Tohatsu MFS5B Specifications
| Engine Model: Tohatsu MFS5B |
| Engine Type: 4-stroke 1-cylinder OHV gasoline outboard engine |
| Total Displacement: 7.5 cu.in (123 cc) |
| Rated Engine Power: 5 Hp (3.7 kW) at 5500 rpm |
| Fuel System: Carburetor |
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The Tohatsu MFS5B is a technologically refined
four-stroke outboard that distinguishes itself through its lightweight
and compact design, weighing as little as 57 lbs (26 kg). Its
engineering focus is on reliability, user convenience, and environmental
responsibility, highlighted by its ultra-low emission rating and quiet
through-the-hub exhaust.
Users benefit from a front-mounted gear lever for easy operation, a
digital CD ignition system for quick starts, and a thermostatically
controlled cooling system with a stainless steel water pump housing for
consistent engine temperature and outstanding durability.
The engine is engineered for superior corrosion resistance,
incorporating high-grade marine aluminum alloy and zinc coating on
internal water passages, making it a reliable and long-lasting
powerplant for small boat applications in both fresh and salt water. An
alternator is available as an option for battery charging.
Engine Model: Tohatsu MFS5B (MFS5BS short shaft), MFS5BL (long shaft),
MFS5B UL (ultra-long shaft)
Engine Type: 4-stroke, single-cylinder, OHV (OverHead Valve), gasoline
outboard engine
Number of Cylinders: 1
Displacement: 7.5 cu in (123 cc)
Cylinder Bore: 2.32 in (59.0 mm)
Piston Stroke: 1.77 in (45.0 mm)
Maximum Engine Power: 5.0 hp (3.7 kW)
Maximum Engine Speed: 4500-5500 rpm
Idle Speed in Neutral Gear: 1300 rpm
Trolling Speed in Forward Gear: 1150 rpm
Compression Ratio: 9.6:1
Lubrication System: Wet sump with forced lubrication
Exhaust System: Through propeller hub
Cooling System: Water cooling with thermostat
Ignition System: Flywheel Magneto CDI (Capacitor Discharge Ignition)
Starting System: Recoil starter
Electrical System Rating: 12 Volts
Charging System: Alternator (optional)
Cylinder Bore Inside Diameter: 2.322-2.324 in (59.00-59.03 mm)
Cylinder Bore (Maximum Out of Round): 0.002 in (0.050 mm)
Crank Pin Outside Diameter: 1.1791-1.1793 in (29.95-29.98 mm)
Crankshaft Runout (Maximum): 0.002 in (0.050 mm)
Connecting Rod Inside Diameter (Small End): 0.6301-0.6303 in
(16.006-16.014 mm)
Connecting Rod Oil Clearance (Big End): 0.0016-0.0026 in (0.040-0.066
mm)
Connecting Rod Side Clearance (Big End): 0.008-0.016 in (0.20-0.40 mm)
Piston Skirt Diameter: 2.321-2.322 in (58.95-58.97 mm)
Piston to Cylinder Clearance: 0.0008-0.0032 in (0.020-0.055 mm)
Piston to Piston Pin Clearance: 0.0001-0.0005 in (0.003-0.012 mm)
Piston Pin Outside Diameter: 0.6301-0.6303 in (15.995-16.000 mm)
Top Ring End Gap: 0.006-0.014 in (0.15-0.35 mm)
Second Ring End Gap: 0.012-0.020 in (0.30-0.50 mm)
Oil Ring End Gap: 0.008-0.016 in (0.20-0.40 mm)
Top Ring Side Clearance: 0.0016-0.0032 in (0.04-0.08 mm)
Second Ring Side Clearance: 0.0012-0.0028 in (0.03-0.07 mm)
Oil Ring Side Clearance: 0.0004-0.0071 in (0.01-0.18 mm)
Cylinder Head Warp Limit: 0.002 in (0.050 mm)
Valve Clearance (Intake): 0.06-0.14 mm (0.002-0.006 in)
Valve Clearance (Exhaust): 0.11-0.19 mm (0.004-0.008 in)
Valve Stem Outside Diameter (Intake): 0.2154 in (5.47 mm)
Valve Stem Outside Diameter (Exhaust): 0.2142 in (5.44 mm)
Valve Guide Inside Diameter (Intake): 0.2165 in (5.50 mm)
Valve Guide Inside Diameter (Exhaust): 0.2165 in (5.50 mm)
Valve Stem to Guide Clearance (Intake): 0.0008-0.0017 in (0.020-0.044
mm)
Valve Stem to Guide Clearance (Exhaust): 0.0018-0.0028 in (0.045-0.072
mm)
Valve Seat Width (Intake): 0.0315 in (0.8 mm)
Valve Seat Width (Exhaust): 0.0315 in (0.8 mm)
Valve Spring Free Length: 1.38 in (35.0 mm)
Cam Height (Intake): 1.115 in (28.33 mm)
Cam Height (Exhaust): 1.115 in (28.33 mm)
Camshaft Journal Outside Diameter: 0.5504 in (13.98 mm)
Fuel System Type: Carburetor (vertical butterfly type)
Fuel Pump Type: Mechanical
Fuel Type: Unleaded gasoline, 90 octane minimum
Fuel Consumption: 1.7 L/hr
Fuel Tank Capacity (Integral tank model): 1.05 qts (1.00 L)
Fuel Tank Capacity (Separate tank model): 3.17 gal (12.0 L)
System Type: Wet sump, forced lubrication
