1970s–1980s Yanmar 2QM20(H) & 3QM30(H) Marine Diesel Engine Service Manual (P/N F027A2223)

This Yanmar service manual covers the 1970s–1980s 2QM20(H) and 3QM30(H) marine diesel engines, with specifications and configuration details for the 2QM20B and the Y and F variants.

• Engine overhaul: Cylinder-block and liner inspection, cylinder-head service, piston and crankshaft measurements, camshaft checks, and timing-gear assembly.
• Fuel injection: Pump disassembly, component testing, injection-timing adjustment, nozzle inspection, and centrifugal-governor service, including idle and injection-limiter settings.
• Marine gearboxes: Reduction-and-reversing-gear inspection and rebuilding, with separate procedures for mechanical wet single-disc and multi-disc clutch designs.
• Cooling circuits: Water-pump inspection, thermostat testing, heat-exchanger service, and anticorrosion-zinc maintenance for sea-water and fresh-water configurations.
• Lubrication: Trochoid oil-pump inspection, filter servicing, pressure-regulator checks, and oil-pressure measurement procedures within the engine lubrication circuit.
• Electrical diagnosis: Starter-motor servicing, alternator component tests, wiring diagrams, and checks for the warning-alarm and tachometer circuits.
• Installation and controls: Propeller selection, engine mounting, shaft alignment, exhaust piping, and adjustment of clutch, throttle, decompression, and stop controls.

Written for service engineers and technicians familiar with diesel-engine maintenance, the manual assumes that basic engine principles and workshop practices are already understood.

Engine Inspection and Assembly

Engine cross-sections accompany cylinder-block construction and bore-measurement data. Inspection sections cover piston rings, crankshaft journals, camshafts, timing gears, valve recess, valve-spring free length, and rocker arms.

The manual links rust at the liner-seat ledge with excessive cylinder-liner projection, compression loss, and gasket damage. Its disassembly and reassembly chapters also identify special tools, sealing locations, and assembly checks.

Injection Pump and Governor Service

Injection-pump exploded views accompany the YPFR-2K and YPFR-3K procedures. Coverage includes plunger operation, delivery-valve sealing, nozzle spray tests, injection timing, and delivery-quantity adjustment. Calibration after reassembly requires an injection-pump tester.

A specific caution connects overtightened delivery-valve holders with plunger-barrel distortion and increased control-rack resistance. Centrifugal-governor coverage includes the injection limiter, idle adjustment, and no-load speed control.

Reduction and Reversing Gears

Separate gearbox sections describe clutch inspection, dismantling, reassembly, and clearance adjustment. Power-transmission diagrams distinguish the single-disc and multi-disc assemblies. The KH-18 oil-pump section specifies replacement of the complete assembly when faulty.

Cooling and Lubrication Systems

Sea-water and fresh-water flow diagrams distinguish direct cooling from the Y/F heat-exchanger configurations. Procedures cover impellers, the optional bilge pump, heat-exchanger leakage checks, thermostats, and anticorrosion zincs. The cooling-system safety warning concerns burns from hot coolant escaping when the pressurized filler cap is opened.

Lubrication coverage includes trochoid-pump wear checks, oil-filter and bypass-valve operation, the pressure regulator, and pressure-measurement arrangements.

Electrical Faults and Troubleshooting

Wiring diagrams and the alternator regulator circuit support charging and starting diagnosis. Starter procedures include brush and armature checks; alternator tests address rotors, stators, and diodes.

Troubleshooting tables connect hard starting, overheating, and clutch creep with possible causes and corresponding checks. This helps distinguish control or adjustment faults from component wear when planning service work.

Installation, Controls, and Routine Service

Performance curves and exterior dimensioned views support propeller selection and engine installation. Further sections address propeller-shaft coupling alignment, stern equipment, exhaust piping, Morse MS/MT2 controls, decompression and stop cables, and the chain-overdrive hand starter. Periodic inspection schedules accompany operating and storage instructions.

Technical Preview: Liner Projection and Thermostat Temperatures

Inspection data includes cylinder-liner projection of 0.03–0.10 mm above the block for the 2QM20(H)/3QM30(H) engine family.

The sea-water thermostat begins opening at 42°C and is fully open at 52°C. For the fresh-water-cooled 2QM20Y/F and 3QM30Y/F variants, the corresponding temperatures are 71°C and 85°C.

PDF Navigation, Diagram Detail, and Included Pages

Chapter bookmarks and circuit detail: Embedded bookmarks link to the chapters and numerous subsections. Text search is unavailable. The main wiring diagram and alternator-regulator circuit contain small labels that need zooming and remain legible when enlarged.

Supplied as one printable English-language PDF containing 349 pages. The total includes the front and back covers, foreword, and main contents page (four pages), plus 15 chapter-opening pages and two cooling-section dividers.