A Johnson outboard motor's lower unit contains the propeller shaft or, in the case of the jet drive, an impeller shaft. It also houses the drive gears, the driveshaft that comes down from the engine and the water pump that cools the motor. There are slight differences between the method for removing a light duty lower unit, most often found on motors of less than 70 horsepower, and for removing a heavy duty lower unit used on motors of 70 horsepower and up. The method for removing the jet drive is the same, regardless of its horsepower.
Items you will need
Needle-nose pliers
Socket wrench
5/8-inch socket
9/16-inch socket
Heavy Duty Lower Unit for Four- and Six-cylinder Models Including 70 HP and Up
Remove the propeller from the propeller shaft. Ensure the gear shift is in the "Neutral" position. Use a pair of needle-nose pliers to remove the cotter pin from the shift rod connector on the front face of the motor, just below the motor's swivel bracket, and discard the pin.
Unscrew the trim tab retaining bolt and remove the trim tab. Remove the seven bolts threaded upward from the lower unit into the motor's midsection with a 5/8-inch socket wrench: three bolts are on each side of the lower unit, and the seventh is the bolt inside the cavity beneath the removed trim tab.
Pull straight down on the lower unit, taking care not to bend the driveshaft or shift rod. The water tube will pull free from the rest of the motor.
Light Duty Lower Unit for Two-cylinder Motors Including 40, 48 and 50 HP Models
Remove the shift rod screw that protrudes from beneath the engine cover. Remove the lower unit bolt that's threaded upward beneath the anticavitation plate in front of the trim tab with a thin-walled, 5/8-inch socket.
Unscrew the two bolts on each side of the lower unit that are threaded upward from the lower unit into the exhaust housing of the motor.
Pull the lower unit straight down, without bending the driveshaft or shift rod or damaging the water tube.
Jet Drive
Unscrew all six bolts that secure the intake housing to the jet housing assembly with a 5/8-inch socket. Bend the lock tab washer back from the impeller nut with a pair of pliers. Remove the impeller nut with an adjustable wrench. Remove and discard the lock tab washer.
Remove the impeller and any shims installed below it. Remove the impeller key and sleeve and any shims installed above the impeller. Unsnap the shift link from the reverse gate.
Unscrew the 9/16-inch adapter-to-jet-housing bolt threaded downward from the adapter flange to the jet housing. Remove the four bolts underneath the jet drive assembly inside the impeller cavity that are threaded upward into the adapter. Lower the jet drive assembly from the adapter.
Warnings
- Always disconnect the negative cable from the battery before beginning any mechanical work on your motor.
Tips
- Keep track of all of the jet drive shims, even if the impeller is being replaced. The shims give a starting point for making adjustments. Also, keep close track of the bolts: these are different lengths and must return to their original mounting holes. Note, too, that the jet drive bolts are outboard from the bearing housing.
References
- "Johnson Outboards 1.25-70HP 2001-2009 -- Lower Unit/Gearcase Assembly -- 70 Hp (1298cc) EFI Motors; 2009
- "Johnson Outboards 1.25-70HP 2001-2009 -- Lower Unit/Gearcase Assembly -- 2-Cylinder Motors Including 40 (Except 40RW, 40RP and 40WR), 48 and 50 HP Models"; EFI Motors; 2009
- "Johnson Outboards 1.25-70HP 2001-2009 -- Lower Unit/Gearcase Assembly -- Jet Drive Assembly -- Removal and Installation"; EFI Motors; 2009
Tips
- Keep track of all of the jet drive shims, even if the impeller is being replaced. The shims give a starting point for making adjustments. Also, keep close track of the bolts: these are different lengths and must return to their original mounting holes. Note, too, that the jet drive bolts are outboard from the bearing housing.
Warnings
- Always disconnect the negative cable from the battery before beginning any mechanical work on your motor.
Writer Bio
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.
