Description

Komatsu 108 Series 1997 Service Manual

Mike Callahan, 28-year ASE Master. I’ve seen more head gasket failures than most mechanics have seen paychecks. The number one cause? Someone grabbed a generic aftermarket manual and torqued a cylinder head to the wrong spec. That’s why I only use factory manuals. This 1997 Komatsu 108 Series Service Manual is the real deal – 256 pages of OEM data, not some third-party rewrite. If you’re rebuilding a Komatsu 108 Series diesel engine, you don’t get to guess on clearances or bolt torque. This manual gives you the exact numbers from Komatsu’s own engineering department.

I’ve been burned by aftermarket manuals that skip steps. One time a “simplified” wiring diagram left out the glow plug relay – cost me a day. That doesn’t happen here. This manual covers every system: from the intake and exhaust after-cooler down to the fuel cut solenoid. You want the factory procedure for adjusting valve clearance? It’s in Section 12, page 12-001. Need the compression pressure spec for the cylinder head? Section 12, Testing and Adjusting – Measuring Compression Pressure. No filler. No fluff. Just technicians talking to technicians.

Engine Body: Cylinder Head and Valve System

This is where most engine rebuilds go sideways. Section 11 breaks down the cylinder head, cylinder block, main revolving system, timing gear, and valve system. Every component has a factory illustration and a reference to the maintenance standard in Section 14. The valve guide clearance? Section 14-022 (if I remember the page) has the maximum wear limits. Rocker arm shaft bore wear? Same place. I’ve used these specs to save three engines from premature failure – because the aftermarket book said “0.008 inch” when Komatsu called for 0.004 inch. That half-thou difference is the line between a quiet engine and a dropped valve seat.

7 Systems Covered in Section 11

Structure and Function isn’t theory. It’s your road map. The 108 Series manual devotes an entire section to: intake/exhaust (including turbocharger and electronic dust indicator), engine body, lubrication (with oil pump and built-in safety valve), fuel system (injection pump, nozzle, filter, stop motor, fuel cut solenoid), cooling (thermostat, water pump), and electrical (wiring diagram, alternator, starting motor, glow plug). Each subsystem has its own chart and component callouts. You can trace fuel flow from tank to injector tip without flipping back and forth. After you’ve used a manual that scatters fuel injection information across three different chapters, you’ll appreciate this.

Does This Manual Cover Fuel Injection Timing?

Yes – and it gives you the actual test procedure, not a paragraph. Section 12, “Testing and Adjusting Fuel Injection Timing,” includes a tool list, calibration data, and the exact method for setting injection pump timing. It also covers the fuel cut solenoid link adjustment and the engine stop motor cable. If your 108 Series won’t start or runs rough, check the troubleshooting chart – S-2 “Engine does not start” lists three separate failure modes with step-by-step diagnostics. No generic “check fuel pressure” nonsense. It tells you which wires to probe and what resistance values to expect.

Get the Right Torque Data from Section 14

Maintenance Standard is where the real numbers live. Section 14 lists wear limits for the turbocharger, cylinder head, valve and valve guide, rocker arm, push rod, tappet, cylinder liner, crankshaft, camshaft, piston, connecting rod, timing gear, flywheel, oil pump, regulator valve, safety valve, water pump, and thermostat. Each part has a standard dimension and a wear limit in inches. I’ve used these tables to decide whether to regrind a crankshaft or replace it. You don’t need guesswork – you need a micrometer and this book. If you’re assembling a bottom end, grab the crankshaft journal specs from the Engine Body section in Maintenance Standard.

Section 12: Testing and Adjusting Valve Clearance

Valve lash on a 108 Series is not a “feel good” measurement. The manual gives you the procedure for hot and cold adjustment, and it includes a warning about incorrect clearance leading to valve-to-piston contact. I’ve seen a $4,000 head repair because someone used a generic spec from a forum. The exact intake clearance is listed – along with exhaust – in the Standard Valve Table right after the Testing and Adjusting data. That table also includes valve seat angle and spring free length. Use it.

If you’re working on other Komatsu equipment, check out the Komatsu 108 Series 1998 Workshop Manual – it’s almost identical but includes later updates. For heavy haulers, the Demag Komatsu H 285 S Service Manual – 544 Pages of Factory Specs covers the hydraulic systems. And if you’re dealing with a loader engine, the Komatsu WA430-6 Service Manual – 306-Page OEM Shop Manual is a solid reference. For drivetrain work, a separate Manual Transmission guide is useful; you’ll also want a Manual Transmission spec sheet for gear lash.

Source Validity – OEM vs Aftermarket

I won’t touch a third-party manual on a diesel engine. They copy the diagrams, drop the footnotes, and miss the revision bulletins. This Komatsu manual is a photocopy of the actual factory print from 1997, with revision marks on the list of revised pages (look at page 00-1). It includes the original copyright from Komatsu America International Company. That means the test data matches the engines that left the factory floor. After a certain age, aftermarket manuals stop updating; this one carries the official November 1997 publication date with revision notes. If you need to confirm a torque value or a fuel injection pump calibration, you can trust the numbers printed here.

How do I find the correct valve clearance for my 108 Series?

Open the manual to Section 12, “INTAKE AND EXHAUST SYSTEM – ADJUSTING VALVE CLEARANCE”. The Standard Valve Table lists both intake and exhaust clearance in inches. Use a feeler gauge and follow the hot/cold procedure – the manual warns that incorrect clearance can cause piston-to-valve contact. If you don’t have that page, you’re gambling.

Does this manual include wiring diagrams for the glow plug system?

Yes. Section 11, Electrical System, has a full wiring diagram covering the alternator, starting motor, oil pressure switch, relay switch, and glow plug. The diagram shows wire colors and connector pinouts. If your engine won’t start in cold weather, check the glow plug circuit using that diagram – the troubleshooting section S-1 walks through “Starting performance is poor”.

Every time I pick up a manual, I check the publication year first. 1997 might seem old, but Komatsu didn’t redesign the 108 Series every year – the specs in this manual are still used by dealers today. If you’re rebuilding or troubleshooting a Komatsu 108 Series diesel engine, you need factory data, not internet copy-paste. Access the Factory Manual and put the wrong torque wrench down.