Yamaha F50AET Specifications
| Engine Model: Yamaha F50AET |
| Engine Type: 4-stroke inline 4-cylinder OHC 8-valve gasoline outboard engine |
| Total Displacement: 57.1 cu.in (935 cc) |
| Rated Engine Power: 50 Hp (36.8 kW) at 5500 rpm |
| Fuel System: Carburetors |
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The Yamaha F50AET is a 50-horsepower,
four-stroke, inline four-cylinder outboard motor renowned for its smooth
operation, fuel efficiency, and advanced engineering. This engine is
designed for boaters who demand quiet performance, excellent
acceleration, and long-term reliability for a wide variety of vessels.
At its heart is a 935 cc powerhead featuring a single overhead camshaft
(OHC) and eight valves, delivering strong, responsive power across the
entire rpm range. The F50AET utilizes a sophisticated microcomputer
ignition system and Yamaha's Prime Start enrichment for effortless
starting in all conditions.
A key feature is its four-carburetor induction system, which provides
crisp throttle response and optimal fuel metering for each cylinder.
This model, designated F50AET, features electric start, power trim and
tilt, and is designed for remote control operation, making it a
versatile choice for fishing boats, pontoons, and small cruisers.
Engine type: In-line, 4-stroke, OHC, 8 valves.
Number of cylinders: 4.
Total displacement: 935 cc (57.1 cu in).
Bore and stroke: 63.0 x 75.0 mm (2.48 x 2.95 in).
Maximum output: 36.8 kW (50 hp) at 5,500 rpm.
Full throttle operating range: 5,000-6,000 rpm.
Maximum fuel consumption: 17.3 L/hr (4.57 US gal/hr, 3.81 lmp gal/hr) at
6,000 rpm.
Compression ratio: 9.3:1.
Fuel system: 4 carburetors with acceleration pump.
Ignition system: Microcomputer CDI.
Ignition timing: 5 ± 3° BTDC to 35 ± 3° BTDC.
Starting system: Electric with Prime Start enrichment.
Control system: Remote control.
Alternator output: 12V, 10A with rectifier/regulator.
Spark plug: NGK DPR6EA-9.
Spark plug gap: 0.8-0.9 mm (0.031-0.035 in).
Cooling system: Water, thermostatically controlled.
Exhaust system: Through propeller boss.
Lubrication system: Wet sump.
Recommended fuel: Regular unleaded gasoline (86-91 octane).
Engine oil type: 4-stroke motor oil, API SE, SF, SG, SH, 10W-30, 10W-40,
or 20W-40.
Engine oil capacity (with oil filter): 2.2 L (2.3 US qt, 1.9 lmp qt).
Gear oil type: Hypoid gear oil.
Gear oil grade: API SAE 90 GL-4.
Gear oil capacity: 0.43 L (0.45 US qt, 0.38 lmp qt).
Gear ratio: 1.85 (24/13).
Gear shift positions: Forward - Neutral - Reverse.
Reduction gear type: Spiral bevel gear.
Clutch type: Dog clutch.
Propeller shaft type: Spline.
Propeller direction (rear view): Clockwise.
Trim system: Power Trim and Tilt.
Trim angle range: -4 to +20 degrees.
Tilt-up angle: 69 degrees.
Steering angle: 40 + 40 degrees.
The Yamaha F50AET is constructed around a precision-engineered 935 cc
inline four-cylinder powerhead. The cylinder block is made from
high-strength aluminum alloy, providing a lightweight yet rigid
foundation for the internal components. The cylinder bore and stroke are
configured at 63.0 mm and 75.0 mm respectively. The cylinder head
features a single overhead camshaft (OHC) operating eight valves via
rocker arms, with two intake and two exhaust valves per cylinder.
The powerhead is designed for durability, incorporating features like a
hardened crankshaft and precision-machined bearing surfaces. The SOHC
valve train in the F50AET requires periodic valve clearance inspection
and adjustment to maintain optimal performance and quiet operation. The
intake valve clearance, measured with the engine cold, is specified at
0.15-0.25 mm (0.0059-0.0098 in).
The exhaust valve clearance, which operates under higher thermal loads,
is set to 0.25-0.35 mm (0.0098-0.0138 in). The camshaft is driven by a
timing belt, which must be inspected and replaced at recommended
intervals to prevent catastrophic engine damage.
The valve train components are lubricated by pressurized oil from the
wet sump system. The cylinder head incorporates a gasket that is not
reusable upon removal, requiring replacement during any disassembly. The
valve system works in concert with the four-carburetor induction to
provide efficient combustion across the engine's operating range.
