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Mitsubishi K4N Engine

The Mitsubishi K4N is a heavy-duty, industrial-grade 4-stroke, water-cooled, in-line 4-cylinder diesel engine. Known for its reliability and high torque profile at lower operational speeds, it is widely utilized as prime power for construction and agricultural machinery, notably powering compact hydraulic excavators such as the Caterpillar 305CR, 305SR, and various Kobelco SK045 / SK45 models. The engine is engineered to comply with Tier II / Stage II emissions standards, featuring a robust cast-iron cylinder block optimized for prolonged structural endurance under high cyclic loads.

The overhead valve (OHV) arrangement utilizes 8 valves in total (2 valves per cylinder: 1 intake, 1 exhaust) driven via a conventional timing gear-driven camshaft, pushrods, and rocker assemblies. Cylinder Bore: 90 mm. Piston Stroke: 90 mm. Total Displacement: 2.29 liters (2290 cc). Forced-feed lubrication is driven by a high-efficiency Gerotor (trochoid) oil pump mounted to the engine front gear case. The system flows oil through a full-flow, spin-on paper element filter cartridge to supply pressurized oil directly to the main bearings, connecting rod journals, and overhead valvetrain components.

The fuel distribution setup incorporates a mechanical, in-line Bosch M-type (cam-type) injection pump driven directly by the engine timing gears. Fuel delivery is synchronized with a centrifugal flyweight mechanical governor to regulate engine speed under varying load demands. An electric fuel transfer pump draws diesel through a primary water separator and fine fuel filter. Pressurized fuel is delivered to the combustion chambers through mechanical nozzle and holder assemblies, featuring a valve opening threshold calibrated between 13.7 and 21.6 MPa. A 12V pre-heating system utilizing electric glow plugs is standard to facilitate cold starting.

The engine utilizes a closed-loop, pressurized liquid cooling setup. Coolant circulation is forced via a belt-driven centrifugal water pump through the internal engine block jackets and cylinder head passages. Temperature regulation is managed by a wax-pellet type inline thermostat controlling flow to a heavy-duty radiator core, assisted by an engine-driven cooling fan.

General Technical Data

Engine Specifications

Engine Model ............... Mitsubishi K4N
Engine Type ............... 4-cycle inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.54 (90.0)
Engine Stroke, in (mm) ............... 3.62 (92.0)
Displacement, cu.in (L) ............... 140 (2.29)
Rated Engine Power, hp (kW) ............... 41.7 (31.1)
Rated Engine Speed, rpm ............... 2400
Peak Torque ............... 142 Nm (105 lb-ft) at 1600 rpm
Idle Speed ............... 750-850 rpm
Max No-Load Speed, rpm ............... 2650
Minimum Idle Speed, rpm ............... 750
Aspiration Type ............... Naturally Aspirated
Operating Speed ............... 2400 rpm
Compression Ratio ............... 18.0:1
Firing Order ............... 1-3-4-2
Combustion Chamber ............... Direct injection spherical type
Direction of Rotation ............... Counter-clockwise facing flywheel
Valve Configuration ............... Overhead valve
Number of Valves per Cylinder ............... 2
Camshaft Drive Type ............... Gear driven
Crankcase Ventilation System ............... Closed type
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron
Lubrication System ............... Full-pressure
Oil Pump Type ............... Gear-driven
Oil Filter Type ............... Full-flow, spin-on
Cooling System ............... Liquid-cooled
Water Pump Type ............... Belt-driven, centrifugal
Air Cleaner Type ............... Dry dual-stage
Starting System ............... Electric Starter
Electrical System ............... 12V or 24V
Alternator Capacity, A ............... 50
Starter Motor Capacity, kW (hp) ............... 2.0 (2.7)

