Yamaha T50LB Specifications
| Engine Model: Yamaha T50LB |
| Engine Type: 4-stroke inline 4-cylinder SOHC 8-valve gasoline outboard engine |
| Total Displacement: 60.8 cu.in (996 cc) |
| Rated Engine Power: 50 Hp (36.8 kW) at 5500 rpm |
| Fuel System: Electronic Fuel Injection (EFI) |
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The Yamaha T50LB is a 50-horsepower,
four-stroke, in-line four-cylinder outboard engine from Yamaha's
specialized High Thrust series, engineered for applications demanding
maximum thrust and precise control rather than outright speed.
This model is configured for remote control operation and is equipped
with electric starting and a hydraulic power trim and tilt system,
offering boaters a purpose-built power source optimized for exceptional
low-end torque and superior maneuverability.
Built on a refined 996cc platform, the T50LB is renowned for its
distinctive 2.33:1 gear ratio and larger lower unit, providing
dramatically increased thrust in both forward and reverse, making it a
dependable and powerful choice for pontoon boats, sailboats, workboats,
and any vessel that requires serious muscle.
The Yamaha T50LB is constructed around a specialized powerhead and lower
unit combination. It features a 4-stroke, SOHC, in-line 4-cylinder,
8-valve engine configuration. The engine displacement is precisely 996
cc (60.8 cu in), achieved through a bore and stroke of 65.0 mm x 75.0 mm
(2.56 in x 2.95 in).
This powerhead produces a maximum prop shaft output of 36.8 kW (50 hp)
at 5,500 rpm. The engine is engineered to operate within a full throttle
operating range of 5,000 to 6,000 rpm, with a specified engine idle
speed of 700-800 rpm. The compression ratio is stated as 9.5:1.
The power unit of the T50LB is engineered for durability, efficiency,
and smooth power delivery. The 1.0 litre, eight-valve, single-overhead
camshaft, four-cylinder, long stroke design delivers ultra-smooth,
usable power with low noise and vibration levels.
The valve train requires periodic adjustment, with specified valve
clearances of 0.15-0.25 mm (0.006-0.010 in) for the intake valves and
0.25-0.35 mm (0.010-0.014 in) for the exhaust valves when the engine is
cold.
The T50LB features Yamaha's advanced Electronic Fuel Injection (EFI)
system, which precisely meters fuel for optimal combustion under all
conditions. The multi-point EFI system ensures quick, reliable starts,
crisp throttle response, smooth idling, and optimal fuel economy across
the RPM range, while also contributing to cleaner emissions and
consistent performance regardless of temperature or altitude. The
recommended fuel is regular unleaded gasoline with a minimum octane
rating of 87. The engine is supplied with fuel from a separate tank.
The lubrication system is a wet sump type, meaning the engine oil is
stored in a sump within the engine. The recommended engine oil is
high-quality 4-stroke outboard motor oil, such as Yamalube 4M, in SAE
10W-30 or 10W-40 viscosities, meeting API SE, SF, SG, SH, SJ, or SL
service classifications. The engine oil capacity with oil filter
replacement is 2.1 L (2.2 US qt).
The cooling system is raw-water with thermostatic control, drawing water
from the body of water to cool the engine. A freshwater flushing system
is integrated for easy maintenance, allowing connection of a hose to
flush salt and dirt from the outboard without having to run the engine.
Exhaust gases are expelled through the propeller boss for efficient
underwater exhaust and noise reduction.
The ignition system is a TCI (Transistor Controlled Ignition)
microcomputer unit, providing precise spark timing for reliable starting
and efficient power across the RPM range. The specified spark plugs are
NGK DPR6EB-9, with a required gap of 0.8-0.9 mm (0.031-0.035 in).
The charging system incorporates a high-output alternator of 12V - 16A
at WOT with a built-in rectifier/regulator to maintain battery charge
for the electric start and other electrical accessories.
| Mid Section and Lower Unit |
The defining characteristic of the T50LB is its High Thrust "T" series
designation, featuring a specialized lower unit with a larger gearcase
and a significantly higher gear ratio of 2.33:1 (28/12) , compared to
1.85:1 on standard 50HP outboards. This specialized design allows it to
swing a larger, low-pitch propeller, generating immense pushing power
for heavy loads and providing exceptional thrust for precise
maneuvering, especially in reverse.
