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Tohatsu M5B / M5BS two-stroke (102 cc) service guide

Oil, gear oil, spark plugs and the service schedule for the Tohatsu M5B / M5BS two-stroke (102 cc) (5 hp, two-stroke), from the factory service manual, plus how we service it in Hawaiʻi.

Models covered: Tohatsu M5B (369) and M5BS (369). 1 cylinder, 102 cc, bore 55 x stroke 43 mm, 5 PS at 5000 rpm, maximum speed running range 4500 to 5500 rpm, gasoline/oil mixture (TOHATSU ENGINE OIL) 50:1, water cooled with a rotary rubber impeller, recoil start, flywheel magneto C.D. ignition, Keihin Seiki BCK 21-15 carburetor, dog clutch, gear reduction 13:28, prop exhaust. M5B has a 2.5 L tank, M5BS a 13 L portable tank. Premix, no oil injection.

Quick answers

What two-stroke oil does a Tohatsu M5B / M5BS two-stroke use?
TOHATSU ENGINE OIL.
What is the fuel to oil ratio for a Tohatsu M5B / M5BS two-stroke?
50:1 gasoline to TOHATSU ENGINE OIL. Break-in after engine parts are replaced: 20:1 for about 10 hours.
What gear oil does a Tohatsu M5B / M5BS two-stroke use, and how much?
TOHATSU gear oil (#80). Quantity: Approx. 195 cc.
What spark plug does a Tohatsu M5B / M5BS two-stroke use?
NGK BP7HS10 or Champion L82YC, qty 1. Gap: 1.0 mm (0.9 to 1.0 mm); limit over 1.25 mm.
How often should a Tohatsu M5B / M5BS two-stroke be serviced?
The factory schedule lists: Initial 10 hours; Initial 20 hours; Every 30 hours; Every 50 hours; Every 100 hours; Every 200 hours. In Hawaiʻi's salt water we do a full yearly service every 200 hours or 1 year, whichever comes first, and a new engine needs its first (break-in) service.
When should the water pump impeller be replaced on a Tohatsu M5B / M5BS two-stroke?
The factory schedule says to replace it at 200 hours, and we follow that. In any case we never let it go longer than a year in Hawaiʻi's salt water.
What is the idle speed of a Tohatsu M5B / M5BS two-stroke?
850 to 900 rpm with the clutch in FORWARD; 1000 to 1050 rpm in NEUTRAL.
What is the propeller nut torque on a Tohatsu M5B / M5BS two-stroke?
Standard 8 (3 x 200 x 200); optional 7 for heavy loads and 9 for light loads.

Maintenance specs

Two-stroke oilTOHATSU ENGINE OIL
Fuel to oil mix50:1 gasoline to TOHATSU ENGINE OIL. Break-in after engine parts are replaced: 20:1 for about 10 hours
Gear oilTOHATSU gear oil (#80)
Gear oil quantityApprox. 195 cc
Gear oil upper and lower oil plugs2 oil plugs on the gear case.
Spark plugNGK BP7HS10 or Champion L82YC, qty 1
Spark plug gap1.0 mm (0.9 to 1.0 mm); limit over 1.25 mm
Spark plug torque2.5 to 3.0 kg-m (14 mm)
Idle speed850 to 900 rpm with the clutch in FORWARD; 1000 to 1050 rpm in NEUTRAL.
AnodesCheck for signs of wear every 3 to 6 months; replace if required
PropellerStandard 8 (3 x 200 x 200); optional 7 for heavy loads and 9 for light loads.

Service schedule

The factory maintenance intervals, with what is replaced and what is checked at each. Rows marked Hawaiʻi are our shop's yearly service for salt water use.

  1. Initial 10 hours

    Replace: gear case plug gaskets

  2. Initial 20 hours

    Replace: gear case oil, gear case plug gaskets

  3. Every 30 hours

    Replace: gear case plug gaskets

    Check: spark plugs

  4. Every 50 hours

    Replace: gear case plug gaskets, propeller cotter pin

    Check: fuel filter, gear case oil

  5. Every 100 hours

    Replace: gear case plug gaskets, propeller cotter pin

    Check: fuel filter, gear case oil, water pump impeller, anodes

  6. Every 200 hours

    Replace: gear case oil, gear case plug gaskets, propeller cotter pin, water pump impeller

    Check: fuel filter, anodes

Source: Tohatsu M5B/M5BS service manual. Specs can change by model year and serial number, so always confirm your exact model from the serial tag on the clamp bracket.

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