Ever since I was a kid,
I've been fascinated by things that blow up. When I was barely a teenager, I
blew up the garage. I was unsupervised and messing around with some powerful
chemicals. As a parent, I can see clearly now that I should have never had
gotten my hands on them. One rainy day, in my garage laboratory, I was mixing up
combinations of powders to make a home-made bomb. The Potassium Chlorate is very
unstable stuff. The result was a blown up laboratory and permanent injuries. Now
I confine my fascination to store-bought fireworks.
I may like explosions,
but there's one kind that I hate, and that's when an engine blows up. And,
exploding engines can be very dangerous to life and limb. They can throw large
masses of metal with great force. Everyone in car racing knows about a scatter
shield. One of the most feared truck engines with the worst reputation is the
Detroit Diesel which has massive flywheels that have been known to fly
off.
Actually, it happens in
three states. First, a linkage problem throws the engine into an uncontrolled
free rev -- full throttle. The linkage for the rule rail is very tricky. This
can easily happen when the fuel rack control rods jamb -- holding the fuel rack
wide open. The first thing a student in diesel truck school learns about this
engine is the importance of the fuel control rods.
If you get them installed
wrong, they will jamb the throttle resulting in a ran away. And because this
engine has this tendency, it comes fitted with a "Slam Door" and a big heavy
metal door that is built right into the intake air box. If the engine starts to
run away, you can crop the slam door and close off the incoming air, and kill
the engine. At least, that's the idea.
But, it doesn't always
work. They don't call them oil burners for nothing. By having the habit of
feeding on its own oil, the Detroit
engine is one of the worst offenders. The reputation partly comes about because
that engine is a two-stroke. It has ports on the sides of the cylinder lines for
air intake.
This is important here,
because it provides a place for the oil to be introduced into the engine. If the
air box gaskets are weak, they will be sucked right into the screaming engine.
This unwanted source of air will allow it to keep running away. Then it begins
feeding on its own oil as superheated oil, which is being pumped past the rings
into the combustion chamber, fuels the fire even more.
Finally, it runs out of
oil and seizes up. That's what launches the flywheel, the crankshaft suddenly
stops turning and something's got to give! The flywheel bolts shear off, and the
massive fly wheel comes crashing right out of the bellhousing.
But that's nothing new to
race fans. Exploding clutches have brought the requirement for scatter shields
on race cars. I guess it took enough severed legs to find out the need for this
protective 'device. But there is nothing to protect you from the flywheel off a
runaway Detroit Diesel. I've heard that the massive flywheel will go through
concrete walls.
And what a noise it
makes! It's one of the most terrifying sounds in engine can make. When I say
screaming, a runaway Diesel is louder than a speeding train engine. And, at the
same time, it belches smoke like a blast furnace. I happen to know firsthand,
because I had an opportunity to witness one that ran away. It happened while I
was attending night school for heavy-duty mechanics at Sequoia Diesel
Institute.
One of the students
jammed the rack levers on a Detroit Diesel and the engine went full rev as soon
as it was started. The teacher pulled the lever for the slam door, and the
engine slowly died. But for one terrifying moment, it. screamed and roared like
a metal monster gone amuck. That's when I first heard the story of the runaway
Detroit Diesel flywheel busing through walls. The teacher saw it happen. The
engine ran away, exploded when it seized up. The flywheel came off and went
through three walls before coming to a stop halfway into a fourth.
And that was where I
learned about CO2 fire extinguishers. The teacher explained that in case the
slam door didn't stop the runaway, we should use a CO2 fire extinguisher to stop
it.
Since CO2 doesn't burn,
it stops the engine dead in its tracks by starving it of oxygen. It's quick,
efficient and works every time.
Years later, while I was
wrenching for a Mercedes-Benz dealership in Palo Alto, I was instructed on the
MBZ way of shutting down a diesel engine. According to factory protocol, the
proper method is to open the fuel injector high pressure supply lines, starving
the engine of fuel. While this worked okay, it was really messy and takes up
valuable time. And when an engine is at full-rev, every second counts. First,
you had to find the correct wrench size for the injector fuel lines. Then you
had to break them open one by one, which creates quite a mess. Diesel fuel
spurts over the entire engine compartment.
