Suzuki DF40A Specifications
| Engine Model: Suzuki DF40A |
| Engine Type: 4-stroke 3-cylinder DOHC gasoline outboard engine |
| Total Displacement: 57.4 cu.in (941 cc) |
| Rated Engine Power: 40 Hp (29.5 kW) at 6000 rpm |
| Fuel System: Multi-point sequential electronic fuel injection |
____________________________________________________________________________________
The Suzuki DF40A is a four-stroke,
three-cylinder outboard engine featuring a Double Overhead Camshaft
(DOHC) design with twelve valves. The engine displacement measures 57.4
cubic inches or 941 cc, achieved through a cylinder bore of 2.85 inches
(72.5 mm) and a piston stroke of 2.99 inches (76.0 mm). The powerhead
produces a maximum output of 40.0 Hp, equivalent to 29.5 kW or 29.4 kW
depending on market specifications. The engine is designed to operate
within a wide-open throttle range of 5000 to 6000 rpm, maintaining a
stable idle speed of 800 rpm, plus or minus 50.
The compression ratio is specified at 9.7:1. Lubrication is managed by a
trochoid-type oil pump operating within a wet sump configuration. The
engine utilizes a water-cooled system and expels exhaust through the
propeller hub. Ignition is handled by a full-transistorized or
solid-state direct ignition system. Starting is facilitated by an
electric starter with Suzuki's Easy Start System, which eliminates the
need to hold the key once the starting sequence is initiated. The
electrical system operates on a 12-volt basis, with charging provided by
a 19-amp alternator.
The foundation of the DF40A engine is its cylinder block, machined to
precise tolerances. The cylinder bore inside diameter is specified at
2.8543 to 2.8551 inches, or 72.500 to 72.520 mm, with a maximum
allowable out-of-round measurement of 0.002 inch (0.050 mm). The
rotating assembly incorporates a crankshaft with thrust play of 0.004 to
0.012 inch (0.11 to 0.31 mm). Crankshaft journal outside diameter
measures 1.7709 to 1.7717 inches (44.982 to 45.000 mm), maintaining an
oil clearance of 0.0006 to 0.0013 inch (0.014 to 0.034 mm).
Crank pin outside diameter is 1.4954 to 1.4961 inches (37.982 to 38.000
mm) with a width of 0.7913 to 0.7953 inch (20.100 to 20.200 mm).
Connecting rods feature a big end inside diameter of 1.6142 to 1.6149
inches (41.000 to 41.018 mm), resulting in an oil clearance of 0.0012 to
0.0019 inch (0.031 to 0.049 mm). The connecting rod side clearance at
the big end is 0.0039 to 0.0098 inch (0.100 to 0.250 mm), with a rod
width of 0.7854 to 0.7874 inch (19.950 to 20.000 mm). The small end
inside diameter measures 0.7088 to 0.7092 inch (18.003 to 18.013 mm).
Pistons are manufactured with a skirt diameter of 2.8531 to 2.8539
inches (72.470 to 72.490 mm), establishing a piston-to-cylinder
clearance of 0.0008 to 0.0016 inch (0.020 to 0.040 mm). The piston pin
outside diameter is 0.7085 to 0.7087 inch (17.995 to 18.000 mm), fitting
into a piston pin bore of 0.7089 to 0.7092 inch (18.006 to 18.014 mm)
with a clearance of 0.0002 to 0.0007 inch (0.006 to 0.019 mm). The
piston ring set includes a top ring with a width of 0.040 to 0.041 inch
(1.02 to 1.04 mm) and an end gap of 0.0059 to 0.0118 inch (0.15 to 0.30
mm).
The second ring measures 0.048 to 0.049 inch (1.21 to 1.23 mm) in width
with an end gap of 0.0118 to 0.0177 inch (0.30 to 0.45 mm). The oil ring
width is 0.079 to 0.080 inch (2.01 to 2.03 mm). Side clearance for the
top ring is 0.0012 to 0.0028 inch (0.030 to 0.070 mm), while the second
ring operates with a side clearance of 0.0008 to 0.0024 inch (0.02 to
0.06 mm).
The cylinder head assembly incorporates the double overhead camshaft
valvetrain and must remain within a warp limit of 0.002 inch (0.050 mm).
The intake valves feature a head diameter of 1.05 inches (26.6 mm) with
a minimum head thickness of 0.040 inch (1.00 mm). Exhaust valves have a
head diameter of 0.85 inch (21.5 mm) with a head thickness of 0.045 inch
(1.15 mm).
