Komatsu D20A-6, D20P-6, D20PL-6, D20PLL-6, D21A-6, D21E-6, D21P-6, D21PL-6, D20P-6A, D21P-6A, D21P-6B Operation and Maintenance Manual (P/N SEAM01010601)

Komatsu’s Operation & Maintenance Manual (P/N SEAM01010601) covers 1980s–1990s D20 and D21 Series 6 bulldozers in the model and serial-number range listed above. It describes machine operation, lubrication, scheduled maintenance, checking, and adjustment.

PDF Bookmarks, Diagram Detail, and Page Count

Section access and small labels: Embedded PDF bookmarks lead to operating, maintenance, adjustment, troubleshooting, and safety sections. Body-text search is unavailable. Small labels in the fuse arrangement and battery-connection illustrations are readable when enlarged.

One printable, English-language PDF contains 121 pages, including the original cover and the 23-page Safety and Operation section.

Machine Operation, Service, and Undercarriage Adjustment

The following is a selection of covered tasks. Other topics include transportation and long-term storage.

• Machine handling: Pre-start inspections, instrument and warning-lamp functions, gear shifting, inching-pedal operation, steering, parking, and cold-weather starting.

• Fuel and cooling: Step-by-step instructions for fuel-filter replacement and fuel-system bleeding, water-separator draining, radiator cleaning, and cooling-system flushing.

• Drivetrain maintenance: Oil changes and strainer cleaning for the main clutch and transmission, with separate D20 and D21 servicing references.

• Controls and undercarriage: Steering-lever, brake-pedal, main-clutch, and inertia-brake adjustments; track-tension checks, link-pitch measurement, and idler-guide adjustment.

• Blade equipment: Lubrication diagrams for hydraulic tilt and angle-tilt dozers, cutting-edge and end-bit replacement, and angle-circuit air bleeding.

• Troubleshooting and electrical references: Symptom-based engine, electrical, and chassis checks, fuse arrangement and circuit information, and battery booster-cable connection illustrations.

This manual is suited to operators and owners carrying out routine machine care; engine valve-clearance work is referred to a Komatsu distributor because special tools are required.

Daily Operation and Cold-Weather Preparation

Separate operating instructions distinguish the D20 main-clutch controls from the D21 transmission and inching controls. The D21 coverage also explains the different inching-pedal behavior of the two-speed and three-speed versions.

Cold-weather coverage combines preheating guidance, antifreeze mixing tables, and battery specific-gravity conversion data. After-work precautions address frozen undercarriage components and water on hydraulic-cylinder rods, which can damage cylinder seals when frozen.

Scheduled Maintenance and Fluid Selection

Maintenance tables organize work from 50 through 4,000 service hours, with separate initial-service and when-required tasks. Oil-filler and level-gauge position views identify the service points, while grease-fitting illustrations distinguish hydraulic tilt equipment from angle-tilt frames.

Fuel-filter servicing includes both feed-pump bleeding and use of the automatic air-bleed mechanism. Air-cleaner instructions distinguish cleaning the outer element from replacing the inner element.

The fuel, coolant, and lubricant tables relate fluid selection to ambient temperature and distinguish total system capacity from normal refill quantity. That distinction helps owners interpret fluid requirements when planning routine service.

Clutch, Track, and Blade Service

The adjustment section provides illustrated procedures for steering and brake travel, D20 clutch-pedal play, and the main-clutch inertia brake. Incorrect inertia-brake adjustment can damage transmission gears and the gearshift lever.

Undercarriage inspection covers grouser height, track-roller diameter, link pitch, and idler-guide wear. Track-shoe bolt instructions include tightening-sequence drawings and distinguish shoe bolts from master-link connecting bolts.

Blade servicing covers reversing or replacing cutting edges and end bits. The hydraulic sections describe angle-circuit bleeding and warn that improper initial cylinder bleeding can damage piston packing.

Troubleshooting Scope and Service Precautions

The troubleshooting guide links symptoms such as overheating, starting difficulty, charging faults, poor steering, and slow blade lift to checks or corrective actions. It is a guide to common faults rather than a complete diagnostic or internal-overhaul manual.

Scheduled valve-clearance checking, alternator and starter repair, and water-pump repair or replacement are referred to a Komatsu distributor.

Always secure the machine on level ground and follow the manual’s blade-support and hydraulic-pressure precautions before hands-on work.

Examples of Idler-Clearance and Track-Wear Data

Idler-guide adjustment data distinguish clearance exceeding 1.5 mm from the adjusted clearance of 0.5 mm at one end. Individual shims are 1.0 mm thick.

Track-link inspection lists a standard pitch of 135 mm and a reversing limit of 138 mm. These dimensions accompany the link-pitch measurement illustration and the guidance to involve a Komatsu distributor when repair or reversing limits are reached.