Fuel System

Fuel Injection Pump Type ............... Bosch M type in-line plunger
Fuel Feed Pump Type ............... Mechanical diaphragm type
Fuel Injector Type ............... Multi-hole nozzle type
Fuel Injector Opening Pressure, psi (MPa) ............... 2058 (14.2)
Fuel Filter Element Type ............... Spin-on cartridge element
Fuel Transfer Pump Delivery Pressure, psi (kPa) ............... 4.4-7.3 (30-50)
Recommended Fuel Grade ............... Diesel light oil No. 2-D
Governor Type ............... Mechanical centrifugal
Fuel Injection Timing ............... 14 degrees BTDC
Injection Plunger Diameter, in (mm) ............... 0.236 (6.0)
Injection Plunger Stroke, in (mm) ............... 0.276 (7.0)
Delivery Valve Standard Opening Pressure, psi (MPa) ............... 355 (2.45)
Fuel Injection Pipe Outer Diameter, in (mm) ............... 0.236 (6.0)
Fuel Injection Pipe Inner Diameter, in (mm) ............... 0.079 (2.0)
Fuel Injection Pipe Length, in (mm) ............... 15.75 (400.0)
Fuel Water Separator Type ............... Bowl type with float sedimentor
Fuel Cut-Off Solenoid Type ............... Energized to run or energized to stop
Maximum Fuel System Pressure, psi (MPa) ............... 4350 (30.0)
Injection Nozzle Hole Number ............... 4
Injection Nozzle Hole Diameter, in (mm) ............... 0.009 (0.23)
Injection Nozzle Spray Angle, degrees ............... 150
Fuel Feed Pump Minimum Stroke, in (mm) ............... 0.197 (5.0)
Fuel Feed Pump Spring Free Length, in (mm) ............... 1.378 (35.0)
Fuel Injection Pump Oil Supply Type ............... Engine splash or pressure line

Dimensions and Weight

Overall Length, in (mm) ............... 26.5 (675)
Overall Width, in (mm) ............... 19.9 (505)
Overall Height, in (mm) ............... 25.8 (655)
Dry Weight, lbs (kg) ............... 408 (185)
Wet Weight, lbs (kg) ............... 434 (197)

Maintenance Data

Service Information

Compression Pressure, psi (MPa) ............... 426 (2.94)
Minimum Compression Pressure, psi (MPa) ............... 355 (2.45)
Max Pressure Difference Between Cylinders, psi (MPa) ............... 36 (0.25)
Oil Pressure at Rated Speed, psi (MPa) ............... 43-57 (0.30-0.39)
Oil Pressure at Low Idle, psi (MPa) ............... 14 (0.10)
Cooling System Cap Pressure Rating, psi (kPa) ............... 13.0 (90.0)
Thermostat Initial Opening Temperature, F (C) ............... 170 (76.5)
Thermostat Full Open Temperature, F (C) ............... 194 (90.0)
Maximum Coolant Temperature, F (C) ............... 221 (105)
Normal Coolant Temperature, F (C) ............... 176-194 (80-90)
Fan Belt Deflection Under 22 lbs Force, in (mm) ............... 0.39-0.59 (10.0-15.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0098 (0.25)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0098 (0.25)

Engine Oil and Coolant

Engine Oil Type .................. SAE 30W, SAE 10W-30, or 5W-20
API Service Classifications ......................... CF or CH-4
Engine Oil Capacity with Filter, qt (L) ............... 6.9 (6.5)
Engine Oil Capacity without Filter, qt (L) ............... 6.1 (5.8)
Cooling System Capacity, qt (L) ............... 4.2 (4.0)
Cooling Capacity with Radiator, qt (L) ............... 9.5 (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 200 hours

