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Tohatsu M2.5A2 Specifications
| Engine Model: Tohatsu M2.5A2 |
| Engine Type: 2-stroke 1-cylinder gasoline outboard engine |
| Total Displacement: 4.6 cu.in (74.5 cc) |
| Rated Engine Power: 2.5 Hp (1.8 kW) at 5200 rpm |
| Fuel System: Carburetor |
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| General Technical Data |
The Tohatsu M2.5A2 is a two-stroke,
single-cylinder gasoline outboard engine. The engine displacement
measures 4.6 cubic inches or 74.5 cc, achieved through a cylinder bore
of 1.85 inches (47.0 mm) and a piston stroke of 1.69 inches (43.0 mm).
The powerhead produces a maximum output of 2.5 Hp, equivalent to 1.8 kW.
The engine is designed to operate within a wide-open throttle range of
3800 to 5200 rpm, with a trolling speed of 1100 rpm. Lubrication is
provided by oil mixed directly with the gasoline. The engine utilizes a
forced water cooling system and expels exhaust underwater. Ignition is
handled by a flywheel magneto Capacitor Discharge Ignition (CDI) system.
Starting is accomplished through a manual recoil starter.
| Powerhead |
The cylinder block of the M2.5A2 is machined to precise tolerances. The cylinder bore inside diameter is specified at 1.850 to 1.851 inches, or 47.00 to 47.01 mm. Pistons are manufactured to provide a piston-to-cylinder clearance of 0.0023 to 0.0035 inch (0.06 to 0.09 mm).
The piston ring end gap measures 0.007 to 0.013 inch (0.18 to 0.33 mm), with a piston ring side clearance of 0.0004 to 0.002 inch (0.01 to 0.05 mm). The piston-to-piston pin clearance is 0.0002 to 0.0006 inch (0.005 to 0.016 mm). The connecting rod big end side clearance is set at 0.0051 to 0.0125 inch (0.13 to 0.32 mm).
| Fuel System |
The M2.5A2 employs a carburetor for fuel delivery. The engine operates
on a fuel mixture of unleaded gasoline with a minimum octane rating of
87 and genuine two-stroke outboard oil meeting TCW-III specifications.
The recommended fuel-to-oil ratio is 50:1, meaning 50 parts unleaded
gasoline to 1 part genuine two-stroke engine oil. The engine features a
1.40-liter (1.47 US quart) integral fuel tank. Fuel consumption is rated
at 0.4 liters per hour. The system includes a fuel cock and an air vent
screw on the fuel tank cap for proper operation.
| Lubrication System |
Lubrication for the M2.5A2 is achieved through the pre-mix system. Engine oil meeting TCW-III specifications must be thoroughly mixed with the gasoline in the fuel tank at a 50:1 ratio before operation. There is no separate engine oil sump or pump.
| 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, driven by the driveshaft, circulates cooling water through passages in the engine block and cylinder head to maintain operating temperatures. The system is designed to be flushed with fresh water after operation, particularly in salt or brackish conditions, to prevent corrosion and deposit buildup.
| 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 underwater for quieter operation. The lower unit contains a bevel gear reduction system with a ratio of 1.85:1.
The gearcase holds 0.10 US quart or 0.09 liter of gear lubricant, which must meet API GL5 specifications with a viscosity of SAE 80 or SAE 90. The gear shift mechanism provides only forward gear, with neutral being achieved when the engine is not in gear and reverse requiring the engine to be turned on its swivel bracket.
| Trim and Tilt System |
The M2.5A2 features a manual trim and tilt system. Trim angle adjustment is achieved by repositioning a thrust rod in one of four available positions on the stern bracket to suit the boat's running attitude. The maximum tilt angle is 70 degrees. For full tilt-up, a tilt stopper is provided to hold the engine in the raised position when the boat is not in use, which helps protect the propeller and lower unit.
| Propeller Information |
The M2.5A2 is equipped with a three-bladed propeller. The propeller diameter measures 7.4 inches or 188 mm. A range of pitch options allows adaptation to different boat loads and applications. Standard pitch offerings include 5.7 inches (145 mm) and 7.0 inches (177 mm). Propellers are available in both aluminum and plastic materials. Propeller selection should ensure the engine operates within its recommended full-throttle range of 3800 to 5200 rpm.
| Dimensions and Weight |
The Tohatsu M2.5A2 is offered in both short and long shaft configurations. Overall length measures 21.7 inches or 550.0 mm. Overall width is 13.6 inches (345.0 mm). The short shaft version has an overall height of 37.6 inches (955.0 mm) with a transom height of 17 inches (435 mm). The long shaft version stands 42.6 inches (1080.0 mm) tall with a 22-inch (560-mm) transom height.
Weight varies slightly by shaft length. The short shaft model weighs 27.5 lbs (12.5 kg), while the long shaft model weighs 28.6 lbs (13.0 kg). These weights make the M2.5A2 one of the most portable outboard motors available.0
| Maintenance Data |
Routine maintenance is essential for reliable operation. The engine operates on a fuel mixture of unleaded 87 octane gasoline and TCW-III two-stroke oil at a 50:1 ratio. The gearcase capacity is 0.10 US quart (0.09 liter) of GL5 SAE 80 or 90 gear oil. Ignition timing is set at 20 degrees Before Top Dead Center.
The specified spark plug is NGK BP6HS-10 or BPR6HS-10, with a gap setting of 0.035 to 0.039 inch, or 0.9 to 1.0 mm. A maintenance schedule guides service intervals.
Every 50 hours of operation, inspections should include spark plug condition, fuel line integrity, fuel tank cleaning, anode condition, gear oil level, propeller condition, and starter rope function.
Every 100 hours, the cooling system, water pump, and carburetor should be checked. Gear oil changes and spark plug replacement are 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 11 Nm or 8.2 lb-ft. The magneto nut requires 44 Nm (32.5 lb-ft). Stern bracket nuts are torqued to 15.5 Nm (11.5 lb-ft).
The emergency stop switch should be tightened to 2.5 Nm (1.9 lb-ft). When mounting the outboard to the boat transom, the clamp screws or mounting bolts must be tightened to 30 Nm or 13 lb-ft to ensure the motor is securely fastened. Spark plugs are installed at 27 Nm or 20.0 lb-ft.
| Boat Applications |
The Tohatsu M2.5A2 is ideally suited for a range of small, lightweight
watercraft. Its compact dimensions and exceptionally 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. Sailboat owners frequently
use the long shaft version as a reliable and easily stowable auxiliary
power source.
For recreational anglers operating small jon boats or lightweight
fishing skiffs, the M2.5A2 provides ample power for maneuvering in
protected waters. The simplicity of its two-stroke design and manual
operation makes it particularly accessible for beginners and those
seeking a low-maintenance, hassle-free boating experience.
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