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Cummins 6CT8.3 Engine

The Cummins 6CT8.3 is a heavy-duty, inline 6-cylinder, 4-stroke diesel engine widely utilized in commercial marine vessels, agricultural machinery, construction equipment, and heavy automotive applications. Part of the C-Series engine family, it features a robust cast-iron block engineered with replaceable wet-type cylinder liners, which allows for straightforward in-chassis rebuilding and enhanced durability compared to parent-bore designs. The "CT" designation indicates that the engine is turbocharged and jacket-water aftercooled, utilizing exhaust-driven forced induction and a dedicated induction air cooling circuit to optimize combustion efficiency, minimize thermal stress, and maximize power-to-weight density. The engine displaces a total volume of 8.3 liters (504 cubic inches). This displacement is achieved through an internal cylinder geometry consisting of a standard bore of 114 mm (4.49 inches) and a longer stroke of 135 mm (5.32 inches), providing a high-torque, under-square design.

The fuel architecture relies entirely on a mechanical high-pressure direct injection system. Fuel is delivered via a gear-driven Bosch P7100 inline injection pump or a Bosch MW inline pump, depending on the manufacturing year and emission tier, and is regulated by a mechanical governor. The supply circuit uses a mechanical lift pump to draw fuel through a dual spin-on fuel filter assembly containing an integrated water separator. High-pressure steel lines route the fuel to multi-hole, mechanical capsule-type injectors centered in the combustion chamber. An overflow valve on the injection pump maintains correct internal fuel gallery pressure and directs excess fuel back to the supply tank for cooling.

Engine lubrication is managed by a high-delivery, gear-driven oil pump that circulates oil through a combination full-flow and bypass spin-on filtration system. An integrated, plate-type oil cooler regulates oil temperatures under continuous load. Standard operating oil pressure at rated speed ranges from 44 to 65 psi, with a minimum safe limit of 15 psi at a hot idle. Thermal regulation is maintained by a liquid-cooled, pressurized system controlled by dual mechanical thermostats for rapid warm-up and stable temperature control. A high-capacity, belt-driven water pump circulates coolant through the engine block, cylinder head, and fluid coolers. Industrial applications utilize a heavy-duty radiator and fan arrangement, while marine configurations employ a sea-water-cooled heat exchanger or a keel-cooling loop.

General Technical Data

Engine Specifications

Engine Model ............... Cummins 6CT8.3
Engine Type ............... 4-cycle inline 6-cylinder direct injection turbocharged liquid-cooled diesel
Number of Cylinders ............... 6
Cylinder Arrangement ............... In-line
Engine Bore, in (mm) ............... 4.49 (114.0)
Engine Stroke, in (mm) ............... 5.31 (135.0)
Displacement, cu.in (L) ............... 505 (8.3)
Rated Engine Power, hp (kW) ............... 150-260 (112-194)
Rated Engine Speed, rpm ............... 1800-2200
Peak Torque ............... 650-1050 Nm (479-774 lb-ft) at 1300-1600 rpm
Idle Speed ............... 650-750 rpm
Aspiration Type ............... Turbocharged
Compression Ratio ............... 17.0:1-18.0:1
Firing Order ............... 1-5-3-6-2-4
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 ............... 50-120

Fuel System

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

Dimensions and Weight

Overall Length, in (mm) ............... 47.2-55.1 (1200-1400)
Overall Width, in (mm) ............... 29.5-35.4 (750-900)
Overall Height, in (mm) ............... 43.3-51.2 (1100-1300)
Dry Weight, lbs (kg) ............... 1320-1650 (600-750)

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) ............... 0.012 (0.305)
Exhaust Valve Clearance, in (mm) ............... 0.024 (0.610)

Engine Oil and Coolant

Engine Oil Type .................. SAE 10W-30, 15W-40
API Service Classifications ......................... CI-4, CJ-4, or CK-4
Engine Oil Capacity, qts (L) .................. 19.9-23.1 (18.0-22.0)
Coolant Capacity, qts (L) ............... 26.3-31.5 (25.0-30.0)

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 2500 hours
Drain water separator ............... As required
Belt inspection ............... As required

Service Specifications

Cylinder Bore Inside Diameter, in (mm) ............... 4.4882-4.4894 (114.000-114.030)
Crankshaft Journal Outside Diameter, in (mm) ............... 3.8568-3.8588 (97.962-98.013)
Crank Pin Outside Diameter, in (mm) ............... 2.9906-2.9926 (75.962-76.013)
Crankshaft End Play, in (mm) ............... 0.0051-0.0150 (0.130-0.380)
Intake Valve Stem Outside Diameter, in (mm) ............... 0.3721-0.3732 (9.451-9.479)
Exhaust Valve Stem Outside Diameter, in (mm) ............... 0.3713-0.3724 (9.431-9.459)
Intake Valve Guide Inside Diameter, in (mm) ............... 0.3745-0.3760 (9.512-9.550)
Exhaust Valve Guide Inside Diameter, in (mm) ............... 0.3745-0.3760 (9.512-9.550)
Intake Valve Stem to Guide Clearance, in (mm) ............... 0.0013-0.0039 (0.033-0.099)
Exhaust Valve Stem to Guide Clearance, in (mm) ............... 0.0021-0.0047 (0.053-0.119)
Intake Valve Spring Free Length, in (mm) ............... 2.366 (60.10)
Exhaust Valve Spring Free Length, in (mm) ............... 2.366 (60.10)
Intake Cam Height, in (mm) ............... 1.881-1.906 (47.78-48.42)
Exhaust Cam Height, in (mm) ............... 1.898-1.924 (48.22-48.86)
Piston Pin Outside Diameter, in (mm) ............... 1.7714-1.7719 (44.993-45.005)
Piston Pin to Piston Bore Clearance, in (mm) ............... 0.0002-0.0008 (0.005-0.021)
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) ............... 0.0118-0.0217 (0.30-0.55)
Second Ring End Gap, in (mm) ............... 0.0157-0.0256 (0.40-0.65)
Oil Ring End Gap, in (mm) ............... 0.0098-0.0217 (0.25-0.55)

Tightening Torque Specs

Cylinder-head bolts ............... 190-210 Nm (140-155 lb-ft)
Main-bearing caps ............... 245-260 Nm (181-192 lb-ft)
Connecting-rod bolts ............... 75-85 Nm (55-63 lb-ft)
Flywheel bolts ............... 135-150 Nm (100-111 lb-ft)
Crankshaft damper bolt ............... 270-300 Nm (199-221 lb-ft)
Oil drain plug ............... 40-50 Nm (30-37 lb-ft)
Fuel line nuts ............... 25-30 Nm (18-22 lb-ft)
Water pump bolts ............... 25-30 Nm (18-22 lb-ft)
Timing gear cover bolts ............... 20-25 Nm (15-18 ft-lb)
Injector hold-down ............... 25-30 Nm (18-22 lb-ft)

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• Cummins Engines Specs
  
• Cummins 6C8.3 Specs
  
• Cummins 6CTA8.3 Specs
  
• Cummins 6CTAA8.3 Specs
  

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