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How to Remove the Lower Unit on a 120 HP Force

by Will Charpentier

Removing the lower unit of the Force 120-horsepower outboard motor, regardless of the reason for the removal, offers multiple maintenance opportunities. You can change the oil and inspect its condition, in addition to whatever required you to remove the lower unit in the first place. When you want or need to remove the lower unit, remember that there are five fasteners that hold the lower unit in place.

Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor. This will prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box. After the work is complete, reconnect the negative battery cable.

Position a clean 1-quart container beneath the lower unit. Unscrew and remove the drain plug from the bottom right side of the motor's propeller shaft housing, using a screwdriver. Remove the oil vent screws on the upper right side of the lower unit and allow the gearcase oil to drain from the lower unit.

Rub the gearcase oil between your fingers, feeling for bits of metal. Look at the oil and check for a pale thick appearance, like that of milk. The presence of bits of metal indicates serious damage to the gears, while a milky look to the oil indicates that water has penetrated the gearcase. Take the unit to your outboard dealer for further inspection.

Shift the motor into "Forward." Turn on the ignition switch and use the tilt/trim control to raise the motor fully. Move the tilt lock lever to the "lock" position to keep the motor fully tilted. Disconnect the negative wire from the boat's battery.

Make a mark with a grease pencil that extends from the center of the trim tab -- located on the underside of the anti-cavitation plate above the propeller -- onto the anti-cavitation plate. Remove the trim tab with a 14 mm socket.

Locate and remove the 14 mm retaining bolt formerly hidden by the base of the trim tab.

Remove the four lock nuts and washers -- two on either side of the lower unit "split" from the rest of the motor -- with a 14 mm thin-walled socket. Pull straight down on the lower unit to separate it from the rest of the motor.

Items you will need

  • Screwdriver
  • Clean 1-qt. container
  • Grease pencil
  • 14 mm socket
  • 14 mm thin-walled socket
  • 5/16-inch box-end wrench

References

  • "Force Outboard Repair Manual, 3 to 150 HP, 1984 - 1999"; Seloc Marine; 2007

About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.