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 3.5433-3.5445 (90.000-90.030)
Cylinder Bore Wear Limit Max, in (mm) ............... 3.5512 (90.200)
Cylinder Bore Taper and Out of Round, in (mm) ............... 0.0004 (0.010)
Cylinder Block Top Surface Flatness, in (mm) ............... Under 0.0020 (0.050)
Cylinder Head Bottom Surface Flatness, in (mm) ............... Under 0.0020 (0.050)
Con Rod Small End Bushing Inner Diameter, in (mm) ............... 1.1031-1.1039 (28.020-28.040)
Main Journal Outer Diameter, in (mm) ............... 2.5583-2.5591 (64.980-65.000)
Main Bearing Shell Thickness, in (mm) ............... 0.0787 (2.000)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0012-0.0030 (0.030-0.076)
Crankpin Outer Diameter, in (mm) ............... 2.0465-2.0472 (51.980-52.000)
Con Rod Bearing Shell Thickness, in (mm) ............... 0.0591 (1.500)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Crankshaft End Play, in (mm) ............... 0.0020-0.0071 (0.050-0.180)
Connecting Rod Side Play, in (mm) ............... 0.0059-0.0138 (0.150-0.350)
Piston Outer Diameter, in (mm) ............... 3.5413-3.5425 (89.950-89.980)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0016-0.0031 (0.040-0.080)
Piston Pin Outer Diameter, in (mm) ............... 1.1024-1.1028 (28.001-28.010)
Piston Pin Bore Inner Diameter, in (mm) ............... 1.1024-1.1026 (28.000-28.006)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0004 (0.001-0.010)
Piston Pin to Small End Bushing Clearance, in (mm) ............... 0.0004-0.0015 (0.010-0.039)
First Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.25-0.40)
Second Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.25-0.40)
Oil Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.20-0.40)
First Ring Side Clearance, in (mm) ............... 0.0024-0.0039 (0.06-0.10)
Second Ring Side Clearance, in (mm) ............... 0.0020-0.0035 (0.05-0.09)
Oil Ring Side Clearance, in (mm) ............... 0.0012-0.0028 (0.03-0.07)
Valve Stem Outer Diameter (Intake), in (mm) ............... 0.3134-0.3142 (7.960-7.980)
Valve Stem Outer Diameter (Exhaust), in (mm) ............... 0.3122-0.3130 (7.930-7.950)
Valve Guide Inner Diameter Standard, in (mm) ............... 0.3150-0.3157 (8.000-8.018)
Valve Stem to Guide Clearance (Intake), in (mm) ............... 0.0008-0.0023 (0.020-0.058)
Valve Stem to Guide Clearance (Exhaust), in (mm) ............... 0.0020-0.0035 (0.050-0.088)
Valve Face Angle, degrees ............... 45
Valve Seat Angle, degrees ............... 45
Valve Margin Thickness, in (mm) ............... 0.0394 (1.000)
Valve Spring Free Length, in (mm) ............... 1.815 (46.10)
Camshaft Journal Outer Diameter (Front), in (mm) ............... 1.8886-1.8894 (47.970-47.990)
Camshaft Journal Outer Diameter (Middle), in (mm) ............... 1.8492-1.8500 (46.970-46.990)
Camshaft Journal Outer Diameter (Rear), in (mm) ............... 1.8102-1.8110 (45.970-45.990)
Camshaft Bearing Inner Diameter (Front), in (mm) ............... 1.8906-1.8917 (48.020-48.050)
Camshaft Bearing Inner Diameter (Middle), in (mm) ............... 1.8512-1.8524 (47.020-47.050)
Camshaft Bearing Inner Diameter (Rear), in (mm) ............... 1.8122-1.8134 (46.020-46.050)
Camshaft Journal Oil Clearance, in (mm) ............... 0.0012-0.0031 (0.030-0.080)
Cam Lobe Height (Intake), in (mm) ............... 1.5177 (38.550)
Cam Lobe Height (Exhaust), in (mm) ............... 1.5177 (38.550)
Camshaft End Play, in (mm) ............... 0.0020-0.0098 (0.050-0.250)
Rocker Shaft Outer Diameter, in (mm) ............... 0.7469-0.7476 (18.970-18.990)
Rocker Arm Bushing Inner Diameter, in (mm) ............... 0.7480-0.7491 (19.000-19.028)
Rocker Arm Bushing to Shaft Clearance, in (mm) ............... 0.0004-0.0023 (0.010-0.058)
Tappet Outer Diameter, in (mm) ............... 0.9429-0.9437 (23.950-23.970)
Tappet Guide Hole Inner Diameter, in (mm) ............... 0.9449-0.9457 (24.000-24.020)
Tappet to Guide Hole Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Idler Gear Bushing Inner Diameter, in (mm) ............... 1.3386-1.3396 (34.000-34.025)
Idler Gear Shaft Outer Diameter, in (mm) ............... 1.3366-1.3376 (33.950-33.975)
Idler Gear Bushing to Shaft Clearance, in (mm) ............... 0.0010-0.0030 (0.025-0.075)

