Yanmar 2GM20F Specifications
| Engine Model: Yanmar 2GM20F |
| Engine Type: 4-stroke 2-cylinder OHV freshwater cooled diesel |
| Total Displacement: 38.8 cu.in (0.64 L) |
| Rated Engine Power: 18 Hp (13.4 kW) at 3600 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 2GM20F is a 2-cylinder, vertical,
4-stroke, freshwater-cooled diesel engine belonging to the GM series.
Produced as a compact marine auxiliary powerplant, this engine was
developed for sailboats and small power vessels requiring reliable
propulsion with a low profile and reduced weight. The “F” designation
indicates the freshwater-cooled (heat exchanger) version, which uses an
internal closed-loop cooling system to protect the engine block from
saltwater corrosion, a critical feature for marine applications.
The Yanmar 2GM20F employs indirect injection utilizing a swirl
pre-combustion chamber system, a design that reduces combustion noise
and provides smooth operation across the engine speed range. The engine
is naturally aspirated and is equipped with an electric starting system
with a manual backup.
The freshwater cooling system incorporates a heat exchanger that
transfers heat from the engine coolant to raw seawater, which is then
discharged overboard. The engine is paired with a hydraulic or
mechanical cone clutch transmission, offering multiple forward reduction
ratios. The 2GM20F is recognized for its compact dimensions, low
profile, and durability in the harsh marine environment.
The Yanmar 2GM20F is a water-cooled, four-stroke, naturally aspirated
diesel engine configured for longitudinal mounting in marine
applications. Its design emphasizes compact size, low weight, and
reliable operation under continuous load conditions.
Engine Type: Vertical inline-2, 4-cycle, water-cooled, naturally
aspirated diesel
Displacement: 0.636 liters (38.8 cu.in)
Bore and Stroke: 75.0 mm (2.95 in) x 72.0 mm (2.83 in)
Compression Ratio: 23.0:1
Combustion System: Indirect injection (swirl pre-combustion chamber)
Firing Order: 1-2
Maximum Output: 13.4 kW (18 hp) at 3,600 rpm
Continuous Output: 11.8 kW (16 hp) at 3,400 rpm
Idle Speed: 750-850 rpm
Maximum Engine Speed: 3,600 rpm (governor limited)
The cylinder block is constructed from gray cast iron, a material
selected for its exceptional rigidity, vibration-damping properties, and
resistance to corrosion when protected by the freshwater cooling system.
The inline two-cylinder configuration provides a compact, narrow engine
package with a low profile suitable for installation beneath cockpit
floors and small engine compartments. The block features a closed-deck
design where the cylinder bores are fully supported by the water jacket
structure.
Cast-in-place cylinder bores are machined directly into the iron
casting. The block incorporates three main bearing webs with two-bolt
main bearing caps. The crankshaft is supported by three bearings and is
constructed from forged steel. A stamped steel oil pan is sealed to the
lower crankcase, providing the oil reservoir. The block incorporates
mounting points for the heat exchanger, alternator, and starter motor.
Block Material: Gray cast iron
Bore Diameter (finished): 75.0 mm (2.95 in)
Main Bearing Caps: Cast iron, two-bolt design
Cylinder Bore Deformation Limit: 0.05 mm (0.0020 in)
The cylinder head is manufactured from cast iron, matching the block
material to ensure uniform thermal expansion across the cylinder head
gasket interface. This all-iron construction provides exceptional
durability and resistance to thermal cycling in marine applications. The
head incorporates the swirl pre-combustion chambers, which are
replaceable inserts that create turbulence in the air-fuel mixture
before ignition, reducing combustion noise and improving cold-start
performance.
The valvetrain is of overhead valve (OHV) design. The camshaft is
located in the cylinder block and is driven by gears from the
crankshaft. Valves are actuated by pushrods and rocker arms. Valve
clearance is adjusted manually via threaded adjusters on the rocker
arms. The engine is of interference design.
