Yanmar 2QM20 Specifications
| Engine Model: Yanmar 2QM20 |
| Engine Type: 4-stroke 2-cylinder water-cooled diesel |
| Total Displacement: 38.7 cu.in (0.64 L) |
| Rated Engine Power: 19.7 Hp (14.7 kW) at 3600 rpm |
| Fuel System Type: Indirect injection |
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The Yanmar 2QM20 is a 2-cylinder naturally
aspirated marine diesel engine, part of Yanmar's storied QM series.
Produced from the late 1970s into the 1990s, it was engineered as a
robust auxiliary powerplant for sailboats and small workboats. Unlike
its freshwater-cooled successors (the 2GM series), the 2QM20 was built
around a thick-wall, cast-iron block designed to absorb vibration and
provide decades of service life. It operates on the four-stroke cycle
using indirect injection (IDI) and a swirl pre-combustion chamber, which
permits smoother, quieter running than direct injection units of its
era.
The engine is universally recognized for its high torque at low
revolutions, a direct result of its long-stroke design and heavy
flywheel. While the standard 2QM20 utilizes direct seawater cooling (raw
water), the "F" variant (2QM20F) introduced a freshwater cooling system
with a heat exchanger, drastically extending engine life in saltwater
environments by preventing internal corrosion. The engine is started via
a 12V electric starter (1.0 kW), with a manual hand-crank backup, and is
governed by a centrifugal all-speed governor, making it highly
responsive to load changes during docking.
The engine operates on a four-stroke diesel cycle with a naturally
aspirated induction method. It is configured for direct drive or
reduction gear applications in marine environments. Engine management is
mechanical, utilizing a centrifugal governor and a Bosch-type in-line
injection pump.
Engine Type: Vertical inline-2, water-cooled, 4-stroke diesel
Displacement: 0.635 liters (38.7 cu.in)
Bore x Stroke: 75.0 mm x 72.0 mm (2.95 in x 2.83 in)
Compression Ratio: 20.0:1 (Specific to indirect injection swirl chamber)
Firing Order: 1-2
Idle Speed: 900 - 1000 rpm
Maximum Power (Continuous): 11.8 kW (15.8 hp) @ 3,400 rpm
Maximum Power (Intermittent): 14.7 kW (19.7 hp) @ 3,600 rpm
Maximum Torque: Approx. 45 Nm (33 lb-ft) @ 2,200 rpm
Governed Maximum Speed: 3,600 rpm (full load)
Combustion System: Indirect injection (IDI) with swirl pre-combustion
chamber
The cylinder block is constructed from high-grade cast iron with a
closed-deck design. It features thick wall sections to dampen vibration,
a trait necessary for multi-cylinder diesels without balance shafts. The
block incorporates three main bearings supporting the crankshaft.
Cylinder Bore Diameter: 75.0 mm (2.95 in)
Main Bearing Journal Diameter: 55.0 mm (2.16 in)
Piston Material: High-temperature aluminum alloy with iron-coated ring
grooves
Crankshaft: Forged carbon steel, fully counter-weighted
Connecting Rods: Forged steel with a large end cap design for high load
capacity
Cylinder Block Construction: Cast iron with deep skirt and integral
mounting feet
The cylinder head is manufactured from cast iron to match the block's
thermal expansion. It houses the overhead valve (OHV) arrangement
(pushrod design, not OHV). The head incorporates the swirl-type
pre-combustion chambers (IDI) which are removable. The valvetrain
utilizes mechanical tappets requiring periodic screw-type adjustment.
Valvetrain: Pushrod (OHV), gear-driven camshaft located in the block. 4
valves total (2 per cylinder: 1 intake, 1 exhaust).
Intake Valve Diameter: 32.0 mm (1.26 in)
Exhaust Valve Diameter: 28.0 mm (1.10 in)
Pre-Combustion Chamber: Swirl-type, mounted vertically in the cylinder
head
Valve Seat Material: Heat-resistant stainless steel alloy
Valve Clearance (cold engine, mechanical
adjustment):
Intake: 0.20 mm (0.008 in)
Exhaust: 0.25 mm (0.010 in)
The fuel system utilizes an indirect injection (IDI) configuration. Fuel
is delivered by an in-line mechanical injection pump (Bosch-type) to
pintle-type nozzles located in the swirl pre-combustion chambers. The
system is governed by a mechanical, all-speed centrifugal governor
integrated into the injection pump housing.
