Description

Komatsu D31A, GD22AC, GD28AC, EC50V, EC75Z 1984 Workshop Manual

If you’re tearing into a Komatsu 4D105-3 diesel engine without the factory manual, you’re wasting time and risking a comeback. I’ve seen guys guess the injector timing and end up with a bent pushrod. Don’t be that guy. The Komatsu D31A, GD22AC, GD28AC, EC50V, EC75Z 1984 Workshop Manual is the only document I trust when I need the exact charge pressure or the right way to reseat a valve. 252 pages of factory data, not some reprint that blurs the torque table.

This manual came off a real Komatsu press in April 1984. Printed in Japan. No aftermarket guesses, no third-party shortcuts. Every spec is the one the assembly line used. Period.

Why This 1984 Komatsu Manual Belongs on Your Bench

Pop the hood on a D31A dozer or an EC50V excavator, and you’re looking at the 4D105-3 engine family. The manual covers the following machine models directly: D31A (P,S,Q-16), GD22AC-1A, GD28AC-1A, EC50V,VS-1, EC75Z,ZS-1, plus the EG45, CD40, W40, and BC100 variants. Each engine variant has its own specs, and they’re not interchangeable. Page 1 of the manual lists the exact engine-model pairing so you don’t put the wrong injection pump on a GD22AC. Page 01-004 gives you the full specifications table — bore, stroke, compression ratio, firing order, fuel injection timing. That page alone saves a blown head gasket.

7 Sections That Matter

The manual is laid out in a logical sequence, not a random pile of scans. You get:

• 01 GENERAL – General view drawings, performance curves, weight tables, and a general assembly drawing of the engine.
• 11 STRUCTURE AND FUNCTION – How the fuel system, lubrication, and cooling circuits work. Essential before you touch a wrench.
• 12 TESTING AND ADJUSTING – This is where the time is saved. Compression test values, injector pop pressure, governor adjustments. Page 12-001 starts the procedures.
• 13 DISASSEMBLY AND ASSEMBLY – Step-by-step order for pulling the head, splitting the block, and reassembling with correct clearances.
• 14 MAINTENANCE STANDARD – Wear limits, allowable tolerances, and when to replace vs. reuse.
• 15 REPAIR AND REPLACEMENT – What to do when the standard is exceeded: boring, sleeving, grinding valves.

Each section is indexed with its own page range, so you jump straight to 13-xxx without flipping through the whole Manual Transmission? No, wait — that’s a different topic. Stick to the book.

Testing and Adjusting: Get the Numbers Right

Section 12 isn’t a suggestion. It’s the difference between a engine that runs 5000 hours and one that smokes at 500. For the EC50V, the injection timing is listed for the 4D105-3L engine. For the GD28AC, it’s the 4D105-3G. If you use the wrong timing, you’ll burn pistons. The manual gives you the exact procedure — which gauge, where to set the dial indicator, and the correct plunger lift. No guessing.

Does It Cover the D31A and GD22AC Differently?

Yes. The D31A gets the 4D105-3C engine; the GD22AC gets the 4D105-3D. The oil pump, injector, and even the front cover differ. The manual spells out the differences in the general view drawing on page 01-002 and in the specifications table. You don’t need to cross-reference multiple books — it’s all here. For the EC75Z, the manual includes the magnetic valve and wiring details that aren’t in the D31A section. That’s why you need the full document, not a generic diesel manual.

Related Manuals Worth Having

• Komatsu EC Series Shop Manual
• Komatsu EC Series Service Manual: EC50V, EC35V, EC105V, EC170V, EC260V
• Komatsu D31A D31E D31P D31PL D31PLL Workshop Manual 404 Pages

Source Authenticity: OEM vs Aftermarket

This is an original Komatsu Shop Manual, not a copy from a third-party site. I’ve used aftermarket manuals that list the wrong oil capacity for a 4D105-3. One misprinted torque value on a connecting rod bolt and you’re buying a new engine. The factory manual comes with the Komatsu part number SEBE61300300 and the print date 04-84. You can verify it against Komatsu’s own parts database. That’s the level of certainty you need when a customer’s machine is down. If you’re working on a manual transmission for a different project, that’s another manual. For this engine, this is it.

FAQ

Does this manual cover the fuel injection pump?

Yes, section 11 covers structure and function.

Can I use this for a 1985 model?

This manual is printed in 1984 and covers specific machine models as listed. For D31A it’s the -16 series. If your model differs, cross-reference the engine serial number. The 4D105-3 engine remained largely unchanged through the mid-80s, but always verify with Komatsu service bulletins. The manual includes maintenance standards and repair limits that apply to the 4D105-3 family. Use it as your baseline, but check for updates.

You need a workshop manual that doesn’t waste your time with fluff or reprints. This is the factory spec document for the Komatsu 4D105-3 series. 252 pages, original OEM print, and every torque value verified on the shop floor. Access the Factory Manual now and get your machine running right.