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Isuzu 3LB1 Engine

The Isuzu 3LB1 is a compact, 3-cylinder, 4-cycle, water-cooled industrial diesel engine utilizing a vertical in-line layout. Known for its quiet design and low exhaust emissions, this engine features an indirect injection system combined with a high compression ratio of 22:1. It incorporates a GQOS-III glow plug system for optimized fast starting in cold weather environments. The engine is widely deployed in compact machinery, such as mini-excavators, generator sets, and small agricultural or construction power units.

The cylinder head layout uses an Overhead Valve (OHV) pushrod configuration with 2 valves per cylinder (a total of 6 valves across the engine block) driven via a conventional rocker assembly and camshaft arrangement. Bore diameter: 77.4 mm (3.05 inches). Stroke length: 79.7 mm (3.14 inches). Total Displacement: 1.124 liters (68.6 cubic inches).

The fuel architecture relies on an Indirect Injection (IDI) design utilizing swirl combustion chambers. High-pressure fuel delivery is provided by an in-line, multi-plunger Bosch-type or similar injection pump geared to the main timing train. The system features an integrated mechanical governor for engine speed regulation, low-emission multi-hole nozzles, an inline fuel filter, and a standard fuel return line back to the tank reservoir.

The engine uses a forced lubrication layout pressurized by a trochoid type oil pump driven directly by the crank gear. The specification mandates high-quality diesel engine oil rated API service classification CC or CD. Filtration is handled by a spin-on cartridge oil filter mounted on the side of the engine block. Thermal regulation uses a pressurized water circulation system driven by a centrifugal vane-type water pump, which is powered via a conventional V-belt linked to the crank pulley. Airflow across the radiator is maintained by a belt-driven 15-inch cooling fan.

General Technical Data

Engine Specifications

Engine Model ............... Isuzu 3LB1
Engine Type ............... 4-cycle inline 3-cylinder indirect injection liquid-cooled diesel
Number of Cylinders ............... 3
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 3.05 (77.4)
Engine Stroke, in (mm) ............... 3.14 (79.7)
Displacement, cu.in (L) ............... 68.6 (1.124)
Rated Engine Power, hp (kW) ............... 25.4 (19.0)
Continuous Engine Power, hp (kW) ............... 22.4 (16.7)
Rated Engine Speed, rpm ............... 1800-3000
Peak Torque ............... 51.9 lb-ft (70.4 Nm) at 1800 rpm
Continuous Torque ............... 45.7 lb-ft (62.0 Nm) at 1800 rpm
Idle Speed ............... 800-900 rpm
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 22.0:1
Firing Order ............... 1-3-2
Cylinder Block Type ............... Cast iron
Cylinder Head Type ............... Cast iron OHV
Rotation Direction ............... Counterclockwise viewed from flywheel side
Combustion Chamber Type ............... Swirl chamber, indirect injection
Valves per Cylinder ............... 2
Lubrication System ............... Full-pressure fed
Oil Pump Type ............... Trochoid type gear-driven
Oil Filter Type ............... Full-flow spin-on cartridge
Cooling System ............... Liquid-cooled pressurized forced circulation
Water Pump Type ............... Belt-driven centrifugal vane type
Air Cleaner Type ............... Dry element dual-stage
Starting System ............... Electric starter motor
Electrical System ............... 12V DC
Alternator Capacity, A ............... 20

Fuel System

Injection Pump Type ............... Bosch PFR inline mini pump individual units plunger actuated
Injection Nozzle Type ............... Throttle type multi-hole or pintle design
Fuel Injection Pressure, psi (MPa) ............... 1991-2133 (13.7-14.7)
Fuel Transfer Pump Type ............... Mechanical diaphragm plunger type
Fuel Filter Type ............... Cartridge element spin-on with water sedimenter separator
Fuel Injection Timing ............... 15 deg BTDC
Fuel Feed Control ............... Mechanical rack linked directly to internal centrifugal governor
Maximum Fuel Return Flow, qt/min (L/min) ............... 0.42 (0.40)
Governor Type ............... Mechanical centrifugal variable speed

Dimensions and Weight

Overall Length, in (mm) ............... 26.7 (675)
Overall Width, in (mm) ............... 22.4 (570)
Overall Height, in (mm) ............... 36.6 (930)
Dry Engine Weight, lbs (kg) ............... 372 (170)

