Reply To: 1956 Evinrude Big Twin #25022 water pump

[frankr]

Bob Wight wrote:

There was an article on this topic on page 51 of the July 2018 Antique Outboarder on this bleed hole issue. Frank, how does this work when the length of the water tube rubber grommet blocks the outside hole?

The hole is drilled at an angle, from the pump outlet area, through to the well in the center. Thus, water flows into the well, providing a water seal to keep air/exhaust from entering the pump through the drive shaft hole. Yes, the grommet blocks the outer end of the hole, and no water squirts out there. What’s important is that the angled hole be open between the pump outlet area and center well.

BTW, the water intake screen is positioned so that at higher speeds, and in gear, the prop force-feeds the intake screen. In neutral, the prop is not feeding the intake screen, so you are depending on pump suction to draw water in. The pump is acting as a positive-displacement pump at slow speeds, so it has a bit of suction—but not much. At high speeds, the pump vanes flex back and the pump acts as a centrifugal pump, aided by the mentioned force-feed.

Clear as mud??