Fuel Injectors: Pintle-type valves, opening pressure 10.0 - 11.0 MPa
(1,450 - 1,595 psi)
Injection Pump: In-line, jerk-type pump with individual plungers per
cylinder
Injection Timing: 10 degrees before top dead center (static)
Fuel Filter: Cartridge-type primary and secondary filters (mechanical
separation)
Fuel Requirement: Diesel fuel meeting minimum cetane rating of 45, light
viscosity marine gas oil
The lubrication system is a fully pressurized wet-sump design utilizing
a trochoid pump integrated into the engine front cover. The system
includes a full-flow cartridge paper element oil filter. Oil cooler is
optional depending on the installation.
Oil Pump Type: Trochoid pump
Recommended Oil Viscosity: SAE 30 (monograde) or 15W-40
Oil Capacity (engine sump): 5.1 liters (5.4 qt)
Oil Pressure (at operating speed, warm): 200 - 300 kPa (29 - 43 psi)
Oil Pan Material: Cast iron or fabricated steel deep sump
The cooling system is the primary
distinction between variants:
Yanmar 2QM20 (Standard): Direct seawater cooling. A rubber impeller pump
draws raw water, circulates it directly through the cast iron engine
block, and ejects it out the exhaust.
Yanmar 2QM20F (Freshwater): Indirect cooling. A closed freshwater loop
circulates coolant through the block, which is then cooled by seawater
in a tubular heat exchanger.
Coolant Type (2QM20F only): Fresh water with rust inhibitor
Coolant Capacity (2QM20F - engine loop): 3.5 liters (3.7 qt)
Seawater Pump: Flexible neoprene impeller pump
Thermostat Opening Temperature: 70 - 75 °C (158 - 167 °F)
Reversing Gear (Kanzaki KBW10): Mechanical transmission utilizing a
multi-disc clutch. It permits neutral, forward, and reverse gears.
Transmission Oil: ATF (Dexron) or SAE 20/30W depending on the specific
clutch plate revision. The standard spec for the KBW10 is ATF Type A.
Transmission Capacity: 0.7 liters (0.74 qt). Reduction Ratio: 2.14:1
(standard).
Starting System: 12V electric starter (1.0 kW) with solenoid shift.
Backup manual starting via crank handle.
Engine Management: Mechanical centrifugal governor. No ECU or electronic
control module is present. Engine speed is controlled by a manual cable
connected to the injection pump rack.
Overall Length: 592 mm (23.3 in)
Overall Width: 465 mm (18.3 in)
Overall Height: 508 mm (20.0 in)
Dry Weight (Engine Only): 104 kg (229 lbs)
Weight (with Gearbox): 110 kg (242 lbs)
Intake Valve Clearance: 0.20 mm (0.008 in).
Exhaust Valve Clearance: 0.25 mm (0.010 in).
Valve Clearance: Inspection every 250 hours.
Injection Pump Timing: Check every 500 hours.
Engine Oil Change Interval: 100 hours or annually (SAE 30 or 15W-40).
Transmission Fluid Change (KBW10): 250 hours (Use ATF or specific oil).
Primary Fuel Filter Cleaning: Every 50 hours.
Secondary Fuel Filter Replacement: Every 200 hours.
Raw Water Impeller: Inspect every 100 hours; replace annually or if
cracked.
Zinc Anode (Heat Exchanger): Check every 6 months in saltwater (2QM20F
only).
Cylinder Head Nuts (M12): 75 Nm (55 lb-ft)
Connecting Rod Cap Nuts (M10): 32 Nm (23.6 lb-ft)
Main Bearing Cap Bolts: 60 Nm (44 lb-ft)
Flywheel Bolts: 40 Nm (29.5 lb-ft)
Injection Nozzle Holder: 70 Nm (52 lb-ft)
Rocker Arm Shaft Brackets: 25 Nm (18 lb-ft)
Oil Pan Bolts: 12 Nm (9 lb-ft)
Crankshaft Pulley Nut: 110 Nm (81 lb-ft)
The Yanmar 2QM20 engine was widely utilized in sailboats and small
commercial vessels during the late 20th century.
Sailboats: Production boats from the 1980s including the Albin Vega,
Tanzer 22, CandC 27, and various Island Packet yachts where a reliable,
low-RPM diesel was preferred.
Workboats: Small displacement fishing vessels and harbor utility
launches (e.g., 20-25 foot hulls).
Backup Power: Repowered installations in classic wooden motor launches
and narrowboats requiring a heavy-duty, low-vibration plant.
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