Yanmar 6LPA STP Specifications
| Engine Model: Yanmar 6LPA STP |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 254 cu.in (4.16 L) |
| Rated Engine Power: 315 Hp (232 kW) at 3800 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6LPA-STP is a high-performance,
six-cylinder marine diesel engine designed primarily for pleasure craft.
This engine belongs to the LPA series, a compact, lightweight,
high-speed diesel family that Yanmar developed for sportfishing boats,
express cruisers, and other planing hull vessels. The STP designation
indicates a high-output rating with turbocharging and an intercooler.
The 6LPA-STP is nearly identical to the later STP2 model, released to
meet different era-specific emissions standards.
This powerplant is renowned for its exceptional power-to-weight ratio,
delivering 232 kW (315 hp) at 3800 rpm from a dry weight of only 408 kg
(899 lb) without marine gear. The engine uses an in-line six-cylinder
configuration with four valves per cylinder, optimizing airflow for
high-rpm power generation. A boost-compensated distributor-type fuel
pump manages mechanical direct injection, incorporating a system to
reduce black smoke during acceleration.
The cooling system uses freshwater circulation through a heat exchanger,
with a rubber impeller seawater pump for raw water flow. The electrical
system operates at 12V with a high-output starter motor rated at 2.5 kW
and an 80A alternator. Yanmar designed this engine for a specific duty
cycle: operation at maximum throttle (3800 rpm) for less than five
percent of total running time and at cruising speeds between 2800 and
3600 rpm for less than 90 percent of operation.
The Yanmar 6LPA-STP is a vertical, four-stroke, water-cooled diesel
engine. Total displacement measures 4.163 liters, equivalent to 254
cubic inches. Bore is 94 mm (3.70 in) with a stroke of 100 mm (3.94 in),
producing a slightly oversquare configuration favorable for higher
engine speeds. The cylinder count is six arranged in-line. The
valvetrain uses four valves per cylinder, resulting in 24 valves total.
Aspiration is turbocharged with an intercooler. Maximum output at the
crankshaft is 232 kW (315 hp) achieved at 3800 rpm. Continuous output
rating is 188 kW (255 hp) at 3600 rpm.
The compression ratio is not specified in the source data but is
consistent with high-speed turbocharged marine diesels at approximately
16.0 to 17.0:1. The combustion system uses mechanical direct injection.
Rotation is counter-clockwise as viewed from the flywheel end. Dry
weight without marine gear is 408 kg (899 lb). The electrical system
operates at 12V DC with a 2.5 kW starter motor and an 80A alternator.
The fuel system is mechanical direct injection with a boost-compensated
distributor-type fuel pump.
The cylinder block is constructed from high-strength cast iron with an
inline six-cylinder arrangement. The block features a deep-skirt design
extending below the crankshaft centerline, providing enhanced torsional
stiffness and vibration damping at high engine speeds. Replaceable
wet-type cylinder liners are pressed into the block. Each liner is
manufactured from centrifugally cast iron and contacts engine coolant
directly along its full exterior surface.
The wet liner design provides superior heat dissipation from the
combustion zone to the coolant, reducing thermal stress on the block
casting. Each liner features a flanged top that seats against a
precision-machined counterbore in the block deck, with multiple sealing
rings at the lower end. The cylinder block incorporates seven main
bearing webs with reinforced bulkheads. An integral timing gear housing
is cast into the front face of the block.
The cylinder block includes mounting pads for the fuel injection pump,
starter motor, alternator, turbocharger, intercooler, and seawater pump.
Cast internal oil galleries direct pressurized lubricant to all main
bearings, connecting rod bearings, camshaft bearings, and piston cooling
jets. Cooling passages surround each cylinder liner along the full
stroke length. The block uses a bedplate construction on some variants,
where a separate structural lower crankcase reinforces the main bearing
caps.
A single cast-iron cylinder head spans all six cylinders. The head
incorporates a cross-flow design with intake ports on one side and
exhaust ports on the opposite side. The valvetrain operates as an
overhead valve (OHV) configuration with four valves per cylinder - two
intake and two exhaust - for a total of 24 valves. Four valves per
cylinder provides increased total valve area, improving volumetric
efficiency at high engine speeds.
