Yanmar 3JH40 Specifications
| Engine Model: Yanmar 3JH40 |
| Engine Type: 4-stroke inline 3-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 100.2 cu.in (1.64 L) |
| Rated Engine Power: 40 Hp (29.4 kW) at 3000 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 3JH40 is a 3-cylinder, 4-stroke,
vertical, water-cooled marine diesel engine. It holds the distinction of
being the world’s smallest common rail inboard marine diesel engine in
displacement, physical dimensions, and weight. Introduced in 2018 and a
winner of the Miami Innovation Award, this powerplant was designed to
bring the efficiency and performance advantages of electronically
managed common rail fuel injection to smaller leisure boats and
light-duty commercial craft. The Yanmar 3JH40 is a naturally aspirated,
indirect freshwater-cooled engine with a 1.642-liter displacement.
Its electronic common rail system provides precise injection control,
resulting in minimal fuel consumption, exceptionally low noise levels,
and compliance with stringent EPA Tier 3 and EU RCD Tier 2 emission
regulations. The engine is offered with multiple transmission options,
including KM35A and KM35P mechanical cone clutch gears and an SD60
saildrive, making it suitable for monohull sailing yachts and catamarans
up to 45 feet, small motorboats, and sloops.
The Yanmar 3JH40 represents a significant technological advancement for
the sub-40 horsepower marine diesel segment. Traditional mechanical
injection systems in this power class are replaced by a sophisticated
Bosch common rail system, which uses a high-pressure pump and a shared
accumulator rail to deliver fuel to each injector under electronic
control.
The engine displaces 1,642 cc, achieved through bore and stroke
dimensions of 88 mm by 90 mm. This square geometry produces maximum
output of 40 metric horsepower (29.4 kW) at 3,000 rpm, with maximum
torque of 108 Nm at 2,200 rpm. The compression ratio is 23.5:1,
supporting excellent cold-start performance without excess smoke.
The engine block is constructed from cast iron, with a cast aluminum
cylinder head containing the overhead valve (OHV) arrangement. The
valvetrain uses pushrods and rocker arms actuated by a camshaft located
in the block. Mechanical lifters require periodic manual valve lash
adjustment. The forced lubrication system employs a trochoid-type oil
pump with a total system capacity of 5.5 liters.
The indirect freshwater cooling system uses a heat exchanger to separate
engine coolant from raw seawater, preventing salt corrosion in the
engine block The standard electrical system includes a 12-volt, 1.4 kW
starter motor and a high-output 125-ampere alternator, a substantial
capacity for small auxiliary loads and battery charging at low rpm. The
dry engine weight is 192 kg (423 lb) without transmission, rising to
approximately 204 kg (450 lb) with the KM35P gear attached.
Engine Type: 4-stroke, vertical, water-cooled, inline-3 diesel.
Valvetrain: Overhead valve (OHV), 6 valves (2 per cylinder) with
pushrods and rocker arms.
Aspiration: Naturally aspirated.
Displacement: 1.642 L (100.2 cu.in).
Bore: 88.0 mm (3.46 in).
Stroke: 90.0 mm (3.54 in).
Compression Ratio: 23.5:1.
Combustion System: Direct injection, Bosch common rail system with
electronic control.
Maximum Output: 40 hp (29.4 kW) @ 3,000 rpm.
Maximum Torque: 108 Nm (79.7 lb-ft) @ 2,200 rpm.
Maximum Engine Speed (Rated): 3,000 rpm.
Low Idle Speed: 750 rpm (factory setting).
Direction of Rotation (viewed from stern/flywheel end):
Counterclockwise.
The cylinder block is a monobloc casting manufactured from high-strength
gray cast iron. The block uses an open-deck design with integral,
non-replaceable cylinder bores machined directly into the casting. The
bores receive a plateau honing finish to promote piston ring sealing and
oil control. The block is of a deep-skirted design, extending below the
crankshaft centerline to enhance rigidity.
