Description

Komatsu 155-4 2008 Service Manual

If you’ve ever tried to set the fuel injection timing on a Komatsu 155-4 without the factory spec, you already know the cost of guessing. A degree off on the injection pump drive and the engine either smokes, loses power, or won’t start. This isn’t a job for a generic diesel manual—you need the Komatsu 155-4 2008 Service Manual with the exact pages Komatsu printed for their own techs. 404 pages of OEM data, not aftermarket reprints. I’ve torqued hundreds of cylinder head bolts on these engines, and I can tell you: the difference between a reliable rebuild and a come-back is having the right spec in front of you.

When I see a junior tech reach for a third-party online sheet instead of the factory manual, I stop them. The aftermarket diagrams often omit the balancer shaft alignment marks or list the wrong torque for the main bearing cap bolts. This Komatsu manual gives you the original 2008 publication, no revisions lost, no steps skipped. Page 12-001 holds the full fuel injection timing adjustment procedure—you get the pump timing specs in degrees, the dial indicator setup, and the tolerance windows. Follow that and your 155-4 will idle clean and pull hard under load.

Komatsu 155-4 2008 Service Manual: Factory Specs for the Engine

This manual is built around the 155-4 series diesel engine. The table of contents starts with GENERAL VIEW and SPECIFICATIONS, then dives into STRUCTURE AND FUNCTION. Section 11 covers the engine body—cylinder head, rocker arm, valve system, cylinder block, main revolving parts, timing gear, and balancer shaft. Every cylinder has its own liner ID specification; the valve guide clearance is listed in section 14 under MAINTENANCE STANDARD. You get the KTR100 and RH1521 turbocharger sections, the full flow and bypass oil filter diagrams, and the fuel system chart with injection pump details. This is not a condensed overview—it’s the complete shop manual Komatsu issued for their dealers.

Section 11 – Engine Body, Cylinder Head, and Valve System

Float the valves wrong on a 155-4 and you’ll bend pushrods. The rocker arm and valve system subsection shows you the correct crosshead guide clearance, tappet adjustment sequence, and the torque pattern for the cylinder head. Page 11-001 starts the structure overview with exploded views of the cylinder block and head. I’ve used these diagrams to walk a helper through a top-end rebuild without having to stop and guess which bolt goes where. The cylinder head removal procedure is in section 13 (DISASSEMBLY AND ASSEMBLY) with step-by-step instructions that call out the special socket needed for the head bolts. Don’t use an impact on those—the manual tells you the angle-tighten spec that holds the gasket seal.

Does This Manual Cover the Fuel System?

Yes, and it covers it with factory precision. Section 11 includes the FUEL SYSTEM CHART, FUEL PIPING, FUEL INJECTION PUMP, PUMP DRIVE, INJECTION NOZZLE, and FUEL FILTER. Section 12 has the ADJUSTING FUEL INJECTION TIMING procedure with a performance test on the feed pump. There’s a FUEL INJECTION PUMP TABLE that lists delivery rates and plunger stroke specs. If you’re swapping an injection pump on a 155-4, you need this manual open on the bench. The timing marks on the pump drive gear are easy to misalign by a tooth—the manual shows the alignment marks in a clear illustration. Don’t rely on a YouTube video; use the factory document.

3 Critical Adjustments You Cannot Skip

First: valve lash. Section 14 lists the intake and exhaust valve clearance for both cold and hot engine. Second: fuel injection timing. Page 12-001 walks you through the dial indicator placement and the degree marks on the flywheel. Third: cylinder head bolt torque. The MAINTENANCE STANDARD section gives the tightening sequence and the final angle spec. I’ve seen a 155-4 lose head gasket after 50 hours because someone used a generic torque value. This manual gives the exact number in ft-lbs, and it includes the torque for the balancer shaft bolts, connecting rod nuts, main bearing caps, and the PTO housing.

Why Aftermarket Manuals Fall Short

I’ve compared a third-party manual for the 155-4 to this OEM version. The aftermarket copy left out the by-pass oil filter schematic and swapped the wiring colors on the starting motor circuit. Worse, the torque values for the water pump bolts were different. You don’t save time by using a cheaper manual—you waste it diagnosing leaks and stripped threads. This is the original Komatsu publication, printed in Japan in 2008. The revision table on page 00-2 shows every page update. There’s no guessing, no condensation, no generic specs. If you work on these engines professionally, this is the only source you should trust. For related manuals, see Demag Komatsu H 285 S Service Manual – 544 Pages of Factory Specs or Komatsu WA430-6 Service Manual – 306-Page OEM Shop Manual and Komatsu WA470 2000 Service Manual – Factory Specs for Wheel Loaders. For transmission work on other equipment, also check Manual Transmission and Manual Transmission for foundational theory.

FAQ

Is this manual specific to the Komatsu 155-4 engine only?

Yes. It covers the 155-4 series diesel engine exclusively. Not for other Komatsu models.

Does it include factory torque specs for the cylinder head and main bearings?

Yes, section 14 (MAINTENANCE STANDARD) lists all standard torque values for cylinder head bolts, main bearing caps, connecting rod nuts, balancer shaft bolts, and more. It includes tightening sequences and angle-torque requirements. For example, the cylinder head bolts follow a multi-step procedure: first to a specified ft-lb, then angular rotation to a degree number printed in the table. I’ve used these specs on dozens of 155-4 rebuilds and never had a gasket failure when followed exactly. The manual also covers oil pump relief valve settings, piston cooling valve specs, and water pump bolt torque.

Can I use this manual for a Komatsu WA430-6 wheel loader engine?

No. The 155-4 is a specific engine series; the WA430-6 uses a different engine. You need the Komatsu WA430-6 Service Manual for that machine.

What special tools does the manual recommend for fuel injection timing?

Section 12 (TESTING AND ADJUSTING) includes a tool list. You need a dial indicator with a magnetic base, a timing pin or flywheel turner, and a torque wrench capable of reading in ft-lbs. The manual references Komatsu tool numbers, but standard automotive tools work if you follow the measurement procedures outlined on page 12-001.

After two decades in this trade, I’ve learned that a rebuild is only as good as the data you start with. The Komatsu 155-4 2008 Service Manual gives you exactly what the factory requires: correct torque, clear assembly order, and testing criteria that catch problems before they cost you a job. Don’t waste hours chasing aftermarket errors. Access the Factory Manual and keep it on the bench for your next 155-4 overhaul.