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Cummins 4BT3.9-G2 Engine

The Cummins 4BT3.9-G2 is a heavy-duty, 4-stroke, inline 4-cylinder, turbocharged industrial diesel engine. Designed specifically for generator drive applications (G-drive), it utilizes an integrated cylinder block and cylinder head design to significantly reduce the overall parts count, minimize potential leak points, and ensure robust operation under sustained heavy loads. This engine features a highly reliable, pure mechanical-driven design with an electronic or mechanical governor system to enforce rigid frequency controls required for power generation. It relies on a Holset turbocharger with an integral wastegate valve to ensure rapid load response and stable power density within a compact physical footprint. Cylinder bores utilize a platform mesh honing design combined with advanced piston ring configurations to achieve optimal oil control, low emissions, and maximum thermal efficiency.

The fuel system uses a premium high-pressure direct injection layout configured to achieve precise engine speed droop parameters under varying electrical loads. High-pressure fuel injection pump: BYC ASIMCO / Wuxi Premium "A" style inline injection pump assembly. Governing architecture: GAC or RSV mechanical-electronic governor with a rigid maximum speed droop limit of 5%.

The engine uses a full-pressure lubrication loop powered by a gear-driven internal oil pump. The system incorporates a dedicated high-capacity oil cooler, a full-flow spin-on oil filter element, and a specialized combination piston cooling nozzle setup to maintain thermal stabilization under high load. The integrated block layout contains internal rifle drillings for cross-main bearing oil delivery, drastically mitigating external oil line failure risks. Engine cooling is handled by a forced liquid-circulation loop managed by an integrated belt-driven water pump and a high-flow radiator setup. Thermostat modulating operational range: 82C to 95C opening thresholds.

General Technical Data

Engine Specifications

Engine Model ............... Cummins 4BT3.9-G2
Engine Type ............... 4-cycle inline 4-cylinder direct injection turbocharged 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) ............... 47-87 (35-65)
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 ............... Turbocharged
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) ............... 750-840 (340-380)

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

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