A camshaft located within the cylinder block actuates the valvetrain.
Pushrods transfer motion through vertical bores in the cylinder head to
rocker arms. Hardened valve seat inserts are pressed into the cylinder
head. Valve guides are pressed-in cast-iron sleeves. Valve lash is
adjustable using a screw-and-locknut mechanism on each rocker arm. The
direct injection system places the fuel injector centrally in each
cylinder head.
The intake ports are designed to generate swirl motion within the
cylinder for improved air-fuel mixing. The cylinder head gasket is a
multilayer steel (MLS) design. Seven head bolts per cylinder provide
clamping force, with a torque-to-yield procedure specified for final
tightening. The cylinder head incorporates an integral water jacket
surrounding the valve seats and injector sleeves.
The fuel system uses mechanical direct injection with a
boost-compensated distributor-type fuel pump. A mechanical gear-type
lift pump draws fuel from the tank through a primary spin-on filter and
water separator. The lift pump supplies low-pressure fuel to the
injection pump. The distributor-type injection pump is driven by the
engine timing gears. The pump contains a single plunger that distributes
fuel to each cylinder in the correct firing order (1-5-3-6-2-4).
The pump includes a boost compensator, a diaphragm-actuated device that
senses intake manifold pressure from the turbocharger. Under
acceleration, the boost compensator increases fuel delivery in
proportion to boost pressure, preventing the over-fueling that would
otherwise produce black smoke. A mechanical centrifugal governor
regulates fuel delivery based on engine speed and load.
A fuel shutoff solenoid provides engine stop control. Six high-pressure
steel injection lines carry fuel from the pump to the injectors. Each
injector is a hole-type nozzle with multiple orifices, producing a
finely atomized spray. Injectors are installed in the cylinder head and
positioned to spray fuel directly into the piston bowl. A fuel return
line routes excess fuel and injector leakage back to the fuel tank.
The lubrication system is a pressurized, full-flow filtration design
using a gear-type positive displacement pump. The pump is mounted on the
front timing gear cover and driven by the crankshaft gear. Oil is drawn
from the oil pan through a pick-up tube fitted with a coarse mesh
strainer. Total oil capacity is not specified in the source data but
generally ranges from 11 to 13 liters (11.6 to 13.7 U.S. quarts) for the
6LPA series.
A spin-on full-flow oil filter is mounted externally on the block. The
system includes an oil cooler, a seawater-cooled heat exchanger that
reduces oil temperature before it returns to the engine. A piston
cooling jet system directs oil streams to the underside of each piston
crown for thermal management, essential for high specific output. A
pressure relief valve limits maximum oil pressure.
The system supplies lubricant to the seven main bearings, six connecting
rod bearings, camshaft bearings, rocker arm assembly, timing gears,
turbocharger center housing, and injection pump driveshaft. Operating
oil pressure at rated speed is maintained between 345 and 450 kPa (50
and 65 psi). The oil pan is constructed from aluminum or stamped steel
and includes a drain plug with a magnetic insert.
The cooling system uses indirect freshwater cooling with a heat
exchanger. A closed freshwater circuit containing antifreeze and
corrosion inhibitor circulates through the engine block, cylinder head,
oil cooler, and turbocharger. A centrifugal freshwater pump is
belt-driven from the crankshaft pulley. A wax-pellet thermostat located
in a housing on the front of the cylinder head controls freshwater flow.
The thermostat begins to open at 82°C (180°F) and reaches full open at
95°C (203°F). Freshwater passes through a shell-and-tube heat exchanger
mounted on the engine. Seawater is drawn through a hull strainer by a
flexible impeller-type raw water pump mounted on the front of the
engine. This seawater flows through the heat exchanger, absorbing heat
from the freshwater circuit before discharging through the exhaust
elbow.
