Yanmar 4JH2E Specifications
| Engine Model: Yanmar 4JH2E |
| Engine Type: 4-stroke inline 4-cylinder naturally aspirated water-cooled diesel |
| Total Displacement: 110.9 cu.in (1.82 L) |
| Rated Engine Power: 51 Hp (37.5 kW) at 3600 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 4JH2E is a 4-cylinder, naturally
aspirated marine diesel engine from the highly regarded JH2 series,
produced from the late 1980s through the 1990s. This engine was
engineered as a reliable, mechanically simple powerplant for cruising
sailboats, motorboats, and small commercial vessels where fuel
efficiency and low maintenance take precedence over raw power.
The Yanmar 4JH2E is a 4-cycle, vertical, water-cooled diesel featuring
indirect injection with a swirl pre-combustion chamber - a design
providing quieter operation and smoother running than direct injection
engines of the era. With a bore and stroke of 82 mm x 86 mm, the engine
displaces 1.817 liters and produces 51 hp at 3,600 rpm (maximum output)
and 45 hp at 3,400 rpm (continuous rating).
The cooling system is a freshwater indirect arrangement with a heat
exchanger, isolating the engine block from corrosive seawater. The
lubrication system uses forced lubrication with a trochoid pump and an
oil cooler. Weighing 203 kg (448 lb) dry, the 4JH2E became a standard
powerplant for cruising yachts and remains supported by an extensive
parts network.
Engine Code: 4JH2E
Engine Family: Yanmar JH series
Configuration: Inline 4-cylinder
Cycle: 4-cycle diesel
Type: Vertical, water-cooled
Valvetrain: Overhead Valve (OHV), 8 valves (2 per cylinder)
Displacement: 1.817 liters (1,817 cc; 110.9 cu.in)
Bore: 82.0 mm (3.23 in)
Stroke: 86.0 mm (3.39 in)
Firing Order: 1-3-4-2
Combustion System: Indirect injection (swirl pre-combustion chamber)
Aspiration: Naturally aspirated
Maximum Output (crankshaft): 37.5 kW (51 hp) at 3600 rpm
Continuous Rating: 33.1 kW (45 hp) at 3400 rpm
Maximum Torque: 113 Nm (83.4 lb-ft) at 2000-2200 rpm
Rotation Direction (viewed from flywheel): Counter-clockwise
Propeller Shaft Rotation: Bi-rotation
Cruising RPM Range: 2800-3100 rpm
The cylinder block is constructed from cast iron, providing the
structural rigidity, vibration damping, and thermal mass required for
sustained marine diesel operation. The block features a vertical,
in-line 4-cylinder configuration with a deep-skirt design. The cylinder
bores are machined directly into the cast iron casting.
The crankshaft is supported by five main bearings. The connecting rods
are forged steel. The pistons are aluminum alloy with a combustion bowl
designed to work with the indirect injection pre-combustion chamber
system. The block incorporates mounting feet for flexible marine engine
mounts.
The cylinder head is manufactured from cast iron, ensuring uniform
thermal expansion with the cylinder block and providing a robust sealing
surface for the head gasket under diesel compression pressures. The
valve arrangement is overhead valve (OHV) with two valves per cylinder -
one intake and one exhaust - actuated by pushrods from a camshaft
located within the cylinder block.
The valvetrain incorporates mechanical lash adjusters, requiring
periodic valve clearance inspection and manual adjustment. Valve
clearance (cold) is 0.20 mm (0.008 in) for both intake and exhaust
valves.
The distinctive feature of the cylinder head is the integrated swirl
pre-combustion chamber - a compact antechamber where fuel is partially
burned before entering the main combustion chamber. This indirect
injection system produces quieter operation, smoother running, and lower
emissions compared to direct injection designs of the era. The cylinder
head incorporates intake and exhaust passages and is drilled with
dedicated cooling channels around the valve seats and pre-combustion
chamber.
The fuel system employs indirect injection with a mechanical in-line
injection pump. The pump is mounted to the side of the cylinder block
and is driven from the front gear train. The injection pump type is
YPES-4CL. The injectors are mechanical, spring-loaded pintle-type
nozzles. The injection pressure is specified at 1960-2060 kPa (2844-2986
psi).
A mechanical centrifugal governor controls fuel delivery based on engine
speed and load demand. The system includes a fuel filter with a water
separator between the fuel tank and injection pump. The governor
includes an engine stop device and cold start device for reliable
starting in low temperatures. The injection timing is set at 17° BTDC ±
10°.
The lubrication system is a pressurized, full-flow wet-sump design
utilizing a trochoid-type oil pump (a compact, positive-displacement
pump with inner and outer rotors). The oil pump is driven from the
crankshaft and the system includes an oil cooler to maintain optimal
lubricant temperatures under sustained marine operation.
A full-flow spin-on oil filter is mounted to the engine. The total oil
capacity is 6.52 liters (6.9 qt) with the KM3P2, KBW20, or KBW21 marine
gear, and 8.02 liters (8.5 qt) with the KM4A gear. Recommended oil
viscosity is 15W-40 conforming to API CD, CE, CF-4, or higher diesel
specifications.
The cooling system is a freshwater indirect cooling arrangement with a
heat exchanger - a design that isolates the engine block from corrosive
seawater. A belt-driven centrifugal fresh water pump circulates coolant
through the cylinder block and cylinder head. A wax-element thermostat
regulates coolant flow. The heat exchanger transfers heat from the
freshwater circuit to the seawater circuit.
A separate seawater pump (rubber impeller type) draws raw water through
a sea strainer and circulates it through the heat exchanger, oil cooler,
and exhaust mixing elbow before discharging overboard. The freshwater
capacity (engine and heat exchanger) is 6.02 liters (6.4 qt). The
seawater pump is detailed in parts catalog diagrams.
| Intake and Exhaust Systems |
Intake System: The intake system includes a dry-type air filter suitable
for marine engine room environments. The suction manifold distributes
air to each cylinder.
