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Show OWNERS REPLACE CAR SPARK PLUG Annual Practice Has Advantages Ad-vantages in Better Motor Work and Economy. May 5 to 11 has been designated es National Change Week for 1929. During that time millions of motor car owners will replace the spark plugs in their cars with new sets, having hav-ing learned by experience that the practice has advantages in iconomy and improved engine performance. One reason why spark plugs should be changed at least once a year is shown in the accompanying photomicrographs photomi-crographs of a spark plug's electrodes after that length of service. Electrode Burned Away. The center electrode is burned away. The ground electrode is likewise pitted pit-ted and burned and its surface Is no longer parallel to that of the center electrode. This results In a small spark, of no great Intensity, and a gap setting altogether too wide for the spark to Jump under load conditions, condi-tions, heavy pulls and rapid acceleration. accelera-tion. Obviously, the corrosion means a weaker spark, a heavy loss o power and waste of fuel. Exhaustive laboratory tests have proved that each spark plug fires its These photomicrographs show what a spark plug looks like after firing an automobile engine twelve i.ionths. The carbon-crusted surface of the Insulator and the pitted electrodes divert the current which Is weakened weak-ened and diffused Instead of sending send-ing a hot intense spark across the flap, with the result that fuel and power are wasted. Engineers advise changing spark plugs at least once a year In automobiles and oftener In power plants of tractors, trucks and stationary engines. charge more than 20,000.000 times In driving a car 10,000 miles. The Intense heat, the ravages of chemical reactions which are set up and the tremendous mechanical shock to which spark plug's are subjected in such an ordeal inevitably take their toll. tncrusted With Carbon. The Insulator becomes encrusted with bits of carbon. In time ntitl with the aid of intense temperatures these carbon particles Impregnate the surface of the Insulator, causing a partial short circuit. The result In the cms" of the spark plus Is a diffusion dif-fusion of current from the electrode, a consequent loss of Intensity in the spnrk and of elh'ciencj in engine operation. op-eration. Experiments of automotive engineers engi-neers have shown that changing spark plugs every 10.000 miles, or once a .venr. tint only saves their cost In ens and oil hut restores In rarge measure new car power, speed and acceleration, accelera-tion, with all the pleasure that any , car owner derives from these features ot h! motoring. J |