"Confound you, Beelzebub! I wish
I knew what was making you miss so" Young George Armstrong stared
disgustedly at the motor in his beloved red roadster and wondered what test
to try next.
"But, George," ventured the girl in
the car, "it doesn't seem to miss when you don't go so fast. Why not
drive a little slower and forget about it?"
"Huh!" George grunted. "That's
just like a woman! You'd drive a car till the wheels fell off, without
ever trying to find out what's the matter with it."
The girl offered no more suggestions,
and George went on with his tinkering.
"Can't be a spark plug, because I just
cleaned them," he muttered. "Besides, it doesn't seem to be all in one
cylinder. I've cleaned the timer contacts and they look good.
Maybe it's water in the carburetor."
He looked up at this point in his
speculations and caught sight of a service car coming down the road.
He shouted and waved. "Hey, Gus! Got a minute to see what's the
matter with my bus?"
"Sure have, young feller," grinned Gus
Wilson, as he and Joe Clark, his partner in the Model Garage, pulled up and
climbed out of the service car.
The veteran auto mechanic greeted the
girl in the car. Then: "What seems to be the matter with
Beelzebub today, son?" he inquired.
"Soon as I get to rolling, she starts
to miss, especially if it's a bit of an upgrade and I've got the throttle
pretty well open," young Armstrong explained. "I've cleaned the spark
plugs and the timer contacts and I've tested the spark. It's fully a
quarter of an inch long, and nice and blue. I was just about to pull
the carburetor apart to see if there's some water in it."
Gus never took anything for granted.
He removed the spark plugs and carefully inspected them. Then he asked
the girl to step on the starter pedal while he watched the timer make and
break contact. At the same time he observed the spark jump from the coil
high-tension wire which he held, by means of insulated pliers, about a
quarter of an inch from the cylinder head.
"Why use those trick pliers?"
Armstrong asked. "Is the wire so old you think it will leak and give you a
shock?" "What's the use of taking a chance with high-tension
current?" Gus countered. "There may be a bad spot in the wire,
and then you're due for a swift jolt that will make you jump like a jack
rabbit even though it won't do any real damage.
"And besides," Gus went on, as he
carefully measured the spark-plug gaps, "if the hand you use to grab the
high-tension wire is damp and your other hand is resting on a metal part of
the car, you can get a bit of shock even if the wire is perfect.
That's because your hand acts like one plate of a condenser, with the wire
inside the insulation acting as the other. Any radio shark will tell
you high-frequency current and that's what spark plug current really is,
will travel between the plates of a condenser no matter what's in between."
"Anything the matter with those spark
plugs?" Armstrong asked, as Gus put the last one down and spread out
several blades of his thickness gauge, preparatory to determining the exact
width of the openings of the timer contacts.
Gus did not reply until he had
finished this measurement. "I don't blame you for getting fooled this
time, son," he grinned, as he stood up and stretched himself to straighten
the kinks out of his spine.
"There's a lot of little things the
matter with your ignition. Not one of them would cause any trouble by
itself, but when they gang upon you the result is nearly no spark at high
speed. Take those plugs, for instance. They're clean and in perfect
shape, only the points have burned away a little so the gaps are a little
wide. The breaker points, too, have a clean, gray surface that shows
they're making good contact, but they're set so they open too far.
That means that they don't stay in contact quite long enough at high speed.
On top of that, this is a high-compression motor and there's some carbon
deposit that raises the compression still higher. And the coil, while
it isn't so bad, is not as peppy as it might be.
"Fix any one of those things," Gus
concluded, "and you'd stop a lot of the missing. Fix two of them and I doubt
if it would miss at all - for a while, anyhow."
Gus adjusted the breaker points while
Armstrong finished the plug points. The last the two garage men saw of
Beelzebub was a red dot disappearing down the road to the accompaniment of a
smoothly buzzing exhaust.
"Nice kid, that young Armstrong," Gus
observed to Joe Clark, as he turned the last bend in the road and caught
sight of the garage. Standing in front of the building he saw a shiny
blue sedan, and a man waiting by it.
"Well!" he exclaimed, "Old Fussbudget
Maxon's waiting for us." Probably got a bumblebee stuck in his
radiator, or something just about as important."
"Say, Gus!" Maxon called out,
even before the service car stopped rolling. "This motor doesn't seem
to idle as smooth as it should. Listen a minute and you'll hear it
miss a beat now and then. Would you look it over?"
Gus went through the same routine in
testing Maxon's motor that he had followed in analyzing Armstrong's car.
Watching him, Joe noted, however, that in this case the spark-plug points
were exactly the right distance apart and the breaker contacts opened
precisely the amount the motor manufacturer recommended. The coil gave
a strong, nearly white spark instead of the thin blue one Gus had drawn from
the coil in Armstrong's car.
Therefore, Joe was surprised at Gus's
next move. The veteran mechanic took the end of a screw driver and
bent open the plug points until they were fully fifty percent farther apart
than the manufacturer specified. He put them back in the cylinders and
Maxon started the motor. After it warmed up, it idled with a steady
ticking that brought a smile to Maxon's face.
"I'll be jiggered if I can figure that
out," Joe Clark remarked after the customer had driven off. "First,
you fix a miss in Armstrong's red speedboat by pushing the spark plugs close
together, then you fix a miss in Maxon's bus by spreading them so far apart
you could almost jump between them yourself - and darned if it doesn't work
right in both cases! What's the answer, Gus?"
"Simple enough, if you know what makes
the spark and what it's supposed to do," Gus grinned. "In the first
place, the plug-point gap spacing the makers recommend is no sacred camel.
The motor will run with it bigger or smaller than specified. As a
matter of fact a slightly wider gap will give better performance, at all
speeds, when everything else about the ignition system is in perfect shape.
The makers have to allow for the fact that the average car owner doesn't
keep his car that way for long. Carbon collects in the cylinders and
raises the compression, which has the same effect as widening the plug gaps.
The timer contacts get burned and rough, and that makes the spark weaker.
Coils aren't absolutely uniform' some are weaker or stronger than the
average - or, if they are right to start with, age doesn't make them any
better. That goes for condensers, too. Spark-plug wires leak
current, and so on.
"A miss that is caused by too-wide
plug gaps," Gus continued, "or by something wrong in the ignition system
that weakens the spark, always shows up first at high speed. That's
because when you have the throttle open, the compression is high and at the
same time the breaker contacts don't make contact long enough to get the
full flow of current through the coil. That was what was the matter in
Armstrong's case. And, as you know, he's a speed hound. So if
you give him ignition that won't miss at high speed, he's satisfied.
"On the other hand, Maxon would throw
a fit if he ever saw the speedometer hit forty. Besides that, he's a
bug on gas economy and smooth running at low speed. You don't have to
worry about this ignition cutting capers at high speed; he'll never get
going fast enough. You can open up the plugs quite a way, and the
longer spark gives better ignition when the mixture is thin and the
compression is low because the throttle is nearly closed."
END
