How to Rebuild a Johnson 6HP Outboard Water Pump

The first thing you should do after buying a second-hand outboard is replace the water pump impeller

A water pump failure can burn out the motor completely. Whether the outboard is just a year or 40 years old, make changing out the water pump's impeller a priority. 

Johnson 6HP outboard motor

This guide walks you through replacing the impeller and rebuilding the water pump on a 1978 Johnson 6HP 6R78B outboard. Watch the video above and follow the guide below to learn how to rebuild an outboard motor's water pump.

Tools and Parts Needed - Johnson 6HP Water Pump Rebuild

Tools 

  • Ratchet and extension
  • 10mm socket
  • Flathead screwdriver
  • Pliers

Parts 

Disassembling a Johnson 6HP Outboard Water Pump

Step 1. Put the outboard in the forward gear position.

Step 2. Remove the four 10mm bolts holding the lower casing/gear casing in place. Prevent the casing from sliding down as you remove the last 10mm bolt.

Johnson 6HP outboard engine water pump rebuild

Step 3. Lower the gear casing by a couple of inches, then loosen the 10mm bolt that connects the shift shaft between the upper and lower casings.

NOTE: The bolt has a notch in its head so it can be loosened with a flathead screwdriver.

Johnson 6HP outboard motor gear casing

Step 4. Once the shift shaft bolt is loosened, rotate the lower unit as you pull it down to disengage the shift shaft. Next, remove the lower casing completely.

Johnson 6HP outboard motor lower casing

Step 5. Remove the four screws or bolts from the water pump housing.

PRO TIP: If the water pump still has the original screws, 'shock' the screws before trying to loosen them. To shock the screws, place a screwdriver on them and hit the screwdriver with a hammer. Shocking the screws helps to break them loose and reduces the chance of them shearing off in the gear casing.

Johnson 6HP outboard water pump housing

Step 6. Gently pry the water pump housing up and off the gear casing using a flathead screwdriver. Be careful not to damage the mating surfaces of the lower casing.

Step 7. Slide the impeller off the input shaft if it didn't come off with the housing.

Step 8. Remove the woodruff key from the input shaft, and slide the impeller housing plate off the shaft.

Johnson outboard motor impeller replacement

Rebuilding a Johnson 6HP Outboard Water Pump

Step 1. Install the new impeller housing plate (included in the water pump repair kit), making sure the small tab on the plate is pointing upward.

Step 2. Install the new water pump gasket (included in the kit) and tap the new woodruff key (also included) into place in the input shaft.

Johnson 6HP outboard water pump rebuild replacement

Step 3. Grease the inside of the metal impeller cup (included in the kit), and press the impeller into the cup while rotating it clockwise so that the impeller's blades are twisted the correct way once it's in the cup. 

Johnson 6HP outboard water pump impeller

Step 4. Install the new impeller and cup back onto the input shaft, making sure to line up the notch in the impeller with the woodruff key.

Johnson 6HP outboard woodruff key

Step 5. With the cup installed, rotate the input shaft so the fin on the cup lines up with the cutout in the gasket.

Step 6. Install the new water pump housing (included in the kit).

Step 7. Apply anti-seize lube to the four new water pump housing bolts (included in the kit) and tighten the bolts.

NOTE: The water pump housing is plastic and can easily be broken, so don't over-tighten the bolts.

Step 8. Grease the new water tube grommet (included in the kit) and install it into the water pump housing. Make sure the two pegs on the grommet are seated in the two holes in the housing.

Johnson outboard motor water pump rebuild

Step 9. Grease the splines at the top of the input shaft and grease the inside of the water tube grommet.

Step 10. Make sure the gear shift linkage is fully up. To do this, grip it with a pair of pliers and gently pull it upwards.

Johnson outboard engine 6HP water pump repair

Step 11. Slide the lower casing back onto the outboard, making sure the input shaft slides back into the powerhead; the water pump housing engages with the water pipe; and the shift linkage engages with the shift shaft.

Johnson outboard 6HP motor

Step 12. Tighten the shift shaft bolt, and reattach the gear casing back up to the upper casing with the four 10mm bolts. Apply anti-seize to the 10mm bolts before reinstalling them and you're done.

Johnson 6HP water pump rebuild

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