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.

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

Tools Needed – Mercury 40 Lower Unit Removal

  • Ratchet
  • 14mm, 15mm, 16mm sockets
  • Flat blade screwdriver

Removing Mercury 40HP Lower Unit

Step 1. Remove the top cowling.

Mercury 40HP outboard top cowling removal

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.

Mercury 40 4-stroke lower unit diagram

Mercury 40 lower unit removal

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.

Mercury 40 outboard trim tab lower unit

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.

Mercury 40HP outboard lower unit removal

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.

Mercury 40 outboard gearcase removal

That was easy! 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.




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