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Isuzu 4BD1T Engine

The Isuzu 4BD1T is a 3.9-liter, inline four-cylinder, four-stroke, overhead valve (OHV) turbocharged diesel engine. Renowned for its extreme durability and high torque output at low RPMs, this cast-iron block and cylinder head power plant is widely used in medium-duty trucks, construction equipment, material handling machinery, and marine conversions. It relies on a completely mechanical configuration, making it exceptionally reliable and highly sought after for severe-duty applications and aftermarket vehicle repowers.

The engine uses an overhead valve (OHV) valvetrain layout actuated via a solid-lifter gear-driven camshaft inside the engine block. It features a total of 8 valves (2 valves per cylinder: 1 intake and 1 exhaust). The intake manifold is a separate casting mounted on the right-hand side of the engine (from the driver's perspective), while the exhaust manifold is mounted on the left-hand side. Bore: 102 mm (4.0157 inches). Stroke: 118 mm (4.6457 inches). Total Displacement: 3856 cc (3.9 liters).

The 4BD1T operates on a direct-injection mechanical fuel system. High-pressure fuel delivery is provided by a Bosch/Zexel Type A inline injection pump mounted on the right-hand side of the engine. The injection pump assembly incorporates a mechanical governor for speed regulation and an automatic timing advance mechanism. Fuel is pressurized and delivered directly to the multi-hole mechanical fuel injectors located in each cylinder head opening. Cold starting is supported via internal glow plugs and an injection pump excess fuel delivery feature.

The lubrication system is a force-feed pressure system driven by a gear-type oil pump. Oil is drawn through a strainer in the oil pan and routed through a full-flow oil filter and a built-in water-cooled oil cooler. Pressurized oil channels deliver critical lubrication to the crankshaft main bearings, connecting rod journals, camshaft bearings, overhead rocker assembly, and the turbocharger assembly before draining back into the oil sump.

The engine utilizes a forced-circulation, liquid-cooling system. A centrifugal water pump driven by a V-belt circulates coolant through the cylinder block water jackets and the cylinder head passage ways. System temperature is mechanically regulated by a pellet-type wax thermostat that opens to route hot coolant through an external radiator to dissipate thermal loads under operation.

General Technical Data

Engine Specifications

Engine Model ............... Isuzu 4BD1T
Engine Type ............... 4-cycle inline 4-cylinder direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.02 (102.0)
Engine Stroke, in (mm) ............... 4.65 (118.0)
Displacement, cu.in (L) ............... 235.3 (3.856)
Rated Engine Power, hp (kW) ............... 120-135 (89-100)
Rated Engine Speed, rpm ............... 3000
Peak Torque ............... 314-330 Nm (231-243 lb-ft) at 1800-2200 rpm
Idle Speed ............... 650-750 rpm
Max No-Load Governed Speed, rpm ............... 3200-3400
Aspiration Type ............... Turbocharged
Turbocharger Models ............... IHI RHB6 / Garrett T25
Compression Ratio ............... 17.5:1
Firing Order ............... 1-3-4-2
Combustion Chamber ............... Direct injection
Cylinder Block Type ............... Cast iron with dry liners
Cylinder Head Type ............... Cast iron overhead valve
Valvetrain Configuration ............... OHV gear-driven camshaft with solid lifters
Number of Valves per Cylinder ............... 2
Total Number of Valves ............... 8
Lubrication System ............... Full-pressure circulation
Oil Pump Type ............... Gear-driven trochoid type
Oil Filter Type ............... Full-flow spin-on cartridge
Cooling System ............... Forced liquid circulation
Water Pump Type ............... Belt-driven centrifugal type
Air Cleaner Type ............... Dry element paper filter
Starting System ............... Electric starter motor
Electrical System ............... 12V or 24V
Alternator Capacity ............... 55A / 40A

