Yanmar 4LHA STP Specifications
| Engine Model: Yanmar 4LHA STP |
| Engine Type: 4-stroke inline 4-cylinder turbocharged water-cooled diesel |
| Total Displacement: 211 cu.in (3.45 L) |
| Rated Engine Power: 240 Hp (177 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 4LHA-STP is a high-performance,
4-stroke, vertical water-cooled marine diesel engine representing the
most powerful evolution within the 4LHA series. This engine is
engineered for fast planning hulls, lightweight sportfishing vessels,
and light commercial craft demanding maximum power density from a
compact package. The STP designation signifies the highest output
variant in this family, achieved through aggressive turbocharging,
wastegate control, and an efficient intercooler system.
Operators benefit from a power-to-weight ratio that enables planing
speeds in hulls where heavier engines would compromise performance. The
engine incorporates Yanmar's direct injection combustion system,
delivering fuel efficiency and transient response suited for rapid
acceleration and sustained high-speed cruising.
Common installations include center consoles, express cruisers, patrol
boats, and small passenger ferries where reliability under continuous
high-load operation remains essential. The 4LHA-STP maintains Yanmar's
reputation for corrosion resistance through freshwater-cooled cylinder
blocks and heat exchangers, with only the raw water pump handling
seawater.
Displacement: 3.455 Liters (211 cu.in).
Bore x Stroke: 100 mm x 110 mm (3.94 in x 4.33 in).
Maximum Output (Crankshaft): 240 HP (177 kW) at 3,300 rpm.
Direction of Rotation: Counter-clockwise when viewed from the stern.
Idle Speed: 700 rpm with a tolerance of ±25 rpm.
Maximum No-Load Speed: 3,400 rpm.
Compression Ratio: 16.5:1.
Number of Cylinders: 4 arranged in-line.
Valves per Cylinder: 2 intake, 2 exhaust.
Combustion System: Direct injection with an in-line fuel injection pump
delivering high-pressure fuel through multi-hole nozzles into the
combustion bowl machined directly into the piston crown.
Aspiration: Turbocharged with wastegate and intercooler. The wastegate
limits boost pressure at higher engine speeds to protect mechanical
components while improving low-speed torque. The intercooler reduces
intake air temperature after compression, increasing charge density for
more complete combustion.
The cylinder block is a high-grade cast-iron monobloc design with fully
integrated cooling water jackets surrounding each cylinder bore. The
block architecture features a deep-skirt configuration extending below
the crankshaft centerline, creating a rigid structure that minimizes
bore distortion under high cylinder pressures common at 3,300 rpm.
Wet-type replaceable cylinder liners made from centrifugally cast iron
alloy are pressed into the block with interference fit, allowing
individual liner replacement during overhaul without scrapping the
entire block.
Each liner receives controlled cooling through water passages that
direct coolant flow around the upper liner region where combustion heat
concentration is greatest. The block incorporates six main bearing
bulkheads with four-bolt caps on the center three positions and two-bolt
caps on the end positions, providing crankshaft support for the 110 mm
stroke.
A cast-in oil gallery runs the full length of the block, distributing
pressurized lubricant to each main bearing, connecting rod bearing, and
piston cooling jet. The camshaft is located on the side of the block,
driven by gear train from the crankshaft, with bucket tappets actuating
pushrods that transfer motion to the overhead valve gear. Engine
mounting feet are cast integrally with the block at four positions
designed to align with standard marine engine beds and flexible mounts.
The cylinder head is a single-piece cast-iron cross-flow design where
intake air enters from one side and exhaust gases exit from the opposite
side, eliminating heat transfer between incoming and outgoing gas
streams. Four valves per cylinder operate in a parallel arrangement with
two intake valves and two exhaust valves positioned symmetrically around
the centrally located fuel injector. Intake valve diameter measures 32
mm (1.26 in), constructed from heat-resistant chrome-silicon steel with
induction-hardened stems.
Exhaust valve diameter is 28 mm (1.10 in), manufactured from
nickel-chromium superalloy with Stellite-faced tips and seats to
withstand exhaust gas temperatures. Valve seats are precision-ground
powdered metal inserts pressed into the cylinder head with 25 to 35
microns of interference. The overhead valve train incorporates roller
rocker arms rotating on needle bearings, reducing frictional losses
compared to sliding rocker designs.
Valve clearances are adjustable using screw-and-locknut adjusters at the
rocker arm pushrod interface. Intake valve clearance specification: 0.20
mm (0.008 in) cold. Exhaust valve clearance specification: 0.25 mm
(0.010 in) cold. The cylinder head gasket is a multi-layer steel
construction with embossed sealing beads around each cylinder bore and
fluid passage, providing consistent clamp load retention across the
3,300 rpm operating range. Combustion pressures are sealed using a flame
ring integrated into the gasket structure.
The fuel system uses an in-line mechanical injection pump manufactured
by Zexel, a Yanma subsidiary, mounted directly to the engine timing gear
housing. The pump body contains four independent plunger and barrel
assemblies, each driven by a dedicated cam lobe on the pump camshaft.
