1984 Komatsu-Cummins N-855-C, NT-855-C & NTA-855-C Diesel Engine Shop Manual (SEBE6710A03)

This Komatsu-Cummins shop manual covers the N-855-C, NT-855-C, and NTA-855-C diesel engines used in applications including the PC300-1, HD320-2, and D85A-18. The September 1984 edition was printed in Japan and carries document code SEBE6710A03.

• Engine testing and adjustment: Compression, blow-by, oil-consumption, and fuel-pressure checks, plus injector adjustment, valve clearance, and engine performance testing.

• Cylinder-head repair: Head resurfacing, valve-seat insert replacement, injector-sleeve repair, and valve-guide work, with related inspection standards and special tools.

• Block and rotating assembly: Cylinder-block machining, main-bearing cap replacement, crankshaft reconditioning, bushing replacement, and crankshaft, camshaft, and flywheel gear replacement.

• PT fuel system: Pump calibration data, injector specifications, Cummins VS and MVS governor arrangements, and troubleshooting for fuel-related performance problems.

• Cooling and lubrication: Water-pump, thermostat, and oil-pump configurations, system charts, and diagnostic coverage for overheating, oil leaks, and oil consumption.

• Electrical systems: Alternator and starting-motor wiring diagrams, intake-heater circuits, and fault-finding charts for starting and charging problems.

Written for workshop service mechanics, this manual assumes access to engine test equipment; internal PT pump work and crankshaft reconditioning require specialized facilities.

Engine Layouts and Fault Diagnosis

The N-855-C is naturally aspirated; the NT-855-C is turbocharged, and the NTA-855-C is turbocharged and aftercooled. Assembly views document the cylinder block, crankshaft, timing gears, and intake and exhaust arrangements.

Turbocharger coverage distinguishes Cummins ST-50 and Komatsu KTR-130 installations. Nine performance curves and application-specific weight tables support the specification sections.

Troubleshooting charts address reduced power, exhaust smoke, oil-pressure problems, overheating, vibration, and abnormal noise. The blow-by discussion relates readings to oil consumption, starting behavior, and compression, helping mechanics avoid condemning an engine from one measurement alone.

The general workshop section explains dial-gauge use for gear-backlash checks and engine-to-transmission centering, where misalignment increases stress on rotating parts. General torque tables cover bolts, nuts, flare nuts, and flange bolts.

This is an engine volume; chassis, attachment, and complete machine electrical coverage belongs to separate manuals.

PT Pump Calibration and Injector Adjustment

The calibration tables match machine applications and engine serial ranges to PT pump codes. Fuel System Charts and the PTG-VS fuel-flow diagram explain the pump and governor circuits, including air-fuel control.

Injector and four-valve cylinder-head adjustments vary with engine build. The manual identifies the injector timing fixture 795-140-1604 and distinguishes earlier and later HD320-2 arrangements.

Increasing PT pump pressure above specification, or substituting a pump intended for another model to compensate for low power, can damage the engine. Internal pump inspection, adjustment, and repair require a shop equipped with a test stand.

Cylinder-Head and Crankshaft Repair

Repair and replacement procedures cover oversize valve-seat inserts, injector-sleeve fitting and leak checks, and cylinder-block counterbore machining. Crankshaft reconditioning includes hardness, magnetic-flaw, and fillet inspections; maintenance standards provide the clearances and repair limits used to assess component reuse.

Disassembly coverage: Chapter 13 contains only its divider page. Complete engine disassembly and reassembly procedures are absent from this file, although the component repair procedures and general workshop precautions are included.

General seal-handling guidance warns that incorrect floating-seal assembly can damage O-rings and cause oil leakage.

Important safety notice: Isolate electrical power and release trapped pressure before disassembly; follow the manual's lifting precautions and safeguards around running engines.

Cooling, Lubrication, and Electrical References

Lubrication System Charts distinguish oil-pump arrangements with and without scavenging. Cooling System Charts show the water-pump and thermostat circuits, alongside component descriptions for the air compressor.

Alternator/regulator schematics and starting-motor circuits distinguish installations with and without a starter relay. These engine-component diagrams accompany starting and charging fault charts.

A Preview of Valve, Crankshaft, and Fastener Data

These examples are a small selection of the manual's adjustment values and inspection limits. For HD320-2 NTA-855-C engines numbered 26102754–26155791, cold intake-valve clearance is 0.41 mm at 20°C.

Crankshaft inspection data list standard end play of 0.18–0.43 mm and a clearance limit of 0.56 mm.

The general torque table gives 112 ± 9.8 Nm for 12 mm bolts, except where a specific torque applies or nylon packings or nonferrous washers are used.

Bookmarked PDF and Diagram Readability

Chapter access and circuit detail: Embedded bookmarks link to sections and subsections, but PDF text search is not available. Small labels in the alternator/regulator and starting-motor diagrams require zooming.

Supplied as one printable 279-page PDF. This total includes the original cover, three revision-list pages, and seven chapter divider pages.