Yanmar 4JH3E Specifications
| Engine Model: Yanmar 4JH3E |
| Engine Type: 4-stroke inline 4-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 121.7 cu.in (1.99 L) |
| Rated Engine Power: 56 Hp (41.2 kW) at 3800 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 4JH3E is a 4-cylinder, naturally
aspirated marine diesel engine from the Yanmar JH series. This engine is
a direct injection successor to the 4JH2E, offering improved fuel
efficiency, reduced weight, and a more compact form factor for
sailboats, cruisers, and mid-sized commercial vessels. The Yanmar 4JH3E
features freshwater cooling with a heat exchanger, separating the
internal coolant circuit from external seawater circulation.
The direct injection combustion system eliminates the pre-combustion
chamber found on indirect injection predecessors, resulting in lower
specific fuel consumption and cleaner emissions. The engine is designed
for high torque at low crankshaft speeds, which is essential for
maneuvering in harbors and maintaining steady headway in displacement
hull applications. The Yanmar 4JH3E complies with international emission
standards for marine diesel engines of its production era.
Engine Type: 4-stroke, water-cooled, vertical inline diesel.
Number of Cylinders: 4.
Valvetrain: Overhead valve (OHV), 2 valves per cylinder (8 valves
total).
Displacement: 1995 cc (2.0 L / 121.7 cu.in).
Bore x Stroke: 84 mm x 90 mm (3.31 in x 3.54 in).
Compression Ratio: 22.5:1.
Combustion System: Direct injection.
Aspiration: Naturally aspirated.
Maximum Output (Crankshaft): 41.2 kW (56 hp) at 3800 rpm.
Continuous Rating (Crankshaft): 35.3 kW (48 hp) at 3700 rpm.
Maximum Torque: 132 Nm (97.4 lb-ft) at 1800-2100 rpm.
Cruising RPM Range: 2900-3300 rpm.
High Idle Speed: Approximately 3700-3800 rpm.
Low Idle Speed (in gear, warm engine): 700 ± 25 rpm.
Direction of Rotation: Counterclockwise viewed from the flywheel (stern
side).
Fuel Injection Pump: Mechanical distributor type (Bosch VE / ZEXEL).
Injection Pressure: 200-210 kgf/cm2 (2844-2986 psi).
Starting System: 12V electric starter (1.4 kW).
Alternator: 12V / 60A standard; 12V / 80A optional.
Dry Weight (Engine Only): 186 kg (410 lb) excluding marine gear.
Dry Weight (with Marine Gear): 229-260 kg (505-573 lb).
The cylinder block is manufactured from cast iron, providing a rigid
foundation for the four-cylinder configuration. The inline design with
even firing intervals ensures balanced operation with reduced vibration
compared to three-cylinder engines of equivalent displacement. The block
incorporates dry-type cylinder liners precision-machined into the
casting. The water jacket surrounds each cylinder bore completely,
ensuring uniform heat dissipation from the direct injection combustion
process.
The crankcase is integrated into the block with five main bearing
journals supporting the crankshaft. A deep-skirt design extends the
cylinder walls below the crankshaft centerline, enhancing structural
rigidity and reducing noise transmission. An oil gallery is cast
longitudinally through the block to supply pressurized lubricant to the
main bearings, connecting rods, and camshaft bearings. The block
includes mounting feet for flexible rubber engine mounts, isolating
vibration from the vessel hull.
The cylinder head is constructed from cast aluminum alloy, reducing
overall engine weight for marine applications. The overhead valve (OHV)
arrangement uses a camshaft located in the cylinder block with valve
actuation via pushrods and rocker arms. Each cylinder receives two
valves: one intake and one exhaust. The direct injection system requires
a centrally located injector position with a combustion bowl machined
directly into the piston crown.
The valve seats are manufactured from heat-resistant alloy steel, and
valve guides are press-fitted and replaceable. The intake ports are
designed to generate high swirl motion of the incoming air charge,
promoting thorough mixing with the directly injected fuel. The
valvetrain requires periodic manual valve clearance adjustment using a
screw and locknut mechanism on each rocker arm.
