How to Modify a Yamaha Outboard Water Pump

The Yamaha outboard water pump requires inspection after every 100 hours of operation, or once every boating season. The inspection process requires you to remove the pump and its impeller. If you replace the old impeller that's already stressed by 100 hours of operation, it is more likely to disintegrate under the stress of a new season. Since you already have the pump impeller off the driveshaft, you can give yourself some peace of mind for the coming season with a few extra steps.

Things You'll Need

  • Adjustable wrench
  • Bench vise
  • 13 mm box-end wrench
  • 7 mm open-end wrench
  • Marine grease
  • Pump impeller
  • Thread locker
  • Torque wrench
  • Propeller wrench
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Instructions

  1. Removing the Lower Unit

    • 1

      Shift the engine into "Forward" gear.

    • 2

      Take the lower unit's locknut and washer from the back, center of the cavitation plate, using an adjustable wrench. Remove the trim tab at the same time.

    • 3

      Remove the nuts from the four bolts holding the lower unit to the exhaust housing, using a 13 mm box-end wrench. Remove the bolts.

    • 4

      Grasp the lower unit securely and pull straight down and straight out of the outboard's exhaust housing. Position the lower unit in a bench vise.

    Removing and Installing the Pump

    • 5

      Loosen and remove the 4 pump mounting bolts and washers using a 7 mm open-end wrench. Lift and slide the water pump cover and gasket free of the driveshaft. Discard the gasket.

    • 6

      Lift the pump impeller free from the driveshaft and pull the impeller key from the notch in the driveshaft.

    • 7

      Dab marine grease onto the key and return it to the notch in the driveshaft. Position the new impeller on the driveshaft and push the impeller, turning it to fit it over the key.

    • 8

      Smear a thin coat of marine grease inside the pump cover. Push the upper pump gasket down the driveshaft, followed by the pump cover. Push the cover down the driveshaft and press it into place.

    • 9

      Dip the threads of the pump bolts in thread locker. Insert the bolts through the pump cover and thread them into the top of the lower unit. Tighten the water pump bolts to 60 inch-pounds, using a torque wrench and a crossing pattern.

    Installing the Lower Unit

    • 10

      Ease the lower unit into the exhaust tunnel without bumping either the driveshaft or the shift linkage on the sides of the tunnel. Position the water tube connection on the lower unit so it connects with the water tube in the exhaust tunnel.

    • 11

      Push the lower unit straight up. Align the bolt holes on the lower unit with those on the exhaust tunnel. Push the bolts up through the bores in both the lower unit and the exhaust tunnel. Secure the bolts in place with the nuts. Tighten the bolts to 40 foot-pounds.

    • 12

      Return the lower unit's lock nut and washer to its stud in the back, center of the cavitation plate. Tighten the nut to 22 foot-pounds.