Tohatsu M9.8B Specifications
| Engine Model: Tohatsu M9.8B |
| Engine Type: 2-stroke 2-cylinder gasoline outboard engine |
| Total Displacement: 10.3 cu.in (169 cc) |
| Rated Engine Power: 9.8 Hp (7.2 kW) at 6000 rpm |
| Fuel System: Carburetor |
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The Tohatsu M9.8B is a technologically refined
yet straightforward outboard that distinguishes itself through its
exceptional power-to-weight ratio, weighing as little as 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. Available with manual or
electric start, it remains a popular choice for its performance and
portability.
Engine Model: Tohatsu M9.8B MF (Manual Start, Tiller), and remote
control variants
Engine Model: Tohatsu M9.8B EF (Electric Start, Tiller), and remote
control variants
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: 9.8 hp (7.2 kW)
Maximum Engine Speed: 5000-6000 rpm
Idle Speed in Neutral Gear: 950 rpm
Trolling Speed in Forward Gear: 750 rpm
Lubrication System: Pre-mixed fuel and oil (50:1 ratio after break-in)
Exhaust System: Through propeller hub
Cooling System: Forced water cooling with thermostat
Ignition System: Flywheel magneto CDI (Capacitor Discharge Ignition)
Starting System: Manual recoil starter or electric starter motor with
optional 12V alternator
Alternator Output (Optional on manual models): 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 Kikaki)
Fuel Type: Unleaded gasoline, 87 octane minimum
Fuel Consumption: 5.3 L/hr at WOT
Fuel Tank Capacity: 3.17 gal (12.0 L) separate 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.
| 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
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)
Standard Propeller: 8.5" diameter x 6.5" pitch
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 (M9.8B MF, Short Shaft): 57.0 lbs (26.0 kg)
Outboard Weight (M9.8B EF, Short Shaft): 64.0 lbs (29.0 kg)
Outboard Weight (M9.8B MF, Long Shaft): 60.0 lbs (27.0 kg)
Outboard Weight (M9.8B EF, Long Shaft): 66.0 lbs (30.0 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 6 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: Check cooling
system operation, check water pump, check/adjust carburetor, adjust
ignition timing.
Every 200 Hours: 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)
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)
Spark Plug: 20.0 lb-ft (27 Nm)
The Tohatsu M9.8B 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 up to approximately 3.6 meters in
length. 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 more power than a standard 8hp
but cannot accommodate the weight of a larger engine, where performance
and portability are paramount.
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