Exhaust System: The exhaust manifold is constructed from cast iron with
a mixing elbow where seawater is injected to cool exhaust gases before
they exit through the wet exhaust hose and transom fitting.
Electrical System: The engine is equipped with a 12-volt electric
starting motor rated at 1.4 kW. A standard alternator provides 55
amperes output; an optional 80-ampere alternator is available. Glow
plugs are installed for cold-start assistance. A wire harness and
various sensor configurations are available: B-2 type, C type, D type,
and E type.
Starting System: A key-operated starter switch engages the starter
motor. Glow plugs are pre-heated for 5-10 seconds before starting. A
cold start device is integrated into the injection pump.
Governor System: The mechanical centrifugal governor within the
injection pump maintains engine speed under varying loads, calibrated
for marine propeller law operation. A speed remote control device
enables throttle control from the helm station.
Dry Weight (without marine gear): 203 kg (448 lb)
Dry Weight (with KM3P2 gear): 217 kg (478 lb)
Dry Weight (with KBW20 gear): 226 kg (498 lb)
Dry Weight (with KM4A gear): 228 kg (503 lb)
Length (KBW20/KBW21 configuration): 990-1015 mm (39.0-40.0 in)
Length (KM4A configuration): 1058 mm (41.7 in)
Engine Oil Capacity (with filter): 6.52-8.02 l (6.9-8.5 qt) depending on
marine gear
Engine Oil Specification: 15W-40, API CD, CE, CF-4, or higher diesel oil
Oil Change Interval: 150 hours (normal operation); 50 hours for initial
break-in
Coolant Capacity (engine + heat exchanger): 6.02 liters (6.4 qt)
Coolant Change Interval: 12 months
Coolant Specification: Ethylene glycol-based diesel coolant
Thermostat Opening Temperature: 71-77°C (160-170°F)
Valve Clearance (cold, intake): 0.20 mm (0.008 in)
Valve Clearance (cold, exhaust): 0.20 mm (0.008 in)
Valve Clearance Adjustment Interval: 1,000 hours
Fuel Filter Replacement Interval: 150 hours
Air Filter Replacement Interval: Clean every 250 hours; replace as
required
Marine Gear Oil Capacity (KBW20): 1.47 liters (1.55 qt) maximum
Marine Gear Oil Capacity (KM4A): 1.32 liters (1.40 qt)
Marine Gear Oil Specification: Dexron ATF
Injection Pressure: 1960-2060 kPa (2844-2986 psi)
Injection Timing: 17° BTDC ± 10°
Drive Belt Tension: Manual adjustment via alternator mounting bracket
Idle Speed: 650-750 rpm
Cylinder Head Bolts (Stage 1): 34-44 Nm (25.3-32.5 lb-ft)
Cylinder Head Bolts (Stage 2): 73-83 Nm (54.2-61.5 lb-ft)
Crankshaft V-Pulley: 112-122 Nm (83.2-90.4 lb-ft)
Connecting Rod Cap Bolts: 30 Nm (22 lb-ft)
Main Bearing Cap Bolts: 50 Nm (37 lb-ft)
Flywheel Bolts (to crankshaft flange): 45 Nm (33 lb-ft)
Flywheel Housing to Block Bolts: 35 Nm (26 lb-ft)
Camshaft Bearing Caps: 20 Nm (15 lb-ft)
Injector Clamp Nuts: 15 Nm (11 lb-ft)
Valve Cover Bolts: 8 Nm (6 lb-ft)
Oil Pan Bolts: 12 Nm (9 lb-ft)
Oil Drain Plug: 35 Nm (26 lb-ft)
Thermostat Housing Bolts: 10 Nm (7 lb-ft)
Intake Manifold Bolts: 15 Nm (11 lb-ft)
Exhaust Manifold Nuts: 20 Nm (15 lb-ft)
Rocker Shaft Bracket Nuts: 15 Nm (11 lb-ft)
Injection Pump Mounting Nuts: 20 Nm (15 lb-ft)
Glow Plug (in cylinder head): 12 Nm (9 lb-ft)
Cruising Sailboats (30-40 feet): The
4JH2E became a standard powerplant for cruising yachts in the 30-40 foot
range, valued for its mechanical simplicity and reliability. The engine
is installed in sailboats with shaft drive, driving a fixed or
feathering propeller. The fresh water cooling system prevents corrosion
in marine environments.
Motorboats and Trawlers (30-35 feet):
Small displacement motorboats and trawlers utilize the 4JH2E for its
fuel efficiency at displacement speeds (6-8 knots). The 45 hp continuous
rating suits trawler-style vessels designed for long-range cruising.
Small Commercial Vessels: The engine
is installed in small commercial craft including launches, harbor
workboats, and light fishing vessels, where the 4,000-5,000 hour service
life before major overhaul suits commercial duty cycles.
Marine Gear Pairings: The engine
mates with multiple marine gear options:
KBW20 / KBW21: 2.62:1, 3.06:1, or 3.28:1 reduction ratios; mechanical
multi-disc wet clutch.
KM3P2: 2.36:1 or 3.16:1 reduction; mechanical multi-disc wet clutch with
built-in cooling fan.
KM4A: 2.14:1 or 2.63:1 reduction; mechanical multi-disc wet clutch with
built-in cooling fan.
Generator Drive (Marine Auxiliary Power):
The 4JH2E powers marine generator sets for auxiliary electrical supply
aboard yachts and small commercial vessels. The engine provides 50 Hz or
60 Hz output depending on governed speed.
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