Four main bearing bulkheads are cast integrally with the block,
supporting a forged steel crankshaft with induction-hardened journal
surfaces. The crankcase incorporates cast-in oil galleries that feed
pressurized oil to the main bearings and cylinder head. Engine mounting
feet are cast into the block sides for flexible mounts that isolate
vibration from the hull.
The cylinder head is a cross-flow casting manufactured from cast
aluminum alloy. The combustion chambers are of the direct-injection type
with a re-entrant bowl machined into the piston crown. The cylinder head
carries two valves per cylinder: one intake and one exhaust, arranged in
a straight line along the head centerline. Valves are constructed from
heat-resistant steel, with exhaust valves featuring hardened seats for
durability. The valvetrain operates via a camshaft located in the
cylinder block.
Mechanical lifters follow the camshaft lobes and transfer motion through
hardened pushrods to cast rocker arms. The rocker arms pivot on a
through-shaft mounted above the cylinder head. Valve lash adjustment
uses a screw-and-locknut arrangement at the rocker arm-to-valve stem
interface. Adjustments are performed with the engine cold. The cylinder
head gasket is a multi-layer steel (MLS) design with elastomer sealing
beads.
The fuel system is an electronically controlled common rail (CR) design,
supplied by Bosch. A gear-type high-pressure fuel pump, mounted on the
engine and driven by the timing gear train, draws fuel from the tank
through a water-separating pre-filter. The pump pressurizes fuel to
approximately 1,600-1,800 bar (23,200-26,100 psi) and delivers it to a
common rail (accumulator) mounted on the top of the engine.
The rail stores pressurized fuel and supplies it to three electronically
controlled injectors, one per cylinder. Each injector is actuated by a
solenoid under command from the engine control unit (ECU). The ECU
determines injection timing, injection duration, and multiple injection
events (pilot and main injections) based on inputs from the crankshaft
position sensor, camshaft position sensor, boost pressure sensor,
coolant temperature sensor, and throttle position sensor.
A mechanical lift pump or an electric feed pump (installation dependent)
delivers fuel from the tank to the high-pressure pump. Excess fuel from
the injectors and high-pressure pump returns to the fuel tank through a
return line for system cooling and aeration prevention. The common rail
system enables extremely precise fuel metering, resulting in reduced
smoke, lower noise, and improved fuel efficiency compared to mechanical
injection systems.
The lubrication system is a forced, full-flow wet-sump design. A
trochoid-type oil pump is mounted internally on the camshaft or
crankshaft within the timing gear case. The trochoid pump uses an inner
rotor with lobed teeth rotating inside an outer rotor, providing
consistent flow with low pulsation. The pump draws oil through a
screened pickup tube from a cast aluminum oil pan. The oil capacity is
5.5 liters including the full-flow spin-on oil filter. The engine oil
pan contains 5.0 liters of oil, with an additional 0.5 liters in the
filter and galleries.
Oil passes through the trochoid pump and then through a full-flow,
spin-on oil filter mounted on the cylinder block. An integral bypass
valve within the filter housing allows unfiltered oil to circulate if
the filter becomes restricted. From the filter, pressurized oil enters
the main oil gallery, a longitudinal passage drilled through the
cylinder block. The main gallery distributes oil to all four main
bearings through cross-drilled passages.
Connecting rod bearings receive oil from the main bearings via diagonal
passages drilled through the crankshaft. A separate vertical passage in
the cylinder block carries oil to the cylinder head, where it reaches
the rocker shaft and rocker arms through hollow pushrods. Oil pressure
is regulated by a spring-loaded relief valve located on the oil pump
housing. The recommended oil grade is SAE 15W-40 or SAE 10W-40,
diesel-rated (API CF-4, CG-4, CH-4, or higher).
The cooling system is an indirect freshwater (closed) cooling design
with a separate seawater circuit. The freshwater circuit is sealed and
thermostatically controlled. A belt-driven centrifugal fresh water pump
circulates coolant through the cylinder block water jacket, cylinder
head, and the tube side of a tubular heat exchanger. A wax-pellet
thermostat is located in a housing at the front of the cylinder head.
