1992–2003 Komatsu D20/D21 Series Bulldozer & Crawler Loader Shop Manual (P/N SEBM01040604)

This Komatsu factory shop manual, publication SEBM01040604, covers the 1992–2003 D20 and D21 series dozers and S/Q crawler loader variants listed above, with machine serial numbers 60001 and up. It combines machine-specific testing, adjustment, disassembly, assembly, and inspection standards for workshop repair.

• Engine testing and service: Compression and blow-by checks, fuel injection timing, valve adjustment, cylinder-head removal and installation, and engine removal and alignment.

• Powertrain repair: D20 main-clutch and manual-transmission overhaul, D21 Hydroshift transmission disassembly and assembly, clutch-piston air checks, and control-valve service.

• Steering and final drives: Steering-clutch overhaul, brake-linkage and lining-clearance adjustment, bevel-gear setup, final-drive disassembly, and component inspection standards.

• Undercarriage service: Track-frame, recoil-spring, idler, roller, and track-shoe removal and installation, with separate dry-link and lubricated-link wear standards.

• Hydraulics and work equipment: Pressure testing, cylinder-drift diagnosis, angle-cylinder circuit bleeding, control-valve overhaul, cylinder repair, and blade or bucket removal.

• Diagnostic diagrams: Powertrain and steering hydraulic circuits, work-equipment schematics, transmission section views, troubleshooting charts, and an electrical wiring diagram.

This manual is written for service workshop personnel; its pressure tests, transmission overhaul procedures, and lifting operations call for mechanical experience and the specified workshop equipment.

Engine Service and Its Limits

The engine section covers removal and installation of the starting motor, alternator, water pump, fuel injection pump, nozzle holders, thermostat, radiator, and radiator guard. Cylinder-head installation includes the staged head-bolt tightening specifications and subsequent valve adjustment.

Engine installation includes mount-cushion identification and alignment checks using a dial gauge and centering tool 790-411-1100. Compression, blow-by, exhaust-smoke, and injection-timing checks provide diagnostic information before the engine is removed.

Internal engine overhaul: The opening page directs engine-detail work to the separate 95 Series Engine Shop Manual. This machine manual covers the engine tests and removal/installation work described here; it does not replace that separate engine publication for a full internal overhaul.

Powertrain Diagnosis and Overhaul

Separate procedures address the D20 main-clutch drivetrain and the different D21 Hydroshift configurations. Hydroshift coverage extends into the transfer assembly, planetary gear sets, clutch housings, piston seals, modulating valve, and selector/inching valve.

The transmission sections distinguish the earlier and later builds of D21E-6, D21P-6B, and D21S-6A. That distinction matters when selecting clutch-stack information and evaluating piston travel during an overhaul.

Troubleshooting charts address failure to move, low drawbar pull, delayed engagement, harsh shifting, and oil-level changes between transmission and bevel-gear cases. They connect symptoms with pressure measurements and control checks, helping narrow the fault before teardown.

The transfer-assembly procedures identify a bearing-damage risk during pinion installation. They also warn that incorrect use of forcing screws during bearing-cage removal can damage the cage or bearing end.

Undercarriage, Hydraulics, and Work Equipment

Track service is supported by inspection tables for links, pins, bushings, idlers, track rollers, and carrier rollers. Dry and lubricated track constructions receive separate maintenance standards rather than a single generic wear table.

Hydraulic diagnosis covers weak or slow blade movement, excessive cylinder drift, unstable blade control, and loader lift or bucket-dump faults. Pressure-test locations, control-valve section views, and work-equipment circuit diagrams support these checks.

Repair coverage includes hydraulic control-valve disassembly and assembly, cylinder seal work, and removal of blade lift, angle, tilt, bucket lift, and bucket dump cylinders. Power-angle-and-tilt dozer, straight-tilt dozer, and bucket/link arrangements are treated separately.

Always review the factory-specified safety protocols inside the documentation before beginning mechanical work, particularly operations involving raised equipment, stored hydraulic pressure, or heavy components.

Electrical and Workshop Reference Data

The wiring diagram identifies starting, charging, lighting, instruments, glow plugs, and the D21 neutral-safety circuit. The electric-wire-code tables explain conductor thickness and color markings for tracing the diagram.

Component weight tables support lifting preparation. Lubricant tables distinguish specified system quantities from normal refill amounts, while the maintenance-standard sections provide inspection clearances, wear limits, and component-specific tightening data.

Examples of Variant-Specific Specifications

The modulating-valve operating description gives a circuit setting of 27 kg/cm² for D21A-6, D21P-6, D21S-6, D21Q-6, and D21P-6A, compared with 20 kg/cm² for D21E-6, D21P-6B, and D21S-6A.

For the latter transmission group, the No. 4 clutch-piston standard stroke changes from 2.4 mm at serial numbers 60001–64855 to 3.1 mm at 64856 and up. The assembly section documents the associated air-check procedure and seal-leakage assessment.

Bookmarks, Diagram Detail, and PDF Format

Search and navigation: PDF text search is not available. Embedded bookmarks provide chapter and procedure navigation. Small wiring labels and connector numbers are readable when enlarged.

One printable, English-language PDF contains 493 pages, including the original cover/model-coverage page and the front-matter contents, revision lists, safety information, and reference tables. The separate 95 Series Engine Shop Manual is not included.