The gear shift positions are the standard Forward-Neutral-Reverse
(F-N-R), engaged via a positive-action dog clutch. The propeller shaft
utilizes a spline drive system, and the propeller direction, when viewed
from the rear, is clockwise (right hand standard). The correct lubricant
for the lower unit is hypoid gear oil meeting API GL-4 SAE 90
specifications, with a gear oil capacity of 0.67 L (0.70 US qt).
This outboard is equipped with a hydraulic power trim and tilt system,
allowing for effortless adjustment of the engine angle with the touch of
a button. The trim angle can be adjusted from -4 degrees to +16 degrees,
enabling the operator to fine-tune the boat's attitude for optimal
performance, fuel efficiency, and ride quality under various load and
water conditions.
Negative trim settings allow for improved acceleration and the ability
to bring the boat onto the plane more quickly. For shallow water
operation and trailering, the system provides a maximum tilt-up angle of
69 degrees. The steering angle is 40 degrees to both port and starboard.
The Yamaha T50LB is designed to work optimally with Yamaha's optional
Dual Thrust series propellers, which feature a larger diameter and a
unique design that redirects exhaust flow to provide significantly
enhanced thrust in both forward and reverse. Documented propeller
applications include a 13 5/8 x 13 aluminum propeller used on a Robalo
R160 boat and a 14 x 11 aluminum propeller used on a Godfrey Mighty G
1476 Cruise pontoon boat.
Authorized Yamaha dealers can recommend the correct propeller based on
boat hull, load, and intended use to ensure the engine operates within
its recommended full-throttle RPM range of 5,000-6,000 rpm. The
propeller is optional equipment.
The Yamaha T50LB is available in a long shaft configuration with a
20-inch shaft length. The overall length is 698 mm (27.5 in) and the
overall width is 386 mm (15.2 in). The overall height is 1,476 mm (58.1
in) with a transom height of 527-534 mm (20.7-21.0 in). The dry weight
for this model is 113-118 kg (249-262 lb) depending on configuration and
year.
Regular maintenance is essential for the longevity of the T50LB. The
engine oil and oil filter should be changed according to the
manufacturer's schedule. The gear oil in the lower unit should be
checked regularly for the presence of water or metal particles and
changed annually or every 100 hours. The water pump impeller is a wear
item that should be inspected and replaced periodically, every 1-2 years
or if there are signs of reduced cooling water flow, to prevent
overheating.
The spark plugs should be removed, inspected, cleaned, and the gap
adjusted annually, and replaced as needed. Valve clearance inspection
and adjustment should be performed at recommended intervals. All moving
parts, such as steering linkages and tilt tube, require regular greasing
with water-resistant marine grease to prevent corrosion and ensure
smooth operation. The Enhanced Ultimate Corrosion Protection System
(UCP) is a standard feature for long-term durability.
Yamaha's variable trolling control allows precise adjustment of the
engine's idling speed from 600 to 1000 RPM in 50 RPM increments via the
optional Command Link System, allowing fishermen to perfect their lure
presentation. The recommended fuel filtration includes an external
Yamaha 10-Micron Fuel/Water Separating Filter. The factory warranty is 3
years for pleasure boat use and 1 year for commercial use.
Spark plug: 18 Nm (13.5 lb-ft)
Propeller nut: 35 Nm (25 lb-ft)
Oil drain plug: 28 Nm (21 lb-ft)
Oil filter: 18 Nm (13.5 lb-ft)
The Yamaha T50LB is a specialized power source ideally suited for boats
where thrust and maneuverability are paramount over speed. Its High
Thrust lower unit and higher 2.33:1 gear ratio make it a perfect match
for pontoon boats, including models like the Godfrey Mighty G 1476
Cruise and Bennington 18 SXL , providing the strong pushing power needed
for acceleration, cruising, and superior maneuverability in tight
marinas. It is also ideal as an auxiliary engine for sailboats, offering
powerful thrust for docking and navigating currents.
The T50LB serves larger aluminum fishing boats and utility boats,
especially those carrying heavy loads or requiring precise slow-speed
control for trolling. Commercial applications include workboats, patrol
boats, and other vessels where dependable, low-speed power and
exceptional reverse thrust are required for maneuvering in tight
quarters. The engine is also used as safety boat power, as evidenced by
a Richmond Yacht Club Boston Whaler equipped with a T50LB. An optional
tiller handle kit is available for those preferring tiller-steer
operation.
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