Thanks everyone for the answers!

Tim wrote:

I'd change it ASAP, but for the heck of it, remember..you can't tear up
junk

Some of the other guys said it very easily might not be junk. Does this
mean I shouldn't run it for twenty hours cruising around with my family
this weekend before changing the head gasket?

In case you forgot any of the details of my engine here is my original post:

-----
I have a '79 Yanmar 2QM15 on my Hunter 33 that runs smoothly at some RPM
and clanky at others, with black smoke at start up and sometimes for a
while with heavy loads. I noticed very tiny air bubbles and a very small
amount of oil dripping from the head gasket just under the forward cylinder.

Not sure how many hours the motor has on it. It starts kind of hard too
but seems to be improving the more I run it. Anyway, I'm afraid to put
too much money into the motor because I don't know what shape the bottom
end is in. I have a guy who will change the gasket for $300, $85 for all
the gaskets.

Anyway, is it surely bad to run the motor much with the gasket like
that? Must I change it ASAP? I want to take the family cruising around
on some easy cruises this weekend. We have a backup motor. Bad idea? Any
other advise about what I should look for during the head gasket change
when I finally do it?

Thanks for any help!
------


I'd pull the valve cover first, and re-torque the head bolts. it's
possible that the bolts at the front of the head may have come loose or
have probably streached.

My half-whacked diesel mechanic seems to think there is no point in
trying this. Maybe I should insist. Or, um try it before I go on the
trip, um, because it will only take an hour or so to do?

that wouldn't be a permanent fix by any means.
but should "get you by" for a while. But don't stall a good repair. I
can understand that you don't want to put a lot of money in an engine
repair, but then again, you don't want to ruin an expensive head
either.

Those engines have a very tough lower end


Helpful, thanks! Are there any signs I should look for to shut down the
engine to avoid damage, if I live dangerously and go on the cruise this
weekend? Um, if you all recommend that, that is?

--
Stephen