Head Material: Cast iron
Valve Configuration: OHV, 2 valves per cylinder with pushrods and rocker
arms
Valve Diameter (Intake): 32.0 mm (1.26 in)
Valve Diameter (Exhaust): 29.0 mm (1.14 in)
Valve Stem Diameter: 7.0 mm (0.28 in)
Valve Seat Angle: 45 degrees
Interference Design: Yes
The 2GM20F employs an indirect injection system utilizing a swirl
pre-combustion chamber. A Bosch-type mechanical in-line injection pump
delivers fuel at high pressure through individual injection lines to the
injector nozzles mounted in the pre-combustion chambers. The injection
pump is mechanically governed, with a centrifugal governor controlling
fuel delivery based on engine speed and load.
The swirl pre-combustion chamber creates controlled turbulence in the
injected fuel before combustion propagates into the main combustion
chamber. This design reduces combustion noise, allows for smooth
operation across a wide range of engine speeds, and improves cold-start
performance compared to direct injection systems of the era. A manual
fuel shut-off lever provides positive engine shutdown. The fuel system
is robust and tolerant of fuel quality variations encountered in marine
applications.
Injection Type: Indirect injection (swirl pre-combustion chamber)
Injection Pump: Bosch-type mechanical in-line pump
Injection Pressure: 16.7 MPa (2,418 psi) at nozzle opening
Injection Timing: 18° before top dead center (static)
Fuel Requirement: Diesel fuel meeting applicable marine standards
The lubrication system is a fully pressurized, wet-sump design utilizing
a gear-type oil pump driven from the camshaft or crankshaft. The oil
pump draws lubricant from the stamped steel oil pan through a mesh
strainer and circulates it through a full-flow, replaceable oil filter
before entering the main oil gallery. From the gallery, pressurized oil
is distributed to the crankshaft main bearings, connecting rod bearings,
camshaft bearings, rocker arm assemblies, and timing gears.
A pressure relief valve integrated into the oil pump maintains system
pressure within operational limits. The lubrication system is designed
for the sustained load conditions of marine operation.
Oil Type: SAE 15W-40 or 20W-50 (API CD, CE, CF, or higher)
Oil Capacity (total): 2.0 liters (2.1 US qt)
Oil Pressure (at rated speed): 294-392 kPa (42.6-56.9 psi)
Oil Pump Type: Gear-type
Oil Filter Type: Spin-on, full-flow
The 2GM20F utilizes a freshwater (closed-loop) cooling system with a
heat exchanger. This system isolates the engine block and cylinder head
from raw seawater, preventing internal saltwater corrosion. A
centrifugal-type water pump, driven by the camshaft or front belt,
circulates freshwater coolant through the engine block, cylinder head,
and heat exchanger. A second raw water pump, often of the rubber
impeller type, draws seawater from the external environment and
circulates it through the heat exchanger to absorb heat from the
freshwater circuit before discharging overboard.
A wax-pellet thermostat regulates fresh water flow to maintain optimal
operating temperature. The heat exchanger is constructed from
corrosion-resistant materials such as cupronickel or titanium in
marine-grade units. An expansion tank allows for coolant expansion and
air separation. The freshwater cooling system enables the engine to
operate at a consistent temperature regardless of seawater conditions.
Coolant Type: Ethylene-glycol based antifreeze with corrosion inhibitors
(marine grade)
Coolant Capacity (freshwater side): 2.5-3.0 liters (2.6-3.2 US qt)
Thermostat Opening Temperature: 70-80 °C (158-176 °F)
Thermostat Full-Open Temperature: 90 °C (194 °F)
Heat Exchanger: Shell-and-tube or tube-bundle type
Raw Water Pump: Rubber impeller type
| Intake and Exhaust Systems |
Intake System: Cast iron intake manifold with a single inlet from the
air cleaner. The intake system incorporates an air cleaner housing with
a dry-type paper or foam filter element.
