This 398-page Yanmar 4LH Series Service Manual (OEM #AOA 1030-1) delivers factory procedures for the 4LH-TE, 4LH-HTE, 4LH-DTE, and 4LH-STE marine diesels. The documentation provides wiring diagrams for the complete electrical system, comprehensive torque tables, and step-by-step teardown instructions. Coverage spans both fuel injection types (Distributor and YPES-AL), turbocharger service, lubrication, and the full cooling water circuit. Troubleshooting charts and piping system diagrams clarify the layout before you pull the first fitting. You will find exact specifications, such as torquing cylinder head bolts in three passes (5 kg-m, 10 kg-m, then 15 kg-m on the TE, HTE, and DTE variants) and the oil pressure alarm trigger point (below 0.3 kg/cm²). Bookmarked by chapter and keyword-searchable, this PDF loads instantly on any device.
What's Inside This Yanmar 4LH series Manual
| System | Pages | Key Topics |
|---|---|---|
| General | 7-29 | Exterior Views, Specifications, Service Data Sheet, Performance Curves, Dimensions, Piping Diagrams, Electrical Diagrams |
| Basic Engine | 30-68 | Disassembly and Reassembly Tools, Cylinder Block, Cylinder Liners, Cylinder Head, Piston and Piston Pins, Connecting Rod, Crankshaft and Main Bearing, Camshaft and Tappets |
| Distributor Type Fuel Injection | 69-124 | Fuel Supply System, Bleeding and Checking Injection Timing, Fuel Injection Pump Outline, Fuel System, Injection Pump Construction and Operation, Governing Mechanism |
| Ypes-Al Type Fuel Injection | 125-180 | Fuel Supply System, Disassembly, Reassembly and Inspection of Governor, Reassembly and Inspection of Fuel Injection Pump, Fuel Injection Pump and Governor |
| Intake Manifold | 184-196 | Tools, Troubleshooting, Service Data, Fuel Injection Pump Specifications, Intake and Exhaust System, Intake Silencer |
| Turbocharger | 197-228 | - |
| Breather | 229-237 | Mixing Elbow |
| Lube Oil Pump | 238-242 | Lubrication System |
| Rotary Waste Oil Pump (Optional) | 243-250 | Lube Oil Cooler, Lube Oil Filter, Oil Pressure Control Valve, Piston Cooling Nozzle |
| Sea Water Pump | 251-256 | Cooling Water System |
| Pressure Cap and Sub Tank | 257-263 | Fresh Water Pump, Heat Exchanger |
| Bilge Pump and Bilge Strainer (Optional) | 264-390 | Sea Water Filter (Optional), Thermostat, Kingston Cock (Optional) |
| Lubrication System | 391-398 | Lube Oil Pump, Lube Oil Filter |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Oil pressure alarm trigger point | below 0.3 kg/cm² (1.42 ~ 4.26 lb/in.²) | p. 397 |
| Cylinder head bolt tightening torque (4LH-TE, -HTE, -DTE) | 1st: 5 kg-m, 2nd: 10 kg-m, 3rd: 15 kg-m | p. 14 |
| Cylinder head bolt tightening torque (4LH-STE) | 1st: 11 kg-m, 2nd: 17 kg-m, 3rd: 19 kg-m | p. 14 |
| Fuel injection nozzle clamp nut tightening torque (4LH-TE, -HTE, -DTE) | 0.4 ~ 0.5 kg-m | p. 14 |
| Fuel injection nozzle clamp nut tightening torque (4LH-STE) | 0.6 ~ 0.7 kg-m | p. 14 |
| Fuel filter replacement interval | Every 50 hours operation | p. 123 |
| Lube oil filter replacement interval | Every 200 hours of engine operation | p. 397 |
| Fuel injection nozzle starting pressure | 195 ~ 205 kg/cm² (2773 ~ 2915 lb/in.²) | p. 122 |
| Fuel injection nozzle contact surface wear limit | 0.1 mm (0.0039 in.) | p. 121 |
| Intake silencer cleaning interval | Every 500 hours operation | p. 185 |
| Number of cylinders | 4 | p. 12 |
| Displacement | 3.455 L | p. 12 |
Yanmar 4LH series Common Problems This Manual Covers
Yanmar 4LH marine diesel hard starting after sitting, cranks but won't fire p. 69
Bleed the fuel system at the injection pump vent screw. Air locks are the top cause of cold no-starts on this engine. Replace the fuel filter at the 50-hour interval (page 123) and confirm fuel cetane is above 45 (page 14). If it still won't fire, bench-test injector opening pressure: spec is 195 to 205 kg/cm² (page 122).