Plunger diameter measures 9 mm with a 10 mm stroke, delivering injection
pressure of 1,200 bar (17,400 psi) at rated speed. Fuel injection timing
is adjustable by rotating the pump mounting flange relative to the drive
gear, with factory setting at 14 deg btdc at 3,300 rpm.
High-pressure injection lines constructed from double-walled steel
tubing route fuel from the pump to each injector, with line length
calibrated to equalize injection timing across all four cylinders. The
injectors are pencil-type nozzle assemblies with 5-hole tips, each hole
diameter 0.23 mm, producing a finely atomized fuel spray pattern
directed into the piston combustion bowl. Injector opening pressure is
set to 200 bar (2,900 psi), with a secondary pressure adjustment shim
stack controlling needle lift.
A hand-operated priming pump mounted on the secondary fuel filter
housing assists in bleeding air from the system after filter changes or
fuel system service. The fuel transfer pump is a diaphragm-type unit
driven by an eccentric lobe on the injection pump camshaft, drawing fuel
from the tank and delivering it to the filter head at 0.5 bar (7 psi). A
fuel cooler integrated into the return line reduces fuel temperature
before fuel returns to the tank, preventing vapor formation in high
ambient temperature operation.
The lubrication system is a forced-feed design using a gear-type oil
pump mounted internally to the front timing cover and driven directly by
the crankshaft gear. The pump delivers oil to a full-flow spin-on filter
element located on the left side of the engine block. Oil filter
filtration rating is 15 microns absolute, with a built-in bypass valve
opening at 1.5 bar (22 psi) differential pressure to maintain flow
during cold starts or filter restriction.
Oil pressure regulation occurs through a spring-loaded relief valve
located in the oil pump housing, set to maintain main gallery pressure
between 3.5 and 4.5 bar (50 to 65 psi) at rated speed. Warm idle oil
pressure is not less than 0.7 bar (10 psi). Piston cooling jets are
threaded directly into the main oil gallery, each jet directing a
continuous stream of oil at the underside of each piston crown to manage
thermal loading at power outputs above 50 kW per cylinder.
The oil pan is a pressed steel construction with a 11.5 Liter (3.0 U.S.
Gal) capacity for standard shallow-sump marine installations. A
deep-sump option increases capacity to 15.0 Liters (4.0 U.S. Gal) for
vessels operating in rough sea conditions where oil slosh and aeration
become concerns. Oil specification requires API rating CD or higher with
SAE viscosity 15W-40 for normal operating temperatures between 0°C and
40°C (32°F to 104°F). SAE 10W-30 is permissible for ambient temperatures
below 0°C (32°F). Oil change interval: 250 operating hours under
recreational duty or 150 hours under commercial duty.
The cooling system employs a dual-circuit architecture separating fresh
water coolant from raw seawater. The fresh water circuit circulates
ethylene glycol-based antifreeze through the cylinder block, cylinder
head, and turbocharger housing using a belt-driven centrifugal pump.
Coolant capacity for the fresh water circuit is 8.5 Liters (2.25 U.S.
Gal).
A wax-pellet thermostat located in the fresh water outlet housing
maintains operating temperature between 75°C and 85°C (167°F to 185°F),
opening fully at 82°C (180°F). Overpressurization protection is provided
by a 0.9 bar (13 psi) radiator cap on the expansion tank. Heat rejection
from fresh water to seawater occurs within a tube-and-shell heat
exchanger manufactured from cupronickel alloy for seawater corrosion
resistance.
The seawater circuit begins at a rubber impeller pump mounted on the
front of the engine, driven by the crankshaft pulley. The impeller pump
delivers seawater at 150 Liters per minute (40 U.S. Gal per minute) at
3,300 rpm through the heat exchanger tubes, then through the exhaust
manifold water injection elbow where it mixes with exhaust gases for
silencing and cooling. The seawater pump impeller requires inspection
every 200 operating hours and replacement every 500 hours or annually.
Anodes of zinc or aluminum are installed in the heat exchanger end caps
and the exhaust elbow to prevent galvanic corrosion.
| Intake and Exhaust Systems |
The exhaust system features a water-cooled single-piece cast iron
manifold that directs exhaust gases to the turbocharger turbine inlet.
After exiting the turbocharger, exhaust passes through a water-injected
mixing elbow where raw seawater is introduced, reducing exhaust gas
temperature from 550°C to below 60°C (1,022°F to 140°F) before discharge
through the transom or underwater exhaust outlet.
The air intake system includes a dry-type air filter with cellulose
media rated for marine conditions, followed by a rubber intake hose
connecting to the turbocharger compressor inlet. The turbocharger is a
Mitsubishi TD04HL-15G unit with a 48 mm compressor wheel and an integral
wastegate actuator set to open at 0.85 bar (12.3 psi) boost pressure.
The electrical system operates on 12 V DC with a 2.5 kW starter motor
featuring planetary gear reduction for high cranking torque at low
battery voltage. The starter is protected by a magnetic switch that
engages only when the neutral safety circuit is satisfied. An 80 A
alternator with built-in voltage regulation maintains battery charge
under full electrical load, including navigation electronics, radar,
lighting, and fish-finding equipment.