Fuel System

Injection Pump Type ............... Mechanical inline Bosch A-type licensed Kiki
Governor Type ............... Mechanical centrifugal RSV variable speed or RLD
Fuel Feed Pump Type ............... Plunger piston type driven by pump camshaft
Fuel Injection Timing ............... 13-15 deg BTDC
Injection Nozzle Type ............... Multi-hole orifice nozzle
Number of Injection Nozzle Holes ............... 4 or 5
Nozzle Hole Diameter, in (mm) ............... 0.011 (0.28)
Primary Injection Pressure, psi (kPa) ............... 2557-2698 (17630-18600)
Secondary Injection Pressure, psi (kPa) ............... 2844-2987 (19610-20590)
Fuel Filter Type ............... Spin-on dual cartridge with water separator
Fuel Transfer Pump Pressure, psi (kPa) ............... 22-36 (150-250)
Maximum Fuel Return Flow, gal/hr (L/hr) ............... 10.5 (40.0)
Fuel Return Line Diameter, in (mm) ............... 0.236 (6.0)
Fuel Line Material ............... Double-wall seamless steel tubing
Injection Timing Control ............... Automatic mechanical timer
Fuel Supply Control ............... Mechanical rack linked to governor assembly
Cold Start Aid ............... Glow plugs in cylinder head inlet area or intake heater

Dimensions and Weight

Overall Length, in (mm) ............... 31.3 (795)
Overall Width, in (mm) ............... 27.8 (705)
Overall Height, in (mm) ............... 29.7 (755)
Dry Weight, lbs (kg) ............... 772 (350)
Wet Weight, lbs (kg) ............... 816 (370)

Maintenance Data

Service Information

Minimum Compression Pressure, psi (kPa) ............... 384 (2648) at 200 rpm
Standard Compression Pressure, psi (kPa) ............... 441 (3040) at 200 rpm
Compression Variance Between Cylinders, psi (kPa) ............... 28.4 (196)
Oil Pressure at Idle Speed, psi (kPa) ............... 14.2-28.4 (98-196)
Oil Pressure at Rated Speed, psi (kPa) ............... 42.6-64.0 (294-441)
Oil Pressure Relief Valve Setting, psi (kPa) ............... 99.5 (686)
Oil Gallery Regulating Valve Setting, psi (kPa) ............... 64.0 (441)
Thermostat Opening Temperature, F (C) ............... 180 (82)
Thermostat Full Open Temperature, F (C) ............... 203 (95)
Coolant System Operating Pressure, psi (kPa) ............... 12.8 (88)
Radiator Cap Pressure Rating, psi (kPa) ............... 13.0 (90)
V-Belt Deflection under 22 lbs force, in (mm) ............... 0.31-0.47 (8.0-12.0)
Intake Valve Clearance, Cold, in (mm) ............... 0.0157 (0.40)
Exhaust Valve Clearance, Cold, in (mm) ............... 0.0157 (0.40)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, or SAE 15W-40
API Service Classifications ......................... CF-4 or CH-4
Engine Oil Capacity with Filter, qt (L) ............... 8.97 (8.5)
Engine Oil Capacity without Filter, qt (L) ............... 7.92 (7.5)
Cooling System Fluid Capacity, qt (L) ............... 14.8 (14.0)

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 1500 hours
Change coolant ............... Every 2000 hours
Compression test ............... Every 1000 hours
Belt inspection ............... Every service cycle

