Cummins 4BT3.9-G2 Specifications
| Engine Model: Cummins 4BT3.9-G2 |
| Engine Type: 4-cycle inline 4-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 239 cu.in (3.9 L) |
| Rated Engine Power: 53-67 Hp (40-50 kW) at 1500 rpm |
| Aspiration Type: Turbocharged |
____________________________________________________________________________________
The Cummins 4BT3.9-G2 is a compact, durable,
and fuel-efficient industrial diesel engine that belongs to Cummins’
renowned B-Series family. Known globally for its rugged mechanical
simplicity, long service life, and exceptional reliability, the
4BT3.9-G2 is widely used in generator sets, agricultural machinery,
construction equipment, transport refrigeration units, pumps, and
various mobile industrial applications. As a mechanically governed,
inline 4-cylinder engine, it is especially valued for its minimal
electronic reliance, easy maintenance, and strong low-end torque.
The G2 configuration is designed primarily for generator-drive duty,
offering stable power output, excellent fuel economy, and extended
service intervals. Its cast-iron block, gear-driven components, and
robust fuel system make it ideal for harsh environments where
continuous-duty operation and predictable performance are essential.
The Cummins 4BT3.9-G2 is a four-stroke, water-cooled, inline
four-cylinder diesel engine with a displacement of 3.9 liters (239 cubic
inches). Bore measures 102 mm (4.02 in), while stroke is 120 mm (4.72
in), giving the engine a long-stroke configuration optimized for high
torque output and fuel efficiency.
Compression ratio: approximately 17.5:1
Idle speed: 750–850 rpm
Firing order: 1-3-4-2
Peak torque: 200–260 Nm (148–192 lb-ft) at 1,400–1,600 rpm.
Power ratings for G2 generator
configuration:
– Prime: 35–45 kW (47–60 hp) at 1,500 rpm
– Standby: 40–50 kW (53–67 hp) at 1,500 rpm
– 60 Hz versions: 50–65 kW (67–87 hp) at 1,800 rpm
Governed speed:
– 1,500 rpm (50 Hz)
– 1,800 rpm (60 Hz)
The crankshaft is forged steel supported by five main bearings. Pistons
are cast aluminum alloy with reinforced crowns and cooling galleries.
Connecting rods are forged steel with replaceable bearings. The camshaft
is gear-driven for long-term timing accuracy and minimal maintenance.
The engine block is made of high-strength cast iron and utilizes
parent-bore cylinders.
Features include:
– Deep-skirt casting
– Reinforced stiffening ribs
– Wide bearing saddles for stability
– Full coolant circulation around cylinders
The block supports multiple overhauls when kept within machining
tolerances.
The cast-iron cylinder head incorporates:
– Two valves per cylinder
– Direct-injection combustion chambers
– Hardened valve seats and guides
– Mechanical rocker-arm valvetrain
Cold valve lash settings:
– Intake: 0.254 mm (0.010 in)
– Exhaust: 0.508 mm (0.020 in).
The 4BT3.9-G2 features a fully mechanical direct-injection fuel system
designed for durability and resistance to poor fuel quality.
Components include:
– Mechanical lift pump
– Inline mechanical injection pump (Bosch type)
– Multi-hole mechanical injectors
– Primary water separator
– Secondary fine fuel filter
Standard injection pressures: 250–350 bar.
Fuel-system service:
– Fuel filters every 250–300 hr
– Drain water separator daily
– Injector inspection every 1,000–1,500 hr
– Injection timing check during overhauls.
Lubrication is full-pressure wet-sump with a gear-driven pump.
Oil capacity: 9–12 liters (9.5–12.7 qt)
Oil pressure:
– Operating: 275–380 kPa (40–55 psi)
– Idle: 70–100 kPa (10–15 psi)
Recommended oil: SAE 15W-40 diesel oil meeting API CI-4/CJ-4/CK-4
Oil change interval: 250 hours (generator duty).
Cooling is provided by:
– Belt-driven centrifugal water pump
– Thermostat-regulated coolant circulation
– Radiator or remote cooling configurations
Thermostat settings:
– Opening: 82°C (180°F)
– Full open: 95°C (203°F)
Cooling-system capacity: 12–16 liters (12.7–17 qt)
System pressure: 70–100 kPa (10–15 psi).
| Intake and Exhaust Systems |
Intake:
– Dry-type air filters
– Optional dual-stage filtration
– Optional pre-cleaners
Turbocharging:
While some 4BT models are turbocharged, the 4BT3.9-G2 in many generator
configurations is naturally aspirated. Turbocharged variants may exist
in specific OEM packages.
Exhaust manifold:
– High-strength cast iron
– Generator-style elbows available.
| Electrical and Starting Systems |
Standard systems include:
– 12V or 24V starting system
– Alternator: 35–70 amps
– Oil pressure and coolant temperature sensors
– Tachometer pickup
There is no ECM; the engine is entirely mechanical.
Depending on the installation:
– Radiator or remote cooling packages
– Generator head adapters
– Hydraulic pump drives
– PTO pulley drives
– Belt-driven auxiliaries.
Approximate physical dimensions:
– Length: 900–1,000 mm (35–39 in)
– Width: 700–800 mm (28–31 in)
– Height: 900–1,000 mm (35–39 in)
Dry weight: 340–380 kg (750–840 lb).
– Oil and filter: 250 hr
– Fuel filters: 250–300 hr
– Air filter: inspect every 50–100 hr
– Valve-lash: every 1,000 hr
– Injector service: every 1,000–1,500 hr
– Coolant replacement: every 2 years
– Compression test: every 2,000 hr
– Belt inspection: each service interval.
– Cylinder-head bolts: 135–150 Nm (100–111 lb-ft) + angle torque
– Main-bearing caps: 175–190 Nm (129–140 lb-ft)
– Connecting-rod bolts: 65–75 Nm (48–55 lb-ft)
– Flywheel bolts: 100–120 Nm (74–89 lb-ft)
– Crankshaft pulley bolt: 200–225 Nm (148–166 lb-ft)
– Oil drain plug: 40–50 Nm (30–37 lb-ft)
– Injector hold-downs: 20–25 Nm (15–18 lb-ft).
The Cummins 4BT3.9-G2 is used in:
– Diesel generator sets (35–65 kW class)
– Agricultural tractors
– Telehandlers
– Wheel loaders
– Forklifts
– Skid-steer loaders
– Marine auxiliary power
– Industrial pumps and compressors
– Irrigation systems
– Construction site machinery.
____________________________________________________________________________________
| Industrial Engines Technical Specifications |
| Small Engines Technical Specifications |
| Car Engines Technical Specifications |
| Outboard Engines Technical Specifications |