The thermostat is rated to begin opening at 71-76°C (160-169°F) and is
fully open by 85°C (185°F). When the thermostat is closed, coolant
recirculates within the engine for rapid warm-up. When open, coolant
flows through the heat exchanger.
The seawater circuit uses a rubber-impeller raw water pump, belt-driven
from the crankshaft pulley. The raw water pump draws seawater through a
hull inlet and strainer and then pumps it through the shell side of the
heat exchanger, absorbing heat from the freshwater coolant. From the
heat exchanger, seawater is injected into the exhaust mixing elbow to
cool exhaust gases before discharge overboard. The system includes a
coolant recovery reservoir connected to the heat exchanger filler neck.
A galvanic corrosion protection system (zinc anode) is installed in the
heat exchanger to prevent electrolytic damage.
| Intake and Exhaust Systems |
Intake System: Air enters through a flame-arresting intake silencer (air
cleaner) that reduces intake noise while preventing flame propagation
from the engine into the engine room in the event of a backfire. The
intake manifold distributes air evenly to all three cylinders.
Exhaust System: A water-cooled cast-iron exhaust manifold collects
exhaust gases. The manifold is jacketed with engine coolant to maintain
low external surface temperatures. A mixing elbow injects seawater from
the raw water pump into the exhaust stream, cooling exhaust gases to
below 100°C (212°F) before discharge through a water-lift muffler and
through-hull fitting. The exhaust pipe diameter is 76 mm (3.0 in).
The engine is equipped with a 12-volt, negative-ground marine electrical
system. A 12-volt, 1.4 kW starter motor engages the flywheel ring gear
through a solenoid. The charging system uses a high-output 12-volt,
125-ampere alternator, which provides substantial charging capacity for
multiple batteries, navigation electronics, and onboard appliances. The
alternator is of an earth-type or isolated ground type depending on the
installation requirements.
Electronic Control Unit (ECU): A sealed marine-grade ECU manages all
engine functions. The ECU receives inputs from the crankshaft position
sensor (flywheel-mounted), camshaft position sensor, common rail
pressure sensor, intake manifold pressure sensor, coolant temperature
sensor, fuel temperature sensor, and electronic throttle position
sensor. Outputs control the high-pressure fuel pump regulator, the three
injector solenoids, and the engine instrumentation. The VC10 or VC20
electronic control system provides a single-lever or dual-lever
interface for throttle and gear shifting, with an optional display panel
showing engine parameters.
Starting Aid: A cold start advance system integrated into the ECU
advances injection timing during cranking when coolant temperature is
below a threshold (approximately 5°C / 41°F). Glow plugs are not
required for starting in moderate climates due to the high compression
ratio (23.5:1).
Overall Engine Length (Front Pulley to Flywheel Housing): 773-774 mm
(30.4-30.5 in).
Overall Engine Width: 554-580 mm (21.8-22.8 in).
Overall Engine Height (From Oil Pan Rail to Valve Cover Top): 622-632 mm
(24.5-24.9 in).
Dry Weight (Engine Only, No Fluids, No Transmission): 192 kg (423 lb).
Weight (With KM35P Marine Gear): 204 kg (450 lb).
Engine Oil:
Grade: SAE 15W-40 or SAE 10W-40 (diesel-rated, API CF-4, CG-4, CH-4, or
higher).
Oil Capacity (Total System, With Filter): 5.5 L (5.8 qt).
Oil Capacity (Oil Pan Only): 5.0 L (5.3 qt).
Normal Oil Pressure (Rated Speed, Hot): 350-450 kPa (51-65 psi).
Minimum Oil Pressure (Hot Idle): 70 kPa (10 psi).
Engine Oil Change Interval: Every 250 hours or annually, whichever
occurs first.
Engine Oil Change Interval: Every 150 hours for severe duty.
Oil Filter Change Interval: Replace at every oil change.