A separate seawater path passes through the oil cooler. The raw water
pump contains a neoprene impeller that requires periodic inspection and
replacement. A sacrificial zinc anode is installed in the heat exchanger
to prevent galvanic corrosion. An intercooler (also called a charge air
cooler) is integrated into the intake system. Seawater or freshwater
flows through the intercooler core, reducing the temperature of
compressed intake air from the turbocharger before it enters the
cylinders.
| Intake and Exhaust Systems |
Air Intake System: Ambient air passes through a dry-type air cleaner
before entering the turbocharger compressor. The turbocharger is a
fixed-geometry unit sized for high-rpm power delivery. Compressed air
exits the turbocharger at elevated temperature, then travels through a
hose to the intercooler (charge air cooler). After cooling, the dense
charge air enters the intake manifold for distribution to each cylinder
via the four-valve ports.
Exhaust System: A cast-iron exhaust manifold collects gases from all six
cylinders. The manifold is designed as a pulse-converging system to
maintain exhaust energy to the turbocharger turbine. The manifold
connects to the turbocharger turbine inlet. A water-cooled exhaust elbow
downstream of the turbine mixes seawater with exhaust gases, cooling
them before they exit through the vessel's exhaust hose.
The electrical system operates at 12V DC. A gear-reduction starter motor
rated at 2.5 kW is mounted on the flywheel housing. A high-output
belt-driven alternator produces 80 amps of charging current. Glow plugs
are installed in the cylinder head, one per cylinder, as a cold start
aid. A glow plug relay manages pre-heat duration. The system includes a
warning buzzer and indicator lamps.
Engine length measured from the front cover to the flywheel housing
mounting face is 1200 mm (47.2 in). Width measured across the widest
points, including the turbocharger, injection pump, exhaust manifold,
and intercooler, is 700 mm (27.6 in). Height measured from the oil pan
rail to the top of the rocker arm cover is 750 mm (29.5 in).
Dry weight of the complete engine, including the flywheel, turbocharger,
intercooler, heat exchanger, alternator, and starter motor, but
excluding oil, coolant, and transmission, is 408 kg (899 lb). The weight
with a full oil charge and coolant adds 20 kg (44 lb). When paired with
a ZF63A marine gearbox, add 55 kg (121 lb). When paired with an HSW630V1
V-drive transmission, add 75 kg (165 lb). The shipping weight on a
pallet with protective packaging is 470 kg (1036 lb).
Engine Oil: Capacity: 12.0 l (12.7 U.S. qt). Oil change interval: 250
hours or annually. Recommended grade: SAE 15W-40 meeting API CI-4 or
higher. Oil Filter: Spin-on full-flow type. Replace at every oil change.
Oil Cooler: Seawater-cooled. Inspect annually for corrosion. Coolant
(Freshwater): Capacity: approximately 10.0 l (10.6 U.S. qt). Change
interval: 1000 hours or 2 years. Antifreeze concentration: 40 to 50
percent. Raw Water Pump Impeller: Flexible neoprene. Inspect at 200
hours. Replace at 500 hours or annually.
Fuel Filter (Primary): Spin-on with water separator. Replacement
interval: 250 hours. Fuel Filter (Secondary): Spin-on on the injection
pump. Replacement interval: 500 hours. Valve Lash (Cold): Intake: 0.20
mm (0.008 in). Exhaust: 0.25 mm (0.010 in). Inspection interval: 500
hours. Air Cleaner: Dry paper element. Clean at 250 hours. Replace at
500 hours. Thermostat: Begins opening at 82°C (180°F). Fully open at
95°C (203°F).
Low Idle Speed: 700 to 750 rpm. High Idle Speed (No Load): 4000 rpm
maximum. Maximum Continuous Speed: 3600 rpm. Maximum Intermittent Speed:
3800 rpm for less than 5 percent of operation. Cruising Speed Range:
2800 to 3600 rpm for less than 90 percent of operation. Injector
Service: Inspect and test opening pressure every 1000 hours. Glow Plugs:
Resistance check at 500 hours. Replace if open circuit.
