Hello,

Just took the boat out and was running fine until i lost major power.
Couldnt go above 3k rpms. Checked the merc 3.0 and saw one spark plug
cable off. So i grabbed it and received a hell of a jolt and noticed the
spark plug had actually broken off clean. Anyone see this happen before?
Any damage by running on 3 cyclinders for about an hour?

TIA!

Shouldn't be any problems unless you want to run it long periods. If you can
remove the damaged plug without dropping the porcelain into the cylinder and
scouring the walls. It will of course run inefficiently and will have to
carry those extra parts and their movement. The fuel will still go into the
cylinder and of course not be burnt, then creep down past the rings and into
the oil. This should just burn off when you reach higher temps, but an oil
change wouldn't hurt, or a oil additive. You should be ok. Correct it
immediately though. Don't go water-ski until it is fixed.










"jim" wrote in message
...
Hello,

Just took the boat out and was running fine until i lost major power.
Couldnt go above 3k rpms. Checked the merc 3.0 and saw one spark plug
cable off. So i grabbed it and received a hell of a jolt and noticed the
spark plug had actually broken off clean. Anyone see this happen before?
Any damage by running on 3 cyclinders for about an hour?

TIA!

jim wrote in message ...
Hello,

Just took the boat out and was running fine until i lost major power.
Couldnt go above 3k rpms. Checked the merc 3.0 and saw one spark plug
cable off. So i grabbed it and received a hell of a jolt and noticed the
spark plug had actually broken off clean. Anyone see this happen before?
Any damage by running on 3 cyclinders for about an hour?

TIA!

Doubtful there was any damage. There are always exceptions, but I'd
bet money on everything being internally fine.

"jim" wrote in message
...


noticed the
spark plug had actually broken off clean. Anyone see this happen before?

I have never seen the top of a spark plug break off all on its own. I see
it a lot when something hits the plug, but never while you were just running
along fine.

I have seen the inside portion of the ceramic insulator break off, usually
as a result of running to lean (and hot) or excessive pinging. If the
inside breaks off it could cause the entire insulator to be pushed out,
leaving just the metal outside with a hole in it.

Any damage by running on 3 cyclinders for about an hour?

Maybe.

If the inside portion of the spark plug broke then it would have fallen into
the cylinder. It is very likely that this would cause some damage, from
scoring the cylinder walls, getting jammed into the cylinder head, or
lodging into the exhaust valve seat. This could have very serious
implications. It is also possible that it broke into small enough pieces
that they just went out the exhaust. Any damage from this would have
happened in the first few seconds after it broke.

As far as running for an hour, it could be really bad for the engine. The
other three cylinders will now be running at full load, and they could
overheat as a result. If you made it back and there wasn't any further
reduction in power, obvious overheating or other indications of bad things
then you are probably okay.

As far as duplicating this in the future, I would be very careful. If the
center insulator is blown out of the spark plug then you have a hole from
the cylinder into your engine compartment. Even though the cylinder is not
running it is still drawing air/fuel in from the carburetor. Instead of
compressing it, however, it pumps it out into your engine compartment,
filling the engine compartment with an explosive fuel mixture. If you have
adequate ventilation you might be alright but there have been cases where
people have tried running with one spark plug out only to have their entire
boat blow up on them.


Rod McInnis

"jim" wrote in message
...
Hello,

Just took the boat out and was running fine until i lost major power.
Couldnt go above 3k rpms. Checked the merc 3.0 and saw one spark plug
cable off. So i grabbed it and received a hell of a jolt and noticed the
spark plug had actually broken off clean. Anyone see this happen before?

Yes. But only when the insulator was already cracked (on installation).

Any damage by running on 3 cyclinders for about an hour?

As long as the internal parts of the plug stayed intact, no.


--
-Netsock

"It's just about going fast...that's all..."
http://home.insight.rr.com/cgreen/