Yanmar 6LY2A STP Specifications
| Engine Model: Yanmar 6LY2A STP |
| Engine Type: 4-stroke inline 6-cylinder turbocharged water-cooled diesel |
| Total Displacement: 354.7 cu.in (5.81 L) |
| Rated Engine Power: 440 Hp (324 kW) at 3300 rpm |
| Fuel System Type: Direct injection |
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The Yanmar 6LY2A-STP is a six-cylinder,
high-output marine diesel engine renowned for its exceptional
power-to-weight ratio. As a more powerful evolution of the 6LYA series,
this engine features a larger displacement and higher performance tuning
specifically developed for planing hulls, sportfishing boats, and fast
cruisers where power density is critical. The Yanmar 6LY2A-STP produces
324 kW (440 hp) at 3,300 rpm from a 5.8-liter displacement, achieving a
dry weight of only 535 kg (1,179 lb) without marine gear.
The engine’s architecture centers on an inline six-cylinder
configuration with direct injection, turbocharging, and a
seawater-cooled intercooler. The bore and stroke dimensions - 106 mm and
110 mm respectively - produce a displacement of 5.813 L per engine. This
near-square configuration balances high-rpm power output with adequate
low-end torque for planing hull acceleration.
The Yanmar 6LY2A-STP utilizes a mechanical distributor-type fuel pump
with a mechanical governor, a design choice that prioritizes reliability
and simplicity over electronic control. The slim block profile,
measuring only 708 mm (27.9 in) in width, permits installation in narrow
engine rooms, a feature inherited from the LY series. The engine is
compliant with IMO Tier 1 emissions standards and is commonly paired
with high-performance hydraulic transmissions such as the KMH61A
down-angle unit or the ZF 220A gearbox.
Engine Type: Vertical inline 6-cylinder, 4-cycle, turbocharged,
water-cooled diesel.
Displacement: 5.813 L (354.7 cu.in).
Bore: 106.0 mm (4.17 in).
Stroke: 110.0 mm (4.33 in).
Compression Ratio: 15.5:1.
Combustion System: Direct injection.
Firing Order: 1-5-3-6-2-4.
Maximum Power Output (crankshaft): 324 kW (440 hp) @ 3,300 rpm.
Continuous Power Output (crankshaft): 272 kW (365 hp) @ 3,100 rpm.
Maximum Torque Output: 1,140 Nm (841 lb-ft) @ 2,200-2,800 rpm.
Idle Speed: 650-700 rpm.
Direction of Rotation: Counter-clockwise when viewed from the flywheel
end.
The cylinder block is manufactured from cast aluminum alloy using
high-pressure die-casting techniques. This material selection
contributes to the engine’s low dry weight of 535 kg (1,179 lb), a
significant advantage for planing vessels where weight distribution
affects performance. The block incorporates a closed-deck design for
enhanced cylinder rigidity under the elevated combustion pressures
generated by high-output turbocharging.
Cylinder bores are cast-in-place gray iron liners, centrifugally cast
and machined to final specification. The liners are replaceable,
allowing for engine overhaul without block replacement. Bore diameter
measures 106.0 mm (4.17 in) with a piston stroke of 110.0 mm (4.33 in),
yielding a total displacement of 5.813 L (354.7 cu.in). This near-square
bore-to-stroke ratio of 0.964 balances high-rpm power production with
adequate low-end torque for planing hull acceleration.
The crankshaft is forged from chromium-molybdenum steel with
induction-hardened journal surfaces. Seven main bearings support the
crankshaft. Thrust washers positioned at the center main bearing control
axial crankshaft play. Connecting rods are forged from high-carbon steel
with an I-beam cross-section and a fracture-split big end design.
Pistons are cast aluminum with a low-expansion silicon alloy, featuring
two compression rings and one oil control ring. The piston crown
incorporates a re-entrant combustion bowl designed for the mechanical
fuel injection system.
The cylinder head is manufactured from cast aluminum alloy with a
cross-flow design positioning intake ports on the inlet side and exhaust
ports on the exhaust side. The combustion chambers are of the pent-roof
configuration with four valves per cylinder and a centrally located fuel
injector. Each cylinder has its own individual cylinder head casting, a
modular design that simplifies maintenance and replacement.
Each cylinder head contains four valves: two intake valves and two
exhaust valves. Intake valve diameter measures 36.0 mm (1.42 in), while
exhaust valve diameter measures 32.0 mm (1.26 in). Valve stem diameter
is 7.0 mm (0.28 in) for both intake and exhaust. The valvetrain utilizes
a single overhead camshaft with roller rocker arms. The camshaft is
driven by a rubber timing belt, requiring periodic replacement.
