Yanmar 3QM30H Specifications
| Engine Model: Yanmar 3QM30H |
| Engine Type: 4-stroke inline 3-cylinder water-cooled diesel |
| Total Displacement: 100 cu.in (1.64 L) |
| Rated Engine Power: 33 Hp (25 kW) at 2800 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 3QM30H is a 1.6-liter,
three-cylinder, naturally aspirated marine diesel engine produced from
the mid-1970s through the late 1980s. As a specific variation of the
3QM30 series, the H designation indicates inclusion of a heavy-duty
marine gearbox - often the Yanmar KH18 or equivalent - and a direct
seawater cooling system. The engine was engineered for auxiliary
propulsion in sailing yachts, small fishing vessels, and workboats where
reliability, fuel efficiency, and compact dimensions were critical.
The Yanmar 3QM30H uses an indirect injection combustion system with a
swirl pre-combustion chamber, providing smooth operation, reduced noise,
and excellent cold-start performance at the expense of some fuel economy
compared to direct injection diesels. The engine features a vertical,
inline-three cast iron construction with an overhead valve valvetrain.
Counter-clockwise rotation viewed from the flywheel side is standard. A
manual hand-crank backup starting system complements the 12-volt
electric starter, a feature valued in marine applications where battery
failure could leave a vessel without power. The 3QM30H remains respected
among classic yacht owners for its robust construction and
serviceability.
The Yanmar 3QM30H is a four-stroke, water-cooled, inline-three diesel
engine with a total displacement of 1,642 cc (1.6 L / 100.2 cu.in). The
bore and stroke dimensions are 88 mm (3.46 in) and 90 mm (3.54 in),
respectively, creating an oversquare configuration that favors smooth
operation and moderate-rpm power delivery. The valvetrain employs an
overhead valve (OHV) design with two valves per cylinder - one intake
and one exhaust - for a total of six valves. The camshaft is positioned
within the cylinder block and actuates the valves through pushrods and
rocker arms.
The combustion system uses indirect injection with a swirl
pre-combustion chamber (swirl chamber) machined into the cylinder head.
This design generates rotational air motion during the compression
stroke, promoting thorough fuel-air mixing before combustion. Induction
is naturally aspirated.
The compression ratio is set at 20.0:1, a high value that provides
reliable cold-start performance and efficient combustion in the indirect
injection system. Continuous power is rated at 22 kW (30 hp) at 2,600
rpm. One-hour rating (maximum power for short durations) is 25 kW (33
hp) at 2,800 rpm. Maximum torque is produced at 2,000 rpm, with a rating
of 93 Nm (9.5 kg-m). Cruising rpm range is 2,200 to 2,400 rpm. The
firing order is 1-2-3, the standard arrangement for inline-three
engines. Rotation viewed from the flywheel side is counter-clockwise.
The cylinder block is constructed from cast iron, a material selected
for its exceptional rigidity, wear resistance, and ability to withstand
the high compressive loads of diesel combustion. The inline-three
configuration incorporates four main bearings supporting a forged steel
or nodular iron crankshaft. The crankshaft is dynamically balanced and
counterweighted to minimize vibration, a particular consideration for
three-cylinder engines which have inherent rocking moments. The
connecting rods are forged steel.
Cylinder bores are machined directly into the cast iron block without
removable liners. A plateau honed finish optimizes oil retention and
piston ring sealing. The water jacket surrounds the cylinders for
effective heat transfer, with seawater circulated directly through the
block in this H variant. The block incorporates a deep-skirt design to
maximize structural stiffness. The timing gear housing is integrated
into the front of the block, housing the gear train that drives the
camshaft and injection pump.
The cylinder head is manufactured from cast iron, matching the thermal
expansion characteristics of the block to ensure consistent head gasket
sealing. The overhead valve (OHV) arrangement positions the camshaft
within the block, with valve actuation provided by pushrods and rocker
arms. The rocker arms pivot on a rocker shaft mounted to the cylinder
head and are adjustable to set valve clearance.
