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Komatsu 4D88E Engine

The Komatsu 4D88E is a heavy-duty, industrial-grade diesel engine manufactured for compact construction and agricultural machinery, such as mini-excavators and tractors. Developed in collaboration with Yanmar (as part of the TNV/E-series platform), this engine features a vertical, in-line, four-stroke architecture designed to meet rigorous EPA emissions regulations. It is highly regarded in workshop environments for its robust cast-iron block design, reliable structural integrity, and clean mechanical fuel control.

The engine employs an overhead valve configuration driven by a conventional pushrod and rocker arm assembly connected to a gear-driven camshaft. It utilizes two valves per cylinder, making a total of eight valves across the entire engine block. Valve clearance inspections and manual adjustments are carried out at the rocker arms using a standard thickness gauge at designated maintenance intervals. The engine features a total displacement of 2.2 liters distributed evenly across four cylinders. The internal dimensions of the cylinder liners are explicitly engineered with a bore diameter of 88 mm and a stroke length of 90 mm.

Fuel System: This engine relies on a high-precision, mechanically governed direct injection combustion system. The fuel delivery circuit pulls diesel directly from the main fuel tank through a primary water separator and sediment bowl. An electric or electromagnetic feed pump transfers the fuel forward through a fine-element fuel filter. It then enters the high-pressure fuel injection pump (MP-pump series), which timed-pulses the fuel through heavy-wall steel lines directly into individual fuel injectors. Unused fuel within the high-pressure pump flows back to the fuel tank via a continuous fuel return line, which simultaneously cools and lubricates internal pump components.

Lubrication System: Engine lubrication is managed via a full-pressure, wet-sump configuration pressurized by a high-efficiency trochoid oil pump integrated directly into the gear train. Engine oil passes through a full-flow, spin-on replacement filter cartridge. An internal pressure regulating valve ensures adequate oil distribution to the main bearings, connecting rods, camshaft journals, and rocker assemblies. A dedicated mechanical oil pressure switch monitors system pressure and triggers an immediate alert if a sudden drop in pressure occurs.

Cooling System: Thermal regulation is achieved through a forced-circulation, liquid-cooled system driven by a belt-powered centrifugal water pump. Coolant circulates through the cylinder block and cylinder head passages to absorb thermal energy before routing back to the radiator. A pellet-type thermostat controls the flow circuit, routing coolant away from the radiator during the warm-up phase and opening fully as the engine reaches normal operational temperature. The radiator assembly is sealed by a pressure-regulating radiator cap to safely raise the boiling point of the fluid.

General Technical Data

Engine Specifications

Engine Model ............... Komatsu 4D88E
Engine Type ............... 4-cycle vertical inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line vertical
Engine Bore, in (mm) ............... 3.46 (88.0)
Engine Stroke, in (mm) ............... 3.54 (90.0)
Displacement, cu.in (L) ............... 134 (2.190)
Rated Engine Power, hp (kW) ............... 24.5-48.1 (18.0-35.4)
Rated Engine Speed, rpm ............... 1500-3000
Idle Speed, rpm ............... 750-850
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 19.0:1
Firing Order ............... 1-3-4-2
Combustion Chamber ............... Direct injection toroid type
Cylinder Block Type ............... Monoblock cast iron
Cylinder Head Type ............... One-piece cast iron 2-valve per cylinder layout
Lubrication System ............... Forced lubrication via trochoid pump
Oil Pump Type ............... Gear-driven trochoid assembly
Oil Filter Type ............... Full-flow spin-on cartridge elements
Cooling System ............... Liquid-cooled with forced centrifugal circulation
Water Pump Type ............... Belt-driven centrifugal impeller
Air Cleaner Type ............... Dry dual-element heavy-duty system
Starting System ............... Electric motor starter mechanism
Electrical System, V ............... 12 or 24
Alternator Rating, A ............... 55-80
Starter Motor Rating, kW ............... 2.3-3.0