Cooling System (Freshwater Circuit):
Coolant Type: Diesel-rated ethylene glycol antifreeze (50/50 mix with
distilled water).
Total Freshwater Capacity (Engine and Heat Exchanger): 3.5-4.0 L
(3.7-4.2 qt).
Thermostat Opening Temperature: 71-76°C (160-169°F).
Thermostat Full Open Temperature: 85°C (185°F).
Heat Exchanger Pressure Cap Rating: 0.7-1.0 bar (10-15 psi).
Coolant Change Interval: Drain, flush, and refill every 1,000 hours or
every 2 years.
Valve Clearance (Cold Engine, Ambient
Temperature):
Intake: 0.20 mm (0.008 in).
Exhaust: 0.20 mm (0.008 in).
Valve Adjustment Interval: Inspect and adjust every 500 operating hours
or annually.
Fuel Filter Change Interval (Pre-filter and Secondary): Replace every
250 hours or annually.
Timing Gear Train: Gear-driven camshaft requires no periodic
replacement.
Impeller Replacement (Seawater Pump): Replace rubber impeller every
250-500 hours or annually.
Injector Testing Interval: Replace every 2,000 operating hours.
Cylinder Head Bolts, Step 1: 25 Nm (18 lb-ft).
Cylinder Head Bolts, Step 2: 50 Nm (37 lb-ft).
Cylinder Head Bolts, Step 3: 80 Nm (59 lb-ft).
Cylinder Head Bolts, Step 4: 100 Nm (74 lb-ft).
Connecting Rod Cap Nuts: 45-50 Nm (33-37 lb-ft).
Main Bearing Cap Bolts: 60-65 Nm (44-48 lb-ft).
Flywheel Bolts (to Crankshaft Flange): 65-70 Nm (48-52 lb-ft).
Crankshaft Pulley Bolt (Front Damper): 120-130 Nm (89-96 lb-ft).
Camshaft Drive Gear Bolt: 35-40 Nm (26-30 lb-ft).
High-Pressure Common Rail Mounting Bolts: 25-30 Nm (18-22 lb-ft).
High-Pressure Injection Lines (Rail to Injector): 25 Nm (18 lb-ft).
Injector Hold-Down Clamp Bolts: 25 Nm (18 lb-ft).
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft).
Oil Pan Bolts (Cast Aluminum Pan): 12-15 Nm (9-11 lb-ft).
Valve Cover Bolts (Perimeter and Center): 8-10 Nm (6-7 lb-ft).
Thermostat Housing Bolts: 15-18 Nm (11-13 lb-ft).
Fresh Water Pump Mounting Bolts: 18-22 Nm (13-16 lb-ft).
Seawater Raw Water Pump Mounting Bolts: 18-22 Nm (13-16 lb-ft).
Starter Motor Mounting Bolts: 35-40 Nm (26-30 lb-ft).
Alternator Mounting Bracket Bolts: 30-35 Nm (22-26 lb-ft).
Engine Flexible Mount Nuts: 45-50 Nm (33-37 lb-ft).
Oil Drain Plug (Oil Pan): 30-35 Nm (22-26 lb-ft).
The Yanmar 3JH40 engine is utilized as the primary marine propulsion
engine for the following vessel types.
Sailboats (Monohulls):
Monohull sailing yachts up to 45 feet (13.7 m) in length.
Make and model independence - suitable for repowering existing
installations or new builds.
Multihulls:
Catamarans up to 45 feet (light displacement, twin-engine
configurations).
Powerboats:
Small motorboats and sloops.
Daysailers and pocket trawlers (25-35 ft range).
Light Commercial Craft:
Small workboats, launches, and harbor utility vessels.
Pilot boats and light patrol craft.
Transmission Options:
KM35A / KM35P: Mechanical cone clutch marine gear. Reduction ratios:
2.33, 2.64.
ZF15MA: Mechanical transmission. Reduction ratios: 2.14, 2.63.
SD60: Saildrive unit (constant mesh with mechanical clutch). Reduction
ratios: 2.23, 2.49.
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