Valves are arranged in-line along the cylinder head axis, with each
cylinder served by one intake valve and one exhaust valve. The indirect
injection system incorporates a swirl pre-combustion chamber for each
cylinder, machined into the cylinder head. This swirl chamber occupies a
portion of the cylinder head volume, with a narrow passage connecting it
to the main combustion chamber above the piston. Valve seat inserts are
pressed into the cylinder head and machined to precise angles. The valve
springs are of the single-coil type. The cylinder head gasket is a
composite or steel design, providing reliable sealing between the cast
iron head and cast iron block.
The fuel system is a mechanical indirect injection system utilizing an
inline injection pump mounted to the cylinder block and driven by the
timing gear train. Each cylinder has its own pump element delivering
high-pressure fuel through steel lines to the injection nozzles. A
mechanical governor integrated into the injection pump maintains engine
speed under varying propeller loads.
The injection nozzles are of the pintle type positioned within each
swirl pre-combustion chamber. The injection pressure is set between 9.8
MPa and 10.8 MPa (100 to 110 kg/cm2 / 1,422 to 1,564 psi). A feed pump,
integral to the injection pump, draws fuel from the marine fuel tank
through a water-separating primary filter and a secondary fine filter. A
manual primer lever allows bleeding of air from the system after filter
replacement, a critical feature for marine applications where fuel
system maintenance may occur at sea.
The lubrication system is a forced pressure circuit utilizing a
trochoid-type oil pump mounted within the timing case. The pump draws
engine oil from a cast aluminum sump through a strainer screen before
directing it through a spin-on full-flow oil filter. An oil pressure
relief valve maintains system pressure. The main oil gallery distributes
pressurized oil to the crankshaft main bearings, connecting rod
bearings, camshaft bearings, and rocker arm assemblies.
The timing gears are lubricated by splash oil. The total engine oil
capacity is 7.0 L (7.4 qt). Recommended oil viscosity is SAE 15W-40 or
10W-30 with diesel ratings of API CD or higher. The gearbox oil capacity
for the KH18 transmission is 1.2 L (1.3 qt), using a separate oil
specification.
The 3QM30H utilizes direct seawater cooling, a system where untreated
seawater is pumped directly through the engine block and cylinder head.
A flexible-impeller seawater pump, mounted to the front of the engine,
draws raw water through a through-hull fitting and strainer. The water
circulates through the cylinder block water jacket, then through the
cylinder head, and is discharged with the exhaust gases through a
water-injected exhaust elbow.
No heat exchanger or freshwater coolant is present in this
configuration. The thermostat is a wax-pellet type positioned on the
coolant outlet, maintaining engine temperature within the range of 70°C
to 85°C (158°F to 185°F) - lower than freshwater-cooled engines to
reduce saltwater scale formation. The seawater pump impeller requires
regular inspection and replacement. Anodes (zinc or aluminum) are
installed in the cooling system to prevent galvanic corrosion.
| Intake and Exhaust Systems |
Intake System: The intake manifold is constructed from cast iron. The
naturally aspirated induction system draws air through a dry-type paper
air filter or a wire mesh flame arrestor, depending on the installation.
An intake silencer reduces induction noise in the confined engine
compartment.
Exhaust System: The exhaust manifold is constructed from cast iron. The
water-injected exhaust elbow mixes seawater from the cooling system with
exhaust gases, cooling the exhaust to safe temperatures for rubber
exhaust hoses and preventing heat damage to the fiberglass hull. A
waterlock (gooseneck) prevents seawater from flowing back into the
engine through the exhaust system.
The electrical system operates on 12 volts with a marine-rated
alternator providing charging current. A high-torque electric starter
motor is mounted to the flywheel housing. For emergency starting, a
manual hand-crank mechanism engages with the front of the crankshaft,
allowing the engine to be started without battery power. Glow plugs are
installed in each swirl pre-combustion chamber for cold-start
assistance, with glow duration controlled by a manual switch or
automatic timer.
