Suzuki DF4 Specifications
| Engine Model: Suzuki DF4 |
| Engine Type: 4-stroke 1-cylinder OHV gasoline outboard engine |
| Total Displacement: 8.4 cu.in (138 cc) |
| Rated Engine Power: 4 Hp (2.9 kW) at 5000 rpm |
| Fuel System: Carburetor |
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The Suzuki DF4 is recognized for its
exceptional portability and ease of use, with a dry weight as low as
26.0 kg depending on the configuration. It is part of a new generation
of portable outboards that have been comprehensively overhauled to be
more compact and lighter than their predecessors, enhancing operability
for users who frequently transport and store their engine.
The engine incorporates user-centric design elements such as an
integrated carrying handle that is rounded and easier to hold, and an
additional grip at the front for balanced two-person carrying. The
overhead integral fuel tank is a significant feature, placed directly
above the carburetor to allow for gravity fuel supply. This design
enables the engine to start instantly after filling fuel, even following
long-term storage, without the need for a primer bulb.
The new lubrication system allows for convenient three-way storage - on
its port, starboard, or front side - without the risk of oil leakage.
Its operation is noted for quiet performance and vibration mitigation,
particularly in the mid-range, contributing to a more comfortable
boating experience.
The engine is built with Suzuki's anti-corrosion system for durability
in marine environments and includes a digital CDI ignition for reliable
starting and an over-revolution limiter for protection. As a
four-stroke, it offers cleaner operation and greater fuel efficiency
compared to traditional two-stroke engines, conforming to some of the
world's strictest emissions standards.
Engine Model - Suzuki DF4
Engine Type - 4-stroke single-cylinder OHV gasoline outboard engine
Number of Cylinders - 1
Displacement - 138 cc (8.4 cu-in)
Cylinder Bore - 62.0 mm (2.44 in)
Piston Stroke - 46.0 mm (1.81 in)
Maximum Engine Power - 2.9 kW (4.0 hp)
Full Throttle Operating Range - 4000 - 5000 r/min
Idle Speed - 1250 - 1350 r/min
Compression Ratio - 9.2:1
Fuel System Type - Carburetor
Carburetor Model - Keihin BC19-13.5
Fuel Type - Unleaded gasoline (87 octane minimum)
Ignition System - Digital CDI
Cooling System - Water-cooled
Exhaust System - Through propeller hub
Starting System - Manual recoil
Choke System - Manual
Throttle Control - Twist grip
Gear Shift - Forward - Neutral - Reverse
Gear Ratio - 1.92:1
Steering System - Tiller
Trim and Tilt System - Manual, 5 tilt pin positions
Transom Height (Short Shaft) - 381 mm (15 in)
Transom Height (Long Shaft) - 508 mm (20 in)
Trim Angle - 4 to 20 degrees
Maximum Tilt Angle - 71 degrees
Dry Weight (Short Shaft) - 26.0 kg (55.1 lbs)
Dry Weight (Long Shaft) - 27.0 kg (57.3 lbs)
Alternator Rating - 12V 5A or 6A (optional)
The powerhead is built around a single-cylinder configuration with a
displacement of 138 cc. The engine utilizes a wet sump lubrication
system with a trochoid-type pump. A notable engineering feature is the
offset crankshaft design, where the crankshaft is positioned slightly
off the center of the cylinder bore. This reduces the lateral force of
the piston against the cylinder wall during the power stroke, resulting
in smoother piston movement and improved operating efficiency.
The cylinder bore inside diameter measures 62.000-62.015 mm, with a
maximum permissible out-of-round of 0.050 mm. The piston skirt diameter
is 61.975-61.990 mm, resulting in a piston-to-cylinder clearance of
0.010-0.040 mm. The piston pin outside diameter is 17.995-18.000 mm,
with a piston pin bore inside diameter of 18.006-18.014 mm, providing a
clearance of 0.006-0.019 mm. The connecting rod big end inside diameter
is 28.015-28.025 mm, with a crank pin outside diameter of 27.990-28.000
mm, resulting in an oil clearance of 0.015-0.035 mm.
Connecting rod side clearance at the big end is 0.20-0.90 mm. The
crankshaft journal outside diameter is 24.959-24.980 mm with an oil
clearance of 0.020-0.062 mm. Maximum crankshaft runout is 0.050 mm. The
piston rings include a top ring, second ring, and oil ring. The top and
second rings have a width of 1.22-1.24 mm. The top ring end gap is
0.20-0.35 mm, while the second ring end gap is 0.35-0.50 mm. Top and
second ring side clearance is 0.03-0.07 mm.
