Don (and Ian),
I'm away from my boat and it's 3GM30F manual, but two things . . . .
First, I know that my 30GM30F is the fresh water version with heat
exchanger, and it has no zincs. However, I am pretty sure that the manual
describes procedures for replacing zincs in the sea water cooled version.
Yanmar has an online forum and help desk which I have found useful,
Yanmarhelp.com.

Good luck,
Scott


"Ian Malcolm" wrote in message
...
David&Joan wrote:

Don:

There are no zincs on a Yanmar 3GM engine, at least not on the few I have
owned. The raw water heat exchanger has cupro-nickel tubes and Yanmar
obvously believes that they won't corrode enough to warrant zincs.

David
Funny, my GM series service manual has details of how to change the zinc
on 1,2 and 3GM and the newer 1GM10, 2GM20 and 3GM30 engines.
SNIP