You're probably wondering
why MBZ diesels run away. First, they rarely throw off their flywheels and
seldom explode. But, it can happen in one of two ways. The first is when the
throttle linkage sticks. This isn't much of a problem as long as you keep the
ball-sockets properly lubricated. MBZ fits the engine with a shut-down lever
that looks like a choke knob. Also, located right above the injection pump, is a
manual fuel cut-off device. But, modem MBZ diesel engines use a shutdown system
that's operated by the ignition key. A small vacuum motor mounted on the rear of
the injection pump performs the shut down.
The second way is when
the vacuum motor diaphragm ruptures. The owner find that the only way to shut
down the engine is to get out, open the hood, and press the manual shut down
lever. Not the sort of thing that MBZ owners could be likely to do, huh? Well,
the replacement of the vacuum motor can be tricky. It has a small tang on it
that must catch in a notch on the injection pump rack. If it doesn't, it'll jamb
the rack in a wide-open-throttle position and bingo, "Runaway
Diesel."
And it happened right
next to me at the MBZ dealership where I worked in Palo Alto. The tech next to
me was installing a vacuum motor and didn't' get the tang right. This launched
the engine into a screaming fit as soon as he started it. And while he was
making a mad dash for his toolbox to find a wrench to open the injector lines, I
grabbed the CO2 fire extinguisher from the wall and shot it into the air intake.
The engine's screaming died right away, even before he got the
wrench!
He stood there amazed.
And when the engine stopped, so did all the work in the shop. You could hear a
pin drop. Everyone was looking at the two of us as we stood there. Me with the
fire extinguisher in my hands and the tech with a wrench in his. That's when the
stop foreman got involved.
He came storming over
shouting, "What the hell do you think you're doing?!" I replied in as calm a
voice as I could muster, "Just a trick I was taught a Sequoia Diesel." "Oh
yeah?!" he shouted back at me. "You just ruined this motor with that stuff." he
said as he began removing the air filter, expecting to find it full of
something. When he lifted the metal cover, it revealed what looks like snow
piled up going into the air filter -- nothing more. He reached over
and touched the frozen
CO2 as it rapidly disappeared into wisps of smoke. He said in a caustic tone as
he turned and walked away, "Well that may be so, but we don't do that
here!"
The only diesel to run
away on me happened when I was working at Larry's Autoworks. And it scared me
big time! I was doing a major service on a Peugeot 504D. It's a pretty
straightforward diesel engine, there isn't much that you can do to hurt it. But
I did find one Achilles heel. The air filter uses foam that resides in an
oil-bath housing. The foam stays wet by the oil bath, which is an old method
used by trap dirt.
And when I cleaned the
foam, I make a big mistake. Unknowing, I cleaned it in the parts washer solvent
and didn't dry it before installing it. Oh sure, parts solvents works really
well at removing grease. But, it became trapped inside the foam. Since it was
combustible, it caused the engine to run away for a brief moment. I remember
standing there, not knowing it happened. It was over so quickly.
But, for just a brief
second, I thought the engine would explode and I would be killed. And it was all
over, and after careful checking, there appeared to be no damage. I didn't say
anything to the owner, for fear of losing my job. Well, I thought I had gotten
way with my mistake until the next day, when the Peugeot showed up on a tow
truck. When I saw it, my heart sank. I feared the worse: a blown engine.
Actually, it only wouldn't start.
The compression was
excellent, and nothing mechanical appeared to be amiss. Further checking
revealed that all four glow-plugs had been burned up by the solvent's fiery
blast. Because it had warmed up when I worked on it, the problem didn't show up
until the next day, when it was dead cold. Here's when I needed the glow-plugs
to start. All it took to fix it was a set of glow-plugs.
But by far the worst
story I know about an exploding engine happened on a diesel-powered car. Those
of you who have been around the diesel engine trade know about the horrible
automotive diesel engine that GM made. They modified the 350 gasoline engine to
run on diesel. Big mistake. It was never designed to hand that kind of
compression or torque. When trying to get one to start, a mechanic was shooting
ether into it. The engine exploded, blowing off of the cylinder heads, which
dismember one of the mechanic's arms. But that's another story.
