How to Install a Johnson 50 Horsepower Water Pump

by Brenna Swanston ; Updated October 20, 2017

If the time has come to replace your boat's water pump, you might want to know how to install a new one on your own. A few different Johnson water pumps run with 50 horsepower, including the 1958-59, 1971-75, 1979-88 and 1989-2005 models, as well as some of the three-cylinder models.

Here's how to replace a Johnson 50 HP water pump:

Remove the Old Water Pump

Before you can start the installation process, you've got to remove the defunct water pump.

  1. Remove the Johnson lower unit from the boat.
  2. Remove the water pump's mounting bolts.
  3. Remove the O-ring from the drive shaft.
  4. Remove the water pump case.
  5. Check for sand, dirt and debris in the power head, and flush it out if necessary.
  6. Use a screwdriver to remove the impeller.
  7. Note the position of the plastic key, then remove and replace it.
  8. Clean the water pump key area.
  9. Use an emery cloth to clean up the shaft, if necessary.
  10. Remove the water pump tube screw.
  11. Remove the gasket compound from the lower unit.

Install the New Water Pump

Now it's time to get that new water pump in your boat. Follow these steps to do so:

  1. Mix the gasket sealing compound well.
  2. Clean the lower unit's water pump surface area.
  3. Place the gasket sealing compound on both sides of the gasket.
  4. Install the wear plate.
  5. Install the impeller key.
  6. Note the position of the key held by the wheel bearing grease.
  7. Install the pump cup in the pump housing.
  8. Line up the pump cup in the pump housing.
  9. Cover the impeller with wheel bearing type grease.
  10. Note the key-way location of the impeller before installing on the drive shaft.
  11. Install the grease impeller on the drive shaft.
  12. Note area for seal or O-ring area.
  13. Place the gasket sealing compound in the seal O-ring area.
  14. Install the large O-ring type pump housing seal
  15. Remove gasket compound from the pump cup.
  16. Place grease in impeller area of the pump cup.
  17. Turn the drive shaft in a clockwise direction, pressing down on the pump housing at the same time.
  18. Note the size of the new impeller and housing.
  19. Turn the drive shaft in a clockwise direction while pressing down.
  20. Rotate it four or five times until the impeller is seated.
  21. Install all bolts, turning them by hand two or three ties to line up with the pump housing.
  22. Complete bolt installation.
  23. Add the gasket compound to the bottom of the tub guide.
  24. Install a screw in the tub guide and base assembly.
  25. Install the grommet on the water pump base.
  26. Note the position of the grommet and the tub guide to ensure clearance.
  27. Clean the O-ring area on the drive shaft.
  28. Clean the spline on the drive shaft.
  29. Install the O-ring on the drive shaft.

About the Author

Brenna Swanston is a freelance writer, editor and journalist. She covers topics including environment, education, agriculture, travel, immigration and religion. She previously reported for the Sun newspaper in Santa Maria, Calif., and holds a bachelor's in journalism from California Polytechnic State University. Swanston is an avid traveler and loves jazz, yoga and craft beer.