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Cummins 4BTA3.9-G11 Specifications
| Engine Model: Cummins 4BTA3.9-G11 |
| Engine Type: 4-cycle inline 4-cylinder direct injection liquid-cooled diesel |
| Total Displacement: 239 cu.in (3.9 L) |
| Rated Engine Power: 67-120 Hp (50-90 kW) at 2200 rpm |
| Aspiration Type: Turbocharged and aftercooled |
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| General Technical Data |
The Cummins 4BTA3.9-G11 is a turbocharged and aftercooled, four-cylinder, direct-injection diesel engine widely used in generator sets, agricultural machines, construction equipment, industrial pumps, and various mobile and stationary platforms requiring a compact and highly durable power unit. As part of the legendary Cummins B Series engine family, the 4BTA3.9-G11 is celebrated for its ruggedness, mechanical simplicity, fuel efficiency, and long overhaul intervals.
The addition of turbocharging and charge-air
cooling improves combustion efficiency, raises horsepower output, and
enhances torque delivery across a wide operating range. This makes the
4BTA3.9-G11 an ideal choice for continuous-duty generator sets where
reliability, stable performance, and long service life are essential.
The 4BTA3.9-G11 is a four-stroke, inline four-cylinder engine with a
displacement of approximately 3.9 liters (239 cubic inches). Bore is 102
mm (4.02 inches), and stroke is 120 mm (4.72 inches), forming a
long-stroke configuration optimized for torque and fuel efficiency. The
compression ratio usually ranges from 16.5:1 to 17.5:1 depending on
calibration. Power output for generator applications generally ranges
from 50 to 90 kW (67–120 horsepower) at 1500–2500 rpm depending on
rating.
Peak torque typically ranges from 300 to 450 Nm
(221–332 lb-ft), available at approximately 1400–1600 rpm. The firing
order is 1–3–4–2. Idle speed is typically set around 800 ± 50 rpm. The
turbocharger increases air density entering the cylinders, and the
aftercooler (charge-air cooler) reduces intake temperature, improving
combustion efficiency and power under continuous load.
The cylinder block is cast from high-strength iron with reinforced
ribbing to minimize torsional flex and vibration during heavy-duty
operation. The inline four-cylinder arrangement ensures balanced firing
intervals and smoother running characteristics. The forged-steel
crankshaft is supported by five main bearings, engineered for extended
service life in continuous-duty environments.
Coolant jackets are cast internally around each
cylinder to promote uniform temperature distribution, while precisely
machined oil galleries ensure reliable lubrication throughout the
rotating assembly. Mounting bosses and threaded ports accommodate
generator couplings, alternators, pumps, and ancillary equipment.
The cast-iron cylinder head houses direct-injection combustion chambers
optimized for turbocharged and aftercooled operation. Each cylinder uses
two intake and two exhaust valves actuated by rocker arms and pushrods
driven by a block-mounted camshaft. Manual valve lash adjustment ensures
correct breathing efficiency and proper sealing.
The combustion chamber design promotes swirl and fine atomization, supporting clean combustion and low fuel consumption. Hardened valve seats and high-temperature-resistant valve guides provide durability under the elevated exhaust temperatures associated with turbocharged operation. Coolant passages in the head maintain stable thermal behavior during long runs.
| Fuel System |
The 4BTA3.9-G11 features a mechanical direct-injection fuel system engineered for reliability and efficiency. Fuel is drawn by a mechanical lift pump from the tank and routed through a sediment bowl or water separator followed by a fine-element filter. The high-pressure inline or rotary injection pump meters and times the injection events. Injection pressures typically range from 260 to 320 bar, enabling precise fuel delivery and efficient combustion.
Multi-hole injectors deliver atomized Diesel fuel into each combustion chamber. Excess fuel circulates back to the tank to cool the pump and injectors. The mechanical governor maintains steady engine speed, particularly important in generator applications where frequency regulation is critical.
| Lubrication System |
The lubrication system is a full-pressure wet-sump arrangement. A gear-driven oil pump draws oil through a pickup strainer and pushes it through a full-flow spin-on filter. Pressurized oil supplies crankshaft main bearings, connecting rod journals, camshaft bearings, rocker arms, turbocharger bearings, and piston cooling jets.