Intake valve stem outside diameter measures 0.2152 to 0.2157 inch (5.465
to 5.480 mm), while exhaust valve stems are slightly smaller at 0.2142
to 0.2148 inch (5.440 to 5.455 mm). Both intake and exhaust valve guides
share an inside diameter of 0.2165 to 0.2170 inch (5.500 to 5.512 mm).
This results in a stem-to-guide clearance of 0.0008 to 0.0019 inch
(0.020 to 0.047 mm) for intake valves and 0.0018 to 0.0028 inch (0.045
to 0.072 mm) for exhaust valves.
Valve seat width is consistent for both intake and exhaust at 0.043 to
0.051 inch (1.1 to 1.3 mm). The valve springs have a free length of 1.30
inches (33.10 mm). Camshaft profiles are ground to specific heights,
with intake lobes measuring 1.5039 to 1.5102 inches (38.200 to 38.360
mm) and exhaust lobes measuring 1.4858 to 1.4921 inches (37.740 to
37.900 mm).
Camshaft journal outside diameter measures 0.9029 to 0.9037 inch (22.934
to 22.955 mm), fitting into a housing with inside diameter of 0.9055 to
0.9063 inch (23.000 to 23.021 mm). The oil clearance for these journals
ranges from 0.0018 to 0.0034 inch (0.045 to 0.087 mm). The DF40A
incorporates a self-adjusting, maintenance-free timing chain running in
an oil bath, equipped with an automatic hydraulic tensioner, offering
increased durability compared to belt-type systems in the same class.
The DF40A employs a multi-point sequential electronic fuel injection
system that delivers precise fuel metering for each cylinder
independently. This system integrates with Suzuki's Lean Burn Control
System, which supplies the optimal air-fuel mixture based on real-time
navigation conditions, delivering significant fuel economy improvements
across all speed ranges, particularly at cruising speeds.
The integral fuel pump draws from a standard 6.6-gallon or 25-liter
remote fuel tank included with the motor. The engine is designed to run
on unleaded gasoline with a minimum octane rating of 87 or 91. The DF40A
also features Suzuki's Troll Mode System, allowing engine speed
adjustment in fifty rpm increments from idle up to 1200 rpm, providing
precise control for trolling applications.
Engine lubrication is maintained through a wet sump system pressurized
by a trochoid-type oil pump. The system requires 2.85 US quarts or 2.70
liters of engine oil meeting API service classifications SG, SH, SJ, SL,
or SM.
Recommended viscosity grades include SAE 10W-30 and 10W-40 for normal
operating conditions. A low oil pressure caution system alerts the
operator to unsafe operating conditions.
Cooling is accomplished through a positive displacement water pump that
draws water from the lower unit. The system incorporates a thermostat to
regulate engine operating temperature, ensuring efficient combustion and
durability.
A freshwater flushing system is integrated into the design, allowing
easy connection of a garden hose for rinsing the cooling passages after
operation in salt or brackish water.
| Mid Section and Lower Unit |
The mid section houses the driveshaft and provides the structural
connection between the powerhead and the lower unit using shear mount
engine mounting. The exhaust system is designed to route gases through
the propeller hub for quieter operation.
The lower unit contains the bevel gear reduction system with a ratio of
2.27:1 or 2.28:1, representing one of the largest reduction gear ratios
in its class, contributing to powerful torque for quick acceleration and
strong pulling capability. The gearcase holds 0.65 US quart or 0.61
liter of gear lubricant, which must meet GL5 SAE 90 specifications. The
gear shift mechanism provides forward, neutral, and reverse functions.
The DF40A models feature a hydraulic power trim and tilt system as
standard equipment, operated by a remote switch or tiller handle-mounted
control for effortless adjustment. The trim angle range extends from
zero to nineteen degrees, while maximum tilt angle reaches seventy-two
degrees.
The system allows precise control of the motor's angle for optimal
performance across various operating conditions. The DF40AT is
configured for remote steering, while the DF40ATH features a tiller
handle.
The DF40A is equipped with a three-bladed aluminum propeller as standard
equipment. Propeller diameters range from 11.25 to 11.5 inches (285 to
292 mm) depending on pitch selection.
A comprehensive range of pitch options from 9 to 17 inches (228 to 406
mm) allows fine-tuning for specific applications, with available pitches
including 9, 10, 11, 12, 13, 14, 15, 16, and 17 inches. Propeller
selection depends on boat type, load, and intended use to achieve
optimal engine performance within the recommended full-throttle
operating range.
The DF40A is offered in both short and long shaft configurations.
Overall width measures 14.8 inches or 377.0 mm. The short shaft version
has an overall height of 49.8 inches (1265.0 mm) with a transom height
of 15 inches (381 mm). The long shaft version stands 54.6 inches (1385.0
mm) tall with a 20-inch (508-mm) transom height.
