Description

Komatsu PC300LC-6, PC300HD-6 1999 Workshop Manual

I’ve been turning wrenches since before most of you were born, and I’ve seen what happens when a shop relies on generic aftermarket data. You get a stripped bolt head, a hydraulic line that blows at 3,000 psi, or a fuel system that won’t prime because the inlet restriction spec was copied wrong. That’s why I’m talking to you about the Komatsu PC300LC-6, PC300HD-6 1999 Workshop Manual. This is the factory binder that came off the engineering bench – 786 pages, original May 1999 print. If you’re working on an A83001-and-up serial number machine, this is your single source for engine, torque, fuel, and hydraulic data. No third-party guesswork. No photocopied diagrams that look like a Rorschach test.

Engine Overhaul and Standard Values

Section 20 – Testing and Adjusting – starts with a Standard Value Table for the engine. You get intake manifold pressure numbers, blow-by pressure limits, and valve clearance specs. That section alone covers measuring engine speed, intake air restriction, fuel filter inlet restriction, coolant temperature, and exhaust color. The manual tells you which tools to use – things like a tachometer, pressure gauge set, and a blow-by meter. If you’ve ever had a Komatsu SAA6D125 engine that won’t fire under load, you’ll use the governor motor lever stroke procedure on page 20-44 to see if the fuel rack is stuck. That page number is in the book, but I’m not spamming it – go find it.

What Torque Specs Are Listed in the Forward Section?

Page 00-5 under “Standard Tightening Torque” gives you the factory values for bolts, nuts, and studs on this machine. These are not generic “tighten to snug” numbers. You get torque ranges for everything from the cylinder head bolts to the final drive mounting flange. The manual also includes a conversion table for inch‑pounds to foot‑pounds. I’ve seen backyard mechanics use a ½‑inch wrench and guess – don’t be that guy. The fuel injection pump mounting bolts, for example, require a specific torque that keeps the pump aligned with the drive gear. Miss it by 10 ft‑lb and you’ll be chasing a vibration that slowly eats the coupling.

Fuel System Testing: Inlet Restriction and Return Flow

Under the fuel section inside Testing and Adjusting, the manual walks you through measuring fuel filter inlet restriction. You hook a vacuum gauge between the primary filter and the transfer pump. If restriction exceeds [DATA NEEDED] in‑Hg at rated engine speed, you’re choking the pump. The manual also covers blow‑by pressure measurement – if you see more than [DATA NEEDED] inH2O, rings or liners are worn. And don’t skip the section on bleeding air from the fuel system. There’s a specific sequence: crack the injection pump bleed screw, crank until fuel flows without bubbles, then tighten. That’s the difference between a machine that starts in one crank and one that has you chasing air locks all morning.

Check the Electrical Wiring Diagrams Before You Solder

Section 10 – Structure and Function – ends with the Electrical Wiring Schematic and Electrical Wiring Diagram. These are full‑page foldouts in the original manual, and the PDF preserves them cleanly. You get connector pin numbers, wire colors (based on the Electric Wire Code table in Forward), and locations of every solenoid valve, PPC valve, and controller. If you’re swapping a boom holding valve or tracing a PPC safety lock valve circuit, you need this diagram. The troubleshooting chapter (20‑60 onward) uses these diagrams to walk you through service codes. For example, code E‑1 checks the governor pump controller power source. Without the factory schematic, you’re cutting wires blind.

786 Pages of Factory-Derived Data

The manual is organized into six main sections: 00 Forward, 01 General, 10 Structure and Function, 20 Testing and Adjusting, 30 Disassembly and Assembly, 40 Maintenance Standard, and 90 Other. That 786‑page count includes every torque table, hydraulic circuit diagram, and troubleshooting chart. The serial number range is A83001 and up for both the PC300LC‑6 and PC300HD‑6 models. This isn’t a reprint of a reprint – it’s the original 1999 Komatsu document. If you have a related model from 1996 or 2002, check the Komatsu PC300LC-6 PC300HD-6 1996 Service Manual or the Komatsu PC300LC-6, PC300-6, PC350-6, PC350LC-6 2002 Workshop Manual and Komatsu PC300LC-6 PC300-6 PC350-6 PC350LC-6 2002 Workshop Manual for coverage differences. Outside of excavators, if you’re curious about how the travel motor compares to a standard automotive transmission, the section on final drive and travel motor in Section 10 covers the mechanics – similar to a Manual Transmission in a vehicle but with hydraulic motors. The control valve logic is like learning to shift a Manual Transmission – timing and pressure matter.

Frequently Asked Questions

Does this manual include the serial number range?

Yes. It covers PC300LC-6 and PC300HD-6 from serial A83001 and up, printed May 1999.

How do I check the LS differential pressure according to the factory procedure?

Find the section “LS Differential Pressure” inside Testing and Adjusting. You’ll need a pressure gauge set. Connect the gauge to the LS pressure port and the pump discharge port. Run the engine at low idle with the work equipment stalled. The differential should be within the standard value range listed in the book. If it’s out of spec, the manual walks you through adjusting the LS-EPC valve or replacing the control valve spool. That procedure is cross‑referenced to the hydraulic circuit diagram in Section 10, so you can trace the line to the valve body. Don’t skip the step about releasing remaining pressure in the hydraulic circuit (also described) – I’ve seen a gauge line blow off because somebody didn’t bleed the system first.

If you’re ready to stop guessing and start working with hard numbers, this is the document that keeps you safe and your machine running. No reprints, no aftermarket data – just the original Komatsu factory file. Access the Factory Manual now and get the torque specs, fuel system adjustments, and wiring diagrams that will keep you from calling the dealer after a weekend of frustration.