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Komatsu 4D94-2 Engine

The Komatsu 4D94-2 is an industrial-grade, vertical in-line, 4-cycle, water-cooled diesel engine. It belongs to the Komatsu 94 Series engine family and is widely utilized in heavy-duty machinery, particularly in Komatsu excavators, forklifts, and specialized material-handling equipment. Engineered for extreme reliability and continuous output under fluctuating load conditions, it features a heavy-duty cast iron cylinder block and a single-piece cylinder head. In shop applications, this engine is known for its accessibility during overhauls, utilizing standard wet-sleeve setups or heavy-walled cylinder boundaries designed for prolonged service intervals.

Valve Configuration: Overhead Valve (OHV) arrangement with an in-line orientation. The system uses standard mechanical lifters, pushrods, and rocker assemblies. The cylinder bore measures exactly 94 mm, and the piston stroke length is 106 mm. Total engine displacement measures 2.94 liters across the 4-cylinder layout. Cooling System: Forced liquid-circulation cooling system. A belt-driven centrifugal water pump continuously circulates coolant through the cylinder block jackets and cylinder head passages to a remote radiator. A cooling fan draws air through the radiator core, and system temperature regulation is maintained by a mechanical wax-pellet thermostat.

Fuel System: Mechanical direct or indirect injection system configured with a firing order of 1-3-4-2. Fuel delivery is governed by a high-pressure Bosch VE-type distributor injection pump featuring an integrated, all-speed mechanical governor and automatic reverse-revolution prevention. High-pressure lines connect the pump to individual fuel injection nozzles set to a standard injection opening pressure threshold between 12.3 MPa and 13.3 MPa. Lubrication System: Forced-feed lubrication system pressurized by a gear-driven oil pump. The oil is driven from the oil pan through a full-flow filtration element before entering the main oil gallery. Pressurized pathways deliver continuous lubrication to the main bearings, connecting rod journals, camshaft lobes, and overhead rocker gear.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 4D94-2
Engine Type ............... 4-cycle vertical inline 4-cylinder water-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.70 (94.0)
Engine Stroke, in (mm) ............... 4.17 (106.0)
Displacement, cu.in (L) ............... 179.4 (2.94)
Rated Engine Power, hp (kW) ............... 32.2-45.6 (24.0-34.0)
Rated Engine Speed, rpm ............... 2200-2500
Peak Torque ............... 119.5-131.3 lb-ft (162.0-178.0 Nm) at 1500 rpm
Idle Speed ............... 700-900 rpm
Aspiration Type ............... Naturally Aspirated
Operating Speed ............... 2200 rpm
Compression Ratio ............... 18.0:1-21.0:1
Firing Order ............... 1-3-4-2
Combustion Chamber ............... Swirl chamber type or direct injection variant
Direction of Rotation ............... Counterclockwise looking from flywheel end face
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron single piece
Lubrication System ............... Full-pressure forced circulation
Oil Pump Type ............... Trochoid gear-driven pump
Oil Filter Type ............... Full-flow spin-on cartridge type
Cooling System ............... Liquid-cooled with radiator expansion tank
Water Pump Type ............... Belt-driven centrifugal impeller pump
Air Cleaner Type ............... Dry dual-element heavy duty paper stage
Starting System ............... Axial reduction electric starter motor
Electrical System ............... 12V or 24V DC

Fuel System

Injection Pump Model ............... Bosch VE type inline mechanical assembly
Feed Pump Type ............... Internal vane positive displacement mechanical model
Injection Nozzle Type ............... Multi-hole throttling needle nozzle assembly
Nozzle Injection Opening Pressure, psi (MPa) ............... 1711-1914 (11.8-13.2)
Fuel Filter Type ............... Spin-on high efficiency paper element cartridge filter
Fuel Delivery Pressure, psi (kPa) ............... 2.9-7.3 (20.0-50.0)
Plunger Diameter, in (mm) ............... 0.47 (12.0)
Injection Timing Angle ............... 12-16 degrees BTDC
Maximum Fuel Consumption, lb/hp-hr (g/kW-h) ............... 0.38-0.41 (230.0-250.0)
Governor Type ............... Mechanical all-speed centrifugal flyweight governor
Fuel Return Line Volume, gal/hr (L/hr) ............... 1.58-2.64 (6.0-10.0)
Fuel Transfer Priming Pump ............... Manual mechanical plunger
Maximum Fuel Inlet Restriction, in-Hg (kPa) ............... 3.94 (13.3)
Maximum Fuel Return Back Pressure, in-Hg (kPa) ............... 5.91 (20.0)

Dimensions and Weight

Overall Length, in (mm) ............... 41.2 (1045)
Overall Width, in (mm) ............... 22.0 (560)
Overall Height, in (mm) ............... 35.4 (900)
Dry Weight, lbs (kg) ............... 662 (300)
Wet Weight, lbs (kg) ............... 695 (315)

