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Page:Popular Science Monthly Volume 89.djvu/279

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Popular Science Montlih/




^^,^TEMP. or PISTON- HEAD 300°-I000-F



���TEMP. OF SUMP OIL lOO - 150 F.

��In many cars the Splash Lubricating System is employed. Oil is supplied to the crankcase. The connecting rods dip into and splash the oil to all other parts of the engine. The tem- peratures of the various parts are indicated in the diagram and show the heat to which the lubricating oil is subjected. The parts that are lubricated are indicated in white

��water and has a curdled appearance; but good oil shows a clean line between the oil and the water. The test indicates whether or not the refiner has removed harmful acid compounds and other im- purities.

Of all these tests those which indicate an oil's viscosity and heat-resisting qualities are the most significant, be- cause they show whether or not an oil is able to form and maintain the film that separates the friction surfaces and i)rc- vents the escape of gases past the piston during the compression and power strokes.

The accompanying pictures .show what happens when poor, clieai) oil is used in a motor car — an oil which fails to meet the tests mentioned. If the oil has insufficient body ami cannot stand

��heat, metal rubs on metal ; piston rings . break; the cylinder walls arc scratched anil scored.

.'\n oil of low \iscosity is easily sucked past the piston rings into the explosion chamber. That means compression losses, because of the poor gas seal formed by the oil. What is more, the carbon of the oil — the carbon which is an indispensable chemical constituent of every oil — is deposited in a more or less thick coat. Subjected to the heat of thousands of exjilosions in a few minutes, this carbon acts like so much coal. Parts of it be- come incandescent. Hence, mixtures are prematurely exploded. "Knocking" of the motor results, which means that the glowing carbon ignites the mixture before the piston has reached the top dead center, thus giving rise to powerful blows

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