Exhaust System: Cast iron exhaust manifold with a water-injected exhaust
elbow. Raw seawater is injected into the exhaust stream at the elbow to
cool exhaust gases, reducing exhaust system temperature and noise.
Starting System: Electric start system with a 12V, 1.0 kW starter motor.
A manual starting crank is provided as a backup on some installations.
The system includes a key switch or push-button control panel with
warning indicators for glow plug operation, oil pressure, and charging
circuit.
Charging System: 12V alternator with 55 ampere output on later models.
The alternator is belt-driven from the crankshaft pulley.
Transmission (KM2P-1): The engine is coupled to a mechanical cone clutch
transmission. The forward ratios available are 2.21:1, 2.62:1, or 3.22:1
depending on the reduction gear specified. The reverse ratio is 3.06:1.
The transmission provides smooth engagement and disengagement of
propeller drive.
Dry Weight (with KM2P transmission): 114 kg (251 lb)
Overall Length: 683 mm (26.9 in)
Overall Width: 455 mm (17.9 in)
Overall Height: 512 mm (20.2 in)
Exhaust Pipe Diameter: 45 mm (1.77 in)
Oil Change Interval: 100 hours of operation under normal conditions.
Oil Change Interval: 50 hours under severe conditions.
Oil Filter Change: At every oil change.
Engine Coolant Replacement (freshwater side): 500 hours or 2 years.
Raw Water Pump Impeller Replacement: Annually or 200 hours; inspect
regularly for wear.
Glow Plug Inspection: Check at each major service; replace as required.
Intake Valve Clearance: 0.20 mm (0.008 in) cold.
Exhaust Valve Clearance: 0.20 mm (0.008 in) cold.
Valve Clearance Adjustment: Inspect and adjust every 500 hours.
Fuel Filter Replacement: 200 hours or annually.
Air Filter Cleaning / Replacement: 200 hours or as indicated by
inspection.
Heat Exchanger Anode Replacement: Annually or as indicated by anode
consumption.
Injection Timing Adjustment: Inspect as required; timing marks on
injection pump drive and front cover.
Idle Speed Adjustment: 750-850 rpm; adjust via idle speed screw on
injection pump.
Cylinder Head Bolts (M10 x 1.25), 1st pass: 25-30 Nm (18-22 lb-ft).
Cylinder Head Bolts (M10 x 1.25), final pass: 55-60 Nm (41-44 lb-ft).
Main Bearing Cap Bolts (M10 x 1.25): 45-50 Nm (33-37 lb-ft).
Connecting Rod Cap Bolts (M8 x 1.0): 25-28 Nm (18-21 lb-ft).
Rocker Arm Shaft Bracket Bolts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Intake Manifold Bolts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Exhaust Manifold Nuts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Glow Plugs: 15-20 Nm (11-15 lb-ft).
Oil Pan Bolts (M6 x 1.0): 8-10 Nm (71-89 lb-in).
Water Pump Bolts (M8 x 1.25): 18-22 Nm (13-16 lb-ft).
Crankshaft Pulley Bolt (M14 x 1.5): 80-100 Nm (59-74 lb-ft).
Flywheel / Drive Plate Bolts (M10 x 1.25): 50-55 Nm (37-41 lb-ft).
Injection Pump Drive Gear Nut (M12 x 1.5): 45-50 Nm (33-37 lb-ft).
0The Yanmar 2GM20F engine is utilized exclusively in marine
applications, primarily as auxiliary propulsion for sailboats and as the
main engine for small power vessels.
Sailboats: Small to mid-size cruising sailboats (up to approximately 32
feet in length) including brands such as Beneteau, Catalina, Hunter,
Jeanneau, and Pearson.
Power Vessels: Small motor cruisers, fishing boats, and utility vessels.
Sail-drive Configurations: Yanmar SD-series sail-drive units paired with
2GM20F engine (freshwater-cooled variant).
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