Yanmar 3JH25A Specifications
| Engine Model: Yanmar 3JH25A |
| Engine Type: 4-stroke inline 3-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 83.2 cu.in (1.36 L) |
| Rated Engine Power: 20.2 Hp (25.4 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 3JH25A is a three-cylinder,
vertical, 4-stroke marine diesel engine from the JH series. This power
unit is designed for propulsion in high-speed commercial marine
applications, including lifeboats, rescue boats, and small workboats.
The engine employs a direct injection combustion system with a
swirl-type cylinder head, providing efficient fuel burn and reduced
particulate emissions compared to indirect injection designs.
The naturally aspirated configuration eliminates turbocharger
complexity, enhancing reliability in emergency service roles where
immediate starting is required. The fresh water cooling circuit with a
seawater-cooled heat exchanger or optional keel cooling permits
operation in varying water salinity and temperature conditions. The
3JH25A meets ISO 3046 and IMO Tier II emission standards. This engine
succeeded earlier Yanmar JH series engines, featuring a higher
power-to-weight ratio for compact boat installations.
Engine Type: 3-cylinder, vertical, 4-cycle, water-cooled diesel,
naturally aspirated
Displacement: 1.363 L (1363 cc / 83.2 cu.in)
Bore x Stroke: 82 mm x 86 mm (3.23 in x 3.39 in)
Compression Ratio: 18.8:1
Combustion System: Direct injection, swirl-type cylinder head
Aspiration: Naturally aspirated (no turbocharger)
Valvetrain: OHV (Overhead Valve), 2 valves per cylinder, 6 valves total
Firing Order: 1-3-2
Direction of Rotation: Counter-clockwise viewed from the stern
(crankshaft)
Rated Output (continuous, SAE J1228): 18.4 kW (24.7 hp) at 3200 rpm
Maximum Output (intermittent): 20.2 kW (27.1 hp) at 3300 rpm
Maximum Torque: 62 Nm (46 lb-ft) at 2200-2400 rpm
Low Idle Speed: 800-850 rpm
High Idle Speed (no-load, governed): 3450-3500 rpm
Emission Standard: ISO 3046, IMO Tier II
The cylinder block is manufactured from cast iron with a closed-deck
design. Three cylinder bores are machined directly into the parent metal
without replaceable wet liners. The block features a siamese bore
configuration where each cylinder shares a common wall with the adjacent
cylinder, reducing overall engine length for installation in constrained
engine compartments. The crankcase extends below the crankshaft
centerline with a deep skirt design.
Four main bearing bulkheads support the crankshaft, with thrust bearing
position at the number two main journal from the flywheel end. The water
jacket surrounds the upper portion of each cylinder bore fully. Cast oil
galleries supply lubricant to the main bearings and camshaft bearings. A
side-mounted spin-on oil filter threads directly onto the block casting.
The block incorporates an integral seawater-cooled oil cooler mounted on
the port side for marine installations. Corrosion-resistant sacrificial
anodes are threaded into the block cooling passages.
Crankshaft: Forged carbon steel with four main journals. Four
counterweights are integrated into the crank web. A rubber torsional
vibration damper is pressed onto the crankshaft nose. Camshaft: Cast
iron, located in the cylinder block on the starboard side. Driven by a
gear from the crankshaft. Camshaft bearings are plain-type machined
directly into the block.
The cylinder head is a single-piece cast iron component with a direct
injection swirl-type combustion chamber. Each cylinder features a
bowl-in-piston design with the injector nozzle oriented vertically. No
pre-combustion chamber is present. The valve train is an overhead valve
(OHV) configuration with pushrods and rocker arms.
Each cylinder receives two valves: one intake and one exhaust, arranged
in a parallel valve layout. Valve stem seals are positive-type on both
intake and exhaust valves for marine operation. Hardened valve seat
inserts on both intake and exhaust sides resist wear under continuous
high-load operation. The camshaft is located in the cylinder block on
the right side.
Valve clearance adjustment uses a screw-and-locknut arrangement on the
rocker arms. The cold clearance specification for intake valves is 0.25
mm (0.010 in) and for exhaust valves is 0.30 mm (0.012 in). The rocker
shaft is supported by three pedestals bolted directly to the cylinder
head. Glow plugs are installed in the intake ports for cold start
assistance.
The fuel system is a mechanical direct injection design with an in-line
injection pump. The pump mounts to the side of the timing gear case and
delivers fuel to each cylinder in the 1-3-2 firing order. The injection
pump incorporates a mechanical centrifugal governor with both idle and
maximum speed control springs. A manual stop lever permits mechanical
fuel shutoff for emergency stops. Steel injection lines route
individually to each injection nozzle located centrally in the cylinder
head.
Injection nozzles are multi-hole type (3 holes, 0.20 mm diameter) with
an opening pressure of 12.0-12.5 MPa (1740-1812 psi). Injection timing
is adjustable by shim between the pump mounting flange and the pump
base. A hand primer lever on the feed pump permits manual bleeding of
air after filter changes. A fuel filter with an integral water sediment
bowl mounts on the engine side of the block. A secondary fuel filter is
optional for severe fuel conditions.