Manual Section: Distributor Type Fuel InjectionEngine overheats under load, coolant temperature alarm sounding at normal cruise RPM p. 12
Check coolant level first: effective capacity is 14 L (page 12). Inspect the seawater pump impeller for wear or delamination; a degraded impeller is the most common heat cause underway. Flush the heat exchanger passages and pressure-test for restriction. If circulation looks good, test the thermostat for stuck-closed condition before opening the engine.
Manual Section: GeneralLoss of power and black smoke under load, engine can't reach max RPM p. 181
Clean the intake silencer every 500 hours (page 185). Remove and inspect the mixing elbow for carbon buildup restricting exhaust flow. Check the turbocharger for shaft play and blade damage. If airflow and exhaust look clear, verify injector opening pressure is within 195 to 205 kg/cm² (page 122) before chasing fuel delivery further.
Manual Section: Intake and Exhaust SystemLow oil pressure alarm activating at idle or just after engine warmup p. 391
Check oil level immediately and top up to the 11 L effective capacity (page 12). The alarm triggers when pressure drops below 0.3 kg/cm² (page 397). Replace the lube oil filter if overdue. If pressure stays low with fresh oil and a new filter, remove and test the lube oil pump per the inspection procedures on page 391.
Manual Section: Lubrication SystemEngine knocking at idle, rough running, or combustion noise getting worse after warmup p. 30
Verify valve clearances with the engine cold: intake 0.1 mm, exhaust 0.3 mm (page 14). A single sticky or tight valve mimics the knock mechanics often chase with injectors. If clearances are correct, check injection timing at the pump. Then bench-test nozzles for spray pattern; nozzle contact surface wear limit is 0.1 mm (page 121).
Manual Section: Basic EngineFrequently Asked Questions
What are the torque specs for Yanmar 4LH cylinder head bolts?
The torque specifications for the cylinder head bolts vary by model. For 4LH-TE, -HTE, and -DTE models, the tightening torque is applied in three steps: 1st at 5 kg·m, 2nd at 10 kg·m, and 3rd at 15 kg·m. For the 4LH-STE model, the torque is applied in two steps: 1st at 11 kg·m and 2nd at 17 kg·m.
What are the replacement specifications for Fuel filter?
The manual specifies maintenance for the fuel filter, recommending to remove the drain cock and drain the sediment bowl every 50 hours of operation. While troubleshooting sections indicate that the fuel filter should be cleaned or replaced if it is clogged, no specific replacement interval or part number is provided for the fuel filter element itself.
How will I receive this Service Manual?
You get a 398-page searchable PDF that downloads instantly after checkout. Open it on your laptop, tablet, or phone — bring it right to the shop floor.
Can I print specific sections of this Service Manual?
The PDF is DRM-free. Print whatever sections you need to take out to the shop. Standard letter or A4 paper works.
Are electrical wiring diagrams included in this Yanmar 4LH series manual?
Included. The Yanmar 4LH series Service Manual covers complete wiring harness diagrams, electrical circuits, and connector pinouts.
Document Quality
This document is a scanned PDF with an OCR layer, allowing you to search and copy the full text. The text throughout is generally crisp and easy to read. Diagrams and illustrations are raster images, which are mostly clear with readable labels, though they may pixelate upon high zoom. Pages are clean, with no significant stains or marks, except for a handwritten note on the cover. You will find several blank pages interspersed, typically after a chapter or section title page.
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