Maintenance Data

Service Information

Compression Pressure (Standard), psi (MPa) ............... 412.0-441.0 (2.84-3.04)
Compression Pressure (Min Limit), psi (MPa) ............... 341.0 (2.35)
Compression Pressure Between Cylinders, psi (MPa) ............... 28.4 (0.20)
Oil Pressure at High Idle, psi (MPa) ............... 42.1-56.6 (0.29-0.39)
Oil Pressure at Low Idle, psi (MPa) ............... 9.94 (0.069)
Thermostat Nominal Opening Temperature, F (C) ............... 159.8 (71.0)
Thermostat Full Open Position Temperature, F (C) ............... 185.0 (85.0)
Cooling Temperature Operational Range, F (C) ............... 167.0-194.0 (75.0-90.0)
Fan Belt Deflection (Standard), in (mm) ............... 0.39-0.55 (10.0-14.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.006-0.010 (0.15-0.25)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.006-0.010 (0.15-0.25)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30, SAE 15W-40, SAE 10W-30
API Service Classifications ......................... CD, CE, CF-4
Engine Oil Capacity with Filter, qt (L) ............... 8.45 (8.0)
Engine Oil Capacity (Sump Only), qt (L) ............... 7.40 (7.0)
Cooling Fluid Capacity (Water Jacket), gal (L) ............... 1.11 (4.2)

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 Inside Diameter, in (mm) ............... 3.7007-3.7015 (94.000-94.022)
Cylinder Bore Out of Round, in (mm) ............... 0.0012 (0.030)
Cylinder Block Top Surface Flatness, in (mm) ............... 0.0020 (0.050)
Crankshaft Main Journal Outside Diameter, in (mm) ............... 2.7512-2.7520 (69.880-69.900)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0015-0.0031 (0.038-0.080)
Crankpin Journal Outside Diameter, in (mm) ............... 2.1213-2.1220 (53.880-53.900)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0014-0.0029 (0.035-0.074)
Crankshaft Axial End Play, in (mm) ............... 0.0043-0.0091 (0.110-0.230)
Connecting Rod Small End Bushing I.D, in (mm) ............... 1.1815-1.1823 (30.010-30.030)
Piston Outside Diameter, in (mm) ............... 3.6968-3.6976 (93.900-93.920)
Piston to Cylinder Wall Clearance, in (mm) ............... 0.0031-0.0047 (0.080-0.120)
Piston Pin Bore Inside Diameter, in (mm) ............... 1.1811-1.1815 (30.000-30.010)
Piston Pin Outside Diameter, in (mm) ............... 1.1807-1.1811 (29.990-30.000)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0004-0.0008 (0.010-0.020)
Top Ring Groove Side Clearance, in (mm) ............... 0.0024-0.0039 (0.060-0.100)
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)
Top Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.250-0.400)
Second Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.250-0.400)
Oil Ring End Gap, in (mm) ............... 0.0078-0.0138 (0.200-0.350)
Cylinder Head Distortion Plane Face Flatness, in (mm) ............... 0.0020 (0.050)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3126-0.3134 (7.940-7.960)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3118-0.3126 (7.920-7.940)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0012-0.0024 (0.030-0.060)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0020-0.0031 (0.050-0.080)
Intake Valve Sink Depth, in (mm) ............... 0.0276-0.0394 (0.700-1.000)
Exhaust Valve Sink Depth, in (mm) ............... 0.0276-0.0394 (0.700-1.000)
Valve Guide Tube Height, in (mm) ............... 0.5512-0.5906 (14.000-15.000)
Valve Spring Free Length, in (mm) ............... 1.8701-1.9094 (47.500-48.500)
Valve Seat Contact Width, in (mm) ............... 0.0472-0.0630 (1.200-1.600)
Camshaft Journal Outside Diameter (Front), in (mm) ............... 1.9642-1.9650 (49.890-49.910)
Camshaft Journal Outside Diameter (Middle), in (mm) ............... 1.9445-1.9453 (49.390-49.410)
Camshaft Journal Outside Diameter (Rear), in (mm) ............... 1.9248-1.9256 (48.890-48.910)
Camshaft Journal Oil Clearance, in (mm) ............... 0.0020-0.0039 (0.050-0.100)
Intake Cam Lobe Height, in (mm) ............... 1.6870-1.6929 (42.850-43.000)
Exhaust Cam Lobe Height, in (mm) ............... 1.6870-1.6929 (42.850-43.000)
Camshaft Axial End Play, in (mm) ............... 0.0020-0.0059 (0.050-0.150)
Rocker Arm Shaft Outside Diameter, in (mm) ............... 0.7854-0.7862 (19.950-19.970)
Rocker Arm Bushing Inside Diameter, in (mm) ............... 0.7874-0.7882 (20.000-20.020)
Rocker Arm Bushing to Shaft Clearance Index, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Idler Gear Shaft Outside Diameter, in (mm) ............... 1.7701-1.7709 (44.960-44.980)
Idler Gear Bushing Inside Diameter, in (mm) ............... 1.7717-1.7726 (45.000-45.025)
Idler Gear Bushing to Shaft Clearance, in (mm) ............... 0.0008-0.0026 (0.020-0.065)