Overall length varies by model, with the DF40AT measuring 27.5 inches
(699.0 mm) and the DF40ATH measuring 32.0 inches (814.0 mm). Weight
varies based on configuration. The DF40AT remote steering model weighs
225.0 lbs (102.0 kg) in short shaft and 229.0 lbs (104.0 kg) in long
shaft. The DF40ATH tiller steering model weighs 238.0 lbs (108.0 kg) in
long shaft configuration.
Routine maintenance ensures reliable operation and longevity for the
DF40A. Engine oil capacity is 2.85 US quarts or 2.70 liters. Gearcase
capacity is 0.64 US quart or 0.61 liter. Ignition timing is set at 2 to
22 degrees Before Top Dead Center. The specified spark plug is NGK
DCPR6E, with a gap setting of 0.031 to 0.035 inch, or 0.8 to 0.9 mm.
Valve lash adjustment requires intake valve clearance of 0.007 to 0.009
inch (0.18 to 0.22 mm) and exhaust valve clearance of 0.011 to 0.013
inch (0.28 to 0.32 mm).
A comprehensive maintenance schedule guides service intervals. Every 100
hours of operation, inspections should include battery condition, spark
plug, breather and fuel line integrity, low pressure fuel filter,
anodes, thermostat function, and propeller nut and pin security, along
with engine and gear oil changes. At 200-hour intervals, tasks expand to
include replacement of the oil filter, checking valve lash, inspecting
the timing belt, verifying idle speed, and examining the water pump and
impeller.
Spark plug replacement and water pump impeller replacement occur every
300 hours. The low pressure fuel filter should be replaced every 400
hours. The maintenance-free timing chain requires no periodic adjustment
or replacement.
Precise fastener torque is critical for proper engine assembly and
operation. Critical torque specifications include the cylinder head
bolts at 59 Nm or 42.7 lb-ft. Crankcase bolts inside the assembly
require 46 Nm (33.5 lb-ft), while outside crankcase bolts are torqued to
25 Nm (18.0 lb-ft). Connecting rod cap bolts are tightened to 15 Nm
(11.0 lb-ft). The flywheel nut demands 166 Nm (120.0 lb-ft).
Camshaft housing bolts receive 11 Nm (8.2 lb-ft). Fuel delivery pipe
bolts are set at 11 Nm (8.2 lb-ft). Intake manifold bolts and nuts
require 23 Nm (16.5 lb-ft). The oil pressure switch tightens to 13 Nm
(9.5 lb-ft). Timing chain guide bolts are torqued to 11 Nm (8.2 lb-ft).
Low pressure fuel pump bolts receive 11 Nm (8.0 lb-ft). Starter motor
mounting bolts take 23 Nm (16.5 lb-ft).
Oil pump bolts are torqued to 11 Nm (8.2 lb-ft). The engine oil filter
requires 14 Nm (10.5 lb-ft). Water pump case nuts are tightened to 8 Nm
(5.8 lb-ft). Power unit mounting bolts and driveshaft housing bolts
share a specification of 50 Nm (36.0 lb-ft). The propeller nut is
torqued to 55 Nm (40.0 lb-ft). Gearcase bolts are set at 23 Nm (16.5
lb-ft). Tiller handle bolts receive 37 Nm (27.0 lb-ft). Cylinder head
cover bolts are torqued to 11 Nm (8.2 lb-ft). Spark plugs are installed
at 10 to 12 Nm or 7.5 to 9.0 lb-ft.
The versatility of the DF40A makes it suitable for a wide range of
watercraft. Its compact dimensions and light weight benefit aluminum
fishing boats, where the balance between power and fuel economy is
essential. The engine is ideal for rigid inflatable boats and other
inflatable crafts, where its light weight prevents transom imbalance.
Skiffs and smaller center console boats used in shallow waters or
nearshore fishing benefit from the power delivery and fuel savings.
Smaller pontoon boats achieve smooth operation and excellent fuel
economy for leisurely lake cruising with the DF40A. The engine's DOHC
performance and efficient fuel delivery make it suitable for boats up to
approximately six to seven meters in length. Commercial operators
appreciate the reliability demonstrated through use in applications such
as Sea Start and Solent RIB Charter, with the engine available with a
five-year leisure warranty or two-year commercial warranty.
The DF40A's advanced anti-corrosion system ensures durability in
saltwater environments, making it equally suitable for coastal and
inland applications. The availability of both remote and tiller steering
configurations, along with standard power trim and tilt, allows the
engine to be matched precisely to boat type and operator preference.
____________________________________________________________________________________
| Outboard Engines Technical Specifications |
| Small Engines Technical Specifications |
| Car Engines Technical Specifications |
| Industrial Engines Technical Specifications |
