2003-2005 Komatsu 6D125-2, S6D125-2, SA6D125-2 & SAA6D125-2 Diesel Engine Shop Manual (P/N SEBM006410)

The Komatsu 125-2 Series Diesel Engine Shop Manual (SEBM006410, printed May 2003) covers the 6D125-2, S6D125-2, SA6D125-2, and SAA6D125-2 engine family. This is the engine volume; complete machine repairs also require the appropriate chassis, electrical, and attachment volumes.

• Engine overhaul: Disassembly and assembly of cylinder heads, liners, pistons, connecting rods, crankshaft, camshaft, timing gears, and rear seals.

• Fuel-system testing: Injection-timing checks by match marks or the delivery valve method, pump calibration data, fuel-cut solenoid testing, and stop-motor adjustment.

• Troubleshooting: Symptom-based charts for hard starting, no-start conditions, hunting, low output, abnormal exhaust, oil-pressure loss, overheating, noise, and vibration.

• Lubrication and cooling: Oil-pump and regulator-valve information, filter and cooler arrangements, water-pump removal and installation, thermostat checks, and fan-drive details.

• Electrical diagrams: Alternator internal connections, starting-motor external wiring, connector specifications, and electrical intake-air-heater connection circuits.

• Inspection and repair standards: Component wear limits, air-compressor inspection data, cylinder-head repair, bushing replacement, crankshaft grinding, and special-tool references.

Written for service-workshop personnel, this manual assumes the measuring equipment, lifting facilities, and technical knowledge needed for industrial diesel repair.

Engine Variants and Pump Calibration

The structure section distinguishes the naturally aspirated engine, turbocharged versions, water-cooled aftercooling, and the air-cooled aftercooler arrangement. General assembly drawings show side, front, rear, and top views; application-specific performance curves plot flywheel output and torque against engine speed.

Pump selection: Calibration sheets identify injection-pump assemblies and distinguish service-test conditions from manufacturer test conditions. CUSTOM, MIGHTY, EXCEL, and USA excavator applications have separate entries. Matching the machine version and installed pump number helps prevent selection of the wrong calibration sheet.

Earlier CUSTOM/MIGHTY serial cutoffs differ between the calibration index and an individual data sheet; confirm the pump assembly number before selecting those data. J6D125E-G1-2 generator coverage also distinguishes mechanical-governor and ZEXEL electronic-governor arrangements.

Internal Repair and Component Inspection

The overhaul chapter covers wet-liner seals, piston and connecting-rod installation, timing-gear alignment, crosshead adjustment, and flywheel runout checks. Separate inspection tables distinguish aluminum-alloy and FCD piston versions.

Repair procedures extend to valve-seat inserts, nozzle-holder sleeves, valve and crosshead guides, cam bushings, flywheel ring gears, connecting-rod small-end bushings, and main bearing caps. Cylinder-head pressure tests and crankshaft grinding inspections include the related acceptance criteria.

Assembly cautions: Plastic-range tightening carries bolt-reuse limits for cylinder-head, main-cap, and connecting-rod fasteners. The liner-installation section warns that gasket sealant on head-gasket grommets can deform them and cause coolant leakage.

Fluid Circuits, Electrical Connections, and Shop Tools

Lubrication system charts trace the oil supply through the pump, cooler, filters, and regulating valves. Fuel system and cooling system charts identify the associated flow paths and components. Air-compressor coverage provides structure, operating specifications, and maintenance standards.

Electrical reference material includes wiring-color classification codes and engine stop-motor circuits alongside the component diagrams. The fuel-cut solenoid section explains how incorrect linkage adjustment can burn out the solenoid coil or damage the injection-pump governor.

Standard tightening-torque tables cover metric bolts, flared nuts, split flanges, and O-ring boss piping joints. Tool lists identify equipment such as injection-timing gauge assembly 795-471-1200 and cylinder-liner removal kit 795-220-1000.

Always consult a certified technician before performing service or maintenance on heavy equipment to ensure safety and compliance.

Valve-Clearance and Liner-Protrusion Preview

The valve-adjustment section specifies 0.33 mm intake clearance and 0.71 mm exhaust clearance, with the engine hot or cold. These measurements apply between the crosshead and rocker arm.

The cylinder-liner installation section gives a protrusion range of 0.07–0.15 mm, measured with the installed liner held down to eliminate lift from the O-ring.

PDF Search, Bookmarks, and Diagram Detail

Finding text and reading connections: Text search works on part of the document; many specification, illustration, and troubleshooting pages have no searchable text. Embedded bookmarks cover the technical chapters and many individual procedures, although some introductory links land on a preceding or blank page. Small connector pin numbers and wiring codes require zooming.

Supplied as one printable, 399-page PDF, including the cover, three revision-list pages, two blank pages, and one closing revision-request form.