Looking to tear down your marine diesel? This 349-page Yanmar 2QM20 Service Manual PDF (OEM #F027A2223) breaks down every rebuild and diagnostic step for the 2QM20, 2QM20(H), 3QM30(H), 2QM20Y, 2QM20F, 3QM30, 3QM30Y, and 3QM30F variants. Open the troubleshooting section to pinpoint rough idle issues, or trace electrical faults using the factory wiring diagrams. You get dedicated chapters on the fuel injection pump, sea water cooling system, and complete reduction and reversing gear overhauls. Verify your sea water cooling thermostat opens at exactly 42 degrees Celsius, then lock down the delivery valve holder to 4 to 4.5 kg-m. Stop guessing at injection pressures when a boat is tied up waiting on repairs. Download the file to your tablet, click the bookmarks to jump straight to your spec, and get that engine running right.
What's Inside This Yanmar 2QM20 / 3QM30 Series Manual
| System | Pages | Key Topics |
|---|---|---|
| Chapter 1 General | 4-43 | Exterior Views, Specifications, Principal Construction, Performance Curves, Features, Engine Cross-Section, Dimensions, System Diagrams |
| Chapter 2 Basic Engine | 44-84 | 1.Cylinder Block, 2.Cylinder Liner, 3.Cylinder Head, 4.Piston, 5.Connecting Rod, 6.Crankshaft, 7.Camshaft, 8.Timing Gear |
| Chapter 3 Fuel System | 85-106 | 1.Construction, 2.Injection Pump, 3.Injection Valve, 4.Fuel Filter, 5.Fuel Feed Pump, 6.Fuel Tank (Option) |
| Chapter 4 Governor | 107-115 | 1.Governor, 2.Injection Limiter, 3.No-Load Maximum Speed Limiter, 4.Idling Adjuster |
| Chapter 5 Intake and Exhaust System | 116-122 | 1.Intake and Exhaust System, 2.Intake Silencer, 3.Exhaust System, 4.Breather Pipe, 5.Intake Manifold [3QM30(H)] |
| Chapter 6 Lubrication System | 123-134 | 1.Lubrication System, 2.Oil Pump, 3.Oil Filter, 4.Oil Pressure Regulator Valve, 5.Oil Pressure Measurement |
| Chapter 7 Cooling System | 135-162 | Sea Water Cooling (Cooling System, Water Pump and Bilge Pump, Thermostat, Anticorrosion Zinc, Kingston Cock, Bilge Strainer) |
| Chapter 8 Chain-Overdrive Hand-Operated System | 163-166 | 1.Chain-Overdrive Hand-Operated System |
| Chapter 9 Reduction and Reversing Gear | 167-223 | For Model 2QM20, 3QM30 (Construction, Installation and Operation, Handling the Reduction and Reversing Gears, Servicing, Disassembly, Reassembly) |
| Chapter 10 Remote Control System | 224-232 | 1.Construction, 2.Clutch and Speed Regulator Remote Control, 3.Decompression Remote Control, 4.Engine Stop Remote Control |
| Chapter 11 Electrical System | 233-262 | 1.Composition, 2.Battery, 3.Starter Motor, 4.Alternator, 5.Alarm Circuit |
| Chapter 12 Installation and Fitting | 263-291 | 1.Propeller Selection, 2.Engine Installation, 3.Stern Equipment, 4.Interior Piping and Wiring, 5.Front Power Take-Off |
| Chapter 13 Operating Instructions | 292-307 | 1.Fuel Oil and Lubricating Oil, 2.Engine Operating Instructions, 3.Troubleshooting and Repair |
| Chapter 14 Disassembly and Reassembly | 308-341 | 1.Disassembly and Reassembly Precautions, 2.Disassembly and Reassembly Tools, 3.Other, 4.Disassembly, 5.Reassembly, 6.Tightening Torque, 7.Packing Supplement and Adhesives |
| Chapter 15 Inspection and Servicing | 342-348 | 1.Periodic Inspection and Servicing |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Delivery valve holder tightening torque | 4 ~ 4.5 kg·m (29 ~ 32.6 lb·ft) | p. 95 |
| Injection pressure | 160 kg/cm² (2,270 lb/in.²) | p. 102 |
| Thermostat opening temperature (sea water cooling) | 42°C | p. 143 |
| Thermostat full open temperature (sea water cooling) | 52°C | p. 143 |
| Oil filter replacement period | Every 300 hours of engine operation | p. 132 |
| Fuel filter cleaning period | Every 50 hours | p. 104 |
| Fuel filter element replacement period | Every 100 hours | p. 104 |