The fuel system is a direct injection design using a mechanical
distributor-type injection pump (Bosch VE or ZEXEL). The pump is mounted
on the engine side and driven by the timing gears. A mechanical fuel
feed pump, integrated into the injection pump body, draws fuel from the
tank through a primary fuel filter. The distributor pump uses a single
plunger to generate high pressure and a rotary distributor head to
direct fuel to the correct cylinder in firing order sequence.
High-pressure steel lines deliver fuel from the injection pump to the
individual injection nozzles located in each cylinder head. The nozzles
are of the pinhole type (YDLLA-P with five holes at 150-degree spray
angle). A fuel filter with an integrated water separator is mounted
between the fuel tank and the feed pump. Fuel return lines route excess
fuel from the injection pump and nozzles back to the fuel tank.
The lubrication system is a forced-feed, pressurized design using a
trochoid oil pump. The trochoid pump, known for its compact dimensions
and quiet operation, is mounted on the timing gear case and driven by
the crankshaft gear. Oil is drawn from the oil sump through a wire mesh
suction strainer. Pressurized oil passes through a full-flow spin-on oil
filter. An oil cooler is integrated into the system to maintain
lubricant temperature under continuous high-load operation.
From the filter, oil enters the main oil gallery. The gallery
distributes oil to the five main bearings, connecting rod bearings,
camshaft bearings, and timing gears. A drilled passage within the
cylinder block directs oil upward to the rocker arm shaft. The rocker
arms receive oil through drilled passages in the shaft and spray oil
onto the valve stems and pushrod ends. The total oil capacity is 5.4-7.5
liters (5.7-7.9 qt), depending on the oil pan configuration. The oil pan
is a pressed steel construction with a drain plug.
The cooling system is a dual-circuit, freshwater-cooled (closed) design
with a heat exchanger. This system separates the engine’s internal
coolant from the external seawater. The freshwater circuit uses a
centrifugal water pump driven by the front belt or gear train. Coolant
circulates through the cylinder block, cylinder head, lubricating oil
cooler, and the freshwater side of the heat exchanger. A thermostat
housed on the cylinder head regulates coolant flow to maintain operating
temperature between 75-85°C (167-185°F).
The seawater circuit uses a flexible impeller-type pump. Seawater is
drawn through a hull strainer and seacock, circulated through the
seawater side of the heat exchanger, then discharged into the exhaust
injection elbow. The freshwater cooling capacity is 6.0-7.2 liters
(6.3-7.6 qt) including the heat exchanger and expansion tank. A coolant
recovery tank is integrated into the system.
| Intake and Exhaust Systems |
Intake System: The intake manifold is a cast aluminum plenum mounted on
the cylinder head. Air enters through a flame arrestor (for engine room
installations) or through a dry-type air cleaner. The naturally
aspirated engine draws air directly into the intake manifold without
forced induction or charge air cooling.
Exhaust System: A water-cooled exhaust manifold is integrated with the
cylinder head or mounted on the side. Exhaust gases pass through the
manifold into a water-injected exhaust elbow where seawater from the
cooling system is introduced. This water cools the exhaust gases and
acts as a silencer. The wet exhaust system discharges through a
waterlock muffler and a gooseneck fitting to prevent seawater siphoning
back into the engine.
Electrical System: The 12V system includes a 1.4 kW starter motor and an
alternator (60A standard, 80A optional). A pre-heat system (intake air
heater or glow plugs) assists cold starting. The recommended battery
capacity is 12V-120Ah or greater. An instrument panel with tachometer,
temperature gauge, oil pressure gauge, and audible alarms is provided.
Marine Gear Options: Various transmission models are available. The
KMH4A is a hydraulic wet multiple clutch transmission with an 8-degree
down angle. Reduction ratios include 2.04:1 and 2.45:1 (forward and
reverse identical). The SD40-4T saildrive unit is available on certain
4JH3 variants. The crankshaft rotation is counterclockwise; the
propeller shaft rotation is clockwise when viewed from the stern.
Overall Length (Engine Only): 718 mm (28.3 in).
Overall Width: 560-581 mm (22.0-22.9 in).
Overall Height: 618-660 mm (24.3-26.0 in).
Dry Weight (Engine Only): 186 kg (410 lb).
