Yanmar 3JH4E Specifications
| Engine Model: Yanmar 3JH4E |
| Engine Type: 4-stroke inline 3-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 100.2 cu.in (1.64 L) |
| Rated Engine Power: 39 Hp (28.7 kW) at 3000 rpm |
| Fuel System Type: Direct injection |
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0The Yanmar 3JH4E is a 3-cylinder, naturally
aspirated, four-stroke marine diesel engine. It is part of the JH4
series, which succeeded the JH3, offering a larger displacement and
improved environmental performance while remaining a popular choice for
30 to 45-foot sailboats. The Yanmar 3JH4E is a compact, lightweight, and
quiet-running engine, incorporating a direct injection combustion system
for improved fuel economy and cold starting performance compared to its
indirect injection predecessor.
The engine meets EPA Tier 2, EU RCD, BSO II, and EMC emission compliance
standards. Available with mechanical (KM35A, KM35P, ZF15MA) or saildrive
(SD50) transmission options, the 3JH4E is a common auxiliary powerplant
for cruising and racing sailboats.
The Yanmar 3JH4E is a four-stroke, water-cooled, naturally aspirated,
inline 3-cylinder diesel engine. The cylinder arrangement is vertical
and in-line, designed for compact mounting in sailboat engine
compartments. The engine block is constructed from cast iron, while the
cylinder head is an aluminum alloy or cast iron unit depending on the
production year.
The valvetrain is an overhead valve (OHV) design with pushrods and
rocker arms, actuated by a camshaft located in the cylinder block. Each
cylinder features two valves - one intake and one exhaust. The rated
maximum output is 28.7 kW (39 hp) at 3,000 rpm. The continuous rating is
26.1 kW (35.5 hp) at 2,907 rpm. Displacement is 1,642 cc (100.2 cu.in),
achieved through a bore of 88.0 mm (3.46 in) and a stroke of 90.0 mm
(3.54 in).
The compression ratio is 16.3:1. The combustion system is direct
injection. The cooling system is indirect freshwater cooling with a heat
exchanger. The starting system is electric start (12V - 1.4 kW). The
standard alternator output is 12V - 60A, with an optional 80A alternator
available. The lubrication system is forced lubrication with a trochoid
pump. The firing order for a 3-cylinder engine is 1-2-3.
The cylinder block is a cast iron, closed-deck design. This construction
provides high rigidity and excellent bore retention under thermal and
mechanical loads. The water jacket surrounds each cylinder bore fully,
promoting even cooling across the engine. The block is configured for
compact mounting in sailboat engine compartments, with the engine mounts
positioned at the front and rear of the block.
The crankshaft is forged or cast nodular iron, supported by three main
bearings. The three-main-bearing configuration is standard for a
3-cylinder engine, providing adequate support for the firing impulses.
Connecting rods are forged steel. Pistons are aluminum alloy with two
compression rings and one oil-control ring. The piston skirts feature a
coating to reduce friction during cold starts. No cylinder liners are
used; the bores are machined directly into the cast iron.
The cylinder head is an aluminum alloy or cast iron cross-flow casting
with a direct injection combustion chamber design. The cross-flow
arrangement places the intake manifold on one side of the head and the
exhaust manifold on the opposite side, improving volumetric efficiency
and reducing heat transfer to the intake charge.
The camshaft is located in the cylinder block and actuates the valves
through mechanical lifters, pushrods, and rocker arms. The valve train
includes adjustable rocker arms with screw-type adjusters and locking
nuts, allowing precise valve clearance setting. Intake and exhaust
valves are fitted with hardened tip inserts to reduce wear at the rocker
arm contact point. Valve seats are induction-hardened directly into the
head or fitted with replaceable inserts. Valve guides are also integral
to the head casting or replaceable. The cylinder head gasket is a
composite or multi-layer steel design.
The fuel system is a mechanical direct injection system. An in-line
injection pump is mounted to the engine timing case and driven by a gear
from the camshaft. The pump generates high-pressure fuel pulses and
distributes them to each cylinder in the firing order (1-2-3). Fuel is
delivered from the pump to the injectors through steel high-pressure
lines.
The injectors are of the multi-hole nozzle type, atomizing fuel directly
into the combustion bowl in the piston crown. The fuel injection
pressure is 200 kg/cm2 (2,844 psi). A mechanical governor is integral to
the injection pump, maintaining engine speed from no-load to full-load
conditions.