The cylinder head incorporates an OverHead Valve (OHV) design with two
valves, one for intake and one for exhaust. The valve train is designed
for quiet operation, with refinements to the rocker arm structure to
minimize excessive movement and noise. The crankshaft bearing has been
changed from a common ball type to a plane bearing, which also
contributes to noise reduction.
The cylinder head warp limit is 0.050 mm. Intake valve head diameter is
24.0 mm, and exhaust valve head diameter is 22.0 mm. Minimum valve head
thickness for both valves is 1.00 mm. The intake valve stem outside
diameter is 5.460-5.475 mm, while the exhaust valve stem is 5.440-5.455
mm. Valve guide inside diameter for both valves is 5.500-5.512 mm.
Intake valve stem-to-guide clearance is 0.025-0.052 mm, and exhaust
clearance is 0.045-0.072 mm.
Intake valve seat width is 0.8-1.0 mm, while exhaust valve seat width is
1.0-1.2 mm. The valve spring free length is 29.50 mm. Camshaft journal
outside diameter is 14.966-14.984 mm for the upper journal and
15.966-15.984 mm for the lower, with an oil clearance of 0.016-0.062 mm.
Intake cam height is 32.401-32.461 mm, and exhaust cam height is
32.538-32.598 mm. Valve clearance is set to 0.03-0.07 mm for both intake
and exhaust valves when cold.
The DF4 features a straightforward and reliable fuel delivery system
centered on a Keihin BC19-13.5 carburetor. An integral 1.5-liter fuel
tank is mounted overhead, positioned above the carburetor. This overhead
placement allows for gravity fuel supply, a significant upgrade that
simplifies the starting procedure by eliminating the need for a primer
bulb to re-fuel the system after the engine has not been used for a
while.
A manual choke is provided for cold starts. The fuel system also
includes a fuel filter that requires periodic inspection. The engine is
designed to run on unleaded gasoline with a minimum octane rating of 87.
A twist-grip throttle on the tiller handle allows for smooth and precise
engine speed control.
The lubrication system is a wet sump design utilizing a trochoid-type
cam-driven oil pump to ensure reliable oil delivery under pressure to
critical engine components, including the upper and lower crankshaft and
connecting rod big end. This pressurised system reduces friction and
wear, enhancing engine longevity. A notable feature in this class of
outboard is the inclusion of a replaceable, cartridge-style oil filter,
which significantly improves the system's long-term reliability by
trapping contaminants.
An oil level window is provided on the side of the engine for easy
visual checks of the actual lubricating condition. This advanced
lubrication system also provides the practical benefit of allowing the
outboard to be stored on any of its three sides - port, starboard, or
front - without risk of oil leakage. The engine oil capacity is 0.70
liters, and it requires SAE 10W-40 oil meeting API service
classifications SE through SJ.
Engine temperature is regulated by a water-cooled system with a
thermostat. Cooling water is drawn into the engine through intakes
located on the gearcase, just below the anti-ventilation plate. A rubber
impeller water pump, driven by the driveshaft, circulates water through
the engine block to absorb heat.
A thermostat regulates the water flow to maintain optimal operating
temperature for efficiency and performance. A tell-tale port provides a
visible stream of water to confirm that the cooling system is
functioning correctly. The system incorporates a fresh water flushing
attachment, allowing owners to easily rinse out saltwater and debris
after use to prolong the engine's life.
| Mid Section and Lower Unit |
The mid-section houses the driveshaft and provides the mounting point
for the engine to the transom bracket via a bushing-type engine mounting
system. The lower unit contains the gearcase, which is filled with 0.19
liters of Suzuki Outboard Motor Gear Oil or GL5 SAE 90 gear oil. The
gears facilitate a reduction ratio of 1.92:1, optimizing propeller speed
for thrust.
The shift mechanism allows for positive engagement of Forward, Neutral,
and Reverse gears with a large, easy-to-use shift lever located on the
starboard side. The exhaust is expelled through the propeller hub, which
also helps to quiet engine operation. The anti-ventilation plate, just
above the propeller, aids in holding the boat on plane and preventing
air from being drawn into the propeller.
Trim and tilt adjustments are performed manually. The engine is equipped
with a manual tilt system that uses a pin in one of five adjustment
holes on the transom bracket. This allows the operator to select from
five different trim positions to optimize the boat's running angle for
various loads and water conditions. The tilt system offers different
up-and-down paths of the shallow drive arm compared to previous models,
with two shallow water drive positions available.