Service Specifications

Cylinder Liner Inside Diameter, Std, in (mm) ............... 4.0165-4.0181 (102.020-102.060)
Cylinder Liner Inside Diameter, Limit, in (mm) ............... 4.0236 (102.200)
Cylinder Liner Out-of-Roundness, Limit, in (mm) ............... 0.0008 (0.020)
Cylinder Liner Taper, Limit, in (mm) ............... 0.0008 (0.020)
Cylinder Block Upper Deck Warpage Limit, in (mm) ............... 0.0079 (0.200)
Cylinder Head Lower Deck Warpage Limit, in (mm) ............... 0.0079 (0.200)
Cylinder Head Height Standard, in (mm) ............... 3.5275-3.5354 (89.600-89.800)
Crankshaft Main Journal Diameter, in (mm) ............... 3.1457-3.1465 (79.900-80.020)
Crankpin Journal Diameter, in (mm) ............... 2.5551-2.5559 (64.900-65.020)
Crankshaft Out-of-Roundness, Limit, in (mm) ............... 0.0004 (0.010)
Crankshaft Main Bearing Clearance, in (mm) ............... 0.0015-0.0033 (0.039-0.085)
Crankshaft End Play, in (mm) ............... 0.0024-0.0094 (0.060-0.240)
Connecting Rod Center-to-Center Length, in (mm) ............... 7.4803 (190.000)
Connecting Rod Bearing Clearance, in (mm) ............... 0.0014-0.0030 (0.035-0.077)
Connecting Rod Big End Inside Diameter, in (mm) ............... 2.7165-2.7171 (69.000-69.015)
Piston Outer Diameter, in (mm) ............... 4.0125-4.0141 (101.919-101.959)
Piston to Cylinder Liner Clearance, in (mm) ............... 0.0039-0.0055 (0.101-0.141)
Piston Pin Bore Diameter, in (mm) ............... 1.3780-1.3783 (35.002-35.010)
Piston Pin Outer Diameter, in (mm) ............... 1.3776-1.3780 (34.991-35.000)
Piston Pin to Piston Pin Bore Clearance, in (mm) ............... 0.0001-0.0007 (0.002-0.019)
Piston Pin to Small End Bushing Clearance, in (mm) ............... 0.0005-0.0013 (0.012-0.034)
Top Ring Groove Width, in (mm) ............... 0.0965-0.0976 (2.450-2.480)
Second Ring Groove Width, in (mm) ............... 0.0811-0.0819 (2.060-2.080)
Oil Ring Groove Width, in (mm) ............... 0.1779-0.1787 (4.518-4.538)
Top Ring Side Clearance, in (mm) ............... 0.0035-0.0049 (0.090-0.125)
Second Ring Side Clearance, in (mm) ............... 0.0020-0.0033 (0.050-0.085)
Oil Ring Side Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)
Top Ring End Gap, in (mm) ............... 0.0118-0.0177 (0.300-0.450)
Second Ring End Gap, in (mm) ............... 0.0118-0.0177 (0.300-0.450)
Oil Ring End Gap, in (mm) ............... 0.0098-0.0177 (0.250-0.450)
Intake Valve Stem Diameter, in (mm) ............... 0.3520-0.3528 (8.940-8.960)
Exhaust Valve Stem Diameter, in (mm) ............... 0.3512-0.3520 (8.920-8.940)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0016-0.0031 (0.040-0.080)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0024-0.0039 (0.060-0.100)
Intake Valve Thickness, in (mm) ............... 0.0669 (1.700)
Exhaust Valve Thickness, in (mm) ............... 0.0669 (1.700)
Intake Valve Seat Contact Width, in (mm) ............... 0.0551-0.0709 (1.400-1.800)
Exhaust Valve Seat Contact Width, in (mm) ............... 0.0669-0.0827 (1.700-2.100)
Valve Guide Inside Diameter, in (mm) ............... 0.3543-0.3551 (9.000-9.020)
Valve Spring Free Length, in (mm) ............... 2.1102 (53.600)
Camshaft Journal Diameter, in (mm) ............... 1.9661-1.9673 (49.940-49.970)
Camshaft Runout, Limit, in (mm) ............... 0.0008 (0.020)
Cam Lobe Height (Intake), in (mm) ............... 1.6575 (42.100)
Cam Lobe Height (Exhaust), in (mm) ............... 1.6575 (42.100)
Camshaft Main Bearing Clearance, in (mm) ............... 0.0012-0.0035 (0.030-0.090)
Camshaft End Play, in (mm) ............... 0.0020-0.0059 (0.050-0.150)
Rocker Arm Shaft Outer Diameter, in (mm) ............... 0.8642-0.8650 (21.950-21.970)
Rocker Arm Inside Diameter, in (mm) ............... 0.8661-0.8673 (22.000-22.030)
Rocker Arm to Shaft Clearance, in (mm) ............... 0.0004-0.0031 (0.010-0.080)
Timing Gear Backlash, in (mm) ............... 0.0039-0.0067 (0.100-0.170)
Tappet Outer Diameter, in (mm) ............... 0.5098-0.5106 (12.950-12.970)
Tappet-to-Block Guide Clearance, in (mm) ............... 0.0012-0.0028 (0.030-0.070)

