Description

Komatsu D20A, D21A, D20P, D21P, D20PL 1981 Workshop Manual

You’re staring at a Komatsu dozer that won’t steer right, or maybe the engine oil pressure sits lower than it should. The aftermarket PDF you obtained last week gave you a torque spec for the final drive that was off by 15 ft-lb. That’s how bolts snap and seals weep. I’ve seen it. This Komatsu D20A, D21A, D20P, D21P, D20PL 1981 Workshop Manual is the original factory book—printed in Japan in 1981, 223 pages of the exact procedures Komatsu wrote for their service techs. It’s not a re-wrap of a Chilton or a scanned library copy with missing pages. It’s the real thing.

Engine Testing and Adjusting: What the Manual Covers

The ENGINE section (Section I, Chapter 12) starts with a full list of standard values for inspection and adjustment. Need the compression pressure range? It’s in there. The intake and exhaust system checks, lubrication system, fuel system, cooling system—each gets its own subsection. Page 1 of the manual shows the machine model and serial number location so you verify you’re working on the correct platform. That matters when you’re ordering parts for a D20PL that’s been modified over 40 years.

7 Systems Covered in This Workshop Manual

Komatsu split this manual into seven major groups: GENERAL, ENGINE, POWER TRAIN, UNDERCARRIAGE, HYDRAULIC SYSTEM, WORK EQUIPMENT, and the front matter with safety notices and foreword. Torque specs aren’t scattered—they appear in the MAINTENANCE STANDARD sections for each component group. For example, the final drive standards (Section 24) list fastener torques, clearance limits, and wear tolerances for the bevel gear shaft, steering clutch, and brake. You don’t have to hunt across three different documents.

Why Factory Torque Specifications Matter

I’ve torqued enough head bolts to know that aftermarket manuals often round up or down to the nearest 10 ft-lb. Komatsu didn’t. The standard values for the engine body (Chapter 12) are given in both metric and imperial, with specific inch-pound values for small fasteners. The HYDROSHIFT TRANSMISSION for the D21-5 models (Section 21) includes hydraulic diagrams and control valve structure. Without the factory pressure numbers, you’ll waste hours chasing a shift problem that’s actually a worn relief valve.

Does This Manual Cover the Undercarriage and Hydraulic System?

Yes. The UNDERCARRIAGE section (III) details the track frame, idler, track roller, carrier roller, recoil spring, and track shoe—with maintenance standard tables for each. The HYDRAULIC SYSTEM section (VI) gives the structure and function of the control valve, main relief valve, safety valve, and suction valve, plus the hydraulic diagram for the cylinder circuit. Bleeding air from the angle cylinder head circuit is covered in Section 62. If you’re rebuilding a D20A’s undercarriage, this manual gives you the wear limits for the idler and track roller. No guessing.

Source Authenticity: Original OEM vs. Aftermarket Copies

This file is a direct scan of the original Komatsu shop manual, SEBMO101D00. You can see the printer mark “PRINTED IN JAPAN 05-81(01)” on page 1. Aftermarket reprints often lose the fold-out diagrams and the subtle shading in the hydraulic schematics. This manual includes the foreword explaining the organization—Structure & Function, Testing & Adjusting, Disassembly & Assembly, Maintenance Standards—which is exactly how I teach my junior techs to approach a repair. If you’ve been burned by third-party docs that skip the safety notes (page 2 has a full safety notice with the symbol ⚠), you’ll appreciate having the real Komatsu document.

Get the Right Data for Your D20P or D21P

The manual covers five model variants: D20A, D21A, D20P, D21P, and D20PL. The serial number breakpoints are listed on the cover—D20,21A,PL-5 from 45001 up, D20,21P-5 from 45003 up. If your machine falls in that range, this book fits. It includes the hydroshift transmission and steering control hydraulic circuit for the D21-5, and the main clutch with inertia brake for the D20-5. Don’t rely on a generic tractor manual that lumps all small dozers together.

FAQ

Does this manual include the engine overhaul procedure with torque specs?

Yes. Section I-12 covers engine testing and adjusting. The standard values table lists head bolt torque, valve clearance, injection timing, and oil pressure specs. The manual does not include step-by-step disassembly photos, but the written procedures and torque values are factory-original.

Can I use this for a D20PL-7 model built in 2008?

No. This manual is for the D20-5 series produced from 1981 onward. For a D20PL-7, you need the 2008 workshop manual. See Komatsu D20PL-7 2008 Workshop Manual — OEM Factory Specs.

Is the wiring diagram included?

No.

What about the hydroshift transmission adjustment?

Section II (Power Train) covers the hydroshift transmission structure, hydraulic diagram, and control valve for D21-5 models. Section 22 includes oil pressure and temperature measurements, lever/pedal travel checks, and operating force measurements. The maintenance standard in Section 24 lists wear limits for the transmission control valve, steering pump, and bevel gear shaft. If you need to adjust the clutch pedal free play or measure transmission oil pressure, it’s all there with factory tolerances. This is the kind of data that prevents you from over-tightening a steering brake bolt and cracking the housing—I’ve seen it happen with generic manuals that don’t list the correct torque for the steering brake retaining bolts.

If you’re rebuilding a Komatsu dozer from this era, you need the book that came from the factory. The aftermarket alternatives will cost you in wasted time and broken hardware. Access the Factory Manual from AutoRepairManuals and get the 223-page OEM document that Komatsu wrote for their own technicians. For related manuals, check the Komatsu WA65-5 WA70-5 WA80-5 2005 Workshop Manual and the Komatsu WH609-1E0 WH613-1E0 WH713-1E0 WH714H-1E0 WH716-1E0 Workshop Manual. For background on how a manual transmission works, see Manual Transmission and Manual Transmission.