351-00011-0 Tohatsu PISTON RING (STD)

Illustration 1 g00281790
7W-2743 Electronic Speed Switch (ESS)
Table 1
(1) 75% Verify button.     (4) Seal screw plug for adjusting the overspeed.    
(2) Reset button.     (5) Seal screw plug for adjusting the crank terminate speed.    
(3) LED overspeed light.     (6) Seal screw plug for adjusting the oil step pressure speed setting.    The electronic speed switch (ESS) is a single unit that contains controls which monitor four functions at the same time:
Engine overspeed
Crank termination
Oil step latch
Engine oil step pressureTwo different electronic speed switches are used. The switches are only different in the location of the mounting holes. The ESS is mounted in the junction box.Engine Overspeed (OS)
Engine overspeed is an adjustable engine speed setting. The normal setting is 118% of rated speed. The setting prevents the engine from running at a speed that could cause damage to the engine. An engine speed that is greater than the engine speed setting will close a switch which shuts off the fuel to the engine. If the optional air inlet shutoff is provided, the switch will also shut off the inlet air.Crank Termination
Crank termination is an adjustable engine speed setting that signals the starter motor that the engine is firing and the cranking must be terminated. A switch will open in order to stop the current flow to the starter motor circuit when the engine speed setting is reached. The starter motor pinion gear will then disengage from the engine flywheel ring gear. Oil Step Latch (3500 Series Engines)
The setting of the oil step latch is not adjustable. After (ESS-17) on the terminal strip of the junction box has been energized by the loss of engine oil pressure, the contacts of the oil pressure step switch are held in the closed position. The oil pressure step switch will remain closed until 2 seconds after the engine has completely stopped. This action will prevent the shutoff from resetting below the oil step speed setting. Engine Oil Step Pressure (3500 Series Engines)
Engine oil step pressure is an adjustable engine speed setting that gives protection from engine failure which is caused by too little engine oil pressure for a specified speed range. In order to maintain oil pressure protection throughout the complete speed range of operation, two different engine oil pressure switches are used. Switch (OPS1) has a low pressure rating and switch (OPS2) has a high pressure rating. The engine oil pressure switches are mounted in the engine oil manifold that is located on the rear side of the junction box.The following conditions are for the operation of the oil step latch:
An engine that uses an oil step latch must maintain an oil pressure that is greater than the rating of the low oil pressure switch (OPS1) when the engine runs below the oil step pressure speed setting.
An engine that uses an oil step latch must maintain an oil pressure that is greater than the rating of the high oil pressure switch ("OPS2") when the engine runs above the oil step pressure speed setting.If one of the two conditions for the engine oil pressure are not correct, the low oil pressure alarm switch (LOPAS1) or (LOPAS2) will energize an alarm. OPS1 or OPS2 also energizes the slave relay (SR1). This process de-energizes the fuel solenoid which shuts off the fuel flow to the engine.The oil pressure switches and the alarm switches are mounted in the engine oil manifold that is located on the rear side of the junction box. The slave relay is mounted in the junction box.Magnetic Pickup (MPU)
Illustration 2 g00281827
Generation of the Magnetic Pickup Signal (1) Clearance dimension. (2) Magnetic pickup. (3) Wires to connector. (4) Locknut. (5) Flywheel housing. (6) Flywheel ring gear.The magnetic pickup is a permanent magnet generator with a single pole. Wire coils surround a permanent magnet pole piece. When the teeth of the flywheel ring gear (6) rotate through the magnetic lines of force that are around the magnetic pickup pole (2), an AC voltage is generated. A positive voltage is generated when each tooth rotates by the pole piece. When the space between the teeth rotates by the pole piece, a negative voltage is generated. Engine speed is measured by the frequency of these signals.
Illustration 3 g00293065
(2) Magnetic pickup sensor that is mounted in the flywheel housing.The magnetic pickup is mounted through the flywheel housing (5) .Oil Pressure Switch (OPS)
Illustration 4 g00281830
Oil Pressure SwitchThe engine oil pressure switch uses a spring loaded piston in order to activate an internal microswitch that is set for a specific pressure rating. This microswitch is very accurate over the operating temperature range. The microswitch also has a high electrical contact rating which improves reliability.
Illustration 5 g00293068
(1) Oil pressure switch (OPS1). (2) Low oil pressure alarm switch (LOPAS1).The engine oil pressure switches and the alarm switches are mounted on the engine oil manifold that is located on the rear side of the junction box.3200 Series, 3300 Series, and 3400 Series Engines
The low oil pressure alarm switch is an optional part. Low oil pressure causes the low oil pressure alarm switch (LOPAS1) to energize an alarm. The oil pressure switch (OPS1) energizes the slave relay (SR1) which then de-energizes the fuel solenoid (FS). This process stops the fuel flow to the engine.3500 Series Engines
The operation of the oil pressure switches are described in the "Engine Oil Step Pressure (3500 Series Engines)" section of this manual.