Part of the Yanmar Repair Manuals.
Pull the end cover off the sea water pump on a 3JH2 and you can measure the impeller against the wear limits printed in this manual before deciding whether an overheating problem is the pump's fault at all. This is Yanmar's service manual for the 3JH2 series marine diesels, the 3JH2E, 3JH2-TE, 3JH25A and 3JH30A, three cylinder engines with an 82 x 86 mm bore and stroke and 1.303 L displacement. The KM3A, KM3P1, KM3P3 and KM35P1 reduction and reversing gears get their own construction, servicing, disassembly and reassembly coverage.
Across 308 pages it works through the basic engine parts, fuel injection pump and governor, turbocharger, lubrication, cooling, remote control and electrical systems, with service data, clearances and tightening torques for a full teardown. It is delivered as a PDF download you can print page by page, so the clearances and torque figures are on the bench when the engine goes back together.
What's Inside This Yanmar 3JH2L / 4JH2L Series Manual
| System | Pages | Key Topics |
|---|---|---|
| General | 6-28 | Exterior Views, Specifications, Engine Outline, Performance Curves, Piping Diagrams |
| Basic Engine Parts | 29-58 | Cylinder Block, Cylinder Head, Piston and Piston Pins, Connecting Rod, Crankshaft and Main Bearing, Camshaft and Tappets, Timing Gear, Flywheel and Housing |
| Fuel Injection Equipment | 59-98 | Fuel Injection Pump Service Data, Governor, Disassembly Reassembly and Inspection of Fuel Injection Pump, Fuel Injection Pump and Governor, Fuel Feed Pump, Fuel Injection Nozzle |
| Intake and Exhaust System | 99-117 | Turbocharger, Mixing Elbow |
| Lubrication System | 118-131 | Lube Oil Pump, Lube Oil Filter, Oil Pressure Control Valve, Lube Oil Cooler, Piston Cooling Nozzle, Rotary Waste Oil Pump(Optional) |
| Cooling Water System | 132-151 | Sea Water Pump, Fresh Water Pump, Heat Exchanger, Pressure Cap and Sub Tank, Thermostat, Kingston Cock(Optional), Sea Water Filter(Optional) |
| Reduction and Reversing Gear | 152-208 | Km3A (Construction, Shifting Device, Servicing, Disassembly, Reassembly), Km3P1, Km3P3, Km35P1 (Construction |
| Remoto Control | 209-215 | Remoto Control System, Remoto Control Installation, Remoto Control Inspection, Remote Control Adjustment |
| Electrical System | 216-271 | Electricai System, Battery, Starter Motor, Alternator, Instrument Panel, Warning Deices, Air Heater(Optional), Electric Type Engine Stop Device(Optional) |
| Disassembly and Reassembly | 272-307 | Disassembly and Reassembly Precautions, Disassembly and Reassembly Tools, Disassembly and Ressembly, Bolt/Nut Tightening Torque, Test Running |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Cylinder head bolt tightening torque (Partial) | 3.5 ~ 4.5 kg-m (25.3 ~ 32.5 ft-lb) | p. 295 |
| Cylinder head bolt tightening torque (Complete) | 7.5 ~ 8.5 kg-m (54.2 ~ 61.5 ft-lb) | p. 295 |
| Sea water pump impeller width (Standard) | 31.6 ~ 31.8 mm (1.2440 ~ 1.2519 in.) | p. 137 |
| Sea water pump wear plate thickness (Standard) | 2 mm (0.0787 in.) | p. 12 |
| Fuel filter filtering method | filter paper | p. 97 |
| Fuel filter filtering area | 840cm² (130.23in.²) | p. 97 |
| Alternator brush length (Maintenance standard) | 16 (0.6299) | p. 5 |
| Alternator brush length (Wear limit) | 9 (0.3543) | p. 12 |
| Lube oil filter filtration area | 800cm² (124in.²) | p. 127 |
| Lube oil filter discharge volume | 20 L/min (1220 in.³/min) | p. 127 |
| Number of cylinders | 3 | p. 10 |
| Bore x Stroke | 82 x 86 mm | p. 12 |
Yanmar 3JH2L / 4JH2L Series Common Problems This Manual Covers
Overheating after the impeller sheds vanes
A tired raw water impeller is the usual reason a 3JH2 runs hot, and the missing vanes end up in the heat exchanger. The Sea Water Pump pages give standard impeller width (31.6 to 31.8 mm) and housing width so you can measure the pump instead of guessing, with heat exchanger and thermostat servicing alongside.
