Yanmar 2QM15 Specifications
| Engine Model: Yanmar 2QM15 |
| Engine Type: 4-stroke 2-cylinder raw water cooled diesel |
| Total Displacement: 40 cu.in (0.66 L) |
| Rated Engine Power: 15 Hp (11.2 kW) at 3000 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 2QM15 is a heavy-duty, two-cylinder,
four-stroke marine diesel engine produced by Yanmar as part of the QM
series. Introduced as a predecessor to the widely recognized GM series,
the 2QM15 was engineered for auxiliary propulsion in sailboats and small
power vessels up to approximately 8 meters (26 feet) in length. Its
design prioritized durability, serviceability, and low-revving torque
over high power output, reflecting the operational requirements of
marine applications where continuous operation at moderate engine speeds
is the norm.
The engine’s architecture centers on a vertical inline two-cylinder
configuration with indirect injection through a pre-combustion chamber,
a design that reduces combustion noise and mechanical stress while
permitting the use of a lower compression ratio than direct injection
equivalents. The Yanmar 2QM15 utilizes direct seawater cooling (raw
water cooling), drawing ambient water from the surrounding environment
to cool the engine block, cylinder head, and exhaust manifold before
discharging it overboard.
This system eliminates the need for a separate heat exchanger and
coolant expansion tank, simplifying installation in confined engine
compartments. The engine is equipped with both an electric starter motor
and a manual hand-crank backup, a feature valued in marine applications
where electrical system reliability is critical. The 2QM15 gained a
reputation for exceptional longevity, with many units remaining in
service decades after manufacture, supported by Yanmar’s comprehensive
parts and service network.
Engine Type: Vertical inline 2-cylinder, 4-cycle, naturally aspirated,
water-cooled diesel.
Displacement: 0.655 L (40.0 cu.in).
Bore: 75.0 mm (2.95 in).
Stroke: 74.0 mm (2.91 in).
Compression Ratio: 22.0:1.
Combustion System: Indirect injection utilizing a pre-combustion chamber
(swirl chamber).
Firing Order: 1-2.
Maximum Power Output (continuous): 9.7 kW (13.0 hp) @ 2,800 rpm.
Maximum Power Output (intermittent): 11.2 kW (15.0 hp) @ 3,000 rpm.
Maximum Torque Output: 38 Nm (28 lb-ft) @ 2,200 rpm.
Idle Speed: 750-850 rpm.
The cylinder block is manufactured from cast iron using conventional
sand casting techniques, providing exceptional rigidity, vibration
damping, and resistance to the corrosive effects of direct seawater
cooling. The block incorporates an open-deck design with cast-in-place
cylinder bores machined directly into the casting.
No removable cylinder liners are utilized; the bores are finished with a
precision honing process that establishes the final surface finish for
piston ring sealing. Bore diameter measures 75.0 mm (2.95 in) with a
piston stroke of 74.0 mm (2.91 in), yielding a total displacement of
0.655 L (40.0 cu.in). This near-square bore-to-stroke ratio balances
low-end torque generation with moderate-rpm capability.
The crankshaft is manufactured from forged carbon steel with
induction-hardened journal surfaces. Three main bearings support the
crankshaft, with main bearing journal diameter measuring 50.0 mm (1.97
in). 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. Pistons are cast aluminum with a low-expansion
silicon alloy, featuring two compression rings and one oil control ring.
The piston crown incorporates a shallow combustion bowl that aligns with
the pre-combustion chamber in the cylinder head.
The cylinder block incorporates a raw water cooling jacket surrounding
each cylinder bore. Seawater is admitted directly into the block through
a water inlet fitting, flows around the cylinders, then passes upward
into the cylinder head before discharging to the exhaust manifold
injection elbow.
The cylinder head is manufactured from cast iron, consistent with the
cylinder block material. This all-iron construction provides superior
corrosion resistance in seawater-cooled applications and ensures
reliable gasket sealing under the thermal cycling characteristic of
marine engine operation. The head is secured to the cylinder block using
six head bolts per cylinder.
Each cylinder features a pre-combustion chamber (swirl chamber) located
within the cylinder head casting. This chamber receives fuel from the
injection nozzle, and initial combustion occurs within this confined
space before expanding into the main cylinder. The pre-combustion
chamber design reduces combustion noise, lowers peak cylinder pressures,
and provides smoother operation at low engine speeds.
