TM-9-2815-225-34-P
ENGINE, DIESEL: 6 CYLINDER IN-LINE TURBOCHARGED, CUMMINS MODEL NTC-400
TECHNICAL MANUAL; DIRECT SUPPORT AND GENERAL SUPPORT MAINTENANCE MANUAL INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST
JULY 2005
TM-9-2815-225-34-P - Page 28 of 736
TM 9-2815-225-34&P
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THEORY OF OPERATION (Contd)
ENGINE FEATURES
The Cummins NTC-400 diesel engine is used on all M915 through M920, M915A1, and M915A4 trucks.
It is a turbocharged, liquid-cooled, overhead valve, four-cycle engine of in-line, six-cylinder design. The
NTC-400 engine has a compression ratio of 13.5:1 (Big Cam I) and 14.0:1 (Big Cam III) and develops
400 horsepower at 2100 rpm. Peak torque is 1150 lb-ft at 1500 rpm (Big Cam I) and 1300 lb-ft at 1300
rpm (Big Cam III).
The following engine characteristics and features apply to both Big Cam I and Big Cam III engines,
except where differences are noted.
Camshaft:
2 1/2-inch diameter camshaft with gear drive controlling all valve and injector movement.
Made of induction hardened alloy steel. Camshaft followers are roller-type.
Connecting Rods:
Drop-forged, rifle-drilled for pressure lubrication.
Crankshaft:
High-tensile steel forging. Bearing journals and fillets are induction hardened. Fully
counterweighted.
Cylinder Block:
Alloy cast iron with removable wet liners.
Cylinder Heads:
Each head serves two cylinders. Drilled fuel supply and return lines. High
temperature inserts on exhaust valve seats.
Turbocharger:
Model T-50 (Big Cam I); Model T-46-B (Big Cam III) has a redesigned compressor
wheel, compressor housing, turbine wheel and shaft, bearing housing assembly, location of oil inlet line,
and V-bands.
Exhaust Manifold:
Conventional log-type (Big Cam I). Pulse-type for less restriction (Big Cam III).
Fuel System:
Integral flywheel-type governor.
Injectors:
Camshaft actuated top stop-type.
Intake Manifold:
Conventional aftercooler (Big Cam I); triple-pass water aftercooler (Big Cam III).
Lubrication Oil Cooler:
Conventional oil cooler and filter with separately mounted bypass oil filter
on engine firewall (Big Cam I). Demand flow automatically regulates oil pressure and routes engine
coolant through engine oil cooler twice.
Engine and cooler cores are made of cast aluminum and incorporate mounting adapters for spin-on-type
full-flow and bypass oil filters; also incorporate a bypass valve and pressure sending unit (Big Cam III).
Oil Pan:
Made of cast aluminum (Big Cam I). Made of stamped steel (Big Cam III).
Water Transfer Tube:
Made of cast iron (Big Cam I). Made of stamped, welded steel (Big Cam III).
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