Fuel System

Fuel Injection Pump Type ............... Yanmar MP distributor type integrated block
Fuel Feed Pump Type ............... Mechanical trochoid drive configuration
Fuel Feed Pump Drive Method ............... Camshaft gear integrated bevel interface
Fuel Injection Nozzle Type ............... Multi-orifice hole design assembly
Number of Nozzle Orifices ............... 5 hole distribution pattern
Nozzle Hole Diameter, in (mm) ............... 0.008 (0.20)
Governor Type ............... Mechanical all-speed centrifugal governor
Fuel Injection Timing, deg ............... 12-16 BTDC
Primary Injection Opening Pressure, psi (bar) ............... 2842-2987 (196-206)
Secondary Injection Opening Pressure, psi (bar) ............... 3132-3277 (216-226)
Fuel Filter Assembly Type ............... Spin-on element with water bowl
Water Separator Assembly ............... Integrated float sensor with drain cock
Fuel Transfer Pump Delivery Pressure, psi (bar) ............... 2.9-4.3 (0.2-0.3)
Fuel Camshaft Lift, in (mm) ............... 0.275 (7.0)
Plunger Diameter, in (mm) ............... 0.315 (8.0)
Plunger Stroke, in (mm) ............... 0.275 (7.0)
Injection Pipe Outer Diameter, in (mm) ............... 0.236 (6.0)
Injection Pipe Inner Diameter, in (mm) ............... 0.078 (2.0)
Fuel Feed Line Diameter, in (mm) ............... 0.315 (8.0)
Fuel Return Line Diameter, in (mm) ............... 0.236 (6.0)
Recommended Fuel ............... Ultra-low sulfur diesel ASTM D975 No. 2-D

Dimensions and Weight

Overall Length, in (mm) ............... 26.5 (675)
Overall Width, in (mm) ............... 19.6 (500)
Overall Height, in (mm) ............... 26.8 (680)
Dry Weight, lbs (kg) ............... 397 (180)
Wet Weight, lbs (kg) ............... 422 (191)

Maintenance Data

Service Information

Compression Pressure (Standard), psi (bar) ............... 412-441 (2.84-3.04)
Compression Pressure (Minimum), psi (bar) ............... 341 (2.35)
Oil Pressure at Rated Speed, psi (bar) ............... 42.6-56.8 (2.9-3.9)
Oil Pressure at Low Idle, psi (bar) ............... 8.5 (0.58)
Radiator Cap Opening Pressure, psi (bar) ............... 12.8-15.6 (0.88-1.08)
Oil Temperature Normal Range, F (C) ............... 185-230 (85-110)
Cooling Temperature Normal Range, F (C) ............... 167-194 (75-90)
Thermostat Opening Temperature, F (C) ............... 160-165 (71-74)
Thermostat Full Open Temperature, F (C) ............... 185 (85)
V-Belt Deflection Under 22 lbs (98 N) Force, in (mm) ............... 0.39-0.59 (10.0-15.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.0059-0.0098 (0.15-0.25)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.0059-0.0098 (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
Engine Oil Capacity (Deep Pan), qt (L) ............... 7.82 (7.4)
Engine Oil Capacity (Shallow Pan), qt (L) ............... 6.13 (5.8)
Coolant Capacity (Engine Only), qt (L) ............... 2.85 (2.7)