The fuel system includes a fuel filter with a water separator. A manual
primer pump is located on the injection pump or fuel filter head to
bleed air from the system after filter changes. Fuel lift pump is
mechanically driven from the engine camshaft.
The lubrication system is a full-pressure, trochoid pump design. The oil
pump is driven by the crankshaft or camshaft gear train. Oil is drawn
from the oil pan through a screened pickup and passed through the pump
before being routed through a full-flow spin-on oil filter.
Pressurized oil travels to main galleries machined into the cylinder
block, delivering to the crankshaft main bearings and connecting rod
bearings through drilled passages. A separate oil passage directs
pressurized oil upward through the cylinder block and cylinder head to
the rocker shaft assembly. The system includes a pressure relief valve.
The total oil capacity is 5.0 liters (5.3 US qt), with an effective
(service) capacity of 2.1 liters (2.2 US qt) per the service manual
specifications.
The cooling system is an indirect freshwater (closed) cooling system
with a heat exchanger. The system includes a belt-driven seawater pump
(rubber impeller type) and a belt-driven freshwater circulation pump.
Freshwater coolant is circulated through the cylinder block and cylinder
head. The freshwater then passes through the heat exchanger, where
seawater pumped from outside the vessel absorbs heat from the freshwater
before being discharged overboard.
A wax-pellet thermostat, with an opening temperature of 71°C to 82°C
(160°F to 180°F), regulates freshwater coolant flow to maintain stable
operating temperatures. A seawater strainer is installed between the
hull intake and the seawater pump to prevent debris from entering the
cooling system. The coolant system capacity depends on the installation.
| Intake and Exhaust Systems |
Intake System: The intake system consists of a dry-type replaceable
paper air filter or a flame arrestor (marine requirement) and a cast
iron intake manifold.
Exhaust System: A cast iron exhaust manifold collects gases from all
three cylinders. The manifold is connected to a water-injected exhaust
elbow, where seawater is mixed with exhaust gases before discharge
through the vessel's exhaust hose and through-hull fitting. The exhaust
pipe diameter is 76 mm (3.0 in). The exhaust system operates at elevated
temperatures; proper water flow is critical to prevent overheating of
the exhaust hose.
The engine is equipped with a 12-volt electrical system. The starter
motor is a 1.4 kW gear-reduction type. The standard alternator output is
60A. An optional 80A alternator is available. The electrical system
includes a key switch with pre-heat (glow plug) position, warning lamps
for oil pressure and coolant temperature, and a tachometer signal output
from the alternator W terminal.
Seawater Cooling System (Raw Water): The seawater pump is a flexible
impeller pump. The impeller requires inspection and periodic
replacement. A zinc anode is installed in the heat exchanger or seawater
circuit to prevent galvanic corrosion.
Transmission Options: The engine is available with multiple transmission
options. The KM35A and KM35P are mechanical cone clutch transmissions
with forward reduction ratios of 2.33 or 2.64. The SD50 is a saildrive
unit with a constant mesh gear and dog clutch, with a reduction ratio of
2.32. The ZF15MA is a mechanical transmission with reduction ratios of
2.14 or 2.63.
Length, measured from the front pulley to the flywheel housing mounting
face, is 773 mm (30.4 in). Width, measured across the cylinder head and
intake manifold, is 540 mm (21.3 in). Height from the bottom of the oil
pan to the top of the valve cover is 622 mm (24.5 in). Dry weight of the
engine only (without transmission) is 173 kg (381 lb). Dry weight with
the KM35A transmission is 186 kg (410 lb). The weight with the SD50
saildrive is 197 kg (434 lb).
Oil Capacity (Total): 5.0 liters (5.3 US qt). Oil Capacity
(Effective/Service): 2.1 liters (2.2 US qt). Oil Change Interval: Under
normal marine service, the engine oil and filter should be changed every
250 operating hours or annually, whichever comes first. Oil Filter:
Spin-on full-flow filter. Replacement interval coincides with each oil
change. Fuel Filters: Fuel filter with water separator. Replacement
interval is 500 operating hours or annually. Fuel Filter Change
Interval: 250 operating hours or annually.
Seawater Pump Impeller: Replace every 500 operating hours or 2 years,
whichever comes first. Inspect annually. Valve Clearance (Cold): Adjust
with the engine at ambient temperature. Intake valve clearance is 0.20
mm (0.008 in). Exhaust valve clearance is 0.20 mm (0.008 in). Valve Lash
Adjustment Interval: Every 1,000 operating hours. Idle Speed: 750 to 800
rpm. Air Filter (Flame Arrestor) Service: Clean with solvent and re-oil
(if oiled type) every 250 hours.