The F50AET employs a sophisticated fuel system featuring four individual
carburetors, one dedicated to each cylinder. This design ensures precise
fuel metering and distribution for optimal combustion efficiency and
throttle response. The carburetors are equipped with an acceleration
pump that provides an extra shot of fuel during rapid throttle openings,
eliminating hesitation and providing smooth, powerful acceleration.
The Prime Start enrichment system automatically adjusts the fuel mixture
for cold starts, eliminating the need for a manual choke. The fuel
system includes a fuel filter that requires periodic inspection and
replacement. The engine operates on regular unleaded gasoline with a
minimum octane rating of 86-91. The carburetors are synchronized to
ensure equal airflow to each cylinder, and this synchronization must be
checked and adjusted periodically as part of routine maintenance.
The Yamaha F50AET utilizes a wet sump lubrication system, where engine
oil is stored in an integrated oil pan at the base of the engine. A
trochoidal oil pump, driven by the crankshaft, circulates oil under
pressure throughout the engine, delivering lubricant to the crankshaft
main bearings, connecting rod bearings, camshaft journals, and valve
train components.
The system includes a full-flow oil filter that removes contaminants
from the oil. An oil pressure switch monitors system pressure and
triggers a warning if pressure drops below a safe level; this switch is
torqued to 9 Nm (6.5 lb-ft). The recommended oil is a high-quality
4-stroke motor oil meeting API SE, SF, SG, or SH specifications, with
viscosities of SAE 10W-30, 10W-40, or 20W-40 suitable for most operating
conditions.
The engine oil capacity, including the filter, is 2.2 liters (2.3 US
quarts). The oil drain plug is torqued to 18 Nm (13 lb-ft), and the oil
filter to 18 Nm (13 lb-ft). Regular oil and filter changes are essential
for engine longevity.
The cooling system is a raw-water, thermostatically controlled design. A
water pump, driven by the driveshaft, draws water from the body of water
through an inlet in the lower unit and circulates it through water
jackets in the cylinder block and cylinder head. The system is regulated
by a thermostat that maintains optimal operating temperature by
controlling water flow; when closed, it allows the engine to warm up
quickly, and when open, it permits full flow to prevent overheating.
The cooling system includes a pilot water outlet that provides a visual
indication of proper water pump operation. Flushing the cooling system
with fresh water after operation in salt, brackish, or polluted water is
essential to prevent corrosion and blockage. A flushing attachment can
be used to connect a garden hose to the cooling system for this purpose.
| Mid Section and Lower Unit |
The mid section houses the driveshaft and exhaust passage, connecting
the powerhead to the lower unit. The lower unit contains the reduction
gearing and propulsion components. The gear ratio is 1.85:1, achieved
with a pinion gear and forward gear set of 24/13 teeth.
The reduction gears are of the spiral bevel type, selected for their
strength and smooth, quiet operation. The clutch mechanism is a dog
clutch, providing positive engagement for shifting. Gear shift positions
are forward, neutral, and reverse. The propeller shaft is splined to
accept a wide range of propeller options. The lower unit housing is
constructed from corrosion-resistant materials and incorporates
sacrificial anodes to protect against galvanic corrosion.
The gear housing is filled with hypoid gear oil meeting API GL-4 SAE 90
specifications, with a total capacity of 0.43 liters (0.45 US quarts).
The lower unit bolts (M10) are torqued to 40 Nm (29 lb-ft). Regular
inspection and periodic changing of the gear oil are necessary to detect
water ingress or wear particles.
The Yamaha F50AET is equipped with a power trim and tilt system,
allowing effortless adjustment of the engine angle relative to the boat
transom. The system uses an electro-hydraulic pump and dual hydraulic
cylinders to raise and lower the engine. The trim angle range extends
from -4 degrees (trimmed fully in, forcing the bow down for planing) to
+20 degrees (trimmed out for optimal running attitude).
The system also provides a tilt-up angle of 69 degrees for beaching,
launching, trailering, or shallow water operation. The power trim and
tilt system includes a trim bar with multiple adjustment holes, allowing
the operator to preset the lower limit of the trim range. This feature
helps achieve consistent handling characteristics and prevents the
engine from being trimmed too far down under power. The system is
controlled by rocker switches on the remote control.
Selecting the correct propeller is essential for optimizing the
performance of the Yamaha F50AET. The engine is designed to operate
within its full throttle rpm range of 5,000-6,000 rpm, and the propeller
pitch must be chosen so that, with a normal boat load, the engine
reaches the upper half of this range at full throttle. Yamaha offers a
comprehensive range of genuine propellers for the F50AET in both
aluminum and stainless steel constructions.
