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Cummins ISB 4.5 Engine

The Cummins ISB4.5 is an inline four-cylinder, four-stroke, medium-duty diesel engine widely used in on-highway commercial vehicles, transit buses, and demanding industrial applications. Representing an evolutionary advancement in the B-series engine family, this unit features a cast-iron cylinder block and head engineered to handle the thermal and mechanical loads of high-pressure combustion. It integrates a rear gear train drive to reduce structural vibration and operational noise. Operating under full electronic management via an Engine Control Module (ECM), the ISB 4.5 shifts away from mechanical subsystems to prioritize precision fuel delivery, reduced emissions footprint, and continuous diagnostic monitoring.

The valvetrain uses an Overhead Valve (OHV) architectural design with a single camshaft located in the cylinder block. The engine features a 4 valves per cylinder cross-flow head configuration, totaling 16 valves (8 intake, 8 exhaust) to maximize gas exchange efficiency. The valves are actuated via solid pushrods, bridge guides, and overhead rocker assemblies. Valves must be measured and set cold during standard service intervals according to factory tolerances.

Fuel delivery is handled exclusively via a Bosch High-Pressure Common Rail (HPCR) injection system. Low-pressure fuel is drawn through a primary filter and water separator unit by an electronic lift pump before reaching the high-pressure injection pump. The pump creates structural pressures within a shared fuel rail. Centrally positioned, vertical electronic injectors utilize multi-hole nozzles to atomize fuel directly into the center of the piston bowls. The timing, duration, and multi-pulse injection cycles are entirely regulated by the ECM based on real-time sensor feedback.

The lubrication circuit utilizes a highly efficient gerotor-design oil pump driven directly by the crankshaft rather than traditional camshaft gear engagement, optimizing oil flow velocity during low-temperature cold starts. Pressurized oil flows through an integrated cooling module housing a liquid-to-liquid plate element heat exchanger before traveling through a spin-on full-flow filtration unit equipped with a built-in bypass valve. Thermal regulation is structured as a closed-loop liquid-cooled system governed by an integrated cooling module that consolidates the water pump, oil filter housing, and oil cooler into a single assembly to improve pressure distribution. The centrifugal water pump is belt-driven from the front accessory drive.

General Technical Data

Engine Specifications

Engine Model ............... Cummins ISB4.5
Engine Type ............... 4-cycle inline 4-cylinder common rail direct injection liquid-cooled diesel
Number of Cylinders ............... 4
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.21 (107.0)
Engine Stroke, in (mm) ............... 4.88 (124.0)
Displacement, cu.in (L) ............... 275 (4.5)
Rated Engine Power, hp (kW) ............... 100-175 (74-130)
Rated Engine Speed, rpm ............... 2200-2500
Peak Torque ............... 450-600 Nm (332-443 lb-ft) at 1500-1600 rpm
Idle Speed ............... 750-800 rpm
Aspiration Type ............... Turbocharged
Compression Ratio ............... 16.5:1-17.5:1
Firing Order ............... 1-3-4-2
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 Rating, Amps ............... 60-120

Fuel System

Fuel System ............... Common rail direct injection
Fuel System Control ............... Electronic
Governor Type ............... Electronic
Injection Pressure ............... 1700 bar
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 35.3-39.4 (900-1000)
Overall Width, in (mm) ............... 27.6-33.5 (700-850)
Overall Height, in (mm) ............... 35.4-43.4 (900-1100)
Dry Weight, lbs (kg) ............... 950-1100 (430-500)

Maintenance Data

Service Information

Thermostat begins opening ............... 82C (180F)
Thermostat fully open ............... 95C (203F)
Cooling system pressure ............... 90-110 kPa (13-16 psi)
Operating oil pressure ............... 300-500 kPa (44-72 psi)
Idle oil pressure ............... 100-150 kPa (15-22 psi)
Intake Valve Clearance, in (mm) ............... 0.254 (0.010)
Exhaust Valve Clearance, in (mm) ............... 0.508 (0.020)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, 15W-40
API Service Classifications ......................... CI-4, CJ-4, CK-4
Engine Oil Capacity, qts (L) .................. 11.6-13.6 (11.0-13.0)
Coolant Capacity, qts (L) ............... 12.6-14.7 (12.0-14.0)

Service Intervals

Change oil and filter ............... Every 250 hours
Replace fuel filters ............... Every 300 hours
Inspect air filter ............... Every 100 hours
Replace air filter ............... Every 300 hours
Change coolant ............... Every 2000 hours
Valve-lash adjustment ............... Every 1000 hours
Injector inspection ............... Every 1500-2000 hours
Compression test ............... Every 2500 hours
Drain water separator ............... As required
Belt inspection ............... As required

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 4.2126-4.2138 (107.000-107.030)
Crankshaft Journal Outside Diameter, in (mm) ............... 3.2662-3.2682 (82.962-83.013)
Crank Pin Outside Diameter, in (mm) ............... 2.7150-2.7170 (68.962-69.013)
Crankshaft End Play, in (mm) ............... 0.0040-0.0170 (0.102-0.432)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.2740-0.2748 (6.960-6.980)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.2740-0.2748 (6.960-6.980)
Intake Valve Guide Inside Diameter, in (mm) ............... 0.2760-0.2776 (7.010-7.050)
Exhaust Valve Guide Inside Diameter, in (mm) ............... 0.2760-0.2776 (7.010-7.050)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0012-0.0035 (0.030-0.090)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0012-0.0035 (0.030-0.090)
Intake Valve Spring Free Length, in (mm) ............... 1.880 (47.75)
Exhaust Valve Spring Free Length, in (mm) ............... 1.880 (47.75)
Intake Cam Height, in (mm) ............... 1.7879-1.8115 (45.413-46.013)
Exhaust Cam Height, in (mm) ............... 1.8300-1.8535 (46.480-47.080)
Piston Pin Outside Diameter, in (mm) ............... 1.5746-1.5750 (39.994-40.006)
Piston Pin to Piston Bore Clearance, in (mm) ............... 0.0002-0.0009 (0.006-0.022)
Second Ring Side Clearance, in (mm) ............... 0.0016-0.0033 (0.040-0.085)
Oil Ring Side Clearance, in (mm) ............... 0.0012-0.0030 (0.030-0.075)
Top Ring End Gap, in (mm) ............... 0.0098-0.0157 (0.250-0.400)
Second Ring End Gap, in (mm) ............... 0.0157-0.0256 (0.400-0.650)
Oil Ring End Gap, in (mm) ............... 0.0098-0.0217 (0.250-0.550)

Tightening Torque Specs

Cylinder head bolts ............... 180-210 Nm (133-155 lb-ft)
Main bearing caps ............... 150-180 Nm (111-133 lb-ft)
Connecting rod bolts ............... 70-90 Nm (52-66 lb-ft)
Flywheel bolts ............... 220-260 Nm (162-192 lb-ft)
Crankshaft pulley bolt ............... 240-280 Nm (177-207 lb-ft)
Oil drain plug ............... 30-40 Nm (22-30 lb-ft)
Injector hold-down bolts ............... 20-25 Nm (15-18 lb-ft)

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• Cummins Engines Specs
  
• Cummins ISB 3.9 Specs
  
• Cummins ISB 5.9 Specs
  
• Cummins ISB 6.7 Specs
  

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