Cummins 4B3.9-G11 Specifications
| Engine Model: Cummins 4B3.9-G11 |
| Engine Type: 4-cycle inline 4-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 239 cu.in (3.9 L) |
| Rated Engine Power: 51-67 Hp (38-50 kW) at 1500 rpm |
| Aspiration Type: Naturally aspirated |
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The Cummins 4B3.9-G11 is a compact,
mechanically controlled, 3.9-liter inline-four industrial diesel engine
widely used in generator sets, agricultural equipment, construction
machinery, and industrial pumps. As part of the renowned B-Series
family, the 4B3.9-G11 is recognized for its durability, low operating
cost, high reliability, mechanical simplicity, and excellent
field-serviceability. In generator applications, the G11 configuration
provides stable, fuel-efficient power output with minimal maintenance
needs and an extremely long overhaul life.
Its cast-iron structure, mechanical inline fuel system, parent-bore
block, and low-speed torque delivery make it ideal for continuous-duty
and standby power applications. The 4B3.9-G11, like other B-Series
engines, is designed for industrial environments that demand consistent
power performance, long service intervals, and resistance to fuel
contamination and harsh operating conditions.
The Cummins 4B3.9-G11 is a four-stroke, water-cooled, inline
four-cylinder diesel engine. Total displacement is 3.9 liters (239 cubic
inches). Bore is approximately 102 mm (4.02 in) and stroke is 120 mm
(4.72 in). Its long-stroke geometry supports strong low-RPM torque and
efficient fuel use.
Compression ratio: approximately 17.5:1. Peak torque ranges: 200–260 Nm
(148–192 lb-ft) at 1,400–1,600 rpm. Idle speed is typically 750–850 rpm.
Firing order: 1-3-4-2.
Power ratings for generator-drive G11
configuration:
– Prime output: 35–45 kW (47–60 hp) @ 1,500 rpm
– Standby output: 38–50 kW (51–67 hp) @ 1,500 rpm
– 60 Hz configurations may reach 50–65 kW @ 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 with reinforced crowns and cooling galleries.
Connecting rods are forged steel with replaceable bearings. The camshaft
is gear-driven for long-term timing stability.
The 4B3.9-G11 block is heavy-duty cast iron with parent-bore cylinders
(no replaceable liners). The water jacket surrounds the cylinders for
uniform temperature control.
The block includes:
– Deep skirt casting
– Integral stiffening ribs
– Wide main bearing saddles
– Full-length coolant passages
The cast-iron cylinder head features:
– Two valves per cylinder
– Direct-injection combustion chambers
– Hardened valve seats and guides
– Mechanical rocker-arm valvetrain
Cold valve lash:
– Intake: 0.254 mm (0.010 in)
– Exhaust: 0.508 mm (0.020 in)
The engine uses a fully mechanical
direct-injection fuel system consisting of:
– Mechanical lift pump
– Inline mechanical injection pump (Bosch type)
– Multi-hole mechanical injectors
– Primary water separator
– Secondary fine fuel filter
Injection pressures typically range from 250 to 350 bar.
Fuel-system maintenance:
– Replace filters every 250–300 hr
– Drain water separator daily
– Test injectors every 1,000–1,500 hr
– Check injection timing at major overhaul intervals.
A full-pressure wet-sump system is used.
Oil capacity: 9–12 liters (9.5–12.7 qt)
Oil pressure:
– 275–380 kPa (40–55 psi) operating
– 70–100 kPa (10–15 psi) idle
Recommended oils: SAE 15W-40 diesel oils meeting API CI-4/CJ-4/CK-4
Oil-change interval: 250 hr (generator applications).
Cooling is provided by:
– Belt-driven centrifugal water pump
– Thermostatically controlled coolant flow
– Radiator or remote cooling system
Thermostat:
– Opening temperature: 82°C (180°F)
– Fully open: 95°C (203°F)
Cooling system capacity: approx. 12–16 liters (12.7–17 qt)
System pressure: 70–100 kPa (10–15 psi).
| Intake and Exhaust Systems |
Intake:
– Dry-type air filter
– Optional dual-stage filtration
– Optional pre-cleaner systems
Turbocharging:
Though the 4B series is available in both NA and turbocharged forms, the
4B3.9-G11 generator variant is commonly naturally aspirated but some OEM
versions may include turbochargers for higher power ratings.
Exhaust:
– Cast-iron manifold
– Generator versions often include industrial exhaust elbows.
| Electrical and Starting Systems |
The G11 standard includes:
– 12V or 24V starting system
– 35–70 amp alternator
– Oil-pressure switch
– Coolant-temperature sender
– Tachometer pickup
No ECM is used; the system is fully mechanical.
Depending on installation:
– Generator head mounting (SAE 3/4/5 housing options)
– Hydraulic pump drive optional
– Belt-driven auxiliaries
– Remote radiator connections
– Industrial PTO configurations.
Approximate 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: 340–400 kg (750–880 lb) depending on accessories.
– 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: 1,000–1,500 hr
– Coolant: replace every 2 years
– Compression test: every 2,000 hr
– Belt inspection: each service.
– 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 4B3.9-G11 engine is used in:
– Diesel generator sets (35–65 kW class)
– Agricultural tractors
– Wheel loaders
– Skid-steer loaders
– Telehandlers
– Forklifts
– Marine auxiliary equipment
– Industrial pumps and compressors
– Irrigation systems
– Construction equipment.
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