Description

Komatsu D20A-6, D21A-6, D20P-6, D21E-6, D20P-6A 1990 Workshop Manual

Listen. I’ve seen too many guys try to time a 4D95S-W-1 engine using a PDF they found on some forum. Then they wonder why the valve clearance is off and the exhaust turns black. This is the OEM manual for the Komatsu D20A-6, D21A-6, D20P-6, D21E-6, D20P-6A 1990 Workshop Manual. 493 pages of factory procedures, torque specs, and hydraulic circuit diagrams. You don’t guess with a Komatsu – you use the book that came from the factory.

If you’ve ever chased a hydraulic leak in the steering system or fought with a hydroshift transmission that won’t engage, you know the cost of aftermarket garbage. This manual gives you the exact testing data, assembly sequences, and maintenance standards that Komatsu printed in 1990 for dealer techs. No re-typesetting. No missing pages. Period.

Engine Section: Valve Clearance and Fuel Injection Timing

Section 10 (ENGINE) covers the 4D95S-W-1 diesel from testing to complete overhaul. The sub-section “TESTING AND ADJUSTING” includes the tool list and step-by-step procedures for adjusting valve clearance, measuring compression pressure, blow-by pressure, and adjusting fuel injection timing. You’ll find the exact specs on page 12-1 for TESTING AND ADJUSTING DATA. That’s where you get the clearance numbers – not from a YouTube comment. The manual also covers nozzle holder removal and installation, cylinder head work, and the full engine removal/installation sequence. If you need to pull the engine, you get the hoist points, bolt torques, and alignment checks.

Power Train: Hydroshift Transmission and Steering Systems

Section 20 (POWER TRAIN) is a beast. It starts with structure and function for the D20-6 and D21-6 variants, then dives into the hydroshift transmission hydraulic circuits. You get multiple pages dedicated to transmission control valves, damper and universal joint specs, and the steering hydraulic system. The troubleshooting section in 22 TESTING AND ADJUSTING lists seven common complaints – from “Machine does not move off” to “Time lag is excessive when moving off or gearshifting.” Each one comes with a diagnostic flowchart. For the main clutch (D20-6), there’s removal, disassembly, and assembly instructions complete with torque values.

Why OEM Documentation Beats Aftermarket

This manual is the original Komatsu print – not a scan of a scan. The first few pages include a “LIST OF REVISED PAGES” that shows exactly which pages were updated and when. That’s authenticity you can’t get from a third-party reprint. Komatsu designed this for dealer techs who already knew the basics; it assumes you have a torque wrench and a dial indicator. The wiring diagrams in Section 80 (ELECTRICAL SYSTEM) are factory-correct, not redrawn. If you’ve ever tried to trace a short using an aftermarket schematic, you’ll appreciate the difference.

Audience: Who Needs This Manual?

Home garage enthusiasts who own a D20P-6 or D21E-6 and plan to do their own engine overhauls. Shop owners with a fleet of these dozers who want their techs to stop wasting billable hours guessing. Beginners – but only if you have mechanical experience and a copy of the engine shop manual for the 4D95S-W-1 (this manual references it). The writing is direct, with tool lists at the start of each testing section. You will not find “easy fix” advice. You will find torque specs in ft-lbs and oil pressures in psi.

Tool List and Safety Warnings You Need

Every testing section in this manual includes a “TOOL LIST FOR TESTING AND ADJUSTING.” For example, to adjust fuel injection timing you need a timing light, a dial gauge, and a fixture for the injection pump. The manual tells you the Komatsu part numbers for those tools. Safety warnings appear throughout – like when removing the cylinder head, it tells you to drain the coolant and tag all hoses. Do not skip those. The manual also covers measuring blow-by pressure, which requires a manometer; the standard tolerances are listed in Section 12.

FAQ

Does this manual cover the D20P-6A and D21E-6 models?

Yes. It covers all six models listed in the serial number table: D20A-6, D21A-6, D20P-6, D21E-6, D20P-6A, and additional variants like D20S-6, D21S-6A, etc. Serial numbers 60001 and up.

What engine is covered in this manual?

The Komatsu 4D95S-W-1 diesel engine. For detailed engine overhaul, the manual directs you to the separate 95 Series Engine Shop Manual.

How many pages are dedicated to the power train?

Over 200 pages across sections 20 to 24, including structure, testing, disassembly, and maintenance standards.

Is this a reprint or a copy of the original?

This is the original OEM PDF from Komatsu. The first pages include the list of revised pages and the part number SEBM01040604. No aftermarket alterations.

Before you tighten that cylinder head or adjust the steering brake linkage, get the factory document. If you need manuals for other Komatsu models, check out Komatsu WA65-5 WA70-5 WA80-5 2005 Workshop Manual or the Komatsu WH609-1E0 WH613-1E0 WH713-1E0 WH714H-1E0 WH716-1E0 Workshop Manual. For a smaller dozer, the Komatsu PW95R-2 Workshop Manual – 520 Pages of Factory Specs might be relevant. Before you touch the transmission, read about the basics of a Manual Transmission and the specific Manual Transmission layout used in these models. Access the Factory Manual from AutoRepairManuals. Get the exact same document that Komatsu issued to dealers. No aftermarket re-typesetting. No missing pages. This is the one.