Mitsubishi S12A2 Diesel Engine Service Manual (tp6850)

On a big Mitsubishi S12A2 running in a generator set or marine application, this manual is what I’d keep open when the engine’s down and every minute matters. It helps you trace faults methodically, strip and refit components in the right order, and set things back up so the engine runs clean and within spec. Say you’ve got hard starting and white smoke after a rebuild—this book walks you through checking timing, fuel system components, and valve train setup before you start throwing expensive parts at it.

Applications & Use Cases

Track down performance issues by following logical checks to isolate whether the problem is fuel, air, timing, or mechanical.
Disassemble and reassemble major components with the correct sequence so you don’t miss seals, shims, or alignment steps.
Verify adjustments on items like linkages, clearances, and timing marks after repairs or overhauls.
Confirm a suspected failure (pump, injector, turbo, cooling component) with step-by-step tests before replacement.
Plan preventive maintenance by knowing what must be inspected or renewed when you already have an assembly apart.

FAQ

Q: Can I use this manual on a tablet at the machine?

A: Yes, it’s practical to keep it open on a tablet so you can zoom diagrams and follow procedures right next to the engine.

Q: Is it worth printing sections of this manual?

A: Many techs print the pages for the specific job so they can mark notes, oily fingerprints, and torque steps without risking the whole file.

Safety Note

Always lock out the starter circuit and secure all rotating parts before inspecting or adjusting anything on the engine.

📘 Show Index

Mitsubishi S12A2 Diesel Index:

Chapter 1 GENERAL
1. External View
2. Outline of Systems
3. Contents of Plate and Label
4. Specifications
Chapter 2 SERVICE DATA
1. Maintenance Service Data
2. Tightening Torque Table
Chapter 3 SERVICE TOOLS
1. Special Tools
Chapter 4 OVERHAUL INSTRUCTIONS
1. Determining Overhaul Timing
2. Compression Pressure – Measure
Chapter 5 DISASSEMBLY OF BASIC ENGINE
1. Cylinder Heads and Valve Mechanisms – Disassemble and Inspect
2. Rear Mechanism – Disassemble and Inspect
3. Front Mechanism – Disassemble and Inspect
4. Cylinder Liner, Piston and Connecting Rod – Disassemble and Inspect
5. Crankcase, Crankshaft and Main Bearing – Disassemble and Inspect
Chapter 6 INSPECTION AND REPAIR OF BASIC ENGINE
1. Cylinder Head and Valve Mechanism – Inspect and Repair
2. Rear Mechanism – Inspect and Repair
3. Front Mechanism – Inspect and Repair
4. Piston and Connecting Rod – Inspect and Repair
5. Crankcase and Crankshaft – Inspect and Repair
Chapter 7 ASSEMBLY OF BASIC ENGINE
1. Crankshaft and Main Bearing – Install
2. Cylinder Liner, Piston and Connecting Rod – Assemble
3. Front Mechanism – Assemble
4. Rear Mechanism – Assemble
5. Cylinder Head and Valve Mechanism – Assemble
Chapter 8 FUEL SYSTEM
1. Fuel System – Remove and Inspect
2. Fuel System – Disassemble, Inspect and Assemble
3. Fuel System – Install
Chapter 9 LUBRICATION SYSTEM
1. Lubrication System – Remove and Inspect
2. Lubrication System – Disassemble, Inspect and Assemble
3. Lubrication System – Install
Chapter 10 COOLING SYSTEM
1. Cooling System – Remove and Inspect
2. Cooling System – Disassemble, Inspect and Assemble
3. Cooling System – Install
Chapter 11 INLET AND EXHAUST SYSTEMS
1. Inlet and Exhaust Systems – Remove and Inspect
2. Inlet and Exhaust Systems – Disassemble, Inspect and Assemble
3. Inlet and Exhaust Systems – Install
Chapter 12 AIR START SYSTEM
1. Air Start System – Remove and Inspect
2. Air Start System – Disassemble, Inspect and Assemble
3. Air Start System – Install
Chapter 13 ADJUSTMENT AND OPERATION
1. Engine – Adjust
2. Break-in Operation
3. Engine-Test and Adjustment