Yanmar 2QM20H Specifications
| Engine Model: Yanmar 2QM20H |
| Engine Type: 4-stroke 2-cylinder water-cooled diesel |
| Total Displacement: 67.1 cu.in (1.1 L) |
| Rated Engine Power: 22 Hp (16.2 kW) at 2800 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 2QM20H is a two-cylinder, naturally
aspirated, four-stroke diesel engine from the QM series, which was
widely utilized in marine auxiliary propulsion applications during the
late 1970s and early 1980s. As a "high-power" variant of the 2QM20 base
model, the "H" designation indicates a higher rated output optimized for
continuous marine duty cycles.
This engine features a vertical, water-cooled configuration with
indirect injection via a swirl pre-combustion chamber system. The Yanmar
2QM20H was commonly paired with Kanzaki KBW10 or KH-18 mechanical cone
clutch transmissions, making it a reliable power plant for cruising
sailboats such as the Nicholson 31, Hunter 37, and Jeannerau Melody. The
design emphasizes robustness and mechanical simplicity, utilizing direct
seawater cooling and a trochoid oil pump for forced lubrication.
The Yanmar 2QM20H is a naturally aspirated diesel that operates on the
four-stroke cycle. The combustion system relies on indirect injection
where fuel is sprayed into a swirl-type pre-combustion chamber, allowing
for smoother operation and lower noise compared to direct injection
designs of its era.
Engine Type: 2-cylinder, vertical, 4-stroke, water-cooled diesel
Displacement: 1.100 L / 67.12 cu.in
Bore: 88.0 mm / 3.46 in
Stroke: 90.0 mm / 3.54 in
Maximum Output: 22.0 hp / 16.2 kW at 2,800 rpm
Continuous Output: 20.0 hp / 14.7 kW at 2,600 rpm
Combustion System: Indirect injection (Swirl pre-combustion chamber)
Aspiration: Natural (Naturally aspirated)
Cooling System: Direct seawater cooling (Raw water)
Starting System: Electric start (12V - 1.0 kW) with manual hand-crank
backup
Alternator Output: 12V - 35A
Fuel Injection Pressure: 160-170 kg/cm2 (2,275-2,418 psi)
Lubrication System: Forced lubrication (Trochoid pump)
Engine Oil Capacity (Total): 4.0 L / 4.2 US qt
Rotation (from flywheel): Counter-clockwise
The cylinder block is constructed from high-grade cast iron, designed to
withstand the thermal stresses of marine diesel operation. The block
features a robust vertical orientation with integral waterways for the
direct raw water cooling system. The cylinder bores are machined with a
precision-honed surface.
The block houses the crankshaft, connecting rods, and the camshaft. The
oil pan, integrated as a structural component, is made of stamped steel
and includes baffles to maintain oil pressure even when the vessel is
heeling at extreme angles due to wave action.
The cylinder head is manufactured from cast iron and designed as a
swirl-type pre-combustion chamber setup. This "indirect injection"
feature creates turbulence in a small ante-chamber before combustion
flows into the main cylinder, allowing the engine to run smoother across
a wide RPM range typical for marine generators and propulsion. The valve
mechanism is driven by a dedicated camshaft, pushrods, and rocker arms.
Valve Configuration: Overhead valve (OHV), 2 valves per cylinder (4
total)
Valve Clearance (Cold): 0.20 mm / 0.008 in (Intake and Exhaust)
The fuel system is based on the in-line injection pump configuration.
The Yanmar 2QM20H uses individual injection pumps for each cylinder,
regulated mechanically by a governor to prevent overspeeding when the
propeller comes out of the water.
The pre-combustion chamber injectors are specifically designed to
operate at the high pressures listed above, ensuring fine atomization of
the diesel fuel for efficient heat release.
Lubrication is managed by a forced feed system using a trochoid pump.
This pump draws oil from the sump and forces it through a full-flow
replaceable cartridge filter before distributing it to the crankshaft,
connecting rod bearings, camshaft, and rocker arm assembly.
The external oil cooler is critical for marine applications, using
seawater to reduce engine oil temperature during sustained high-load
operation.
The 2QM20H utilizes a direct seawater cooling system (raw water
cooling). A rubber impeller-type pump draws water from the surrounding
sea. This water is circulated directly through the water jackets in the
cylinder block and cylinder head to absorb heat.
After passing through the block, the heated seawater is injected into
the exhaust elbow, mixing with the exhaust gases to cool the rubber
exhaust hose.
Exhaust System: The engine utilizes a water-injected exhaust system.
Seawater injected into the exhaust manifold cools the gases, reducing
the temperature of the exhaust hose and muffler system significantly.
Transmission (Marine Gear): The standard transmission for the 2QM20H is
the Kanzaki KBW10 (or KH-18). These units feature a mechanical cone
clutch mechanism for forward and reverse engagement. Reduction ratios
commonly available are 2.14, 2.63, or 3.06 forward, with reverse
typically being a higher reduction. A known service torque for the KBW10
output coupling nut is 68.7 lb-ft (93.2 Nm).
Starting System: A 1.0 kW electric starter motor is standard. A manual
hand crank mechanism is installed on the front of the engine for
emergency starting or cold weather operation when the battery is low.
Overall Length (with gear): 852 mm / 33.5 in
Overall Width: 470 mm / 18.5 in
Overall Height: 588 mm / 23.1 in
Dry Weight (with gearbox): 215 kg / 474 lbs
Exhaust Pipe Diameter: 50 mm / 2.0 in (approx)
Adherence to a strict maintenance schedule is required to prevent
corrosion from seawater cooling and to maintain fuel injection
precision. Engine Oil: Change every 100-200 operating hours or annually.
Use API CC/CD or higher 15W-40 or 20W-50 oil. Capacity is 4.0 L (4.2 US
qt).
Raw Water Pump Impeller: Inspect annually. Replace every 1-2 years or
immediately if engine overheats at low RPM. Zinc Anodes: The heat
exchanger and engine block contain pencil zincs that must be inspected
and replaced annually to prevent galvanic corrosion from seawater
contact. Fuel Filters: Replace primary and secondary fuel filters every
250 hours or sooner if water is detected in the separator.
Valve Clearance: Inspect and adjust every 500 hours or annually.
Clearance (cold): 0.20 mm (0.008 in). Injection Pressure: To be checked
by a diesel specialist using a pop tester if hard starting or excessive
smoke occurs (Standard: 160-170 kg/cm2).
Cylinder Head Bolts: 47-51 lb-ft / 65-70 Nm
Connecting Rod Cap Bolts: 29-33 lb-ft / 40-45 Nm
Main Bearing Cap Bolts: 51-55 lb-ft / 70-75 Nm
Flywheel Bolts: 69-73 lb-ft / 95-100 Nm
KBW10 Output Shaft Nut: 68.7 lb-ft / 93.2 Nm
Injector Hold-Down Nuts: 18-22 lb-ft / 25-30 Nm
The Yanmar 2QM20H was exclusively used as a marine auxiliary engine in
sailboats and small motor cruisers during the late 1970s to mid-1980s.
Specific vessels that utilized this power plant as original equipment
include:
Nicholson 31 MkII (1978-1979): A popular offshore cruiser equipped with
a 22 hp version of the 2QM20H.
Hunter 37 (1978-1979): The early models (Cherubini design) featured the
2QM20H before upgrading to a 30 hp 3-cylinder engine in 1980.
Jeanneau Melody (1993): A French-built cruiser fitted with the 19-22 hp
variant, documented with service history involving oil and seawater pump
changes.
Endeavour 32: Fitted with the 2QM20H mated to the Kanzaki KBW10 gearbox.
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