From: rrusk@ssd.csd.harris.com (Bob Rusk)
Newsgroups: rec.boats
Subject: Re: Alpha I Stern Drive Question
Date: 15 Dec 92 15:12:06 GMT
	<1992Dec15.134750.1724@msdhsv.ingr.com>
Reply-To: rrusk@ssd.csd.harris.com
Organization: Harris Computer Systems Division

On Tue, 15 Dec 1992 13:47:50 GMT, scott@bell.b17a.ingr.com (Scott Bell) wrote:

>In article <1992Dec14.165012.27113@tc.fluke.COM>, bmyers@tc.fluke.COM (Bob Myers)
>writes:
>|> 
>|> Has anybody seen this before?

>    Unfortunately, yes.
>|> 
>|> The Corbett II is powered by a 260 HP Mercruiser Alpha One stern
>|> drive.  It's a 1990 model with 91 hours.
>|> 
>|> When warming it up yesterday, I noticed something unusual.  Shortly after 
>|> starting, while idling, some of the bubbles 
>|> churned by by the exhaust contained some sort of oil or gas.  As
>|> they burst they created tiny sheens on the water.
>|> 
>   << description of engine operation while cold deleted.. >>
> 
>|> Last time I ran the boat at speed, there were no problems.  Running the drive
>|> at the dock in forward or reverse causes no unusual sights nor sounds.
>|> 
>|> My speculation is that the bubbles are caused buy either miscellaneous engine
>|> oil being blown through the exhaust when the engine is cold (and hasn't been 
>|> run for a week or more) and/or gas from the rich mixture at cold start.
>|> 
>|> Anybody have any thoughts on this curiosity?

>    My Evinrude OB does the same thing, and I haven't been able to fix this 
>    either. It always happens when the engine is first started and/or cold,
>    like you described. This is basically because the engine is fuel rich upon
>    first starting, which has too much oil/gas to initially burn it all up. Also
>    when the engine warms up, the piston rigns 'hug' the cylinder wall better.
>    This probably doesn't cause the oil/fuel blow-by, though.

>    If you let your engine sit awhile it will probably do the same thing, even
>    when warm. This is because some of the oil may still be in the exhaust 
>    manifold/outlet, and not burned off. I wonder if VRO's do this?

>    Any thoughts?

For your Evinrude (especially non-VRO models), this is normal.  You burn a
mixture of oil and gasoline in this engine.  At low-speed conditions, your
two-stroke powerhead does not burn the fuel/oil charge sufficiently to
avoid having some gas/oil dumped out in the exhaust.  This is worse when
the engine is cold and combustion is even more incomplete.

The MerCruiser is just a 350 Chevy in drag.  It is a four-stroke engine,
and burns straight gasoline.  Oil and fuel do not normally get mixed in
any great quantity in the MerCruiser, hence there should not be any oil
in the exhaust.

On the MerCruiser, I would keep an eye on the oil level.  If it's not using
much/any oil and it's running well, I would learn to live with the problem.
It may well be that your valve seals are bad.  This is common on engines that
sit for long periods, although I wouldn't expect to see it on a two-year-old
engine that hasn't seen heavy use or been overheated.

I would also take a look at the oil in the gearcase and in the power trim
pump.  This is a long shot, but if either looks creamy, you've found the
probable source of the oil, and your vigilance may have saved you some
expensive repairs.  If this is the case, get it fixed quickly.

--
 Bob Rusk
 rrusk@ssd.csd.harris.com
 My thoughts, probably not Harris'.