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

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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 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.

Mercury 40 trim tab lower unit

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. 

Mercury 40 outboard gearcase removal

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

Mercury 40HP outboard gearcase removal

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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