Engine Coolant (Freshwater): Long-life antifreeze. Change interval is
1,000 operating hours or 2 years. Injection Pump Timing: Static timing
is set by shim adjustment. Factory set; no field adjustment required.
Injector Opening Pressure: 200 kg/cm2 (2,844 psi). Glow Plug Operation:
Pre-heat for 5 to 10 seconds before starting in cold weather (below 10°C
/ 50°F). Anti-Siphon Valve Inspection: Inspect the anti-siphon valve in
the seawater cooling circuit every 500 operating hours to prevent
seawater backflow into the engine.
Cylinder Head Bolts, Stage one: 40 Nm (30 lb-ft).
Cylinder Head Bolts, Stage two: 80 Nm (59 lb-ft).
Connecting Rod Bolts: 45 Nm (33 lb-ft).
Main Bearing Cap Bolts: 55 Nm (41 lb-ft).
Flywheel Housing to Cylinder Block Bolts: 50 Nm (37 lb-ft).
Flywheel to Crankshaft Bolts: 60 Nm (44 lb-ft).
Intake Manifold Nuts: 15 Nm (11 lb-ft).
Exhaust Manifold Nuts: 20 Nm (15 lb-ft).
Injection Pump Mounting Nuts: 25 Nm (18 lb-ft).
Injector Clamp Bolts: 30 Nm (22 lb-ft).
High-Pressure Fuel Line Nuts: 25 Nm (18 lb-ft).
Glow Plugs: 15 Nm (11 lb-ft).
Valve Cover Bolts: 8 Nm (6 lb-ft).
Oil Pan Bolts: 12 Nm (9 lb-ft).
Oil Filter (Spin-On): 15 Nm (11 lb-ft) or 3/4 turn after gasket contact.
Water Pump Mounting Bolts: 20 Nm (15 lb-ft).
Thermostat Housing Bolts: 10 Nm (7 lb-ft).
Crankshaft Pulley Bolt: 100 Nm (74 lb-ft).
Starter Motor Mounting Bolts: 35 Nm (26 lb-ft).
Alternator Pivot and Adjustment Bolts: 25 Nm (18 lb-ft).
Seawater Pump Mounting Bolts: 15 Nm (11 lb-ft).
Heat Exchanger Mounting Bolts: 15 Nm (11 lb-ft).
The Yanmar 3JH4E engine was utilized almost exclusively as a marine
auxiliary propulsion engine for sailboats and small power vessels. Its
primary applications include sailboats ranging from 30 to 45 feet in
length. The engine serves as auxiliary power for cruising yachts, racing
sailboats, and daysailers. The engine is also used in small power
vessels such as motor sailers and launches. The 3JH4E is compatible with
shaft drive installations (using KM35A, KM35P, or ZF15MA transmissions)
and saildrive installations (using the SD50 unit).
Sailboat Applications:
Beneteau sailboats (31 to 40-foot models).
Jeanneau sailboats.
Hunter sailboats.
Catalina sailboats.
Dufour sailboats.
Bavaria sailboats.
Moody sailboats.
Power Vessel Applications:
Small power cruisers (up to 35 feet).
Motor sailers.
Launches and workboats as auxiliary power.
Other Applications:
Commercial vessel auxiliary power (small fishing boats).
Generator set power source (limited production).
The 3JH4E is a current production engine as of 2026, with continuing
parts availability through Yanmar's global marine dealer network. Its
combination of compact dimensions, low weight, low vibration, and
emission compliance makes it a preferred auxiliary engine for sailboat
owners seeking a reliable diesel powerplant.
Transmission Data: KM35A / KM35P: Mechanical cone clutch transmission.
Forward reduction ratios: 2.33 or 2.64. Dry weight: 32 kg (71 lb).
Intended for shaft drive installations. SD50: Saildrive unit with
constant mesh gear and dog clutch. Reduction ratio: 2.32. Includes a
lower gear housing with a horizontal propeller shaft and a vertical
drive shaft passing through the boat hull. Dry weight: 42 kg (93 lb)
including the lower unit. ZF15MA: Mechanical transmission (by ZF
Marine). Reduction ratios: 2.14 or 2.63. Dry weight: 30 kg (66 lb).
Intended for shaft drive installations.
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