The lubrication system uses a trochoid-type oil pump driven directly
from the crankshaft gear. The trochoid pump consists of an inner rotor
with four lobes and an outer rotor with five lobes, providing smooth
flow with minimal pulsation. The pump draws oil through a wire mesh
suction strainer positioned at the bottom of the marine oil pan. Oil
passes through a spin-on full-flow filter mounted on the port side of
the cylinder block. A seawater-cooled oil cooler, integrated into the
block casting, maintains oil temperature during sustained high-speed
operation.
A pressure relief valve in the oil pump opens at 0.45-0.55 MPa (65-80
psi) to prevent over-pressurization. The system lacks piston cooling
jets due to the naturally aspirated configuration generating moderate
thermal loads. Oil pressure at rated speed measures 0.30-0.45 MPa (44-65
psi). A low oil pressure switch activates an audible alarm at 0.05 MPa
(7 psi). Standard oil pan capacity is 5.5 L (5.8 qt) for the marine deep
sump configuration.
The cooling system comprises two separate circuits: a high-temperature
fresh water circuit and a low-temperature seawater circuit. The fresh
water circuit cools the engine block, cylinder head, and exhaust
manifold. A belt-driven centrifugal fresh water pump circulates coolant
through the engine.
A salt-resistant cast iron heat exchanger integrates the two circuits.
Seawater, drawn through a hull strainer, passes through the heat
exchanger shell side, absorbing heat from the fresh water before
discharging through the exhaust elbow. A wax-pellet thermostat begins
opening at 71°C (160°F) and reaches full opening at 85°C (185°F).
A bypass circuit permits fresh water circulation within the engine when
the thermostat remains closed. Coolant capacity (fresh water circuit) is
3.5 L (3.7 qt). Optional keel cooling replaces the seawater circuit with
a keel-mounted radiator. A seawater pressure switch activates a warning
device if flow drops below 0.7 bar (10 psi). A sacrificial zinc anode in
the heat exchanger prevents galvanic corrosion.
Cold Start System: Glow plugs in each intake port, rated at 12 V. A glow
controller integrates a timer relay for 5-10 second pre-heat dependent
on seawater temperature. Glow plug indicator lamp signals when pre-heat
is active.
Electrical System: 12 V negative ground. Starter motor power rating is
1.8 kW. Alternator output is 35 A standard (optional 55 A). Starter
incorporates a marine-grade corrosion-resistant housing and sealed
connectors.
Exhaust System: Water-injected exhaust elbow mixes seawater exhaust gas,
reducing exhaust temperature below 60°C (140°F) at the outlet. The
mixing elbow is cast from nickel-aluminum-bronze for corrosion
resistance.
Governor: Mechanical centrifugal governor integral to the injection
pump. Governor droop is 8-10% from no-load to full-load at rated speed.
Length (front pulley to flywheel housing face): 635 mm (25.0 in)
Length (with KM35P1 gearbox, propeller flange): 730.1 mm (28.74 in)
Width (overall, exhaust elbow to injection pump): 543 mm (21.38 in)
Height (oil pan rail to rocker cover peak): 680 mm (26.77 in)
Dry Weight (engine without gearbox): 185 kg (408 lb)
Dry Weight (with KM35P1 marine gearbox): 187 kg (412 lb)
Dry Weight (with KM3P1 marine gearbox): 189 kg (417 lb)
Engine Oil Change Interval: 250 hours or 12 months under normal marine
duty.
Engine Oil Capacity (including filter, standard oil pan): 5.5 L (5.8
qt).
Engine Oil Grade (ambient above 0°C / 32°F): SAE 15W-40, API CF-4 or
higher.
Engine Oil Grade (cold ambient -15°C to 0°C / 5°F to 32°F): SAE 10W-30.
Engine Oil Pressure Relief Valve Setting: 0.45-0.55 MPa (65-80 psi).
Engine Oil Pressure at Rated Speed: 0.30-0.45 MPa (44-65 psi).
Engine Oil Pressure at Low Idle (minimum, hot engine): 0.08 MPa (12
psi).
Coolant Capacity (fresh water circuit, engine only): 3.5 L (3.7 qt).
Coolant Capacity (heat exchanger inclusive): 4.2 L (4.4 qt).
Coolant Specification: Ethylene glycol base marine antifreeze with
low-silicate formulation.
Thermostat Opening Temperature: 71°C (160°F) start; fully open at 85°C
(185°F).
Seawater Pump Impeller Replacement Interval: 500 hours or 12 months.
Heat Exchanger Zinc Anode Replacement Interval: 250 hours or 6 months in
saltwater operation.
Fuel Filter Replacement Interval: 200 hours. Water sediment bowl drain
daily.
Air Filter Service Interval: Clean foam pre-cleaner every 50 hours.
