How to Install a 40Hp Outboard Motor Water Pump

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You wouldn't risk a $5,000 outboard motor for want of a $60 water pump. Even if you aren't mechanically inclined, replacing an outboard water pump doesn't call for digging into the guts of the motor. You're opening a cover, replacing a part within the cover and pushing things back into place. With a wrench to remove a handful of nuts and a replacement part that only fits one way, when the water pump on your 40-horsepower outboard needs changing, change it yourself.

Items you will need

  • Old towels

  • Bench vise

  • Box-end wrench

  • Socket wrench

  • Waterproof marine grease

  • Pump replacement kit

  • Torque wrench

Wrap an couple of old towels around the jaws of your bench vise to hold the lower unit while you work. Tilt your motor up with the tilt control, just like you do when you trailer the boat. Disconnect the boat's battery cables to avoid an accident. Remove the two or three nuts on each side of lower part of the motor that keep the lower unit in place, using a box-end wrench.

Slide the lower unit straight out of the motor. The driveshaft and the shift shaft will come along, since they're attached to the lower unit, and a water tube will pull free of the water outlet as well. Take care not to bump the driveshaft or shift shaft and ignore the water tube. Set the unit upright in the vise and close the jaws just enough to hold the unit in place.

Locate the water pump, a plastic housing that sits atop the lower unit, completely surrounding the driveshaft. Remove the bolts at its corners with a socket wrench. Lift the housing to the top of the driveshaft and remove it.

Remove the part that looks like a six-sided star, the impeller, from the driveshaft as well. Find the comparable part in the pump replacement kit. Grease the ends of each of its vanes and the hole in its center with waterproof marine grease, and slide it back down the driveshaft.

Slide the pump housing, the first part you removed, down the driveshaft and line it up with the bolt holes on the top of the lower unit. Smear some thread locker on the bolts and thread them back through the housing and into the lower unit. Tighten them to 60 inch-pounds with a torque wrench.

Remove the lower unit from the vise and slide it back into place without bending the driveshaft or the shift shaft. Align the water tube so that it fits back into the water outlet. When the lower unit is all the way back on the motor, smear some thread locker on the studs that fit themselves through the mounting holes. Thread the nuts back onto the studs and tighten them to 55 foot-pounds.

Reconnect the battery cables. Lower the motor. Turn the ignition key to "off."


  • When you're working on your motor, remove the nut from the negative battery post, marked with the letters "NEG" or a minus sign, and lift the cable from the battery. This isolates the electrical supply from the boat's common ground, allowing you to work on the boat's electrical or mechanical systems without fear of the motor starting or another system being energized.
  • If you work on your outboard motor when your boat is on its trailer, or your motor is on a storage stand, remove the propeller nut with a 1 1/16-inch wrench and slide the thrust hub, propeller and washers from the propeller shaft. Failure to remove a propeller before operating an outboard out of the water during maintenance or long-term storage is an invitation to a propeller-strike injury, which can maim or kill.
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