The valvetrain consists of four valves: two intake valves and two
exhaust valves. Intake valve diameter measures 32.0 mm (1.26 in), while
exhaust valve diameter measures 30.0 mm (1.18 in). Valve stem diameter
is 7.0 mm (0.28 in) for both intake and exhaust. Valves are actuated by
rocker arms mounted on a shaft running the length of the cylinder head.
Pushrods transmit motion from the camshaft-mounted cam followers to the
rocker arms. The camshaft is located within the cylinder block and is
driven by gears from the crankshaft.
Valve clearance adjustment is accomplished via threaded adjusters with
locknuts at the rocker arm-to-valve stem interface. Cold valve clearance
specification for both intake and exhaust valves is 0.20 mm (0.008 in).
Inspection interval is 250 operating hours.
Valve seat inserts are manufactured from heat-resistant alloy steel,
pressed into the cylinder head casting. Valve guides are cast iron,
pressed into the head with an interference fit. The valve cover is
stamped steel, sealed with a cork or rubber gasket.
The Yanmar 2QM15 employs an indirect injection fuel system utilizing a
Bosch or Yanmar inline injection pump. The injection pump is a
plunger-type unit with individual plunger-and-barrel assemblies for each
cylinder, mounted to the side of the cylinder block and driven by the
camshaft gear train. The pump incorporates a mechanical governor that
maintains engine speed under varying loads by adjusting fuel delivery
volume.
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) measured at the injection pump
delivery valve.
Fuel injectors are of the pintle type with a single-hole nozzle designed
specifically for pre-combustion chamber systems. Nozzle opening pressure
is set to 157-167 bar (160-170 kg/cm2 / 2,276-2,422 psi). Injectors are
installed into the cylinder head with a copper sealing washer.
The fuel system incorporates a hand primer lever on the injection pump
or a separate manual priming pump to facilitate system priming after
filter replacement. A primary fuel filter with water separator is
mounted upstream of the injection pump, with a secondary cartridge-type
filter positioned between the primary filter and the injection pump
inlet.
The lubrication system is a forced-feed, full-flow design utilizing a
trochoid-type oil pump mounted to the front of the crankshaft. The pump
draws oil from the sump through a wire mesh strainer. A pressure relief
valve integrated into the pump maintains system pressure within design
parameters.
Total oil capacity is 2.2 L (2.3 qt) including filter. Recommended oil
viscosity is 15W-40 or 20W-50 for most operating conditions, with API
classification CD, CE, or CF for diesel service. Oil pressure
specifications require a minimum of 1.0 bar (15 psi) at warm idle and
2.5-3.5 bar (36-51 psi) at 2,500 rpm.
The oil filter is a full-flow spin-on type mounted to the cylinder
block. The oil pan is cast aluminum or stamped steel, sealed to the
cylinder block with a gasket. A dipstick is provided for oil level
checking.
The 2QM15 utilizes a direct seawater cooling (raw water) system. A
rubber impeller-type seawater pump, mounted on the front of the engine,
draws raw water through a through-hull fitting and strainer. The pump
delivers water to the cooling jacket at the bottom of the cylinder
block. The water circulates upward around the cylinders, through the
cylinder head, and then to the exhaust manifold injection elbow, where
it mixes with exhaust gases before discharge overboard.
A thermostat is located in the coolant outlet at the rear of the
cylinder head. Thermostat opening temperature is 65-70 °C (149-158 °F).
A bypass circuit allows limited water circulation during warm-up. No
coolant expansion tank is required, as the system is open to atmospheric
pressure at the exhaust injection elbow.
The seawater pump impeller is a wear item requiring inspection and
replacement every 200-300 operating hours. The pump housing is bronze or
aluminum with a neoprene impeller.
Aspiration System: The 2QM15 is naturally aspirated. Intake air passes
through a paper or foam air filter element installed in the air intake
silencer. The intake manifold is cast iron with a single plenum feeding
both cylinders.
Starting System: The engine is equipped with a 12-volt electric starter
motor rated at 1.0 kW, mounted to the flywheel housing. A manual
hand-crank backup is provided, engaging with the front end of the
crankshaft. Hand-cranking is intended for emergency starting only.
Charging System: A 12-volt alternator rated at 35 amperes is belt-driven
from the crankshaft pulley. The alternator charges the starting battery
and supplies power for navigation lights, instruments, and other marine
electrical loads.