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) ............... 3.4645-3.4649 (88.000-88.010)
Cylinder Bore Out-of-Round, in (mm) ............... 0.0003 (0.01) concentricity range
Connecting Rod Small End Bushing I.D, in (mm) ............... 1.0246-1.0251 (26.025-26.038)
Connecting Rod Big End Bearing Bore I.D, in (mm) ............... 1.9685-1.9689 (50.000-50.010)
Connecting Rod Side Play, in (mm) ............... 0.0078-0.0157 (0.200-0.400)
Main Journal Outer Diameter, in (mm) ............... 2.1642-2.1646 (54.964-54.974)
Crankpin Outer Diameter, in (mm) ............... 1.8883-1.8887 (47.964-47.974)
Main Journal Bearing Clearance, in (mm) ............... 0.0014-0.0029 (0.038-0.074)
Crankpin Bearing Clearance, in (mm) ............... 0.0014-0.0029 (0.038-0.074)
Crankshaft End Play, in (mm) ............... 0.0043-0.0082 (0.110-0.210)
Piston Skirt Outer Diameter, in (mm) ............... 0.866 (22.0)
Piston Outer Diameter, in (mm) ............... 3.4626-3.4630 (87.950-87.960)
Piston-to-Cylinder Bore Clearance, in (mm) ............... 0.0015-0.0023 (0.040-0.060)
Piston Pin Bore Inside Diameter, in (mm) ............... 1.0238-1.0242 (26.005-26.015)
Piston Pin Outer Diameter, in (mm) ............... 1.0236-1.0240 (26.000-26.010)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0000-0.0005 (0.000-0.015)
Piston Pin to Small End Bushing Clearance, in (mm) ............... 0.0005-0.0014 (0.015-0.038)
Top Ring Groove Width, in (mm) ............... 0.0807-0.0815 (2.050-2.070)
Second Ring Groove Width, in (mm) ............... 0.0799-0.0807 (2.030-2.050)
Oil Ring Groove Width, in (mm) ............... 0.1185-0.1193 (3.010-3.030)
Top Ring Side Clearance, in (mm) ............... 0.0027-0.0043 (0.070-0.110)
Second Ring Side Clearance, in (mm) ............... 0.0015-0.0031 (0.040-0.080)
Oil Ring Side Clearance, 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)
Cylinder Head Surface Distortion, in (mm) ............... 0.0019 (0.05) or less clearance allowance
Intake Valve Stem to Valve Guide Clearance, in (mm) ............... 0.0009-0.0023 (0.025-0.060)
Exhaust Valve Stem to Valve Guide Clearance, in (mm) ............... 0.0015-0.0029 (0.040-0.075)
Intake Valve Sink Depth, in (mm) ............... 0.015-0.027 (0.40-0.70)
Exhaust Valve Sink Depth, in (mm) ............... 0.015-0.027 (0.40-0.70)
Valve Spring Free Length, in (mm) ............... 1.653 (42.0)
Camshaft Journal Outer Diameter (Front), in (mm) ............... 1.7694-1.7701 (44.945-44.965)
Camshaft Journal Outer Diameter (Middle), in (mm) ............... 1.7675-1.7683 (44.895-44.915)
Camshaft Journal Outer Diameter (Rear), in (mm) ............... 1.7694-1.7701 (44.945-44.965)
Camshaft Oil Clearance, in (mm) ............... 0.0019-0.0035 (0.050-0.090)
Cam Lobe Height (Intake), in (mm) ............... 1.5216-1.5255 (38.650-38.750)
Cam Lobe Height (Exhaust), in (mm) ............... 1.5216-1.5255 (38.650-38.750)
Camshaft Thrust End Play, in (mm) ............... 0.0019-0.0059 (0.050-0.150)
Idle Gear Shaft Outer Diameter, in (mm) ............... 1.8482-1.8489 (46.945-46.965)
Idle Gear Bushing Inside Diameter, in (mm) ............... 1.8503-1.8513 (47.000-47.025)
Idle Gear Shaft-to-Bushing Clearance, in (mm) ............... 0.0013-0.0031 (0.035-0.080)
Tappet Stem Outer Diameter, in (mm) ............... 0.4702-0.4710 (11.945-11.965)
Tappet Guide Bore Inside Diameter, in (mm) ............... 0.4724-0.4731 (12.000-12.018)
Tappet to Guide Bore Clearance, in (mm) ............... 0.0013-0.0028 (0.035-0.073)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.6277-0.6285 (15.945-15.965)
Rocker Arm Bushing Inside Diameter, in (mm) ............... 0.6299-0.6307 (16.000-16.020)
Rocker Arm Shaft to Bushing Clearance, in (mm) ............... 0.0013-0.0029 (0.035-0.075)

