Mercury 40HP Outboard Lower Unit Removal

Whenever you need to service your outboard’s water pump or replace the input/output shaft seals, you’ll have to remove the lower unit first.

Watch the video above and follow the steps below to remove the lower unit from a Mercury 40HP four-stroke outboard engine. 

Tools – Mercury 40 Lower Unit Removal

• Ratchet
• 14mm, 15mm, 16mm sockets
• Flat blade screwdriver
• Soft-blow hammer

Removing Mercury 40HP Lower Unit

Step 1. Remove the top cowling.

Step 2. Disconnect the shift shaft linkage by pushing the plastic retainer clip up off the shift shaft assembly, then pushing it to the left to release the retainer.

Step 3. Mark the trim tab and lower unit so you can reinstall the tab in the correct alignment when you reinstall the lower unit to the outboard.

Step 4. Remove the trim tab bolt and the trim tab, followed by the 15mm lower unit mounting bolt hidden beneath the trim tab.

Step 5. Support the lower unit to prevent it from dropping, and remove the four 16mm lower unit mounting bolts from around the top of the lower unit.

Step 6. Remove the lower unit from the outboard. 

PRO TIP: If the lower unit doesn’t come off the outboard, tap it with a soft-blow mallet to loosen it up.

So now that you have the lower unit removed from your Mercury outboard, what’s next? Are you replacing the water pump impeller or the pump itself? Watch the video below to see how to replace a Mercury 40 water pump.