The 3QM30H’s inline-three architecture was designed for installation in
sailboat engine compartments with limited space. The overall length,
including the heavy-duty KH18 gearbox, is 1,200 mm (47.2 in). Width
across the cylinder head is 500 mm (19.7 in). Height from the bottom of
the oil sump to the top of the cylinder head cover is 700 mm (27.6 in).
The dry weight of the engine, inclusive of the gearbox, starter,
alternator, injection pump, and flywheel but without fluids, is 310 kg
(683 lb).
The 3QM30H requires regular maintenance aligned with marine service
intervals. The engine oil and filter must be replaced after the first 50
hours of operation (break-in), then every 100 operating hours or
annually, whichever comes first. The oil capacity is 7.0 L (7.4 qt).
The gearbox oil requires replacement every 200 operating hours, with a
capacity of 1.2 L (1.3 qt). The fuel filter requires replacement every
200 operating hours or as indicated by reduced engine performance. The
seawater pump impeller requires inspection every 100 hours and
replacement every 200 to 500 hours depending on operating conditions.
Valve clearance adjustment is required at intervals of 500 operating
hours, with cold clearances of 0.40 mm (0.016 in) for both intake and
exhaust valves. The cooling system anodes require inspection every 100
hours and replacement when 50% consumed. The seawater passages should be
flushed and descaled every 500 operating hours.
Cylinder Head Bolts: 100 to 110 Nm (74 to 81 lb-ft).
Main Bearing Cap Bolts: 120 to 130 Nm (89 to 96 lb-ft).
Connecting Rod Bolts: 70 to 80 Nm (52 to 59 lb-ft).
Rocker Arm Shaft Bracket Bolts: 25 to 30 Nm (18 to 22 lb-ft).
Rocker Arm Adjustment Locknuts: 15 to 20 Nm (11 to 15 lb-ft).
Flywheel Bolts: 90 to 100 Nm (66 to 74 lb-ft).
Crankshaft Pulley Bolt: 150 to 180 Nm (111 to 133 lb-ft).
Intake Manifold Bolts: 20 to 25 Nm (15 to 18 lb-ft).
Exhaust Manifold Nuts: 25 to 30 Nm (18 to 22 lb-ft).
Injection Pump Mounting Nuts: 20 to 25 Nm (15 to 18 lb-ft).
Injector Holders: 60 to 70 Nm (44 to 52 lb-ft).
Oil Pan Bolts: 15 to 20 Nm (11 to 15 lb-ft).
Glow Plugs: 15 to 20 Nm (11 to 15 lb-ft).
The Yanmar 3QM30H engine was deployed exclusively in marine
applications, with no automotive or industrial variants.
Sailing Yachts (30 to 36 feet): The 3QM30H was installed as auxiliary
power in numerous sailboat brands, including Pearson, Islander, Cal,
Ericson, and Bristol. The engine provided reliable propulsion for
inlets, docking, and auxiliary power when wind conditions were
unfavorable. The heavy-duty gearbox was well-suited to the propeller
loads of larger displacement hulls.
Small Fishing Vessels: The engine was used in small commercial fishing
boats, including lobster boats and gill-netters, where the direct
seawater cooling system simplified installation and reduced maintenance
costs.
Workboats and Launches: The 3QM30H powered utility launches, harbor
patrol boats, and small workboats used for passenger transport and light
towing. The manual hand-crank starting backup was valued by operators
working in remote locations.
Classic Yacht Repower: The 3QM30H remains a popular repower option for
older vessels originally equipped with gasoline engines or smaller
diesels, providing increased displacement and reliability. Many of these
engines remain in service more than 40 years after their original
production date. Production of the 3QM30H series ended in the late
1980s, replaced by the 3JH series and later 3YM series engines with
freshwater cooling and higher power densities.
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