| Home / Outboard Engines / Tohatsu Engines / Tohatsu MFS6BS |
Tohatsu MFS6BS Specifications
| Engine Model: Tohatsu MFS6BS |
| Engine Type: 4-stroke 1-cylinder OHV gasoline outboard engine |
| Total Displacement: 7.5 cu.in (123 cc) |
| Rated Engine Power: 6 Hp (4.4 kW) at 6000 rpm |
| Fuel System: Carburetor |
____________________________________________________________________________________
| General Technical Data |
The Tohatsu MFS6BS is a four-stroke,
single-cylinder outboard engine featuring an OverHead Valve (OHV)
design. The engine displacement measures 7.5 cubic inches or 123 cc,
achieved through a cylinder bore of 2.32 inches (59.0 mm) and a piston
stroke of 1.77 inches (45.0 mm). The powerhead produces a maximum output
of 6.0 Hp, equivalent to 4.4 kW. The engine is designed to operate
within a wide-open throttle range of 5000 to 6000 rpm, with a trolling
speed of 1150 rpm and an idle speed of 1300 rpm.
The compression ratio is specified at 9.6:1. Lubrication is provided by
a wet sump system. The engine utilizes a water-cooled cooling system and
expels exhaust through the propeller hub. Ignition is handled by a
flywheel magneto Capacitor Discharge Ignition (CDI) system. Starting is
accomplished through a manual recoil starter. The electrical system
operates on a 12-volt basis, with an optional alternator rated at 60 W
and 5 A available for battery charging.
| Cylinder Block |
The foundation of the MFS6BS engine is its cylinder block, machined to precise tolerances. The cylinder bore inside diameter is specified at 2.322 to 2.324 inches, or 59.00 to 59.03 mm, with a maximum allowable out-of-round measurement of 0.002 inch (0.050 mm). Crankshaft runout must not exceed 0.002 inch (0.050 mm).
Crank pin outside diameter measures 1.1791 to 1.1793 inches (29.95 to 29.98 mm). Connecting rods feature a big end oil clearance of 0.0016 to 0.0026 inch (0.040 to 0.066 mm) and a big end side clearance of 0.008 to 0.016 inch (0.20 to 0.40 mm). The small end inside diameter measures 0.6301 to 0.6303 inch (16.006 to 16.014 mm).
Pistons are manufactured with a skirt diameter of 2.321 to 2.322 inches (58.95 to 58.97 mm), establishing a piston-to-cylinder clearance of 0.0008 to 0.0032 inch (0.020 to 0.055 mm). The piston pin outside diameter is 0.6301 to 0.6303 inch (15.995 to 16.000 mm), fitting into the piston with a clearance of 0.0001 to 0.0005 inch (0.003 to 0.012 mm).
The piston ring set includes a top ring with an end gap of 0.006 to 0.014 inch (0.15 to 0.35 mm) and a side clearance of 0.0016 to 0.0032 inch (0.04 to 0.08 mm). The second ring end gap measures 0.012 to 0.020 inch (0.30 to 0.50 mm) with a side clearance of 0.0012 to 0.0028 inch (0.03 to 0.07 mm). The oil ring end gap is 0.008 to 0.016 inch (0.20 to 0.40 mm) with a side clearance of 0.0004 to 0.0071 inch (0.01 to 0.18 mm).
| Cylinder Head |
The cylinder head assembly incorporates the OHV valvetrain and must
remain within a warp limit of 0.002 inch (0.050 mm). Valve clearances
require adjustment, with intake valves set to 0.002 to 0.006 inch (0.06
to 0.14 mm) and exhaust valves set to 0.004 to 0.008 inch (0.11 to 0.19
mm). Intake valve stem outside diameter measures 0.2154 inch (5.47 mm),
while exhaust valve stems are slightly smaller at 0.2142 inch (5.44 mm).
Both intake and exhaust valve guides share an inside diameter of 0.2165
inch (5.50 mm).
This results in a stem-to-guide clearance of 0.0008 to 0.0017 inch
(0.020 to 0.044 mm) for intake valves and 0.0018 to 0.0028 inch (0.045
to 0.072 mm) for exhaust valves. Valve seat width is 0.0315 inch (0.8
mm) for both intake and exhaust. The valve springs have a free length of
1.38 inches (35.0 mm). Camshaft profiles for both intake and exhaust
lobes measure 1.115 inches (28.33 mm). The camshaft journal outside
diameter is 0.5504 inch (13.98 mm).
| Fuel System |
The MFS6BS employs a vertical butterfly-type carburetor for fuel delivery. The fuel pump is mechanically operated. The engine operates on unleaded gasoline with a minimum octane rating of 90 (Research Octane Number). Fuel consumption is rated at 2.0 liters per hour at wide-open throttle. The engine is typically supplied with a 3.2-gallon or 12-liter external remote fuel tank.
| Lubrication System |
Engine lubrication is maintained through a wet sump system. The system requires 0.47 US quart or 0.45 liter of engine oil meeting API service classifications SE, SF, SG, SH, SJ, SL, or SM. Recommended viscosity grades include SAE 10W-30 and 10W-40 for normal operating conditions. A low oil pressure warning indicator alerts the operator to unsafe operating conditions.
| Cooling System |
Cooling is accomplished through a forced water system, drawing water from the body of water in which the engine is operating. A water pump with a stainless steel housing , driven by the driveshaft, circulates cooling water through passages in the engine block and cylinder head. A thermostat regulates the flow to maintain optimal operating temperatures between 115 and 125 F.
| Mid Section and Lower Unit |
The mid section connects the powerhead to the lower unit and houses the driveshaft. The exhaust system is designed to route gases through the propeller hub for quieter operation. The lower unit contains a spiral bevel gear reduction system with a ratio of 2.15:1.