Tightening Torques

Cylinder Head Fasteners (Step 1), lb-ft (Nm) ............... 36.9-43.5 (50.0-59.0)
Cylinder Head Fasteners (Step 2), lb-ft (Nm) ............... 76.0-83.3 (103.0-113.0)
Cylinder Head Fasteners (Step 3), lb-ft (Nm) ............... 95.9 (130.0)
Crankshaft Main Bearing Cap Fasteners (Step 1), lb-ft (Nm) ............... 84.8 (115.0)
Crankshaft Main Bearing Cap Fasteners (Step 2), lb-ft (Nm) ............... 99.6-107.0 (135.0-145.0)
Connecting Rod Big End Cap Nut (Step 1), lb-ft (Nm) ............... 22.1 (30.0)
Connecting Rod Big End Cap Nut (Step 2), lb-ft (Nm) ............... 33.2-43.5 (45.0-59.0)
Flywheel Retaining Bolts, lb-ft (Nm) ............... 57.9-65.1 (78.5-88.3)
Crankshaft Front Pulley Center Damper Bolt, lb-ft (Nm) ............... 86.7-94.4 (117.6-128.0)
Camshaft Thrust Plate Flange Bolts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Camshaft Timing Drive Gear Center Bolt, lb-ft (Nm) ............... 43.5-50.7 (59.0-68.8)
Idler Gear Support Shaft Core Anchor Bolt, lb-ft (Nm) ............... 18.1-21.7 (24.5-29.4)
Timing Gear Case Cover Outer Shell Screws, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Flywheel Housing Rigid Mounting Frame Bolts, lb-ft (Nm) ............... 57.9-65.1 (78.5-88.3)
Rocker Arm Shaft Support Bracket Nuts, lb-ft (Nm) ............... 21.7-28.9 (29.4-39.2)
Rocker Arm Valve Adjuster Lock Screw Nut, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Valve Rocker Mechanism Top Cover Nut, lb-ft (Nm) ............... 5.1-8.7 (6.9-11.8)
Oil Pan Sump Drain Plug, lb-ft (Nm) ............... 36.2-43.5 (49.0-59.0)
Oil Pan Flange Block Attachment Screws, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Fuel Injection Pump Drive Gear Lock Nut, lb-ft (Nm) ............... 43.5-47.0 (59.0-63.7)
Fuel Injection Pump Housing Flange Nuts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Fuel Injection Nozzle Holder Assembly Nut, lb-ft (Nm) ............... 28.9-32.5 (39.2-44.1)
Fuel Injection High Pressure Line Delivery Nuts, lb-ft (Nm) ............... 18.1-21.7 (24.5-29.4)
Fuel Injector Fuel Return Leak Off Line Rail Nuts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Glow Plug Core Terminal, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)
Glow Plug Electrical Power Supply Link Wire Nuts, lb-ft (Nm) ............... 1.4-2.2 (2.0-3.0)
Intake Manifold Casting Core Port Bolts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Exhaust Manifold Core Port Stud Nuts, lb-ft (Nm) ............... 18.1-21.7 (24.5-29.4)
Water Pump Assembly Body Shell Block Mount Bolts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Cooling Fan Blade Assembly to Pulley Bolts, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Water Outlet Thermostat Housing Screws, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Oil Pump Internal Housing Cap Screws, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Oil Pressure Relief Valve Spring Plug Nut, lb-ft (Nm) ............... 28.9-36.2 (39.2-49.0)
Oil Filter Housing Base Adapter Block Bracket Bolts, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Cranking Starter Motor Flange Screws, lb-ft (Nm) ............... 57.9-65.1 (78.5-88.3)
Alternator Pivot Anchor Bracket Mounting Bolt, lb-ft (Nm) ............... 28.9-36.2 (39.2-49.0)
Alternator Slotted Tension Adjuster Link Stabilizer Bolt, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Engine Support Cushion Engine Mount Bracket Bolts, lb-ft (Nm) ............... 57.9-72.3 (78.5-98.0)
Oil Pressure Sensor Sender Unit, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)
Temperature Sensor Sender Head Unit, lb-ft (Nm) ............... 14.5-21.7 (19.6-29.4)
Exhaust Pipe Outlet Flange Gasket Connection Nuts, lb-ft (Nm) ............... 25.3-32.5 (34.3-44.1)
Air Intake Heater Element Casting Block Interface Screws, lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Crankcase Breather Assembly Valve Cover Mount Bolts, lb-ft (Nm) ............... 5.1-7.2 (6.9-9.8)

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