Normal oil pressure at operating speed ranges from 300 to 450 kPa (44–65 psi), while idle pressure generally ranges between 100 and 150 kPa (15–22 psi). Oil capacity typically ranges from 9 to 10 liters (9.5–10.5 US quarts). High-quality diesel-rated oil (API CF or higher) is recommended to ensure long service life.
| Cooling System |
A liquid-cooling circuit maintains stable operating temperatures. A belt-driven centrifugal water pump circulates coolant through the block and head. The thermostat begins opening at approximately 82°C (180°F) and is fully open around 95°C (203°F). Coolant capacity generally ranges from 10 to 12 liters (10.5–12.7 US quarts).
The system is pressurized to approximately 90–110 kPa (13–16 psi). Charge-air cooling is accomplished through an air-to-air intercooler or air-to-water aftercooler depending on the generator or equipment configuration. Keeping the cooling package clean and unobstructed is essential for engines operating under continuous duty.
| Other Systems |
The turbocharger boosts air intake pressure, enhancing power and torque. It is lubricated by the main oil circuit and requires clean oil for reliability. Intake air filtration uses heavy-duty dry-element filters, with dual-stage options for dusty environments. The exhaust manifold is cast iron and designed to withstand high temperatures under turbocharged operation.
Electrical systems are available in 12-volt or 24-volt configurations, with alternators typically providing 35–75 amperes. A reduction-gear starter motor ensures reliable cold starts. Optional PTO drives, hydraulic pump adapters, and auxiliary couplings support various industrial roles. Crankcase ventilation components regulate internal pressure and minimize oil vapor emission.
| Dimensions and Weight |
Standard engine dimensions generally fall within: length 850–950 mm (33.5–37.4 inches), width 650–750 mm (25.6–29.5 inches), and height 900–1000 mm (35.4–39.4 inches). Dry weight commonly ranges between 330 and 380 kg (727–838 lbs) depending on turbocharger configuration, generator frame, and auxiliary equipment. The compact footprint allows flexible installation in generator housings and industrial machinery.
| Maintenance Data |
Oil and filter changes are recommended every 250 operating hours in industrial and generator service. Fuel filters should be replaced every 250–400 hours depending on fuel quality. Air filter servicing intervals range from 100 to 300 hours based on dust exposure. Valve lash should be inspected and adjusted approximately every 500–600 hours.
Coolant replacement is generally advised every two years or 2000 hours. Injector servicing, including cleaning and spray-pattern testing, is recommended every 1500–2000 hours. Compression testing at around 3000 hours helps detect internal wear. Regular inspection of belts, hoses, vibration isolators, turbocharger lubrication lines, and engine mounts ensures long-term reliability.
| Tightening Torques |
Cylinder head bolts typically require 160–180 Nm (118–133 lb-ft). Main bearing caps usually require 150–170 Nm (111–125 lb-ft). Connecting rod bolts generally require 70–85 Nm (52–63 lb-ft). Flywheel bolts must be tightened to 180–220 Nm (133–162 lb-ft).
Crankshaft pulley bolts commonly require 200–240 Nm (148–177 lb-ft). Injector hold-down bolts use 20–25 Nm (15–18 lb-ft). Glow plugs, if used, require 10–15 Nm (7–11 lb-ft). The oil drain plug typically requires 30–40 Nm (22–30 lb-ft).
| Vehicle Applications |
The Cummins 4BTA3.9-G11 powers generator sets, agricultural tractors, small loaders, backhoe loaders, forklifts, pumps, compressors, irrigation equipment, and a wide range of construction and industrial machines. Its balance of compact size, fuel efficiency, and robust torque characteristics makes it ideal for demanding applications requiring continuous or intermittent heavy-duty performance.
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