It seems like the YM's are destined to replace all of the GM's, but I
think the 1GM is still being sold.

The GM and YM series (and others) are rated at or about 3600 RPM.
I've always felt that 3000 is a reasonable cruising rev for my 2GM's,
but a friend who repowered with a 3YM says that everyone has told him
to run all day at 3400 to 3600.


Denis Marier wrote:
Correct, the earlier 2 GM are raw water cool.
Both of my friend have 1982 Yanmar 2 GM that are raw water cool.
BTW. my raw water cool 1982, 1 GM Yanmar was used in sea water all these
years. That is from May to October of every year and winterized with
antifreeze. Now it is completely disassemble and it does not show signs of
rust damages.
The yearly replacement of the internal zinc anodes in the engine and on the
propeller shaft may have something to do with it.
The Yanmar International Rep. stated that the 1 GM raw water cool Yanmar
(6.5 HP) was introduced for use in fresh water mainly the great Lakes. The
more recent 10 GM Yanmar is designed to produce 10 HP at 3300 RPM's.
Correct me if I am wrong but I hear that this 10 GM may be on its way out to
be replaced by the new fresh water cool Yanmar 2YM15 producing 13 HP at 3400
RPM's. Other manufacturers are rating their engine at 3000 RPM. Westerbeke
are rating their 12 C, 12 HP at 3000 RPM.