Replaceing Raw Water Impeller on a Yanmar

While you do not need to replace your impeller with every oil change best to replace yours before a failure. This is a simple procedure anyone can accomplish. The following is a 2GM20F which is similar too most common Yanmar configurations.

Tools
Sockets for removal of pump and pump cover.
Razor or gasket scraper.
Small hammer.
Impeller removal tool (if available).

Supplies
New impeller and gasket.
Lithium Grease

1).IMPORTANT TURN off the engine freshwater thru-hull.
2). Locate pump on starboard front of engine and remove the 2 mounting bolts. Slip belt off pump.

  Once removed loosen the hose clamps and rotate the pump so you can access the pump cover.

3). Remove cover nuts. A light tap on the side of the cover should it stick will make it pop right off.

4). Now with cover removed note the orientation of the impeller blades as you will set the new impeller blades in the same direction.

(you may not see the missing blade yet)

 5) Using an impeller tool if available or simply pull out the old impeller. If it is stuck you may pry out or  grab using slip joint pliers. Just do not score the pump surfaces.

6). Notice the missing blade on the old impeller. It is important to located all the missing blades to ensure no blockage occurs.

Usually blades will be just outside the pump outlet (the right hand side here). In this case the missing blade was found in the hose  before the heat exchanger.

7). Now clean the impeller cover carefully with a razor and remove all old gasket material.

(as the pump wears the cover plate will outline the irregular shape of the impeller gasket).

Applying Grease

 

8). Now liberally grease the impeller pump inside surface and shaft. This allows the pump to run dry until water starts flowing and assist removal of the impeller next time.

9) Reinstall the impeller with all blades oriented the same as the old one. Apply gasket following the same wear lines on the cover. Add cover plate again lining up the wear marks.

10). Tighten the cover nuts in a rotating fashion so you do not warp the pump or plate. Place pump on engine and insert mounting bolts. Make sure to re-tighten any hose clamps you may have loosened.

11). Replace belt and tension with hammer handle and Tighten mounting bolts.

12). Now IMPORTANT Open the thru-hull. Start engine and watch for water. It might take a few seconds for the pump to prime and water appear in the exhaust.

13). Make sure to check for leaks