You can't easily add a zinc to an existing manifold. If you are having a new manifold fabricated, you have an extra 1/4 or 1/8 NPT port added that a standard pencil zinc will thread into.
Most marine engines have zincs on the heat exchanger. I am not sure where Yanmar puts theirs. Volvos (like my engine) are the most common exception to the rule and do not use cooling system zincs on most of their engines.
The Onan has a pencil zinc on the heat exchanger head on the end of the engine opposite the generator. If you haven't replaced it in a long time, you will likely need to replace the brass plug as well as the zinc pencil. If you haven't replaced it in a really long time, the brass plug can crumble when you try to remove it and make a simple project a messy one. And if you don't replace it for a really, REALLY long time, the brass plug can crumble on its own and flood the boat.
Rose Island, Bahamas
, wrote :
How did you attach zink to the raw water manifold?
I do not see zinks on the Yanmar or Onan.