How to Replace the Propeller on a Mercury Outboard

by Will Charpentier

Replacing the propeller, a normal part of preparing your Mercury outboard for winter storage or the spring season's fitting out, is a straightforward mechanical process. The newest version of the propeller hub, the Flo-Torq IV drive hub, maximizes the flow of exhaust gases around the propeller, but involves the installation of more parts on the shaft and in the propeller hub than days past, when you merely had to shove the propeller on and tighten the nut.

Move the throttle/shifter handle into neutral. Bend the tabs on the propeller nut retainer away from the propeller nut with a pair of pliers. Place a plank between the propeller and the anti-cavitation plate--the horizontal fin above the propeller--to jam the propeller in place, keeping it from turning while you remove it.

Remove the propeller nut by turning it counterclockwise with an adjustable wrench. Remove the plank and slide the propeller from the shaft.

Slather the splines of the propeller shaft with white marine grease. Slide the forward thrust hub and the replaceable drive sleeve over the propeller shaft. Turn the propeller so that the octagonal hole in the middle of the propeller aligns with the octagonal replacement drive sleeve, and press the propeller onto the sleeve.

Slide the thrust hub through the center of the propeller and into the center of the replaceable drive. The propeller shaft will protrude through the thrust hub. Slide the propeller nut retainer back onto the propeller shaft.

Thread the propeller nut onto the propeller shaft and slide the plank between the blades of the propeller and the anti-cavitation plate. Tighten the propeller nut with a torque wrench; torque the nut to 55 pound-feet, or 75 Nm. Bend the tabs of the propeller nut retainer over the propeller nut.

Items you will need

  • Pliers
  • Plank
  • Adjustable wrench
  • White marine grease
  • Torque wrench

Tip

  • Lay the new propeller parts out in the order of installation on the propeller shaft before you start working.

About the Author

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.