Exhaust System: The exhaust manifold is cast iron, water-cooled via raw
water injection. Seawater is introduced into the exhaust stream at the
manifold outlet to cool exhaust gases before they enter the rubber
exhaust hose and gooseneck fitting.
Transmission (KH-18): The engine is coupled to a Yanmar KH-18 mechanical
cone clutch transmission. Forward ratios: 2.03:1, 2.48:1, or 3.02:1
depending on propeller specification. Reverse ratio: 3.02:1. The
transmission utilizes SAE 30 engine oil for lubrication.
Overall Length (with KH-18 transmission): 648 mm (25.5 in).
Overall Width: 440 mm (17.3 in).
Overall Height: 524 mm (20.6 in).
Dry Weight (with transmission): 134 kg (295 lb).
Exhaust Pipe Diameter: 40 mm (1.57 in).
Valve Clearance (cold): Intake and exhaust: 0.20 mm (0.008 in).
Inspection interval: 250 operating hours. Adjustment performed via
threaded adjuster and locknut at rocker arm. Valve Inspection and
Adjustment: Every 500 operating hours. Injection Timing (static): 14-16
degrees BTDC. Adjusted by rotating pump body. Injection Nozzle Opening
Pressure: 157-167 bar (2,276-2,422 psi).
Fuel Filter Replacement Interval: 250 operating hours or 12 months.
Compression Pressure: Minimum 2.5 MPa (363 psi) with no cylinder varying
more than 0.2 MPa (29 psi) from the other. Measured with engine warm,
throttle fully open. Injector Testing Interval: Every 500 operating
hours. Cylinder Head Re-torque: After first 50 operating hours, then
every 500 hours.
Engine Oil Change Interval: 250 operating hours or 12 months. Oil Filter
Replacement Interval: Replace with every oil change. Seawater Pump
Impeller Inspection Interval: 200 operating hours. Replacement interval:
300 operating hours or 24 months. Cooling System (raw water) Descaling
Interval: 500 operating hours. Use of a commercial marine descaler
recommended to remove salt deposits.
Cylinder Head Bolts (cold): 65-70 Nm (48-52 lb-ft).
Crankshaft Damper Pulley Bolt: 100-110 Nm (74-81 lb-ft).
Connecting Rod Cap Bolts: 40-45 Nm (30-33 lb-ft).
Main Bearing Cap Bolts: 50-55 Nm (37-41 lb-ft).
Flywheel Bolts: 60-65 Nm (44-48 lb-ft).
Camshaft Bearing Cap Bolts: 25-30 Nm (18-22 lb-ft).
Camshaft Gear Bolt: 80-90 Nm (59-66 lb-ft).
Valve Cover Nuts: 8-10 Nm (6-7 lb-ft).
Intake Manifold Nuts: 18-22 Nm (13-16 lb-ft)
Exhaust Manifold Nuts: 25-30 Nm (18-22 lb-ft).
Oil Pan Bolts: 15-20 Nm (11-15 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 Nozzle Holder: 50-60 Nm (37-44 lb-ft).
Glow Plugs (if equipped): 20-25 Nm (15-18 lb-ft).
Seawater Pump Mounting Bolts: 15-20 Nm (11-15 lb-ft).
Thermostat Housing Bolts: 10-15 Nm (7-11 lb-ft).
Starter Motor Mounting Bolts: 30-35 Nm (22-26 lb-ft).
Alternator Mounting Bracket Bolts: 25-30 Nm (18-22 lb-ft).
KH-18 Transmission Drain Plug: 20-25 Nm (15-18 lb-ft).
Sailboat Auxiliary Propulsion: The 2QM15 was extensively installed as
auxiliary power in sailboats from 7 to 10 meters (23-33 feet) in length,
including designs from Pearson, Catalina, Hunter, Beneteau, and
Jeanneau. The engine provided reliable propulsion for harbor maneuvering
and motor-sailing in calm conditions.
Small Power Vessels: The engine was used as primary propulsion in small
fishing boats, launches, and workboats up to 8 meters (26 feet) in
length, where its low fuel consumption and long service life were
valued.
Recreational Powerboats: Smaller cabin cruisers and express cruisers
received the 2QM15 as an economical power option, particularly in
European and Asian markets where diesel fuel was more readily available
than gasoline.
Industrial Applications: Stationary generator sets, refrigeration
compressors, and small agricultural machinery were powered by the 2QM15,
utilizing a stripped-down version with no seawater cooling and a
radiator or heat exchanger cooling system.
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