Cummins NT 855 Engine Big Cam III & IV Troubleshooting and Repair Manual (P/N 3810298-00)

This 693-page PDF covers Cummins troubleshooting and in-chassis repair for NT 855 Big Cam III and Big Cam IV engines. It is identified as Cummins Bulletin No. 3810298-00, printed June 1986. Cummins organized the material around a service technician's workflow, and its reliance on pressure and vacuum testing, dial-indicator work, timing fixtures, lifting equipment, and chassis-dynamometer procedures makes it best suited to experienced heavy-duty diesel technicians and properly equipped repair shops.

• Symptom-led fault isolation: Logic charts connect cooling, lubrication, smoke, no-start, misfire, surge, low-power, blowby, turbocharger, air-compressor, MVT, and internal engine-noise complaints to numbered test and repair procedures.
• Distinct aftercooling layouts: Big Cam III traditional aftercooling and Big Cam IV optimized aftercooling receive separate coolant-flow coverage, with variant-specific thermostat, housing check-valve, radiator-baffle, balance-orifice, and aftercooler-screen procedures.
• Fuel, air, and lubrication work: Covers PT fuel-pump adjustment and replacement, injector service, AFC and governor diagnosis, fuel-flow and stall-speed checks, DFC lubrication, oil-cooler and regulator work, turbocharger and aftercooler service, and both single- and two-cylinder air-compressor repair.
• Internal and overhead repair: Details crosshead, valve, injector, and Jacobs Engine Brake adjustment; cylinder-head pressure testing; fixed and MVT injection timing; and replacement of heads, liners, bearings, pistons, rings, connecting rods, gears, camshaft parts, crankshaft seals, flywheel, and flywheel housing.
• In-chassis testing and engine handling: Provides chassis-dynamometer testing, loaded run-in procedures, on- and off-highway run-in guidance, engine removal and installation, and engine-mount inspection.
• Factory data and dedicated tooling: Supplies component specifications, inspection limits, system-specific torque tables, adjustment charts, and tool callouts for injection timing, MVT service, liner work, cylinder-head testing, blowby measurement, and engine lifting.

Big Cam III/IV Identification and System Differences

The identification section explains NTC and NTCC model coding and shows where to find the engine serial number, model number, Control Parts List (CPL), and fuel-pump dataplate information. Those identifiers matter because the manual ties correct parts and fuel-pump calibration to the engine's exact build.

Cooling coverage goes beyond generic drain-and-fill work. It includes pressure testing, checks for air or combustion gases, coolant-filter and DCA4 service, fan and shutter diagnosis, water-pump repair, and radiator checks.

The Big Cam IV material addresses its optimized circuit, dual thermostat functions, integral thermostat housing and filter head, aftercooler filter screen, and cooling-system balance features. Big Cam III procedures retain the traditional aftercooled layout and its own thermostat testing and replacement paths.

The MVT chapter likewise separates variable-timing engines from fixed-timing builds. It covers operational checks for actuator air supply and bleed control, the wiring harness, fuel-pressure switch, air solenoid, actuator seal, cam-follower work, and timing verification.

The PT fuel section identifies Type G AFC and AFC-VS connection points and supports pump adjustment with low-power, fuel-consumption, throttle-response, road-speed-governor, and driveability checks.

In-Chassis Test Data, Flow Diagrams, and Cummins Tools

The in-chassis test section monitors oil and coolant pressure, fuel-rail pressure and fuel rate, intake-manifold pressure, inlet restriction, blowby, engine speed, and wheel horsepower. Supporting graphics include Big Cam III and IV cooling-flow charts, the DFC lubricating-system flow diagram, combustion-air flow diagrams, the compressed-air circuit, PT fuel-pump flow and injector-drive diagrams, and engine views showing test-connection locations.

Tool references are specific rather than generic. Examples include the 3375522 Injection Timing Fixture, 3376028 Variable Timing Fixture, ST-1012 Hydrostatic Tester with ST-1013 adapter, 3375150 Blowby Checking Tool, 3376015 Universal Cylinder Liner Puller, and ST-125/ST-1258 Engine Lifting Fixtures.

Repair Boundaries and NT 855 Cautions

This is not the separate full-rebuild book. Cummins places complete component and assembly rebuild procedures in the NT 855 Engine Shop Manual, Bulletin No. 3379076, while fuel-pump, injector, air-compressor, and turbocharger rebuilding is handled in other dedicated publications. Vehicle- or equipment-side faults are also outside this manual's scope.

The run-in section warns that a rebuilt engine must be primed before startup and that using the bypass filter as the priming point can damage the filter. During cylinder-block repair, a cup plug driven too deeply can block cross-drillings; a plug that is not seated straight and flat must be replaced.

The work involves hot pressurized coolant, compressed air, rotating assemblies, electrical isolation, refrigerant-equipped chassis, and heavy lifting. Follow the manual's warnings, the equipment manufacturer's precautions, and standard shop lockout and lifting practices before beginning repair work.