Valve clearance adjustment is accomplished via threaded adjusters with
locknuts at the rocker arm. Cold valve clearance specifications are as
follows: intake valves, 0.20 mm (0.008 in); exhaust valves, 0.25 mm
(0.010 in). Inspection interval is 500 operating hours.
The 6LY2A-STP employs a mechanical direct injection fuel system with a
distributor-type injection pump manufactured by Bosch or Zexel. The pump
incorporates a mechanical governor that maintains engine speed under
varying loads and provides speed droop for stable operation. The
governor is adjustable with a speed droop range of 0 to 5 percent.
Injection timing is adjustable by rotating the injection pump relative
to its drive gear. Static injection timing specification is 14-16
degrees before top dead center (BTDC) at the No. 1 cylinder.
Fuel injectors are of the multi-hole type with five nozzle holes. Nozzle
opening pressure is set to 220-230 bar (3,190-3,335 psi). Injectors are
installed into the cylinder head with a copper sealing washer.
The fuel system incorporates a primary fuel filter with water separator
and a secondary cartridge-type filter. A hand primer is provided for
system priming after filter replacement.
The lubrication system utilizes a forced-feed, full-flow design with a
gear-type oil pump mounted to the front of the crankshaft. A pressure
relief valve integrated into the pump maintains system pressure within
design parameters.
Total oil capacity is 18.0 L (19.0 qt) including filter. Recommended oil
viscosity is SAE 15W-40 meeting API CI-4 or CJ-4 specifications. Oil
pressure specifications require a minimum of 1.0 bar (15 psi) at warm
idle and 4.0-5.0 bar (58-73 psi) at 3,000 rpm.
The oil filter is a spin-on, full-flow type mounted to the cylinder
block. A liquid-to-oil plate-type oil cooler is integrated into the
lubrication system, utilizing engine coolant to stabilize oil
temperature.
The cooling system is a closed-loop fresh water system with a heat
exchanger for seawater cooling. A centrifugal fresh water pump, driven
by the accessory drive belt, circulates coolant through the cylinder
block, cylinder head, and oil cooler. A rubber impeller-type seawater
pump, mounted on the front of the engine, draws raw water through a
through-hull fitting and strainer, then circulates it through the heat
exchanger and the charge air intercooler before discharging to the
exhaust injection elbow.
The thermostat is a wax-pellet unit with an opening temperature of 76-80
°C (169-176 °F). A bypass circuit allows fresh water circulation within
the engine during warm-up.
Total fresh water coolant capacity is 18.0 L (19.0 qt). The heat
exchanger is a shell-and-tube design with a seawater-cooled tube bundle.
Zinc anodes are installed in the seawater circuit to prevent galvanic
corrosion.
Aspiration System: The 6LY2A-STP is equipped with a Mitsubishi TD08H
turbocharger. This high-flow unit is sized for the engine’s 440 hp
output at 3,300 rpm. A seawater-cooled charge air intercooler reduces
intake air temperature by 50-70 °C (90-126 °F) under sustained boost
conditions. Maximum boost pressure is 1.8-2.2 bar (26-32 psi) absolute
depending on load.
Exhaust System: The exhaust manifold is manufactured from cast iron with
a water-cooled jacket. Seawater is injected into the exhaust stream at
the turbocharger outlet to cool exhaust gases before they enter the
rubber exhaust hose.
Electrical System: The engine is equipped with a 12-volt alternator
rated at 80 amperes, driven by a poly-V belt from the crankshaft pulley.
The starting system includes a 2.5 kW electric starter motor.
Transmission: KMH61A Hydraulic Multi-Disc Clutch: Down-angle mounting.
Ratios available: 1.41:1, 1.90:1, 2.22:1, 2.83:1. ZF 220A Marine Gear:
Down-angle mounting. Ratios available: 1.41:1, 1.74:1, 2.04:1, 2.44:1,
2.86:1. ZTF 220-IV V-Drive: For installations requiring V-drive
configuration.
Overall Length (bobtail, without gearbox): 1,165 mm (45.9 in) measured
from front pulley face to flywheel housing flange.
Overall Width: 708 mm (27.9 in).
Overall Height: 784 mm (30.9 in) from oil pan bottom to engine top.
Dry Weight (without gearbox): 535 kg (1,179 lb).
Intake Valve Clearance (cold): 0.20 mm (0.008 in).
Exhaust Valve Clearance (cold): 0.25 mm (0.010 in).
Valve Clearance Inspection interval: 500 operating hours.
Timing Belt Replacement Interval: 1,000 hours or 5 years, whichever
occurs first.
Fuel Filter Replacement Interval: 250 hours or 12 months for primary
filter.
Fuel Filter Replacement Interval: 500 operating hours for secondary
filter.
Engine Oil Change Interval: 250 operating hours or 12 months.