Tightening Torques

Cylinder Head Bolt (1-Stage), lb-ft (Nm) ............... 50.0 (68.0)
Cylinder Head Bolt (2-Stage), lb-ft (Nm) ............... 65.0 (88.0)
Main Bearing Cap Bolt, lb-ft (Nm) ............... 174.0 (235.0)
Connecting Rod Bearing Cap Nut, lb-ft (Nm) ............... 29.0 (39.0)
Flywheel Mounting Bolt, lb-ft (Nm) ............... 29.0 (39.0)
Crankshaft Balancer Center Bolt, lb-ft (Nm) ............... 318.0 (431.0)
Camshaft Thrust Plate Bolt, lb-ft (Nm) ............... 13.0 (18.0)
Camshaft Timing Gear Bolt, lb-ft (Nm) ............... 72.0 (98.0)
Idler Gear A Shaft Bolt, lb-ft (Nm) ............... 22.0 (30.0)
Idler Gear B Shaft Bolt, lb-ft (Nm) ............... 72.0 (98.0)
Timing Gear Case Cover Bolt, lb-ft (Nm) ............... 13.0 (18.0)
Rocker Arm Shaft Bracket Bolt, lb-ft (Nm) ............... 20.0 (27.0)
Valve Cover Nut , lb-ft (Nm) ............... 9.5 (13.0)
Oil Pan Drain Plug, lb-ft (Nm) ............... 61.0 (83.0)
Oil Pan Mounting Bolt, lb-ft (Nm) ............... 13.0 (18.0)
Oil Pump Assembly Mounting Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Oil Pump Cover Screw, lb-ft (Nm) ............... 7.0 (9.5)
Oil Pressure Regulating Valve Plug, lb-ft (Nm) ............... 29.0 (39.0)
Fuel Injection Pump Drive Gear Nut, lb-ft (Nm) ............... 43.0 (59.0)
Fuel Injection Pump Mounting Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Fuel Injection Nozzle Holder Assembly Nut, lb-ft (Nm) ............... 43.0 (59.0)
Fuel Injection Nozzle Gland Nut, lb-ft (Nm) ............... 29.0 (39.0)
Fuel High-Pressure Line Union Nut, lb-ft (Nm) ............... 22.0 (30.0)
Fuel Leak-Off Pipe Nut, lb-ft (Nm) ............... 20.0 (27.0)
Intake Manifold Mounting Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Exhaust Manifold Mounting Nut, lb-ft (Nm) ............... 20.0 (27.0)
Turbocharger to Exhaust Manifold Nut, lb-ft (Nm) ............... 20.0 (27.0)
Turbocharger Compressor Housing Bolt, lb-ft (Nm) ............... 15.0 (20.0)
Turbocharger Turbine Housing Bolt, lb-ft (Nm) ............... 18.0 (24.0)
Water Pump Assembly Mounting Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Water Pump Pulley Nut, lb-ft (Nm) ............... 51.0 (69.0)
Thermostat Housing Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Cooling Fan Blade Mounting Bolt, lb-ft (Nm) ............... 7.5 (10.0)
Starter Motor Mounting Bolt, lb-ft (Nm) ............... 61.0 (83.0)
Alternator Mounting Pivot Bolt, lb-ft (Nm) ............... 30.0 (41.0)
Alternator Adjusting Lock Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Glow Plug, lb-ft (Nm) ............... 18.0 (24.0)
Glow Plug Terminal Nut, lb-ft (Nm) ............... 1.5 (2.0)
Oil Pressure Switch Sensor, lb-ft (Nm) ............... 11.0 (15.0)
Water Temperature Sensor, lb-ft (Nm) ............... 22.0 (30.0)
Engine Rear Oil Seal Retainer Bolt, lb-ft (Nm) ............... 13.0 (18.0)
Flywheel Housing Big Mounting Bolt, lb-ft (Nm) ............... 61.0 (83.0)
Flywheel Housing Small Mounting Bolt, lb-ft (Nm) ............... 14.0 (19.0)
Exhaust Pipe Adapter Nut, lb-ft (Nm) ............... 27.0 (37.0)
Oil Cooler Assembly Bypass Valve Plug, lb-ft (Nm) ............... 22.0 (30.0)

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• Isuzu Engines Specs
  
• Isuzu 4BA1 Specs
  
• Isuzu 4BB1 Specs
  
• Isuzu 4BC1 Specs
  
• Isuzu 4BC2 Specs
  
• Isuzu 4BD1 Specs
  

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