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Cummins 4B3.9-G11 Engine

The Cummins 4B3.9-G11 is a heavy-duty, inline four-cylinder, four-stroke diesel engine designed specifically for fixed-speed generator drive (G-Drive) configurations. Operating on a naturally aspirated air introduction configuration, this unit belongs to the widely utilized Cummins B-Series platform. The engine block and integrated cylinder head assembly are cast from high-strength gray iron, utilizing a deep-skirt design that extends well below the crankshaft centerline to form a rigid structural box capable of resisting high rotational torque. To eliminate common leakage points and minimize total physical component count, the block features fluid passages for oil and coolant integrated directly into the raw casting.

Cylinders are machined straight into the engine block without separate liners, maximizing core structural stiffness and lowering thermal distortion across the piston swept area. It uses a traditional overhead valve (OHV) arrangement operated via mechanical lifters, pushrods, and rocker arms linked to a single camshaft mounted low within the crankcase. The internal cylinder geometry features a precise cylinder bore diameter of 102 mm (4.02 inches) and a piston stroke length of 120 mm (4.72 inches).

The fuel system uses a mechanical direct injection configuration centered around an inline fuel injection pump, specifically a Weifu A-series fuel pump paired with an RSV mechanical governor assembly. The low-pressure side uses a cam-driven mechanical lift pump to pull fuel from the supply tank through a combined primary fuel filter and water separator unit. Fuel is then moved into the injection pump gallery at steady pressure. The inline pump times and measures the fuel, pushing it through heavy-wall steel fuel lines to the individual mechanical injectors at each cylinder. The RSV mechanical governor monitors internal engine speeds, adjusting the fuel rack to maintain precise rotational speed under varying generator electrical loads.

Engine lubrication is maintained via a forced-pressure system managed by a positive-displacement, gear-driven oil pump that delivers oil directly from the lower sump assembly. The minimum required operational system capacity, combining the lower oil pan oil capacity and the primary spin-on full-flow filtration unit, stands at 10.9 liters (2.88 US gallons). Regulated oil pressure at standard governed operating speed is maintained between 300 and 450 kPa (44-65 psi), with a maximum allowable oil temperature limit of 121C (250F) monitored at the main oil gallery.

Thermal control is achieved through an integrated closed-loop liquid cooling system using a belt-driven, high-capacity centrifugal water pump to cycle coolant through the engine block, cylinder head, and a radiator group. A mechanical thermostat automatically regulates cooling fluid flow to stabilize standard working temperatures, protecting the long-term reliability of the cylinder walls and internal sealing gaskets.

General Technical Data

Engine Specifications

Engine Model ............... Cummins 4B3.9-G11
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) ............... 4.72 (120.0)
Displacement, cu.in (L) ............... 239 (3.9)
Rated Engine Power, hp (kW) ............... 51-88 (38-65)
Rated Engine Speed, rpm ............... 1500-1800
Peak Torque ............... 200-260 Nm (148-192 lb-ft) at 1400-1600 rpm
Idle Speed ............... 750-850 rpm
Aspiration Type ............... Naturally Aspirated
Compression Ratio ............... 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 ............... 35-70

Fuel System

Fuel System ............... Direct injection
Injection Pump Type ............... Rotary
Fuel System Control ............... Mechanical
Governor Type ............... Mechanical
Fuel Injector Type ............... Multi-hole
Fuel Type ............... Diesel Fuel

Dimensions and Weight

Overall Length, in (mm) ............... 35.5-39.4 (900-1000)
Overall Width, in (mm) ............... 27.6-31.5 (700-800)
Overall Height, in (mm) ............... 35.4-39.4 (900-1000)
Dry Weight, lbs (kg) ............... 750-880 (340-400)

Maintenance Data

Service Information

Thermostat begins opening ............... 82C (180F)
Thermostat fully open ............... 95C (203F)
Cooling system pressure ............... 70-100 kPa (10-15 psi)
Operating oil pressure ............... 300-450 kPa (44-65 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) .................. 9.5-12.6 (9.0-12.0)
Coolant Capacity, qts (L) ............... 12.6-16.8 (12.0-16.0)

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 3000 hours
Drain water separator ............... As required
Belt inspection ............... As required

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 4.0161-4.0177 (102.000-102.040)
Crankshaft Journal Outside Diameter, in (mm) ............... 3.2661-3.2681 (82.960-83.010)
Crank Pin Outside Diameter, in (mm) ............... 2.7150-2.7169 (68.960-69.010)
Crankshaft End Play, in (mm) ............... 0.0040-0.0170 (0.102-0.432)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3134-0.3142 (7.960-7.980)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3126-0.3134 (7.940-7.960)
Intake Valve Guide Inside Diameter (Installed), in (mm) ............... 0.3157-0.3169 (8.020-8.050)
Exhaust Valve Guide Inside Diameter (Installed), in (mm) ............... 0.3157-0.3169 (8.020-8.050)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0015-0.0036 (0.038-0.091)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0025-0.0046 (0.064-0.117)
Intake Valve Spring Free Length, in (mm) ............... 2.150 (54.61)
Exhaust Valve Spring Free Length, in (mm) ............... 2.150 (54.61)
Intake Cam Height, in (mm) ............... 1.831 (46.51)
Exhaust Cam Height, in (mm) ............... 1.819 (46.20)
Piston Pin Outside Diameter, in (mm) ............... 1.5744-1.5752 (39.990-40.010)
Piston Pin to Piston Bore Clearance, in (mm) ............... 0.0002-0.0007 (0.005-0.018)
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) ............... 0.0114-0.0228 (0.290-0.580)
Second Ring End Gap, in (mm) ............... 0.0346-0.0539 (0.880-1.370)
Oil Ring End Gap, in (mm) ............... 0.0110-0.0303 (0.280-0.770)

Tightening Torque Specs

Cylinder head bolts ............... 160-180 Nm (118-133 lb-ft)
Main bearing caps ............... 150-170 Nm (111-125 lb-ft)
Connecting rod bolts ............... 70-85 Nm (52-63 lb-ft)
Flywheel bolts ............... 180-220 Nm (133-162 lb-ft)
Crankshaft pulley bolt ............... 200-240 Nm (148-177 lb-ft)
Glow plugs ............... 10-15 Nm (7-11 lb-ft)
Oil drain plug ............... 30-40 Nm (22-30 lb-ft)
Injector hold-down bolts ............... 25-30 Nm (18-22 lb-ft)

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• Cummins Engines Specs
  
• Cummins 4B3.9-G2 Specs
  
• Cummins 4BT3.9-G2 Specs
  
• Cummins 4BTA3.9-G2 Specs
  
• Cummins 4BTA3.9-G11 Specs
  
• Cummins 4BTAA3.3-G11 Specs
  
• Cummins 4BTAA3.9 Specs
  

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