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Tohatsu MFS4B 4-Stroke Specifications
The Tohatsu MFS4B is a four-stroke single-cylinder overhead valve shallow water drive gasoline outboard engine. This engine has a carburetor fuel system, mechanical fuel pump, water cooled with thermostat, and flywheel magneto CDI ignition system. A 7.5 cu.in (123 cc) outboard motor has a cylinder bore of 2.32" (59 mm), piston stroke of 1.77" (45 mm), and maximum power of 4 hp (2.9 kW) at 4500-5500 rpm. The boat motor is equipped with a manual starting system, 3-blades aluminum standard propeller, manual trim and tilt, and tiller handle or remote control steering system. The fuel tank has a capacity of 0.3 gal (1 liters).
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| General Technical Data |
Engine Model ................ Tohatsu MFS4B
Engine Type ................ 4-stroke single-cylinder OHV gasoline outboard engine
Number of Cylinders ................ 1
Displacement, cu.in (cc) ................ 7.5 (123)
Cylinder Bore, in (mm) ................ 2.32 (59.0)
Piston Stroke, in (mm) ................ 1.77 (45.0)
Maximum Engine Power, hp (kW) ................ 4.0 (2.9)
Maximum Engine Speed, rpm ................ 4500-5500
Idle Speed, rpm ................ 1300
Trolling Speed, rpm ................ 1150
Compression Ratio ................ 9.6:1
Lubrication System ................ Wet sump
Exhaust System ................ Through hub
Cooling System ................ Water cooling
Ignition System ................ Flywheel Magneto CDI
Starting System ................ Recoil starter
Electrical System Rating, Volts ................ 12
Charging System ................ Alternator
| Dimensions and Weight |
Overall Length, in (mm) ................ 26.7 (680)
Overall Width, in (mm) ................ 12.8 (325)
Overall Height (Short Shaft), in (mm) ................ 42.3 (1075)
Overall Height (Long Shaft), in (mm) ................ 47.2 (1200)
Overall Height (Extra Long Shaft), in (mm) ................ 52.2 (1325)
Transom Height (Short Shaft), in (mm) ................ 17 (435)
Transom Height (Long Shaft), in (mm) ................ 22 (560)
Transom Height (Extra Long Shaft), in (mm) ................ 27 (685)
Outboard Weight (Short Shaft), lbs (kg) ................ 57.3 (26.0)
Outboard Weight (Long Shaft), lbs (kg) ................ 59.5 (27.0)
Outboard Weight (Extra Long Shaft), lbs (kg) ................ 61.7 (28.0)
| Fuel System |
Fuel System Type ................ Carburetor
Carburetor Type ................ Vertical butterfly
Fuel Pump Type ................ Mechanical
Fuel Type ................ Unleaded gasoline (90 octane minimum)
Fuel Consumption, L/hr ................ 1.5
Fuel Tank Capacity, qts (L) ................ 1.05 (1.00)
| Gear Housing |
Shift System ................ Dog clutch
Gear Shift ................ Forward-Neutral
Gear Type ................ Spiral bevel gear
Gear Ratio ................ 2.15:1
Gear Oil Capacity, qts (L) ................ 0.21 (0.20)
| Mid Section |
Trim System ................ Manual Trim and Tilt
Trim Position ................ 6
Transom Height (Short Shaft), in (mm) ................ 17 (435)
Transom Height (Long Shaft), in (mm) ................ 22 (560)
Transom Height (Extra Long Shaft), in (mm) ................ 27 (685)
Steering System (Std) ................ Tiller handle
Steering System (Opt) ................ Remote control
Steering Angle, deg ................ 150
Tilt Angle (Max), deg ................ 75
| Propeller Information |
Diameter, in (mm) ................ 7.9 (200)
Pitch, in (mm) ................ 7 (178), 8 (203), 9 (229)
Number Of Blade ................ 3
Material ................ Aluminum
| Cylinder Block |
Cylinder Bore Inside Diameter, in (mm) ................ 2.322-2.324 (59.00-59.03)
Cylinder Bore (Max Out of Round), in (mm) ................ 0.002 (0.050)
Crank Pin Outside Diameter, in (mm) ................ 1.1791-1.1793 (29.95-29.98)
Crankshart Runout (Maximum), in (mm) ................ 0.002 (0.050)
Connecting Rod Inside Diameter (Small End), in (mm) ................ 0.6301-0.6303 (16.006-16.014)
Connecting Rod Oil Clearance (Big End), in (mm) ................ 0.0016-0.0026 (0.040-0.066)