Tightening Torques

Cylinder Head Bolts (M10), lb-ft (Nm) ............... 54-61 (73.5-83.0)
Cylinder Head Bolts (M12), lb-ft (Nm) ............... 80-87 (108.0-118.0)
Connecting Rod Cap Bolts, lb-ft (Nm) ............... 36-40 (49.0-54.0)
Main Bearing Cap Bolts, lb-ft (Nm) ............... 72-80 (98.0-108.0)
Flywheel Mounting Bolts, lb-ft (Nm) ............... 90-101 (123.0-137.0)
Crankshaft Pulley Center Nut, lb-ft (Nm) ............... 108-123 (147.0-167.0)
Camshaft Thrust Plate Bolts, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Camshaft Gear Center Bolt, lb-ft (Nm) ............... 58-65 (78.0-88.0)
Idler Gear Shaft Mounting Bolts, lb-ft (Nm) ............... 22-27 (30.0-37.0)
Rocker Arm Shaft Bracket Bolts, lb-ft (Nm) ............... 22-27 (30.0-37.0)
Rocker Cover Cap Nuts, lb-ft (Nm) ............... 4.4-5.9 (6.0-8.0)
Timing Gear Case Cover Bolts (M6), lb-ft (Nm) ............... 7.2-8.7 (9.8-11.8)
Timing Gear Case Cover Bolts (M8), lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Oil Pan Mounting Bolts (M6), lb-ft (Nm) ............... 5.1-6.5 (7.0-8.8)
Oil Pan Mounting Bolts (M8), lb-ft (Nm) ............... 11-15 (15.0-20.0)
Oil Pan Drain Plug, lb-ft (Nm) ............... 29-36 (39.0-49.0)
Oil Pump Mounting Bolts, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Oil Relief Valve Plug, lb-ft (Nm) ............... 29-36 (39.0-49.0)
Water Pump Mounting Bolts (M6), lb-ft (Nm) ............... 7.2-8.7 (9.8-11.8)
Water Pump Mounting Bolts (M8), lb-ft (Nm) ............... 14.5-18.1 (19.6-24.5)
Thermostat Housing Bolts, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Intake Manifold Mounting Bolts, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Exhaust Manifold Mounting Bolts, lb-ft (Nm) ............... 18-22 (25.0-30.0)
Fuel Injection Pump Delivery Valve Holder, lb-ft (Nm) ............... 25-29 (34.0-39.0)
Fuel Injection Pump Coupling Bolts, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Fuel Injection Pump Mounting Nuts, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Fuel Injector Assembly to Cylinder Head, lb-ft (Nm) ............... 36-43 (49.0-59.0)
Fuel Injection Pipe Union Nuts, lb-ft (Nm) ............... 18-22 (25.0-30.0)
Fuel Return Pipe Line Bolts, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Glow Plug Terminal Nuts, lb-ft (Nm) ............... 1.1-1.4 (1.5-2.0)
Glow Plugs Body into Head, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Starter Motor Mounting Bolts, lb-ft (Nm) ............... 36-43 (49.0-59.0)
Alternator Mounting Pivot Bolt, lb-ft (Nm) ............... 29-36 (39.0-49.0)
Alternator Adjusting Link Bolt, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Oil Pressure Switch, lb-ft (Nm) ............... 11-13 (15.0-18.0)
Coolant Temperature Sensor, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Flywheel Housing Mounting Bolts (M10), lb-ft (Nm) ............... 36-43 (49.0-59.0)
Flywheel Housing Mounting Bolts (M12), lb-ft (Nm) ............... 58-65 (78.0-88.0)
Rear Oil Seal Case Retainer Bolts, lb-ft (Nm) ............... 7.2-8.7 (9.8-11.8)
Front Crankshaft Seal Slinger Bolts, lb-ft (Nm) ............... 7.2-8.7 (9.8-11.8)
Fan Blade Assembly Mounting Bolts, lb-ft (Nm) ............... 7.2-10.8 (9.8-14.7)
Air Cleaner Bracket Bolts, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Exhaust Pipe Flange Mounting Nuts, lb-ft (Nm) ............... 22-29 (30.0-39.0)
Fuel Feed Pump Mounting Bolts, lb-ft (Nm) ............... 11-15 (15.0-20.0)
Oil Jet Block Check Valve Bolts, lb-ft (Nm) ............... 14-18 (20.0-25.0)
Breather Valve Cover Screws, lb-ft (Nm) ............... 2.2-3.6 (3.0-5.0)

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• Mitsubishi Engines Specs
  
• Mitsubishi K4C Specs
  
• Mitsubishi K4D Specs
  
• Mitsubishi K4E Specs
  
• Mitsubishi K4F Specs
  
• Mitsubishi K4M Specs
  

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