There! Hear that? There it
is again!" Bancroft exclaimed, as he singed the tip of his ear on the
hot exhaust manifold in the attempt to listen more closely. "I tell
you there's something wrong with that motor."
Gus Wilson listened intently for
a few moments.
Mr. Bancroft," said the veteran
auto mechanic, "there's nothing wrong. What you hear is the clicking of the
valve tappets. I can set 'em tighter if you want me to, but I'd advise
against it. If the tappets are set too tight the valves may not seat when
the motor is cold, and the valve seats and the faces of the valves get
burned. I'll check 'em to make sure they are as tight as they ought to be."
After Bancroft was convinced that
his motor was properly adjusted and had driven away, Gus turned to Joe
Clark, his partner in the Model Garage. "It's all right for a man to be
fussy about the condition of his car," he growled, "but that bird Bancroft
makes me tired. He's always got his car working overtime trying to hear
knocks and things in the motor."
"They're not all that way,"
grinned Joe. "Fellow left a car here last night just after you'd gone. The
windshield wiper was on the blink and he wanted it fixed. He spent ten
minutes bragging about what a fine car it is. There it is over in the
corner. Start the motor and see what you think of it."
in and pushed the starter pedal with his hand and the engine started at
"Suffering cats!" he shouted, to
make himself heard above the clattering and thumping of the motor. "I don't
see that the owner of this car has anything to be proud of. Sounds terrible
"Is that so!"
snapped the sarcastic voice of the owner, who had arrived just in time to
catch the end of Gus's remarks. "Trying to drum up trade are you? Maybe
the car is a bit noisy, but I wouldn't hesitate to start for the coast in
that bus any day."
"You could start easy enough, Mr.
Dobey", noting the name of the owner on the repair ticket, "but it's kind of
doubtful if you'd get there. Too many things in the motor in bad shape.
Let's take it out on the road so I can hear what's wrong.
"Now," said Gus as they started
down the road, "keep it running smoothly at about fifteen miles an hour till
we get to the top of that hill."
"What's the sense of going so
slow?" Mr. Dobey inquired.
"At fifteen miles the normal
motor noises don't amount to much, and you stand some chance of hearing the
They drove on for a short
distance, and as they started up the grade Gus said: "It's kind of hard to
dope the knocks when there are so many different ones, but that light knock
is either loose piston rings, a loose piston, or both. Those muffled knocks
indicate that at least two of the connecting rod bearings are loose, and
that thump like somebody pounding on a block of wood with a mallet is the
main bearing. The other jumpy thumping noise means the motor is loose on
the frame. Of course the sharp, metallic knock means thick carbon deposits
on the cylinder head and the top of the piston. The rest of the clatter
comes from the valve mechanism. You might as well turn back now."
"What are you trying to do, kid
me?" sneered Dobey. "The motor couldn't be as bad as that. How do I know
you're not just trying to get away with a fat bill for overhauling?"
mister," Gus smiled. "I've been in this business long enough to know what
I'm talking about. You stick around while I yank the motor out of the
frame, and if any of the things I say are loose turn out to be tight, I'll
do the rest of the job at half price.'
enough," Dobey admitted as they rolled into the Model Garage. He watched
closely as Gus got the portable crane ready to hoist out the motor.
"Of course if only
piston rings and a loose connecting rod needed to be replaced," said Gus,
"there'd be no sense in going to all this trouble. We fix things like that
by dropping the oil pan. But your main bearings are in bad shape and I'd
rather get the engine out where I can do the job right.
"Now before I
start," Gus continued, "Take a look at the bolts holding the motor in
place. This one here is so loose you can turn it with your fingers. If
you'd kept on running the motor in that condition, the pounding would have
busted the motor support and then you'd have been up against a man's size
"No doubt about the looseness
there," Dobey admitted glumly after he had turned one of the bolts with his
fingers. "I thought this talk about telling what's wrong with a motor by
the sound was bunk, but I guess there's something to it after all."
"Like most things," Gus smiled,
"there's some truth mixed with the bunk. Any smart Aleck who tells you he
can spot any trouble in a motor right away just by listening to it is
shooting hot air. But a smart mechanic should be able to locate anything
that's really loose, by the sound.
ways of running down particular troubles. For instance, if you hear a knock
that you think is a loose connecting rod bearing, and you can hear it with
the motor idling, short circuit the spark plugs one at a time. When you cut
out the explosions in the cylinder with the loose connecting rod, the noise
will stop or get weaker. If shorting the plugs doesn't affect the noise,
you can be sure something besides loose connecting rods is setting up most
of the clatter."
"Loose connecting rod and main
bearing cause most of the noise in motors, I suppose," suggested Dobey.
"Some people have that idea," Gus
replied, "and the minute they hear a clank in the motor they suspect the
bearings. Most times the noise comes from the valve operating mechanism.
There may be too much play in the tappets, the push rod guides may be worn
or the cam shaft bearings may be loose. Of course no one wants to ride in a
car that rattles and clanks like an old junk wagon but noises from the valve
mechanism are not so important as loose connecting rod or main bearings.
When bearings get so loose that you can hear them they ought to be fixed
right away. If they're not, pounding may crystallize the shaft and break
it, and that is serious. The valve mechanism can be loose enough to make a
lot of clatter without causing any particular damage. Timing gears can
rattle mighty loud without breaking."
"Gee!" exclaimed Dobey, "I don't
think I'll get any fun out of driving if I have to keep listening for noises
all the time."
"Neither would I," Gus agreed.
"What you want to do is to get your ears accustomed to the sound of the
motor when it's running right. Don't keep trying to hear funny noises -
just let your cars tell you of noises that really are loud enough so there's
no doubt about you hearing them.
"You'll notice too, that the
motor always seems to sound quiet when you're in traffic, but after you've
driven for an hour or two at a steady pace on a trip your cars begin to pick
out and magnify little sounds that don't mean anything.
Then, when you start out again
the next day, you wonder where all the noises went to that you heard near
the end of your trip the day before."
"I get you," nodded
Dobey. "Your idea is to mix a little common sense with the listening."
"Common sense is
handy - even in a car," grunted Gus. "But we'd go out of business if it got