Maintenance Data

Service Information

Compression Pressure, Standard, psi (MPa) ............... 441.0 (3.04)
Compression Pressure, Minimum Limit, psi (MPa) ............... 370.0 (2.55)
Compression Variance Across Cylinders, psi (MPa) ............... 28.4 (0.20)
Oil Pressure, Standard Operating, psi (kPa) ............... 43.0-64.0 (296.5-441.3)
Oil Pressure, Low Idle Limit, psi (kPa) ............... 14.2 (98.0)
Thermostat Opening Temperature, F (C) ............... 170.0 (76.5)
Thermostat Full Open Temperature, F (C) ............... 194.0 (90.0)
Intake Valve Clearance (Cold), in (mm) ............... 0.008 (0.20)
Exhaust Valve Clearance (Cold), in (mm) ............... 0.008 (0.20)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30 or SAE 15W-40
API Service Classifications ......................... CC, CD, or CE
Engine Oil Capacity with Filter, qt (L) ............... 4.75 (4.50)
Engine Oil Capacity without Filter, qt (L) ............... 4.23 (4.00)
Engine Coolant Capacity, qt (L) ............... 2.32 (2.20)

Service Intervals

Change oil and filter ............... Every 250 hours
Inspect air cleaner ............... Every 100 hours
Replace air cleaner ............... Every 500 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
Belt inspection ............... Every service cycle

Service Specifications

Cylinder Bore Standard Diameter, in (mm) ............... 3.0472-3.0484 (77.400-77.430)
Cylinder Bore Maximum Out of Round, in (mm) ............... 0.0078 (0.200)
Piston Outside Diameter, in (mm) ............... 3.0449-3.0460 (77.340-77.370)
Piston to Cylinder Bore Clearance, in (mm) ............... 0.0019-0.0024 (0.050-0.060)
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 Control Ring Groove Side Clearance, in (mm) ............... 0.0008-0.0024 (0.020-0.060)
Top Piston Ring End Gap, in (mm) ............... 0.0079-0.0138 (0.200-0.350)
Second Piston Ring End Gap, in (mm) ............... 0.0079-0.0138 (0.200-0.350)
Oil Ring End Gap, in (mm) ............... 0.0079-0.0157 (0.200-0.400)
Piston Pin Outside Diameter, in (mm) ............... 0.8659-0.8663 (21.995-22.005)
Piston Pin Bore Inside Diameter, in (mm) ............... 0.8665-0.8669 (22.010-22.020)
Piston Pin to Piston Boss Clearance, in (mm) ............... 0.0002-0.0010 (0.005-0.025)
Connecting Rod Small End Bushing Clearance, in (mm) ............... 0.0010-0.0022 (0.025-0.055)
Main Crankshaft Journal Diameter, in (mm) ............... 2.0437-2.0449 (51.911-51.942)
Main Bearing Oil Clearance, in (mm) ............... 0.0013-0.0028 (0.034-0.071)
Connecting Rod Bearing Oil Clearance, in (mm) ............... 0.0013-0.0028 (0.034-0.071)
Crankshaft End Play, in (mm) ............... 0.0024-0.0055 (0.060-0.140)
Cylinder Head Deck Face Flatness Limit, in (mm) ............... 0.002 (0.05)
Intake Valve Head Diameter, in (mm) ............... 1.22 (31.0)
Exhaust Valve Head Diameter, in (mm) ............... 1.06 (27.0)
Valve Guide Inside Diameter, in (mm) ............... 0.2756-0.2762 (7.000-7.015)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.2726-0.2732 (6.925-6.940)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.2717-0.2724 (6.900-6.920)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0016-0.0028 (0.040-0.070)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0024-0.0037 (0.060-0.095)
Valve Spring Free Length, in (mm) ............... 1.5315 (38.900)
Camshaft Journal Outside Diameter (Front), in (mm) ............... 1.5717-1.5728 (39.920-39.950)
Camshaft Journal Outside Diameter (Middle), in (mm) ............... 1.5323-1.5335 (39.920-39.950)
Camshaft Journal Outside Diameter (Rear), in (mm) ............... 1.4929-1.4941 (37.920-37.950)
Camshaft Journal Bearing Oil Clearance, in (mm) ............... 0.0020-0.0035 (0.050-0.090)
Cam Lobe Height, in (mm) ............... 1.2587-1.2602 (31.970-32.010)
Rocker Arm Shaft Outside Diameter, in (mm) ............... 0.5894-0.5902 (14.970-14.990)
Rocker Arm Bushing Inside Bore Hole Diameter, in (mm) ............... 0.5906-0.5917 (15.000-15.030)
Rocker Arm to Shaft Clearance, in (mm) ............... 0.0004-0.0024 (0.010-0.060)
Cylinder Block Tappet Guide Bore Hole, in (mm) ............... 0.8268-0.8276 (21.000-21.020)
Pushrod Runout Radial Bow Distortion, in (mm) ............... 0.0118 (0.300)
Idler Gear Shaft Journal Main Outside Diameter, in (mm) ............... 1.3768-1.3776 (34.970-34.990)
Idler Gear Bushing Internal Bore Diameter, in (mm) ............... 1.3780-1.3795 (35.000-35.040)
Idler Gear to Shaft Oil Clearance, in (mm) ............... 0.0004-0.0028 (0.010-0.070)