Turbocharger: Inspect bearings and shaft play at 1000 hours.
Intercooler: Clean seawater passages at 500 hours. Clean air passages at
1000 hours. Heat Exchanger Zinc Anode: Inspect at 250 hours. Replace
when reduced to 50 percent of original size. Valve Clearance Check
Interval: 500 hours or 2 years. Engine Mounts: Inspect for cracking and
sagging at 500 hours. Seawater Strainer: Clean at every oil change.
0Cylinder Head Bolts (M12 x 1.5): 60 Nm (44 lb-ft).
Connecting Rod Cap Nuts (M10 x 1.25): 45 Nm (33 lb-ft).
Main Bearing Cap Bolts (M12 x 1.5): 60 Nm (44 lb-ft).
Flywheel Bolts (M12 x 1.25): 80 Nm (59 lb-ft).
Crankshaft Pulley Bolt (M16 x 1.5): 200 Nm (148 lb-ft).
Camshaft Thrust Plate Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Rocker Arm Shaft Support Bolts (M10 x 1.25): 35 Nm (26 lb-ft).
Rocker Arm Adjustment Lock Nut (M8 x 1.0): 15 Nm (11 lb-ft).
Valve Cover Nuts (M6 x 1.0): 8 Nm (6 lb-ft).
Injection Pump Mounting Nuts (M10 x 1.25): 25 Nm (18 lb-ft).
Injection Lines (High Pressure) (M14 x 1.5): 25 Nm (18 lb-ft).
Injector Hold-Down Bolts (M8 x 1.25): 25 Nm (18 lb-ft).
Glow Plugs (M10 x 1.0): 15 Nm (11 lb-ft).
Oil Pan Drain Plug (M14 x 1.5): 45 Nm (33 lb-ft).
Oil Filter (Spin-on): 20 Nm (15 lb-ft).
Starter Motor Mounting Bolts (M12 x 1.25): 50 Nm (37 lb-ft).
Alternator Pivot Bolt (M10 x 1.25): 30 Nm (22 lb-ft).
Raw Water Pump Mounting Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Freshwater Pump Mounting Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Thermostat Housing Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Exhaust Manifold Nuts (M10 x 1.25): 35 Nm (26 lb-ft).
Intake Manifold Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Turbocharger Mounting Nuts (M10 x 1.25): 40 Nm (30 lb-ft).
Intercooler Mounting Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
Engine Mount Bracket Bolts (M12 x 1.25): 60 Nm (44 lb-ft).
Heat Exchanger Mounting Bolts (M8 x 1.25): 20 Nm (15 lb-ft).
ZF63A Gearbox to Flywheel Housing Bolts (M12 x 1.25): 80 Nm (59 lb-ft).
The Yanmar 6LPA-STP engine serves exclusively in marine applications as
a propulsion unit for high-performance pleasure craft. Sportfishing
Boats: Express and walkaround sportfishermen from 28 to 35 feet length
overall (LOA). Models including Grady-White 330, 336, and 360 Express.
Boston Whaler 320 Outrage and 330 Outrage. Pursuit 315, 325, and 345.
Regulator 29 and 32. Everglades 295, 315, and 335.
Express Cruisers: Cruisers from 30 to 36 feet. Sea Ray 310 Sundancer,
330 Sundancer, and 340 Sundancer. Chaparral 310 Signature and 330
Signature. Four Winns 350, 360, and 370. Center Console Boats: Large
offshore center consoles from 32 to 38 feet. Contender 32 and 35.
Yellowfin 32 and 34. SeaVee 320, 340, and 370. Downeast Boats:
Semi-displacement Downeast-style cruisers from 30 to 34 feet.
Commercial Applications: Small charter fishing boats. Pilot vessels and
patrol craft. Transmission Options: ZF63A marine gearbox with 8-degree
down angle. Reduction ratios available from 1.5:1 to 2.5:1 forward
rotation. HSW630V1 V-drive transmission for mid-engine or aft-engine
installations requiring forward-facing propeller shaft. Reduction ratios
from 1.8:1 to 2.8:1.
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