Connecting Rod Side Clearance (Big End), in (mm) ................ 0.008-0.016 (0.20-0.40)
Piston Skirt Diameter, in (mm) ................ 2.321-2.322 (58.95-58.97)
Piston to Cylinder Clearance, in (mm) ................ 0.0008-0.0032 (0.020-0.055)
Piston to Piston Pin Clearance, in (mm) ................ 0.0001-0.0005 (0.003-0.012)
Piston Pin Outside Diameter, in (mm) ................ 0.6301-0.6303 (15.995-16.000)
Top Ring End Gap, in (mm) ................ 0.006-0.014 (0.15-0.35)
Second Ring End Gap, in (mm) ................ 0.012-0.020 (0.30-0.50)
Oil Ring End Gap, in (mm) ................ 0.008-0.016 (0.20-0.40)
Top Ring Side Clearance, in (mm) ................ 0.0016-0.0032 (0.04-0.08)
Second Ring Side Clearance, in (mm) ................ 0.0012-0.0028 (0.03-0.07)
Oil Ring Side Clearance, in (mm) ................ 0.0004-0.0071 (0.01-0.18)
| Cylinder Head and Valves |
Cylinder Head Warp Limit ................ 0.002 (0.050)
Valve Clearance (Intake), in (mm) ................ 0.06-0.14 (0.002-0.006)
Valve Clearance (Exhaust), in (mm) ................ 0.11-0.19 (0.004-0.008)
Valve Stem Outside Diameter (Intake), in (mm) ................ 0.2154 (5.47)
Valve Stem Outside Diameter (Exhaust), in (mm) ................ 0.2142 (5.44)
Valve Guide Inside Diameter (Intake), in (mm) ................ 0.2165 (5.50)
Valve Guide Inside Diameter (Exhaust), in (mm) ................ 0.2165 (5.50)
Valve Stem To Valve Guide Clearance (Intake), in (mm) ................ 0.0008-0.0017 (0.020-0.044)
Valve Stem To Valve Guide Clearance (Exhaust), in (mm) ................ 0.0018-0.0028 (0.045-0.072)
Valve Seat Width (Intake), in (mm) ................ 0.0315 (0.8)
Valve Seat Width (Exhaust), in (mm) ................ 0.0315 (0.8)
Valve Spring Free Length, in (mm) ................ 1.38 (35.0)
Cam Height (Intake), in (mm) ................ 1.115 (28.33)
Cam Height (Exhaust), in (mm) ................ 1.115 (28.33)
Camshaft Journal Outside Diameter, in (mm) ................ 0.5504 (13.98)
| Maintenance Data |
Engine Fuel Type ................ Unleaded gasoline (90 octane minimum)
Engine Oil Type ................ SAE 10W-30, 10W-40
API Service Classifications ................ SE, SF, SG, SH, SJ, SL, or SM
Engine Oil Capacity, qts (L) ................ 0.47 (0.45)
Gear Lubricant Type ................ Hypoid Gear Oil or API GL5, SAE 80, SAE 90
Gearcase Capacity, qts (L) ................ 0.21 (0.20)
Ignition Timing, degrees ................ 25 BTDC
Spark Plug Type ................ NGK DCPR6E
Spark Plug Gap, in (mm) ................ 0.031-0.035 (0.8-0.9)
| Service Intervals |
Check Gear Oil ................ Every 50 hours
Check Propeller ................ Every 50 hours
Check Starter Rope ................ Every 50 hours
Check Spark Plug ................ Every 100 hours
Check Fuel Line ................ Every 100 hours
Clean Fuel Tank ................ Every 100 hours
Check Fuel Filter ................ Every 100 hours
Check Anodes ................ Every 100 hours
Change Engine Oil ................ Every 100 hours
Check Cooling System ................ Every 100 hours
Check Water Pump ................ Every 100 hours
Check Valve Clearance ................ Every 100 hours
Check Carburetor ................ Every 100 hours
Check Ignition Timing ................ Every 100 hours
Change Gear Oil ................ Every 100 hours
Replace Spark Plug ................ Every 200 hours
| Tightening Torques |
Cylinder head bolt, Nm (lb-ft) ................ 25 (18.0)
Connecting rod bolt, Nm (lb-ft) ................ 12 (9.0)
Flywheel nut, Nm (lb-ft) ................ 50 (37.0)
Oil drain bolt, Nm (lb-ft) ................ 18 (13.0)
Oil pan bolt, Nm (lb-ft) ................ 25 (18.0)
Pivot bolt, Nm (lb-ft) ................ 25 (18.0)
Pivot adjust nut, Nm (lb-ft) ................ 10 (7.5)
Oil pressure switch, Nm (lb-ft) ................ 9 (7.0)
Recoil starter bolt, Nm (lb-ft) ................ 4 (3.0)
Stern bracket nut, Nm (lb-ft) ................ 13 (9.0)
Power unit mounting bolt, Nm (lb-ft) ................ 7 (5.5)
Spark plug, Nm (lb-ft) ................ 18 (13.0)
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| Engines Technical Specifications |