Tightening Torques

Cylinder Head Bolts (1-Stage), lb-ft (Nm) ............... 21.7 (29.4)
Cylinder Head Bolts (2-Stage), lb-ft (Nm) ............... 43.4 (58.8)
Cylinder Head Bolts (3-Stage), lb-ft (Nm) ............... 57.9-65.1 (78.5-88.3)
Connecting Rod Cap Nuts, lb-ft (Nm) ............... 21.7-25.3 (29.4-34.3)
Crankcase Main Bearing Cap Bolts, lb-ft (Nm) ............... 39.8-47.0 (54.0-63.7)
Flywheel Mounting Bolts, lb-ft (Nm) ............... 57.9-65.1 (78.5-88.3)
Crankshaft Center Pulley Bolt, lb-ft (Nm) ............... 65.1-72.3 (88.3-98.1)
Camshaft Thrust Plate Screw Bolts, lb-ft (Nm) ............... 13.7-21.0 (18.6-28.4)
Rocker Arm Shaft Bracket Holding Nuts, lb-ft (Nm) ............... 15.2-21.7 (20.6-29.4)
Cylinder Head Valve Cover Acorn Cap Nuts, lb-ft (Nm) ............... 5.8-8.7 (7.8-11.8)
Timing Gear Case Front Mounting Bolts, lb-ft (Nm) ............... 13.7-21.0 (18.6-28.4)
Oil Pan Sump Drain Plug Screw, lb-ft (Nm) ............... 36.2-43.4 (49.0-58.8)
Oil Pan Perimeter Flange Bolts, lb-ft (Nm) ............... 5.8-8.7 (7.8-11.8)
Flywheel Housing Outer Rim Case Bolts, lb-ft (Nm) ............... 28.9-36.2 (39.2-49.0)
Injection Pump Delivery Valve Holders, lb-ft (Nm) ............... 25.3-28.9 (34.3-39.2)
Injection Pump High Pressure Fuel Line Nuts, lb-ft (Nm) ............... 18.1-21.7 (24.5-29.4)
Fuel Injection Nozzle Assembly Holding Nut, lb-ft (Nm) ............... 28.9-36.2 (39.2-49.0)
Fuel Injector Retaining Bracket Clamp Bolt, lb-ft (Nm) ............... 13.7-21.0 (18.6-28.4)
Glow Plug Hex Body, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)
Oil Pressure Sensor Switch, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)
Coolant Temperature Sensor Switch, lb-ft (Nm) ............... 14.5-21.7 (19.6-29.4)
Alternator Pivoting Mounting Frame Bolt, lb-ft (Nm) ............... 25.3-36.2 (34.3-49.0)
Starter Motor Holding Gear Housing Bolts, lb-ft (Nm) ............... 36.2-47.0 (49.0-63.7)
Exhaust Manifold Heat Shield Stud Nuts, lb-ft (Nm) ............... 15.2-21.7 (20.6-29.4)
Intake Manifold Plenum Air Intake Induction Bolts, lb-ft (Nm) ............... 13.7-21.0 (18.6-28.4)
Water Pump Assembly Body Housing Bolts, lb-ft (Nm) ............... 13.7-21.0 (18.6-28.4)
Cooling Fan Blade Hub Attachment Lock Screws, lb-ft (Nm) ............... 5.8-8.7 (7.8-11.8)
Oil Pump Cover Plate Retaining Cross Screws, lb-ft (Nm) ............... 4.3-5.8 (5.9-7.8)
Oil Pressure Relief Valve Spring Cap Plug, lb-ft (Nm) ............... 21.7-28.9 (29.4-39.2)
Fuel Transfer Diaphragm Pump Holding Stud Nuts, lb-ft (Nm) ............... 10.8-14.5 (14.7-19.6)
Injection Pump Automatic Timer Gear Drive Lock Nut, lb-ft (Nm) ............... 36.2-43.4 (49.0-58.8)
Governor Housing Cover Plate Rear Screws, lb-ft (Nm) ............... 4.3-5.8 (5.9-7.8)

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• Isuzu Engines Specs
  
• Isuzu 3KC1 Specs
  
• Isuzu 3KC2 Specs
  
• Isuzu 3KR1 Specs
  
• Isuzu 3KR2 Specs
  
• Isuzu 3LD1 Specs
  
• Isuzu 3LD2 Specs
  

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