Dry Weight (with Marine Gear): 229-260 kg (505-573 lb) depending on
transmission.
Dimensions with KMH4A Gear (L x W x H): 886 mm x 581 mm x 635 mm (34.9
in x 22.9 in x 25.0 in).
Engine Oil Capacity (with filter): 5.4 liters (5.7 qt) for standard oil
pan.
Engine Oil Grade: API CF, CF-4, or CI-4. SAE 15W-40 for normal
operation.
Engine Oil Grade: API CF-4, or CI-4. SAE 10W-30 for cold climates below
5°C (41°F).
Oil Change Interval: 250 hours or 12 months, whichever arrives first.
Oil Filter Change Interval: Every 250 hours (with each oil change).
Fuel Filter Change Interval: 250 hours or 12 months.
Fuel Filter Water Drain: Inspect daily; drain when water is present.
Coolant Capacity (Engine + Heat Exchanger): 6.0-7.2 liters (6.3-7.6 qt).
Coolant Specification: Ethylene glycol-based antifreeze with corrosion
inhibitors.
Coolant Change Interval: 500 hours or 2 years.
Seawater Pump Impeller Change: 200 hours or 12 months.
Valve Clearance (Cold): Intake 0.20 mm (0.008 in), Exhaust 0.20 mm
(0.008 in).
Valve Clearance Adjustment Interval: 250 hours or 2 years.
Injection Timing: Check per service manual; adjustment by shimming
injection pump.
Idle Speed Adjustment: Low idle 700 ± 25 rpm.
Compression Pressure: Standard range approximately 3.2-3.8 MPa (464-551
psi).
Compression Variation Between Cylinders: Maximum 10%.
Air Cleaner / Flame Arrestor Service: Clean every 250 hours or as
needed.
Engine Mount Inspection: Every 500 hours or 2 years.
Propeller Shaft Alignment: Check every 250 hours or annually.
Cylinder Head Bolts, Stage 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts, Stage 2: 60 Nm (44 lb-ft)
Connecting Rod Bolts: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts: 60 Nm (44 lb-ft)
Flywheel Bolts: 65 Nm (48 lb-ft)
Crankshaft Pulley Bolt: 135 Nm (100 lb-ft)
Rocker Arm Shaft Bracket Bolts: 25-30 Nm (18-22 lb-ft).
Rocker Arm Adjustment Locknut: 10 Nm (7 lb-ft).
Intake Manifold Bolts: 15-20 Nm (11-15 lb-ft).
Exhaust Manifold Nuts: 15-20 Nm (11-15 lb-ft).
Injection Nozzle Holders: 50-60 Nm (37-44 lb-ft).
High-Pressure Fuel Line Nuts: 18-22 Nm (13-16 lb-ft).
Water Pump Mounting Bolts: 15-20 Nm (11-15 lb-ft).
Oil Pan Bolts: 10-12 Nm (7-9 lb-ft).
Starter Motor Mounting Bolts: 30-35 Nm (22-26 lb-ft).
Alternator Mounting Bolts: 25-30 Nm (18-22 lb-ft).
Sailboats (30-42 ft / 9-13 m): The 4JH3E is installed as auxiliary
propulsion in cruising sailboats including the Wauquiez 40 Pilot Saloon,
Beneteau First series, Jeanneau Sun Odyssey, and Hunter yachts requiring
40-60 hp propulsion.
Trawlers (28-34 ft / 8.5-10.5 m): The engine is used in pocket trawlers
such as the Prairie 29 Coastal Cruiser, Nordic Tug 32, and similar
displacement cruisers where fuel economy and low-speed torque are
prioritized.
Downeast Boats: Wooden and fiberglass Downeast-style cruisers and
lobster boat conversions utilize the 4JH3E for its compact dimensions
and reliable direct injection operation.
Small Commercial Workboats: The engine is installed in small fishing
vessels (under 12 m), harbor launches, pilot boats, and light utility
craft requiring a balance of power and efficiency.
KMH4A Transmission Configuration: The engine with the 2.04:1 or 2.45:1
reduction gear is used in heavier displacement sailboats and trawlers
requiring a larger propeller diameter for efficient low-speed thrust.
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