Manual Section: Cooling Water System p. 132Mixing elbow corrosion and water intrusion
The wet exhaust mixing elbow corrodes from the inside, and once it lets water creep back toward the cylinders you get hard starting, white smoke and weak compression. This manual covers the mixing elbow and the rest of the intake and exhaust path, including the turbocharger on the 3JH2-TE.
Manual Section: Intake and Exhaust System p. 99Hard starting after fuel system work
Air in the fuel lines or a tired injection pump will leave the engine cranking without firing. This section carries injection pump service data, governor adjustment, nozzle inspection and its own troubleshooting pages, so you can work from symptoms back to the component.
Manual Section: Fuel Injection Equipment p. 59Slow cranking and voltage drop
Corroded harness connections and weak batteries show up as slow cranking long before the starter itself fails. The Electrical System section covers the battery, starter motor, alternator, instrument panel and warning devices, with wear limits such as alternator brush length.
Manual Section: Electrical System p. 216Low oil pressure alarm
An oil pressure warning is a stop-now event on a small marine diesel. The Lubrication System section covers the lube oil pump, oil pressure control valve, filter with its bypass valve, oil cooler and piston cooling nozzles, so you can trace the pressure loss instead of just changing the filter.
Manual Section: Lubrication System p. 118Gearbox slips or shifts hard
A marine gear that hesitates going into ahead or creeps in neutral needs the shifting device inspected and adjusted, not just an oil change. This manual covers the KM3A and the KM3P1, KM3P3 and KM35P1 gears through construction, shifting device, servicing, disassembly and reassembly.
Manual Section: Reduction and Reversing Gear p. 152Head bolts torqued wrong on reassembly
A head pulled for valve or gasket work has to go back on in stages: 3.5 to 4.5 kg-m partial, then 7.5 to 8.5 kg-m to complete. The Disassembly and Reassembly section carries the full bolt and nut tightening torque tables, special tools and a test running procedure.
Manual Section: Disassembly and Reassembly p. 272Frequently Asked Questions
Which engines and gearboxes does this manual cover?
The Yanmar 3JH2 series marine diesels: 3JH2E, 3JH2-TE, 3JH25A and 3JH30A. It also covers the KM3A, KM3P1, KM3P3 and KM35P1 reduction and reversing gears, each with construction, shifting device, servicing, disassembly and reassembly coverage.
What are the cylinder head bolt torque specs for the Yanmar 3JH2L / 4JH2L Series marine diesel engine?
Tighten in two stages: 3.5 to 4.5 kg-m (25.3 to 32.5 ft-lb) partial, then 7.5 to 8.5 kg-m (54.2 to 61.5 ft-lb) to complete. The Disassembly and Reassembly section carries the full bolt and nut tightening torque table. p. 272
Does it cover the sea water pump and impeller?
Yes. The Cooling Water System section covers the sea water pump with standard impeller width (31.6 to 31.8 mm) and housing width figures, plus the fresh water pump, heat exchanger, thermostat, pressure cap and the optional Kingston cock and sea water filter. p. 132
Will it help diagnose a no-start condition?
Yes. The Fuel Injection Equipment section has its own troubleshooting pages plus service data for the injection pump, governor, feed pump and nozzles, and the Electrical System section covers the battery, starter motor and instrument panel for cranking and charging problems. p. 59
How quickly can I access this manual after buying?
This is a 308-page searchable PDF ready for immediate download. Works on any device, so pull it up on your phone while you're under the hood. No shipping, no waiting.
Am I able to print pages from this manual?
Yes. The PDF has no DRM restrictions, so print any page or section you need for your shop. Works with any standard printer.
Can I find wiring schematics in this Yanmar 3JH2 Series & variants manual?
Included. The Yanmar 3JH2 Series & variants Service Manual covers complete wiring harness diagrams, electrical circuits, and connector pinouts.
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