"Phew!
That fellow must be burning soft coal instead of gasoline!" whispered Joe
Clark to his partner, Gus Wilson, as the latter walked out of the Model
Garage in response to frantic blasts from a motor horn at the curb.
The car
which had stopped there was emitting dense blue-black smoke in such
tremendous volume that the two garage men were nearly suffocated as it
drifted into the garage.
"My name's
Potter," began the owner of the car, shutting off the motor as Gus
approached. "I've just moved into town, and my neighbors tell me
you're the man to see when an auto needs fixing. And this car sure
needs something done to it. It's got no power or speed, and it runs
rotten all the time. Besides that it starts hard. Look her over
and see what's the matter."
Gus raised
the hood and inspected the level of the oil in the crankcase. Then he
asked for the hand crank and carefully tested the compression in each
cylinder.
"Where did
you get that oil, Mr. Potter?" he inquired.
"It's extra
refined oil and I got it at a great bargain, "Potter answered. "Costs
me only thrity cents a gallon in fifty-gallon drums shipped right from the
refinery."
"Well, I
don't like to discourage you," said Gus, "but using that particular grade of
oil has put this engine on the blink for fair."
"What do
you mean?" snorted Potter indignantly. "I've been using that oil right
along and I never had any trouble with it before."
"That's
because it takes a while for the bad effect of poor oil to show up in the
running of the engine," Gus explained. "You can use poor oil and get
away with it for a time, just as you can neglect your storage battery
without trouble until the battery quite cold and leaves you stranded on the
road.
"Motor oil
has to do only one job - keep the moving metal surfaces from rubbing against
each other. And it takes mighty good oil to do the job right.
The film of oil between the moving metal parts in an engine is thinner than
the thinnest sheet of tissue paper and if the oil is of such poor quality
that the film breaks at any point, the bare metal surfaces will rub against
each other and some of the metal will be worn away.
"Plenty of
poor oil is better than no oil at all because, if the oil film does break
down, it is renewed by the fresh supply and the wear is slow." That's
what has happened to this motor. The oil you are using is poor grade,
but you have evidently kept the crankcase level up to the proper mark and so
it's taken time for the wear to put the motor on the bum."
"How do you
know the oil is no good?" questioned Potter skeptically. "You don't
mean to tell me you can tell poor grade oil just by looking at it!"
"Of course
not," admitted Gus. "Nobody - not even an oil expert - can be sure
about the quality of oil just by looking at it. The color of an oil
doesn't mean much. I can show you two different oils, one dark and one
light, that show up exactly the same in the standard tests. Also, they
are equally good for motor lubrication. Even the thickness or 'body'
of a cold oil doesn't prove much. The important point is a whether the
oil will get too thin at the high temperature of a running motor.
"Your motor
has all the earmarks of poor lubrication. Besides that, I know that
high-grade oil can't be bought for the price you paid.
"Gas engine
oil gets a lot of rough treatment inside the motor, you know. It has
to be thin enough to run in between closely fitted bearings and yet stand
terrific heat without getting so thin that it will be squeezed out by the
pressure.
"Cheap oil
is often a mixture of what the refiners call 'tops' and 'ends' - the higher
oils that come off first when crude oil is distilled with enough of the
heavy parts that come over last to give it about the right body. When
you lubricate a motor with such stuff, the lighter oils evaporate into
clouds of smoke and the heavy portions turn into carbon and gummy deposits.
"That's
what's the matter with your motor. It's chuck full of carbon.
The valves are all gummed up and probably burned and pitted. And
because the oil is such a poor lubricant, the piston rings are worn so that
the compression is no good. The bearings need taking up too."
"I can
hardly believe it's as bad as all that," said Potter.
"All
right," said Gus. "Come around tomorrow and I'll show you just what
the inside of your motor looks like and you can judge for yourself."
Potter
showed up promptly the next morning.
"I had it
sized up about right," said Gus as Potter strolled in. "See - here are
the piston rings. Every one has blackened surfaces where it ought to
be bright. Those dark areas are where the gas is rushing past the
piston into the crankcase. Look at that cylinder head and the tops of
those pistons. The carbon is crusted on nearly a quarter of an inch
thick. These valves are pitted to beat the band. And see how the
carbon has baked on to the stems until they won't seat any longer."
"You win!"
admitted Potter. "It's a mess all right. Anything else wrong?"
"The
bearings are pretty loose," Gus replied, "I'll have to take them up.
And the cylinder walls are burned and slightly scored, but I think the
cylinder hone will clean them up easily enough. That's about all, but
if you have any lingering idea that the oil you were using is good just look
at the gummy deposit sticking to the oil pan."
"Humph!"
groaned Potter. "Counting in the cost of these repairs, that oil will
cost me about two dollars a gallon."
"Pretty
expensive oil," said Gus. "You can buy the best on the market for a
whole lot less. And I'd do it hereafter if I were you."
END