The alternator incorporates a temperature-compensated regulator to
prevent overcharging in hot engine compartments. The instrument panel
includes a key switch with preheat position for glow plug activation,
each cylinder equipped with a 6 V glow plug wired in series to draw 30 A
total during preheat cycles.
Standard instrumentation comprises tachometer with hour meter, coolant
temperature gauge, oil pressure gauge, battery voltage meter, and
audible alarm for low oil pressure, high coolant temperature, or
excessive coolant level. An optional electronic engine monitoring system
provides NMEA 2000 connectivity for integration with multifunction
displays and vessel management systems.
Dry weight, bobtail configuration without transmission or accessories:
365 kg (805 lb).
Length, front crankshaft pulley to flywheel housing face: 878 mm (34.6
in).
Width, maximum across turbocharger and heat exchanger: 590 mm (23.2 in).
Height, from oil pan bottom to valve cover top: 711 mm (28.0 in).
Crankshaft centerline height above oil pan rail: 105 mm (4.1 in).
Flywheel housing dimensions: SAE 3 pattern with 353 mm (13.9 in) bolt
circle diameter.
Flywheel ring gear tooth count: 124 teeth with module 2.5 specification.
Oil and filter change interval: 250 hours recreational service, 150
hours light commercial service. Oil filter replacement at every oil
change using Yanmar part 119775-35151 or equivalent with 15-micron
rating. Valve clearance inspection interval: 500 hours with adjustment
required if outside specified tolerances. Intake valve clearance: 0.20
mm (0.008 in) cold. Exhaust valve clearance: 0.25 mm (0.010 in) cold.
Fuel filter replacement interval: 250 hours for primary and secondary
elements using 10-micron absolute filtration rating. Water separator
draining required every 50 hours or when visible water accumulates in
sight bowl. Cooling system service: Fresh water coolant replacement
every 1,000 hours or two years, whichever arrives first. Seawater pump
impeller replacement every 500 hours or one year.
Heat exchanger zinc anodes replaced every 250 hours or when reduced to
50 percent of original diameter. Air filter element cleaning: 250 hours
by reverse-flow compressed air not exceeding 30 psi. Replacement
required every 500 hours or when element shows visible contamination.
Drive belt tension inspection: 100 hours with deflection of 8 to 10 mm
under 10 kg force applied at mid-span between crankshaft pulley and
water pump pulley.
Injector nozzle inspection: 1,000 hours with opening pressure test and
spray pattern evaluation. Nozzle replacement recommended at 2,000 hours.
Valve guide wear measurement: 2,000 hours with service limit of 0.10 mm
(0.004 in) clearance between guide and stem.
Cylinder head bolts: 69 Nm (51 lb-ft).
Connecting rod cap bolts: 49 Nm (36 lb-ft).
Main bearing cap bolts: 78 Nm (58 lb-ft).
Flywheel to crankshaft bolts: 118 Nm (87 lb-ft).
Flywheel housing to cylinder block: 49 Nm (36 lb-ft) for M10 fasteners.
Flywheel housing to cylinder block: 29 Nm (21 lb-ft) for M8 fasteners.
Injection pump mounting nuts: 24 Nm (18 lb-ft).
Injector hold-down clamp: 25 Nm (18 lb-ft).
High-pressure fuel line nuts: 28 Nm (21 lb-ft).
Rocker arm shaft pedestal bolts: 25 Nm (18 lb-ft).
Valve cover nuts: 8 Nm (71 lb-in).
Oil pan bolts: 12 Nm (9 lb-ft).
Water pump mounting bolts: 24 Nm (18 lb-ft).
Seawater pump mounting bolts: 24 Nm (18 lb-ft).
Starter motor mounting bolts: 39 Nm (29 lb-ft).
Alternator mounting bolts: 24 Nm (18 lb-ft).
Alternator mounting bolts: 39 Nm (29 lb-ft) for pivot bolt.
Turbocharger mounting nuts: 42 Nm (31 lb-ft).
Exhaust manifold nuts: 39 Nm (29 lb-ft).
Engine mounting isolator to block: 69 Nm (51 lb-ft) for M12 studs.
The Yanmar 4LHA-STP is designed for marine propulsion in planing hull
vessels from 7 to 11 meters (23 to 36 ft) overall length. Common
applications include center console fishing boats, walkaround cabin
cruisers, dual-console recreational craft, and light commercial vessels
such as pilot boats, police patrol boats, and small passenger ferries
operating up to 30 knots.
The engine mates with several high-capacity transmissions including the
Yanmar KMH50A with 8-degree down angle and hydraulic clutch, the KMH50V
V-drive for stern-heavy vessel configurations, and the ZF63A with
8-degree down angle and hydraulic clutch.
A sterndrive variant designated 4LHA-STZP integrates with Bravo series
sterndrives for inboard-outboard installations. Engine mounting
orientation accepts standard shaft drive propulsion with propeller pitch
selected for full-load engine speed between 3,250 and 3,300 rpm. Typical
vessel applications achieve cruise speeds of 25 to 28 knots at 3,000 rpm
with wide-open throttle speeds of 32 to 35 knots when propped correctly.
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