.6 (29.4)
Fuel Injection Pump Drive Gear Core Nut, lb-ft (Nm) ............... 46.9 (63.7)
Fuel Injection Pump Flange Cradle Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Fuel Injection High Pressure Line Pipe Nuts, lb-ft (Nm) ............... 21.6 (29.4)
Fuel Injection Nozzle Holder Assembly Bolt, lb-ft (Nm) ............... 21.6 (29.4)
Fuel Injection Nozzle Cap Nut Core Attachment, lb-ft (Nm) ............... 36.1 (49.0)
Fuel Leakage Return Rail Overflow Line Bolt, lb-ft (Nm) ............... 8.6 (11.7)
Rocker Arm Shaft Support Bolts, lb-ft (Nm) ............... 21.6 (29.4)
Valve Clearance Adjusting Jam Lock Nuts, lb-ft (Nm) ............... 10.8 (14.7)
Oil Pan Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Oil Pan Hex Bottom Drain Plug, lb-ft (Nm) ............... 39.7 (53.9)
Oil Pump Internal Bolts, lb-ft (Nm) ............... 8.6 (11.7)
Oil Pressure Valve Internal Cap Plug, lb-ft (Nm) ............... 36.1 (49.0)
Centrifugal Water Pump Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Cooling Fan Hub Pulley Bolts, lb-ft (Nm) ............... 8.6 (11.7)
Cooling Thermostat Housing Cover Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Intake Manifold Mounting Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Exhaust Manifold Flange Block Bolts, lb-ft (Nm) ............... 17.3 (23.5)
Alternator Primary Pivot Long Bolt, lb-ft (Nm) ............... 28.9 (39.2)
Alternator Tensioning Adjustment Bracket Bolt, lb-ft (Nm) ............... 17.3 (23.5)
Crank Starting Motor Stud Nuts, lb-ft (Nm) ............... 36.1 (49.0)
Oil Pressure Sensor Switch, lb-ft (Nm) ............... 10.8 (14.7)
Coolant Temperature Sensor, lb-ft (Nm) ............... 21.6 (29.4)
Air Intake Glow Plug Elements, lb-ft (Nm) ............... 14.4 (19.6)
Glow Plug Connecting Nuts, lb-ft (Nm) ............... 1.4 (2.0)

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