Aluminum G propeller options include: 10 x 15, 10-1/4 x 14, 10-3/8 x 13,
10-5/8 x 12, 10-3/4 x 16, 10-3/4 x 17, and 11-1/4 x 14. Stainless steel
G propeller options provide enhanced durability and performance and
include: 10-1/4 x 14, 10-1/4 x 15, 10-1/4 x 16, 10-5/8 x 13, 11-1/4 x
14, 11-1/2 x 13, 11-3/4 x 12, and 12 x 11.
The propeller nut must be tightened to the specified torque of 35 Nm (25
lb-ft). Propeller selection guides are available to assist in choosing
the appropriate pitch based on boat type, weight, and intended use.
Overall length: 718 mm (28.3 in)
Overall width: 361 mm (14.2 in)
Overall height (F50AETL, long shaft): 1,397 mm (55.0 in)
Overall height (F50AETX, extra long shaft): 1,511 mm (59.5 in)
Transom height (F50AETL, long shaft): 508 mm (20.0 in)
Transom height (F50AETX, extra long shaft): 635 mm (25.0 in)
Weight (F50AETL, long shaft): 108 kg (238 lb)
Weight (F50AETX, extra long shaft): 111.5 kg (246 lb)
After first 10 hours or 1 month: Change engine oil and oil filter.
Inspect gear oil for water contamination. Check and retighten all bolts
and nuts. Every 50 hours or 3 months: Inspect and clean spark plugs.
Check and clean fuel filter. Inspect fuel lines and connections for
cracks or damage. Check gear oil level and condition. Lubricate all
control linkages and moving parts.
Every 100 hours or 6 months: Change engine oil and oil filter. Replace
spark plugs. Inspect and clean cooling water passages. Check condition
of sacrificial anodes, replacing if significantly eroded. Check valve
clearance and adjust as necessary.
Every 200 hours or 1 year: Replace water pump impeller. Inspect and
clean entire fuel system, including carburetors and acceleration pump.
Replace fuel lines if hardened or cracked. Check and adjust ignition
timing and carburetor synchronization. Perform a thorough check of all
electrical connections and controls. Change gear oil.
Cylinder head bolt M6 (1st): 6 Nm (4.3 lb-ft)
Cylinder head bolt M6 (2nd): 12 Nm (8.7 lb-ft)
Cylinder head bolt M9 (1st): 23 Nm (17 lb-ft)
Cylinder head bolt M9 (2nd): 47 Nm (34 lb-ft)
Crankcase bolt M6 (1st): 6 Nm (4.3 lb-ft)
Crankcase bolt M6 (2nd): 12 Nm (8.7 lb-ft)
Crankcase bolt M8 (1st): 15 Nm (11 lb-ft)
Crankcase bolt M8 (2nd): 30 Nm (22 lb-ft)
Connecting rod cap bolt (1st): 6 Nm (4.3 lb-ft)
Connecting rod cap bolt (2nd): 17 Nm (12 lb-ft)
Flywheel magnet nut: 160 Nm (116 lb-ft)
Oil pressure switch: 9 Nm (6.5 lb-ft)
Ignition coil bolt M6: 7 Nm (5.1 lb-ft)
Starter motor bolt M8: 30 Nm (22 lb-ft)
Power unit bolt M8: 21 Nm (15 lb-ft)
Spark plug: 18 Nm (13 lb-ft)
Oil filter: 18 Nm (13 lb-ft)
Drain bolt: 18 Nm (13 lb-ft)
Lower unit bolt M10: 40 Nm (29 lb-ft)
Propeller nut: 35 Nm (25 lb-ft)
The Yamaha F50AET is a versatile and popular power choice for a wide
range of boat types. Its 50-horsepower output, combined with its
lightweight four-stroke design and smooth operation, makes it an ideal
engine for aluminum fishing boats, including jon boats, tiller models,
and center consoles. Pontoon boats and small deck boats benefit from the
engine's reliable power and fuel efficiency for leisurely cruising.
The F50AET is also well-suited for small to medium rigid-hull inflatable
boats (RIBs) used for recreational boating, diving, and watersports.
Skiffs, bay boats, and light utility craft in commercial applications
such as aquaculture or marina support also rely on this engine's
durability and performance. The availability of both long and extra-long
shaft models allows the F50AET to be matched to a variety of transom
heights, further expanding its application range.
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