Oil Filter Replacement Interval: Replace with every oil change.
Coolant Change Interval: 500 operating hours or 24 months.
Seawater Pump Impeller Inspection Interval: 200 operating hours.
Seawater Pump Impeller Replacement Interval: 500 hours or 24 months.
Charge Air Intercooler Cleaning Interval: 500 operating hours.
Heat Exchanger Zinc Anode Inspection: 250 operating hours.
Valve Inspection: Every 500 operating hours.
Compression Pressure (warm): Minimum 3.0 MPa (435 psi).
Injector Testing Interval: 500 operating hours.
Nozzle Opening Pressure: 220-230 bar (3,190-3,335 psi).
Injection Timing (static): 14-16 degrees BTDC.
Cylinder Head Bolts, Step 1: 40 Nm (30 lb-ft).
Cylinder Head Bolts, Step 2: 80 Nm (59 lb-ft).
Crankshaft Damper Pulley Bolt: 300-320 Nm (221-236 lb-ft).
Connecting Rod Cap Bolts: 50-55 Nm (37-41 lb-ft).
Main Bearing Cap Bolts, Step 1: 50 Nm (37 lb-ft).
Main Bearing Cap Bolts, Step 2: 100 Nm (74 lb-ft).
Flywheel Bolts: 90-100 Nm (66-74 lb-ft).
Camshaft Sprocket Bolt: 80-90 Nm (59-66 lb-ft).
Camshaft Bearing Cap Bolts: 20-25 Nm (15-18 lb-ft).
Valve Cover Bolts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Bolts: 18-22 Nm (13-16 lb-ft).
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft).
Turbocharger Mounting Nuts: 35-40 Nm (26-30 lb-ft).
Turbocharger Oil Feed Line: 20-25 Nm (15-18 lb-ft).
Oil Pan Bolts: 8-12 Nm (6-9 lb-ft).
Timing Belt Tensioner Bolt: 20-25 Nm (15-18 lb-ft).
Timing Belt Idler Pulley Bolt: 35-40 Nm (26-30 lb-ft).
Fresh Water Pump Mounting Bolts: 15-20 Nm (11-15 lb-ft).
Seawater Pump Mounting Bolts: 15-20 Nm (11-15 lb-ft).
Thermostat Housing Bolts: 8-12 Nm (6-9 lb-ft).
Heat Exchanger Mounting Bolts: 20-25 Nm (15-18 lb-ft).
Injection Pump Mounting Nuts: 20-25 Nm (15-18 lb-ft).
Injection Pump Drive Gear Nut: 60-70 Nm (44-52 lb-ft).
Fuel Injector Clamp Bolts: 25-30 Nm (18-22 lb-ft).
Glow Plugs: 20-25 Nm (15-18 lb-ft).
Alternator Mounting Bracket Bolts: 25-30 Nm (18-22 lb-ft).
Starter Motor Mounting Bolts: 35-40 Nm (26-30 lb-ft).
Engine Mounts (to block): 50-55 Nm (37-41 lb-ft).
Sportfishing Boats: The 6LY2A-STP is installed as primary propulsion in
sportfishing vessels from 9 to 12 meters (30-40 feet) in length,
including convertibles, express sportfishers, and walkaround cabin
designs. The engine’s 440 hp output enables planing speeds suitable for
offshore fishing operations. Vessel applications include hull designs
from Boston Whaler, Grady-White, Albemarle, Regulator, and Pursuit.
Downeast and Express Cruisers: Downeast-style hulls and express cruisers
from builders including Eastern, Parker, Southport, and Steiger Craft
utilize the 6LY2A-STP in single-engine configuration. The engine’s power
and torque characteristics provide efficient cruising at 2,800-3,100
rpm.
Fast Patrol Boats: Law enforcement and military patrol boats operating
at speeds exceeding 35 knots adopt the 6LY2A-STP for its high
power-to-weight ratio. Single-engine and twin-engine configurations are
found in vessels up to 11 meters (36 feet).
Charter Fishing Boats: Six-pack charter boats and day-fishing vessels
operating in coastal waters install the 6LY2A-STP for its combination of
power output, fuel efficiency, and Yanmar’s service network support. The
engine’s continuous rating of 370 hp at 3,100 rpm matches the
operational profile of commercial charter applications.
Cabin Cruisers: Family cruisers and weekend boats from 10 to 12 meters
(33-40 feet) receive the 6LY2A-STP in single-engine or twin-engine
configurations, where the slim block profile permits installation in
beam-limited hulls.
Sterndrive Applications (6LY2A-STPZ): A sterndrive-compatible model is
available for inboard-outboard configurations, particularly on boats
where sterndrive offers advantages in shallow-water operation and beach
landing capability.
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