How to Remove a Lower Unit
There are several reasons a boat owner, or mechanic, will need to remove the lower unit. Repairing, or replacing the fresh water impeller, or inspection and greasing of gears are just a couple common reasons to have to take the lower unit off. The lower unit is the term given to the bottom half of the drive unit located on the bottom half of the drive, which is located below the engine head on an outboard. It is sometimes protruding from the transom (back wall) with the engine inside the engine compartment on a stern drive.
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Things You'll Need
- Long neck screwdrivers (Philips and Flat)
- Transparent jar or oil pan
- Prop nut tool
- Needle nose pliers
- 3/8, 7/16, 5/8 and 9/16 inch sockets and wrench
- 9/16 gear wrench
- Gear oil
- Vice grip and bench (if drive or outboard is not on the boat)
- Heat gun, or torch
Instructions
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1
Place the outdrive or entire outboard in the vice grip and secure it to a workbench area if it is not still attached to the boat. If the drive unit is still attached to the boat drop the drive into the lowest position.
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2
Unscrew the drip stick screw from the top of the drive unit, and remove the oil drain plug from the bottom of the lower unit with a screwdriver. Let the oil drain from the unit. Collect the oil in a transparent jar so you can see the oil, or into an oil pan. Examine the oil for discoloration, milky appearance, or grit: all indicating a need to repair seals that keep water from entering the oil.
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3
Keep the screws, bolts and other pieces removed from the lower unit safe location to the side, in the order of removal so you know what order to replace them when putting the lower unit back on.
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4
If the drive is attached to a workbench, turn it upside down. If it is on the boat, lift the outdrive unit to the highest position so you can access the bolts underneath easier.
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5
Remove the prop if it is still on the unit by unscrewing the prop nut at the center of the prop with a prop nut tool. Lift the locking tab with a needle nose pliers, or the bottom pointed end of the prop nut tool. Pull the prop off of the prop shaft and place in a safe location.
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6
Remove the round disc metal anode located directly above the prop shaft by unscrewing the bolt and dropping the disc off of the drive.
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7
Use the 5/8ths and 9/16th sockets and the socket wrench to remove the bolts above the prop shaft that attach the lower unit to the upper drive unit. If they are loaded with calcium from water corrosion, soak them in oil, or use a heat gun or torch to heat them up enough to loosen the calcium deposits so you can remove them.
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8
Remove the two 9/16th bolts on each side of the top of the connecting platform between the upper and lower unit with a 9/16 gear wrench.
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9
Slide the lower unit off of the connecting pins on the upper unit. If the two pieces are stuck together with corrosion tap them with a hammer to loosen the bond, or for more severe cases, heat with a torch or heat gun and then let cool. The expanding and contracting from the heating and cooling process will aid in breaking the seal.
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Tips & Warnings
Different brands of outdrives have specifics that are unique to themselves, certain connecting gears, or shaft connections that need to be take apart in a certain way. Always consult the service manual for your particular drive before attempting to remove it. The steps above are common to all drives in order to complete the basics for removing the lower unit.
Always try other methods of loosening bolts, screws or metal connections first before employing heat. Be careful not to overheat any part of the lower unit to the point it could ignite oil or gas fumes from the engine.
References
- Photo Credit propeller image by Gonçalo Carreira from Fotolia.com