Engine Oil Type: SAE 10W-30 or 10W-40, 4-stroke outboard oil
API Service Classification: SE, SF, SG, SH, SJ, SL, or SM
Engine Oil Capacity: 0.47 qts (0.45 L)
Oil Change Interval: Every 100 hours or annually, whichever comes first
System Type: Water cooling with thermostat
Water Pump: Driven by driveshaft, with rubber impeller housed in a
stainless steel housing for outstanding durability
Thermostat: Maintains consistent engine operating temperature
Corrosion Protection: Zinc coating on internal water passages and
high-grade marine aluminum alloy provide superior corrosion resistance
Flushing: Fresh water flushing after use in salt or brackish water is
recommended to maintain cooling passages
| Mid Section and Lower Unit |
Mid Section: Integral driveshaft housing with anti-corrosion coating
Steering System (Std): Tiller handle with twist-grip throttle,
front-mounted gear lever
Steering System (Opt): Remote control
Steering Angle: 150 degrees
Shift System: Dog clutch
Gear Shift: Forward - Neutral
Gear Type: Spiral bevel gear
Gear Ratio: 2.15:1 (13:28)
Gearcase Capacity: 0.21 qts (0.20 L)
Gear Lubricant Type: Hypoid gear oil or API GL-5, SAE 80 to 90
Trim System: Manual Trim and Tilt
Trim Positions: 6 positions
Shallow Water Drive: Standard
Maximum Tilt Angle: 75 degrees
Propeller Types: 3-blade, aluminum or plastic
Propeller Diameter: 7.9 in (200 mm)
Propeller Pitch Range: 7 in (178 mm), 8 in (203 mm), 9 in (229 mm)
Propeller Selection Note: Propeller selection depends on boat load and
intended use; selecting the correct pitch ensures achieving recommended
WOT rpm range of 4,500-5,500
Overall Length: 26.7 in (680 mm)
Overall Width: 12.8 in (325 mm)
Overall Height (Short Shaft): 42.3 in (1075 mm)
Overall Height (Long Shaft): 47.2 in (1200 mm)
Overall Height (Extra Long Shaft): 52.2 in (1325 mm)
Transom Height (Short Shaft): 15 in (381 mm)
Transom Height (Long Shaft): 20 in (508 mm)
Transom Height (Extra Long Shaft): 25 in (635 mm)
Outboard Weight (Short Shaft): 57.3 lbs (26.0 kg)
Outboard Weight (Long Shaft): 59.5 lbs (27.0 kg)
Outboard Weight (Extra Long Shaft): 61.7 lbs (28.0 kg)
Engine Fuel: Unleaded gasoline, 90 octane minimum
Engine Oil: SAE 10W-30 or 10W-40, API SE through SM
Engine Oil Capacity: 0.47 qts (0.45 L)
Gear Lubricant: Hypoid gear oil, API GL-5, SAE 80 to 90
Gearcase Capacity: 0.21 qts (0.20 L)
Ignition Timing: 25 degrees BTDC
Spark Plug Type: NGK DCPR6E
Spark Plug Gap: 0.031-0.035 in (0.8-0.9 mm)
Every 50 hours: Check gear oil
level, check propeller for damage, check starter rope for wear.
Every 100 hours or annually: Check
spark plug, check fuel line, clean fuel tank, check fuel filter, check
anodes, change engine oil, check cooling system operation, check water
pump, check valve clearance, check/adjust carburetor, check ignition
timing, change gear oil.
Every 200 hours or 2 years: Replace
spark plug.
Cylinder Head Bolt: 18.0 lb-ft (25 Nm)
Connecting Rod Bolt: 9.0 lb-ft (12 Nm)
Flywheel Nut: 37.0 lb-ft (50 Nm)
Oil Drain Bolt: 13.0 lb-ft (18 Nm)
Oil Pan Bolt: 18.0 lb-ft (25 Nm)
Pivot Bolt: 18.0 lb-ft (25 Nm)
Pivot Adjust Nut: 7.5 lb-ft (10 Nm)
Oil Pressure Switch: 7.0 lb-ft (9 Nm)
Recoil Starter Bolt: 3.0 lb-ft (4 Nm)
Stern Bracket Nut: 9.0 lb-ft (13 Nm)
Power Unit Mounting Bolt: 5.5 lb-ft (7 Nm)
Spark Plug: 13.0 lb-ft (18 Nm)
The Tohatsu MFS5B is a versatile outboard ideally suited for a wide
range of small, portable watercraft. Its light weight and compact
dimensions make it an excellent choice for powering inflatable boats,
dinghies, and small tenders used as shore craft for larger vessels. It
is also a popular powerplant for small fishing boats, jon boats, and
canoes used on lakes and rivers, where its portability allows for easy
transport and storage.
The engine's four-stroke design, quiet operation, and reliable starting
make it well-matched for recreational boaters, anglers, and as an
auxiliary motor for sailboats, where efficiency, low emissions, and ease
of use are paramount. The availability of integral or separate fuel tank
models and different shaft lengths broadens its adaptability to various
boat configurations.
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