[omc-boats] Last run of the season

I haven't posted for a while, but I thought this was something you'd all
enjoy. I tried posting this yesterday, but for some reason it didn't seem
to go through (or at least I didn't get a copy back). I apologize if
anyone sees it twice.

This has been an unusually good year for my boat, a 1970 Evinrude Explorer
16' with the 155 hp Buick 225 V-6. Unlike previous years, in which I was
fixing something on the boat or trailer every other month, the only service
I've done this year was to replace the tilt motor at the start of the
season.

We've had unseasonably warm weather in Wisconsin these last few weeks,
though I've unfortunately been too busy to enjoy much of it. As air temps
neared 60 this afternoon (normally it'd be near freezing this time of
year), I blew off work early and took the boat out with some friends in
hopes of getting in some late-season wakeboarding.

We were enjoying having the lake entirely to ourselves and were changing
into our wetsuits as we cruised at half-throttle cruise to a good ski area.
We'd made it about halfway when I heard a loud bang from the back. My
buddy who was driving immediately cut the throttle and shut off the engine.
I lifted the engine cover and could see a red-hot spark plug sitting on top
of the engine. The spark plug had fractured, with the outer metal section
remaining threaded into the head and the center ceramic core blowing out.

I had some spare spark plugs in the glove box, but I'd unfortunately put my
tools into the car before setting off (though now that I think of it, I'm
fairly sure there is a rusty old spark-plug wrench that's lived in the boat
since I bought it and fell into a gap between the side locker and the hull
earlier this year).

As we were the only people on the lake, it was nearing dark (we'd only
planned on wakeboarding for 45 minutes), and all my friends have already
put their boats away for the season, our only options were to call the
sheriff or attempt to make it the 2.5 miles back home ourselves.

We tried starting the engine. Aside from the sound of air rushing in and
out through the empty spark plug hole, there were no other bad sounds and
it idled smoothly. It seemed possible that running it on five cylinders
this way might not cause any additional damage to the engine, though I was
concerned about excess fuel in the dead cylinder washing oil off the
cylinder walls and wrecking the rings. I also probably should've been
worried about chunks of the plug damaging the valves, but didn't think of
it at the time. I called a couple mechanic friends on my cell phone and
they told me running like that shouldn't cause any additional damage.

It took about an hour to get back across the lake at idle. The popping
sound from the engine made it sound like a steam engine, and I could see
gasoline mist jetting out of the hole with every pop. With the hood open
it didn't seem to accumulate too much, but I stood by with the fire
extinguisher in case it did. We thought about heading in another direction
to a nearer pier (about 1.5 miles away), but it seemed to be running ok
so we went back to the spot we launched.

[added later] I pulled the remnants of the plug a couple days later. It
came out fairly easily and the outer electrode was fortunately intact. I
didn't have the tools to look inside the cylinder to inspect for damage
to the valves or piston top.

I put up a photo of the inner and outer part of the broken plug here:
  http://homepages.cae.wisc.edu/~brodskye/boat/blown_sparkplug.jpg
(alongside a rusty one I took from my glove box)

Any ideas why this might have happened? Water temp was about 40 F, air
temp was about 60 F. Obviously there's more potential for thermal shock
with such cold water, but we'd run it it already without trouble (though
only for a few minutes). I'd run once since topping off the tank with new
fuel a few weeks ago, but dumped stabil in a few days before this run. The
plugs are 2-3 years old (installed by the previous owner). It was the
middle cylinder in the starboard bank. If you look carefully at the break
surface, it appears to be half black and half clean, which says to me that
the failure took some time. I'd say the plug must've been mechanically
damaged or stressed in the past, but it's pretty well protected between the
valve cover and exhaust manifold. Perhaps I might've hit the wire while
installing the battery and side-loaded it, but I doubt that. The engine
was running fine for about 10-15 minutes before it blew, though I did hear
a some unusual pops (maybe 5-10 total) during that time. I did notice the
exahsut manifolds felt unusually hot right after it blew, but not
excessively so (I could still put my hand on them). I verified that there
was still water going through the engine and it ran cool at idle on the way
home. So I'm very puzzled as to the reason. My best guess is that it was
dropped prior to installation. Needless to say I will be replacing all the
other plugs as well.

I've got a few other projects planned for this winter. I'm going to '
replace the crank on the trailer winch (it's rounded off and slips),
probably with some kind of hex-head or square-drive contraption that I can
use a wrench on if necessary. I'm also hope to get the fenders put back on
the trailer and repair/replace the lights so it's legal again.

On the boat, I want to repair or replace the oil/overtemp light in the dash
(wires fell off the bulb housing). I also want to mount my bottom-finder
transducer in the bottom of the bilge, since it broke off its old mount on
the transom. I have a new automatical bilge pump that I'll probably put in
in place of my old manual one. I need to replace both back seats and I'd
like to also do the front seats, as they're all rotting out. I'd also like
to move the electric fuel pump, pressure regulator, and filter above the
top of the tank so that I'm legal. Finally, I want to repair the panels
under the back seat that seal off the engine compartment.

I'm not sure how much of this will get done, but those are my goals. A lot
of it depends on the weather, as I have to work on it outside.

Anyway, it's supposed to get down to 15 degF by Thursday, so I'm probably
not going to get another chance to go wakeboarding this season. To anyone
in a warmer locale, please take a run for me!

Best wishes,

Ethan Brodsky

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Received on Thursday, 30 November 2006