Tightening Torques

Cylinder Head Bolt (Step 1), lb-ft (Nm) ............... 36.1 (49.0)
Cylinder Head Bolt (Step 2), lb-ft (Nm) ............... 65.0 (88.2)
Cylinder Head Bolt (Step 3), lb-ft (Nm) ............... 79.5-85.1 (107.8-115.6)
Connecting Rod Cap Bolt, lb-ft (Nm) ............... 39.1-43.4 (53.0-58.8)
Main Bearing Cap Bolt, lb-ft (Nm) ............... 72.3-78.1 (98.0-105.9)
Flywheel Mounting Bolt, lb-ft (Nm) ............... 61.4-66.5 (83.3-90.2)
Flywheel Housing Bolt, lb-ft (Nm) ............... 39.1-43.4 (53.0-58.8)
Crankshaft Pulley Center Nut Bolt, lb-ft (Nm) ............... 83.1-90.3 (112.7-122.5)
Camshaft Thrust PlateBolt, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Camshaft Gear Center Driven Hub Bolt, lb-ft (Nm) ............... 57.8-65.0 (78.4-88.2)
Idle Gear Shaft Support Bracket Bolt , lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Fuel Injection Pump Drive Gear Nut , lb-ft (Nm) ............... 43.4-50.6 (58.8-68.6)
Fuel Injection Pump Nuts to Gear Case, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Fuel Injection Nozzle Holder Assembly Bolt, lb-ft (Nm) ............... 18.8-23.1 (25.5-31.4)
High-Pressure Fuel Injection Line Nut, lb-ft (Nm) ............... 21.6-25.3 (29.4-34.3)
Fuel Return Line Overflow Spill Bolt, lb-ft (Nm) ............... 14.4-18.0 (19.6-24.5)
Rocker Arm Shaft Support Bracket Bolt, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Valve Clearance Adjusting Nut Locknut, lb-ft (Nm) ............... 12.3-15.9 (16.7-21.6)
Rocker Cover Insulated Cap Nut, lb-ft (Nm) ............... 5.8-8.7 (7.8-11.8)
Oil Pan Drain Plug, lb-ft (Nm) ............... 36.1-43.4 (49.0-58.8)
Oil Pan Flange Peripheral Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Oil Pump Cover Assembly Fasteners, lb-ft (Nm) ............... 6.5-8.7 (8.8-11.8)
Water Pump Flange Mounting Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Cooling Thermostat Housing Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Intake Manifold Flange Base Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Exhaust Manifold Heat Shield Flange Bolts, lb-ft (Nm) ............... 18.8-24.5 (25.5-33.3)
Exhaust Pipe Connecting Flange Nut, lb-ft (Nm) ............... 28.9-36.1 (39.2-49.0)
Starter Motor Mounting Flange Bolts, lb-ft (Nm) ............... 57.8-65.0 (78.4-88.2)
Alternator Pivot Adjustment Mounting Bolt, lb-ft (Nm) ............... 28.9-36.1 (39.2-49.0)
Alternator Adjustment Link Lock Bolt, lb-ft (Nm) ............... 14.4-18.0 (19.6-24.5)
Oil Pressure Switch Sensor, lb-ft (Nm) ............... 10.8-14.4 (14.7-19.6)
Cooling Temperature Sensor, lb-ft (Nm) ............... 18.1-21.6 (24.5-29.4)
Glow Plug Main Element Body, lb-ft (Nm) ............... 10.8-14.4 (14.7-19.6)
Glow Plug Harness Small Nut, lb-ft (Nm) ............... 0.7-1.1 (1.0-1.5)
Gear Case Cover Attachment Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)
Rear Oil Seal Retainer Bolts, lb-ft (Nm) ............... 17.3-21.6 (23.5-29.4)

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