Air Filter Service Interval: Replace paper element every 200 hours.
Valve Clearance (Cold Engine, Intake): 0.25 mm (0.010 in).
Valve Clearance (Cold Engine, Exhaust): 0.30 mm (0.012 in).
Valve Clearance Inspection Interval: 250 hours.
Injection Timing (static, fuel spill method): 18 deg BTDC at No. 1
cylinder.
Injector Nozzle Opening Pressure: 12.0-12.5 MPa (1740-1812 psi).
Injector Nozzle Type: DLLA-M (multi-hole, 3 x 0.20 mm).
Injector Nozzle Replacement Interval: 1000 hours or as indicated by
black smoke.
Glow Plug Specification: Sheathed type, 12 V. Resistance (cold): 1.0-1.3
ohms per plug.
Compression Pressure (standard): 3.3-3.8 MPa (479-551 psi) at cranking
speed.
Compression Pressure Variation Between Cylinders: Maximum 0.2 MPa (29
psi) difference.
Drive Belt Tension: Deflection of 10-12 mm (0.39-0.47 in) under 10 kg
(22 lb) force at belt midpoint.
Idle Speed Adjustment (low): 800-850 rpm. Adjust via idle stop screw on
injection pump.
Cylinder Head Bolts (Stage 1): 30 Nm (22 lb-ft)
Cylinder Head Bolts (Stage 2): 70 Nm (52 lb-ft)
Connecting Rod Cap Nuts: 50 Nm (37 lb-ft)
Main Bearing Cap Bolts: 70 Nm (52 lb-ft)
Flywheel Bolts (to crankshaft flange): 75 Nm (55 lb-ft)
Flywheel Housing Bolts (to block): 40 Nm (30 lb-ft)
Camshaft Drive Gear Nut: 90 Nm (66 lb-ft)
Camshaft Thrust Plate Bolts: 20 Nm (15 lb-ft)
Rocker Arm Shaft Bracket Bolts: 28 Nm (21 lb-ft)
Rocker Arm Adjusting Lock Nut: 15 Nm (11 lb-ft)
Valve Cover Nuts (with rubber gasket): 8 Nm (6 lb-ft)
Injection Pump Mounting Nuts (to timing case): 35 Nm (26 lb-ft)
Injection Pump Drive Gear Nut: 65 Nm (48 lb-ft)
Injection Line Fittings (pump end): 25 Nm (18 lb-ft)
Injection Line Fittings (nozzle end): 25 Nm (18 lb-ft)
Injector Hold-Down Clamp Nut: 30 Nm (22 lb-ft)
Crankshaft Pulley Bolt: 120 Nm (89 lb-ft)
Oil Pan Bolts (M8): 12 Nm (9 lb-ft)
Oil Pan Drain Plug (magnetic): 40 Nm (30 lb-ft)
Oil Filter (spin-on canister): 15 Nm (11 lb-ft)
Fresh Water Pump Mounting Bolts: 20 Nm (15 lb-ft)
Heat Exchanger Mounting Bolts: 25 Nm (18 lb-ft)
Seawater Pump Mounting Bolts: 20 Nm (15 lb-ft)
Seawater Pump Cover Bolts (impeller access): 10 Nm (7 lb-ft)
Thermostat Housing Bolts: 15 Nm (11 lb-ft)
Exhaust Manifold Bolts (to cylinder head): 25 Nm (18 lb-ft)
Exhaust Elbow Bolts (to manifold): 30 Nm (22 lb-ft)
Starter Motor Mounting Bolts (M10): 45 Nm (33 lb-ft)
Alternator Mounting Bolt (pivot): 35 Nm (26 lb-ft)
Alternator Adjustment Arm Bolt: 20 Nm (15 lb-ft)
Glow Plug (in cylinder head): 20 Nm (15 lb-ft)
Engine Mount Bracket Bolts (to block): 60 Nm (44 lb-ft)
Zinc Anode Plug (in heat exchanger): 15 Nm (11 lb-ft)
Lifeboats: Davit-launched and free-fall lifeboats conforming to SOLAS
regulations. Capacity classes from 25 persons to 70 persons. Commercial
offshore supply vessel lifeboats. Cruise ship tenders with lifeboat duty
classification.
Rescue Boats: Fast rescue craft (FRC) for coast guard and maritime
police. Rigid-hull inflatable boats (RHIB) up to 9 m length. Inflatable
rescue boats (IRB) for surf conditions.
Small Commercial Workboats: Fishing boats up to 12 m (40 ft). Harbour
patrol vessels. Pilot boats and port authority tenders. Aquaculture feed
barges (auxiliary propulsion). Small passenger ferries servicing island
communities.
Sailboat Auxiliary Propulsion: Yachts from 40 ft to 50 ft displacement
hulls. Motorsailers requiring continuous cruising capability. Catamarans
with twin engine installations.
Compact Work Boats: Canal and river maintenance craft. Environmental
monitoring vessels. Small tug tenders.
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