Yanmar GM & HM Series Diesel Inboard Engine Shop Manual

This shop manual covers Yanmar GM and HM series one-, two-, and three-cylinder diesel inboards, including freshwater-cooled F variants. Engines with C (saildrive) or V (V-drive) suffixes are excluded.

• Engine repair: Engine removal, cylinder-head and rocker-shaft service, piston and crankshaft inspection, main bearings, camshaft timing, and timing gearcase procedures.

• Fuel injection and governor: Fuel-system bleeding, injection timing and shim adjustment, injector removal, transfer-pump testing, and governor linkage inspection.

• Cooling and exhaust: Thermostat testing, seawater-pump overhaul, freshwater-pump replacement, heat-exchanger cleaning, cooling-system pressure tests, and exhaust-manifold inspection.

• Maintenance and tune-up: Maintenance schedules, compression testing, valve-clearance adjustment, lubrication service, drive-belt checks, and sacrificial-anode inspection.

• Electrical diagnosis: Alternator output tests, starter and solenoid checks, brush replacement, sender testing, warning circuits, and instrument-panel wiring diagrams.

• Marine transmissions: KM cone-clutch and KBW plate-clutch disassembly, internal inspection, reassembly, bearing adjustment, shifter service, and drive-disc inspection.

• Seasonal storage: Lay-up and fitting-out procedures covering cooling-system draining, corrosion protection, fuel-system preparation, and return-to-service checks.

Written for do-it-yourself owners and professional mechanics, the manual explains basic tools while identifying work that requires specialized equipment or a repair shop.

Engine Inspection and Internal Repair

Separate single-cylinder and multicylinder chapters cover cylinder-head and rocker-shaft work, followed by piston, connecting-rod, crankshaft, and main-bearing inspection. Camshaft timing, timing gearcase service, and oil-pump clearance checks are supported by component specifications and tightening-torque tables. Model-specific lubrication diagrams trace oil flow through the engine.

The 2GM, 3GM, and 3HM sections address removable cylinder liners; the later 2GM20, 3GM30, and 3HM35 sections cover cylinder-bore measurement. The liner inspection guidance explains how excessive protrusion can damage the head gasket, while insufficient protrusion permits compression leakage and liner movement.

Fuel Injection, Timing, and Governor Service

The Fuel Injection System diagram identifies the injection pump, injectors, transfer pump, and return circuit. Timing coverage explains spill timing and adjustment shims. Governor procedures address flyweights, springs, the thrust sleeve, and linkage inspection.

Bleeding procedures and symptom-based troubleshooting help distinguish air in the fuel system from injection-timing or compression problems before components are replaced. Injector service includes removal, external cleaning, and precombustion-chamber inspection; internal injector cleaning and injection-pump overhaul are referred to a diesel specialist.

Sealed maximum-speed and fuel-limiter adjustments are reserved for authorized service. Working with high-compression diesel systems and pressurized fuel lines requires professional care.

Cooling, Exhaust, and Seasonal Service

The Closed Cooling System Diagram and Heat Exchanger view show the separate freshwater and seawater paths. Service coverage includes pump seals and bearings, thermostat testing, leak diagnosis, and cleaning the exchanger’s seawater passages. Exhaust-manifold and elbow inspections address carbon buildup, corrosion, and distorted sealing surfaces.

The seawater-pump section warns that reversing an impeller that has taken a set can cause premature impeller failure and engine overheating. Lay-up and fitting-out guidance distinguishes the draining and refilling requirements of the two cooling arrangements.

Electrical Tests and Instrument-Panel Wiring

Charging-system checks cover Hitachi alternator regulated voltage and current output. Starting-system diagnosis includes solenoid resistance and starter no-load current draw, with separate brush-service procedures for the GM and HM arrangements.

Sender, warning-lamp, alarm-buzzer, and tachometer checks support instrument diagnosis. Four wiring diagrams distinguish early and late models with large and small instrument panels; the small-panel diagrams omit the tachometer. Wire-color keys and connector layouts support circuit tracing.

KM and KBW Transmission Overhaul

The KM chapter uses a Cone Clutch section view and separates the A/C and P shifter arrangements. KBW coverage addresses steel and friction plates, Belleville springs, and shift-fork inspection. Both families include bearing-adjustment shimming and drive-disc damage checks; KBW overhaul requires special tools.

Transmission lubrication guidance distinguishes the engine-oil requirements of KM gearboxes from the Dexron ATF requirements of KBW units.

A Preview of Oil-Pressure and Tachometer Test Data

These examples represent a small selection of the manual’s inspection and electrical test specifications.

For the 3HM and 3HM35, the oil-pressure table specifies 300–400 kPa (43–58 psi) at 3,400 rpm. The troubleshooting chapter pairs these references with an oil-pressure gauge test and possible causes of low pressure.

The tachometer sender check specifies 1,500–1,700 ohms with the engine stopped and at least 1 volt AC with the engine running.

Printable PDF, Search Limitations, and Page Coverage

Search and wiring detail: PDF text search and embedded bookmarks are unavailable. Small wiring labels and wire-color codes are legible when enlarged.

One printable English PDF contains 240 pages, including seven opening pages: one cover, one chapter guide, three contents pages, and two quick-reference pages. The remaining 233 pages contain the chapters, index, and wiring diagrams. Printed page 25 is missing from the file.