JohnH wrote:
If you read the initial 'bad day on the bay' post, you are aware that I had a
problem last Friday.

Inspected the boat on Monday. Found the cause of the smoke to be the overheating
of the insulation on the wiring harness which was laying on the exhaust elbow.
(Probably done by the manufacturer.) Also, the lack of water going through the
starboard exhaust caused the rubber section of exhaust pipe just below the elbow
to melt out, The smoke was due to all the melting rubber.

I removed both sets of risers and manifolds and the other damaged parts on the
starboard side of the engine (5.7L Mercruiser). The wiring harness was
repairable. The riser didn't have an obvious plug.

When the manifold was removed from the starboard side, I noticed a discoloration
in the exhaust port of the third cylinder from the front. By discoloration, I
mean a reddish (rusty) color. I didn't feel it, at the time, but today the
mechanic at the marina said it was wet when he looked at it a day later. The
mechanic didn't do anything further than look at it and feel the wetness with
his finger. I also, today, felt the same port on the manifold, and it was also
wet.

The mechanic wants to run a compression check on Monday. Now I'm concerned that
what I thought was a plugged up riser may be something much more serious.

Questions:

What could cause a wet exhaust port on one cylinder?

I asked &;

The cyl head casting is not too thick around the exhaust ports, so in
salt water, raw cooled, cast iron, etc etc. The "problem" with raw water
cooling is you can't let the salt water get too hot or the salt drops
out, around the exhaust port is where the most heat is.


If there is a problem with that cylinder, how could it have prevented water from
going through the riser?

Probably shouldn't of itself but; is there is salt buildup inside the
head generally? that would. Don't assume this particular leak was the
only cause of the overheat.


If I try to pour water through water channels in the riser, and it either comes
out or doesn't, can that diagnose a plugged riser?

I guess it can indicate a flow path, but it's less than pin holes that
develop near the hot spots which allow salt buildup inside & rusting.
The real fear is that the weeping very tiny "just looks a bit moist"
leaks will eventually allow water back into a cyl between uses, then an
hydraulic lock on start attempt is the risk.


The engine didn't sound like it was missing. On Monday we'll start it and see
what comes out of that exhaust port. (Without manifolds and risers, that should
be a disquieting experience!)

You can have a bad leak in the exhaust port &/or manifold & still run
OK. The exhaust pressure/flow keeps any water going in the right
direction. Starting it will not help much, nor a compression test, you
need to make sure the exhaust port (downstream of the exhaust valve) is
not leaking & a run or compression test won't help with that.


Thanks for any help. Smart assed comments about my lack of V8 expertise will
also be accepted.

I know it is scary bananas but if you take the head or (s) off & take
them to a machine shop, they will bolt them to a flat block of steel &
then pressure test the head itself (apparently it doesn't cost much),
this will find any leaks, into the combustion chamber or out of the
coolant side.

The advice is that chev heads would be so cheap there, just get another
set ex a wrecking yard from a car (run on antifreeze & rust inhib
coolant= good) have the valves serviced, if required & you'll be out
sooner & cheaper.

Harry couldn't lend you the union fund's boat any more than he has ever
owned any boat, he's just a socialist liar:-) (I had to say that for
form:-)

Good luck with it John.

K

John H

On the 'Poco Loco' out of Deale, MD,
on the beautiful Chesapeake Bay!