Tohatsu M8B Specifications
| Engine Model: Tohatsu M8B |
| Engine Type: 2-stroke 2-cylinder gasoline outboard engine |
| Total Displacement: 10.3 cu.in (169 cc) |
| Rated Engine Power: 8 Hp (5.9 kW) at 5500 rpm |
| Fuel System: Carburetor |
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The Tohatsu M8B is a technologically refined
yet straightforward outboard that distinguishes itself through its
exceptional power-to-weight ratio, with the lightest model weighing
approximately 26 kg (57 lbs). Its engineering focus is on reliability
and user convenience, highlighted by the loop-charged induction system
for smooth operation and fuel economy, and a CD ignition system for
quick starts.
Users benefit from a tiller control with forward, neutral, and reverse
gears, an automatic reverse lock, and a shallow water drive for
navigating in low waters. The engine is engineered for durability in
marine environments, incorporating high-grade marine aluminum alloy, a
stainless steel water pump housing, and zinc coating on internal water
passages for superior corrosion resistance.
Engine Model: Tohatsu M8B (various model codes: M8BS (short shaft), M8BL
(long shaft), EPL (electric start/remote)
Engine Type: 2-stroke, two-cylinder, gasoline outboard engine
Number of Cylinders: 2
Displacement: 10.3 cu in (169 cc)
Cylinder Bore: 1.97 in (50.0 mm)
Piston Stroke: 1.69 in (43.0 mm)
Maximum Engine Power: 8.0 hp (5.9 kW)
Maximum Engine Speed: 4500-5500 rpm
Trolling Speed in Forward Gear: 750 rpm
Idle Speed in Neutral Gear: 950 rpm
Lubrication System: Pre-mixed fuel and oil (50:1 ratio after break-in)
Exhaust System: Through propeller hub (through-the-prop exhaust)
Cooling System: Forced water cooling with thermostat
Ignition System: Flywheel magneto CDI (Capacitor Discharge Ignition)
Starting System: Manual recoil starter; electric starter optional on
some models
Alternator Output (Optional): 12V, 80W, 7A
Cylinder Bore Inside Diameter: 1.968-1.969 in (50.00-50.01 mm)
Piston to Cylinder Clearance: 0.0008-0.0020 in (0.02-0.05 mm)
Top Ring End Gap: 0.007-0.013 in (0.18-0.33 mm)
Second Ring End Gap: 0.007-0.013 in (0.18-0.33 mm)
Top Ring Side Clearance: 0.0004-0.0020 in (0.01-0.05 mm)
Second Ring Side Clearance: 0.0004-0.0020 in (0.01-0.05 mm)
Piston to Piston Pin Clearance: 0.0002-0.0031 in (0.01-0.08 mm)
Connecting Rod Big End Side Clearance: 0.008-0.016 in (0.20-0.40 mm)
Fuel System Type: Carburetor (Keihin)
Fuel Type: Unleaded gasoline, 87 octane (R+M)/2 minimum, or RON 91 or
higher
Fuel Consumption: 3.4 L/hr
Fuel Tank Capacity (Separate): 3.17 gal (12.0 L) portable fuel tank
System Type: Pre-mix (fuel/oil ratio)
Engine Oil Type: Genuine two-stroke outboard oil, NMMA TCW-III certified
Engine Oil and Fuel Ratio: 50 parts unleaded gasoline to 1 part
two-stroke engine oil after break-in.
For the initial break-in period (first 10 hours), a 25:1 ratio is
recommended.
System Type: Forced water cooling with thermostat
Water Pump: Driven by driveshaft, with rubber impeller housed in a
stainless steel housing
Flushing: Fresh water flushing after use in salt or brackish water is
recommended to maintain cooling passages, using a flushing attachment or
test tank.
| Mid Section and Lower Unit |
Mid Section: Integral driveshaft housing with anti-corrosion coating
Steering System (Std): Tiller handle with 360-degree steering and
automatic reverse lock
Steering System (Opt): Remote control available on some models
Shift System: Dog clutch
Gear Shift: Forward - Neutral - Reverse
Gear Ratio: 2.08:1 (13:27)
Gearcase Capacity: 0.34 qts (0.32 L)
Gear Lubricant Type: Genuine Tohatsu 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
Propeller Diameter Range: 8.5 in (216 mm) to 8.9 in (226 mm)
Propeller Pitch Range: 5.0 in (127 mm) to 9.5 in (241 mm)
Propeller Nut Torque: 9.0 lb-ft (12 Nm) with a new split pin
Overall Length: 31.2 in (790 mm)
Overall Width: 12.6 in (320 mm)
Overall Height (Short Shaft model): 39.2 in (995 mm)
Overall Height (Long Shaft model): 44.2 in (1120 mm)
Overall Height (Extra Long Shaft model): 49.2 in (1250 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): 57.0 lbs (26.0 kg)
Outboard Weight (Long Shaft): 60.0 lbs (27.0 kg)
Outboard Weight (Extra Long Shaft): 62.0 lbs (28.0 kg)
Outboard Weight (Electric Start, Long Shaft): 64.0 lbs (29.0 kg)
Engine Fuel: Unleaded gasoline, 87 octane minimum
Engine Oil: NMMA TCW-III certified two-stroke oil
Fuel/Oil Ratio: 50:1 (after break-in)
Gear Lubricant: API GL-5, SAE 80 to 90
Gearcase Capacity: 0.34 qts (0.32 L)
Ignition Timing: 24 degrees BTDC
Spark Plug Type: NGK BPR7HS-10
Spark Plug Gap: 0.035-0.039 in (0.9-1.0 mm)
Every 50 hours or 3 months: Check
spark plug, check fuel line, clean fuel tank, check anodes, check gear
oil level, check propeller, check starter rope for wear.
Every 100 hours or 6 months: Check
cooling system operation, check water pump, check/adjust carburetor,
adjust ignition timing.
Every 200 hours or annually: Replace
gear oil, replace spark plug, replace water pump impeller.
Cylinder Head Bolt: 7.2 lb-ft (10 Nm)
Magneto Nut: 43.3 lb-ft (60 Nm)
Crankcase Bolt: 10.1 lb-ft (13.5 Nm)
Intake Manifold Bolt: 10.1 lb-ft (13.5 Nm)
Exhaust Cover Bolt: 7.2 lb-ft (10 Nm)
Mounting Bolts (to transom): 13.0 lb-ft (30 Nm)
Bracket Nut: 11.0 lb-ft (15 Nm)
Gearcase Bolt: 7.2 lb-ft (10 Nm)
Propeller Shaft Housing: 7.2 lb-ft (10 Nm)
Drive Shaft Housing Bolt: 7.2 lb-ft (10 Nm)
Gear Oil Plug: 3.0 lb-ft (4 Nm)
Spark Plug: 20.0 lb-ft (27 Nm)
The Tohatsu M8B is a versatile outboard ideally suited for a wide range
of small to mid-sized portable watercraft. Its exceptional
power-to-weight ratio makes it an excellent choice for powering aluminum
tinnies, jon boats, and small dinghies. It is also a popular powerplant
for inflatable boats (RIBs), small tenders used as shore craft for
larger vessels, and as an auxiliary motor for sailboats.
The engine's design and reliable operation make it well-matched for
recreational boaters and anglers who need a balance of power and
portability for lakes, rivers, and sheltered coastal waters. The
availability of both tiller and remote steering models, as well as
manual and electric start options, broadens its adaptability to various
boat configurations and user preferences.
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