The gear shift mechanism is a dog clutch type, providing forward, neutral, and reverse functions through a side-mounted shift lever. The gearcase holds 0.21 US quart or 0.20 liter of gear lubricant, which must meet API GL5 specifications with a viscosity of SAE 80 or SAE 90.
| Trim and Tilt System |
The MFS6BS features a manual trim and tilt system. Trim angle adjustment is achieved by repositioning a thrust rod in one of six available positions on the stern bracket, which also provides a shallow water drive setting. The maximum tilt angle is 75 degrees.
The steering angle is 150 degrees, and an adjustable steering friction setting allows the operator to customize steering resistance. A tilt stopper mechanism locks the engine in the fully raised position for trailering or mooring.
| Propeller Information |
The MFS6BS is fitted with a three-bladed aluminum propeller as standard equipment. The propeller diameter is 7.9 inches or 200 mm. A range of pitch options from 6 to 9 inches (160 to 229 mm) allows adaptation to different boat loads and applications. Standard pitch offerings include 6, 7, 8, and 9 inches (160, 178, 203, and 229 mm).
The propeller nut must be torqued to the correct specification and secured with a new split pin. Propeller selection must allow the engine to operate within its recommended full-throttle range of 5000 to 6000 rpm.
| Dimensions and Weight |
The Tohatsu MFS6BS is offered in short, long, and extra-long shaft configurations. Overall length measures 26.7 inches or 680 mm. Overall width is 12.8 inches (325 mm). The short shaft version has an overall height of 42.3 inches (1020 mm) with a transom height of 17 inches (435 mm). The long shaft version stands 45.1 inches (1145 mm) tall with a 22-inch (560-mm) transom height.
The extra-long shaft version has an overall height of 50.2 inches (1275 mm) and a transom height of 27 inches (685 mm). Weight varies by shaft length. The short shaft model weighs 55.5 lbs (25.0 kg), the long shaft model weighs 57.3 lbs (26.0 kg), and the extra-long shaft model weighs 59.5 lbs (27.0 kg).
| Maintenance Data |
Routine maintenance is essential for reliable operation. The engine operates on unleaded gasoline with a minimum octane rating of 90. The engine oil capacity is 0.47 US quart (0.45 liter) of SAE 10W-30 or 10W-40 oil meeting API service classifications SE through SM.
The gearcase capacity is 0.21 US quart (0.20 liter) of hypoid gear oil meeting API GL5, SAE 80 or 90 specifications. Ignition timing is set at 25 degrees Before Top Dead Center. The specified spark plug is NGK DCPR6E, with a gap setting of 0.031 to 0.035 inch, or 0.8 to 0.9 mm. A maintenance schedule guides service intervals.
Every 50 hours of operation, gear oil level, propeller condition, and starter rope function should be checked. Every 100 hours, inspections should include spark plugs, fuel line, fuel tank cleaning, fuel filter, anodes, engine oil change, cooling system, water pump, valve clearance, carburetor, and ignition timing, along with a gear oil change. Spark plug replacement is recommended every 200 hours.
| Tightening Torques |
Precise fastener torque is critical for proper engine assembly and safe operation. Critical torque specifications include the cylinder head bolt at 25 Nm or 18.0 lb-ft. Connecting rod bolts require 12 Nm (9.0 lb-ft). The flywheel nut demands 50 Nm (37.0 lb-ft).
The oil drain bolt is torqued to 18 Nm (13.0 lb-ft). Oil pan bolts and pivot bolts are both set at 25 Nm (18.0 lb-ft). The pivot adjust nut requires 10 Nm (7.5 lb-ft). The oil pressure switch is torqued to 9 Nm (7.0 lb-ft). Recoil starter bolts are tightened to 4 Nm (3.0 lb-ft).
Stern bracket nuts require 13 Nm (9.0 lb-ft). Power unit mounting bolts are set at 7 Nm (5.5 lb-ft). When mounting the outboard to the boat transom, the clamp screws or mounting bolts must be tightened to secure the motor firmly. Spark plugs are installed at 18 Nm or 13.0 lb-ft.
| Boat Applications |
The Tohatsu MFS6BS is ideally suited for a range of small, lightweight
watercraft. Its compact dimensions and low weight make it a perfect
choice for dinghies and tenders used as auxiliary boats for larger
vessels. It is also widely used on small inflatable boats, where its
portability is a significant advantage. For recreational anglers
operating small jon boats or lightweight fishing skiffs, the MFS6BS
provides ample power for maneuvering in protected waters.
The Sail Pro version, with its long or extra-long shaft and available
alternator, is specifically designed as a reliable auxiliary power
source for small to medium sailboats, offering efficient thrust and
battery charging capability. The four-stroke engine's quiet operation
and low emissions make it suitable for use in environmentally sensitive
areas. The engine is also available in a version compatible with remote
controls, allowing for flexible helm installation on small center
console boats.
____________________________________________________________________________________
| Outboard Engines Technical Specifications |
| Small Engines Technical Specifications |
| Car Engines Technical Specifications |
| Industrial Engines Technical Specifications |