When raised, it can be locked securely at three different positions.
When lowered, it can be smoothly moved to its lowest position without
catching. A tilt release lever disengages the lock, allowing the engine
to be tilted out of the water for beaching, trailering, or storage.
Grease fittings are provided on the pivot points of the clamp bracket to
prevent seizing and ensure smooth operation over time.
The DF4 is designed to use three-bladed aluminum propellers. The
propeller diameter is 190 mm (7.5 in). To accommodate different boat
types and loading conditions, a range of propeller pitches is available,
generally from 6 to 7 inches.
The standard propeller for many applications is a 7.5-inch diameter with
a 6.5-inch pitch. Selecting the correct pitch is crucial for allowing
the engine to operate within its recommended full-throttle RPM range of
4000-5000 for optimal performance and efficiency.
The overall length is 554.0 mm (21.8 in), overall width is 309.0 mm
(12.2 in). The short shaft model, designed for a 381 mm (15 in) transom,
has an overall height of 1064.0 mm (41.9 in) and a dry weight of 26.0 kg
(55.1 lbs). The long shaft model, for a 508 mm (20 in) transom, has an
overall height of 1190.0 mm (46.9 in) and a dry weight of 27.0 kg (57.3
lbs).
Every 100 hours of operation or annually, the following tasks should be
performed: change engine oil, change gear oil, check and clean the spark
plug (adjusting the gap to 0.8-0.9 mm or 0.031-0.035 in), inspect the
fuel line and breather for leaks or cracks, check the fuel filter,
inspect the condition of the sacrificial anodes, verify thermostat
operation, and check the carburetor, propeller nut, and cotter pin.
Every 200 hours, in addition to the 100-hour checks, the engine requires
inspection of the oil filter by an authorized dealer, inspection and
adjustment of valve clearance, checking and adjusting the idle speed,
and inspecting the water pump and its impeller.
Every 300 hours, the spark plug should be replaced with an NGK CPR6EA-9,
and the water pump impeller must be replaced to prevent cooling system
failure. Every 400 hours, the in-line fuel filter should be replaced.
Engine oil capacity is 0.70 L (0.74 US qt) of SAE 10W-40 oil meeting API
SE through SJ. Gearcase capacity is 0.19 L (6.4 US oz) of Suzuki
Outboard Motor Gear Oil or GL5 SAE 90. Spark plug type is NGK CPR6EA-9
with a gap of 0.8-0.9 mm. Valve clearance (cold) is 0.03-0.07 mm for
both intake and exhaust.
Cylinder head bolt - 28 Nm (20.5 lb-ft)
Connecting rod cap bolt - 21 Nm (15.0 lb-ft)
Crankcase bolt - 10 Nm (7.0 lb-ft)
Cylinder head cover bolt - 8 Nm (6.0 lb-ft)
Flywheel nut - 50 Nm (36.0 lb-ft)
Spark plug - 10-12 Nm (7.5-9.0 lb-ft)
Valve adjusting lock nut - 11 Nm (8.0 lb-ft)
Intake pipe bolt - 10 Nm (7.0 lb-ft)
Carburetor mounting bolt - 10 Nm (7.0 lb-ft)
Fuel pump mounting bolt - 8 Nm (6.0 lb-ft)
Engine oil drain plug - 10 Nm (7.0 lb-ft)
Gearcase bolt - 17 Nm (12.5 lb-ft)
Water pump case bolt - 8 Nm (6.0 lb-ft)
Propeller shaft bearing housing bolt - 8 Nm (6.0 lb-ft)
Tiller handle pivot bolt - 12 Nm (8.5 lb-ft)
Power unit mounting bolt - 10 Nm (7.0 lb-ft)
The Suzuki DF4 is engineered for a wide variety of small watercraft. Its
lightweight, compact, and portable nature make it an ideal primary power
source for small fishing boats, dinghies, tenders for larger yachts,
canoes, and inflatable craft. It is a popular choice for weekend leisure
use, solo boaters, and as a reliable auxiliary or "kicker" motor for
small sailboats or larger fishing vessels, providing a source of
slow-speed maneuvering power.
Its power output of 4 hp, balanced power-to-weight ratio, and enhanced
cooling system make it particularly well-suited for boats with transom
heights of 15 or 20 inches. The engine is saltwater rated and suitable
for use in both freshwater and saltwater environments when properly
maintained, featuring Suzuki's special anti-corrosion treatment to
protect against corrosive elements.
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