Yanmar 1GM10, 2GM20, 3GM30, 3HM35 Service Manual

You got a Yanmar marine diesel that’s knocking or burning oil? Don’t reach for a generic manual. I’ve seen too many guys wreck a good cylinder head using aftermarket torque numbers. What you need is the real thing – the Yanmar 1GM10, 2GM20, 3GM30, 3HM35 Service Manual. 463 pages of factory data that came straight from the engineers in Japan. This isn’t a reprint or a third-party hack job. It’s the same document the dealers use, with every spec you need to rebuild these engines right.

I’ve been turning wrenches since before some of you were born. This manual covers four different Yanmar models: the 1GM10, the 2GM20, the 3GM30, and the 3HM35. All marine diesels. All single-cylinder or multi-cylinder. If you’re rebuilding any of these, you need the factory procedure for the cylinder head torque sequence, the crankshaft end play, and the camshaft timing gear backlash. Chapter 2 has all that. Page 2-30 gives you the crankshaft specifications. Use them.

Basic Engine Rebuild – Cylinder, Crankshaft, and Camshaft

The basic engine section breaks down every rotating and reciprocating part. You get the cylinder block specs, the piston ring gap tolerances, connecting rod alignment, and the crankshaft journal diameters. The camshaft lobe wear limits are on page 2-58. The timing gear backlash is also covered. If you’re doing a full overhaul, start in Chapter 2 and follow the sequence. Do not skip the reassembly precautions in Chapter 14 and 15. The tightening torque table in Chapter 15 will save you from stripping threads. I’ve seen a 3GM30 block crack because a tech torqued the main bearing caps to aftermarket spec. That’s an expensive lesson. Stick to the factory numbers. The manual also includes the flywheel housing bolt torque and the connecting rod bolt torque. All in foot-pounds, as it should be.

Fuel System and Governor Tuning

Chapter 3 walks you through the fuel injection pump removal and installation. The injection nozzle opening pressure is specified. Don’t guess it. The fuel filter replacement interval is also listed. Chapter 4 covers the governor. The injection limiter prevents the engine from over-fueling at startup. The no-load maximum speed limiter controls the top end. Both need to be set with the engine hot. The manual gives you the procedure. If you have a 2GM20 that surges at idle, check the idling adjuster. That’s in Chapter 4 as well.

Cooling System: Direct Sea-Water vs Fresh Water

Two cooling systems are covered. Chapter 7 for direct sea-water cooling: water pump, thermostat, anticorrosion zink. Chapter 8 for fresh water cooling: sea water pump, heat exchanger, expansion tank, thermostat, and water temperature switch. If you’re converting a sea-water cooled engine to fresh water, Chapter 9 gives you the modification procedure. That’s critical for the 3HM35 because it often comes with fresh water cooling. The manual includes piping diagrams and cautions for inboard installation.

Why OEM Specs Matter for These Marine Diesels

Aftermarket manuals lift data from forums. This one is printed by Yanmar in Japan. 463 pages of verified specs. No generic torque values. No second-hand wiring diagrams. The electrical system chapter (Chapter 12) gives you the starter motor circuit, the alternator standard and optional, and the instrument panel wiring. If you’re chasing an electrical gremlin, you need the OEM diagram. Not a sketch. The manual also includes the battery specifications. All in AMP hours and CCA ratings.

3 Things You Should Know About Marine Gear Adjustments

First, the reduction and reversing gear section (Chapter 10) covers four different gear models: KM2P, KM3P, KM3V, and the V-drive. Second, the shim adjustment for the V-drive gear shaft and backlash adjustment are explained with diagrams. Third, the inspection and servicing steps include a detailed disassembly and reassembly procedure. If you’re rebuilding the marine gear, you need the factory clearance specs. The manual has them. For basic understanding of gear types, the Manual Transmission concept applies here, but the marine gear has its own unique adjustments. Also, if you’re comparing to automotive transmissions, the Manual Transmission article might help background, but stick to the Yanmar specs for the actual work.

If you need a more recent version, check the Yanmar 1GM10 2GM20 3GM30 3HM35 2002 Service Manual for any updates. For construction equipment applications, the Ammann Yanmar ViO15-2A, ViO20, ViO25, ViO30, ViO35 2006 Service Manual OEM covers compact excavators. Or the Ammann Yanmar Vi075-A, B7-Σ-A, SV100 2007 Service Manual | OEM Factory Specs for larger machines.

What torque values are given for cylinder head bolts?

Chapter 15 has a torque table. Use them.

Does the manual cover the 3HM35 freshwater cooling system?

Yes. Chapter 8 covers the fresh water cooling system including sea water pump, heat exchanger, expansion tank, thermostat, and water temperature switch. Page 8-10 shows the thermostat. The manual also has a separate chapter (Chapter 9) for modifying a sea-water cooled engine to fresh water. That is critical if you’re changing the cooling setup on a 3HM35. So you do get full coverage for all four models: 1GM10, 2GM20, 3GM30, and 3HM35.

You didn’t spend thousands on a Yanmar marine diesel to rely on guesswork. Get the factory documentation on your bench and do the job right. Download the Factory Manual and start working with real specs.