| Cylinder head packing agent and adhesive | Three Bond No. 4, Three Bond No. 50, Screw Lock Super 203M | p. 341 |
| Cylinder block packing agent and adhesive | Three Bond 388-005 | p. 341 |
| Corrective action for thermostat faulty (cooling water temperature high) | Replace thermostat | p. 307 |
| Bore × Stroke | 88 × 90 mm | p. 9 |
| Displacement | 1088 cc | p. 9 |
Yanmar 2QM20 / 3QM30 Series Common Problems This Manual Covers
Yanmar 2QM20 engine turns over normally but fails to start after prolonged cranking. p. 305
Inspect the fuel lines and replace the filter element if it has exceeded the 100-hour interval shown on page 104. Test the injection pressure to ensure it reaches 160 kg/cm² (2,270 lb/in.²) as specified on page 102. Bleed all air from the system before attempting to start.
Manual Section: Engine Starting IssuesEngine overheats under heavy load despite maintaining normal coolant levels in the expansion tank. p. 307
Check the raw water circuit for blockages. Remove and test the thermostat as detailed on page 143, verifying it begins opening at 42°C. Replace the anticorrosion zinc if it has been in service longer than the 500-hour interval noted on page 145.
Manual Section: Cooling System IssuesExcessive oil consumption accompanied by heavy blue smoke visible in the exhaust. p. 306
Drain the crankcase and replace the oil filter, adhering to the 300-hour replacement period on page 132. Measure the piston ring gap during teardown. Replace any rings exceeding the 1.5 mm wear limit listed on page 65 to restore proper cylinder sealing and compression.
Manual Section: Exhaust and Combustion IssuesSudden power loss under heavy load or rough running with engine RPM dropping unexpectedly. p. 306
Verify the injection pump components are secure. Torque the delivery valve holder to 4 ~ 4.5 kg·m (29 ~ 32.6 lb·ft) as specified on page 95. Clean the fuel block and inspect the governor linkage for binding or excessive wear before restarting the engine.
Manual Section: Engine Operation IssuesFrequently Asked Questions
What injection pressure should the 2QM20/3QM30 injectors be set to?
Set the fuel injection pressure to 160 kg/cm² (2,270 lb/in²), as specified on page 102. Bleed all air from the system before starting.
How often should the fuel filter element be replaced?
Replace the fuel filter element every 100 hours, as shown on page 104.
At what temperature does the 2QM20/3QM30 thermostat open?
The thermostat begins to open at 42°C. Remove and test it as detailed on page 143 if the engine overheats.
When should the anticorrosion zinc be replaced?
Replace the anticorrosion zinc after 500 hours of service, as noted on page 145.
What is the piston ring wear limit on the 2QM20/3QM30?
Replace any piston ring whose gap exceeds the 1.5 mm wear limit listed on page 65 to restore cylinder sealing and compression.
What is the delivery valve holder torque?
Torque the delivery valve holder to 4–4.5 kg·m (29–32.6 lb·ft), as specified on page 95.
Is this a digital download?
Yes. You get the full 349-page Service Manual as a searchable PDF, ready to download the moment checkout completes. Open it on a computer, tablet, or phone.
Can I print this manual?
Yes. The PDF is DRM-free, so you can print any page or section you need to take out to the shop. Standard letter or A4 paper works.
Document Quality
This is a high-quality digital PDF where you can search and copy the full text, indicating a good OCR layer or native digital format. All text is crisp and easy to read, and diagrams are sharp vector-like images with clearly legible labels. The pages are clean, free from scan artifacts, stains, or skewed content, presenting a very professional appearance. You will find several intentional blank pages, typically used as chapter separators, which do not contain content.
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