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Show IGNITION TIMING VERY IMPORTANT Gas Must Be Fully Ignited at Instant Crank Pin Passes Center. Correct Ignition timing Is very Important, Im-portant, says William II. Stewart, Jr., president of the Stewart Automobile school. The charge of gas must be fully Ignited at the instant the crank pin passes dead center. When this is done the full expansive force of the explosion is exerted on the piston and the best results are obtained. When the motor is turning over at the rate of 1,000 revolutions a minute the crank pin passes through top center much faster than when the motor Is turning Dver at the rate of 500 revolutions per minute. Since It takes a certain amount. of time for the charge of gas to become fully Ignited it is necessary to introduce the spark into the cylinder cylin-der a little in advance in order to fully Ignite the charge by the time the crank pin passes dead center. Volume of Spark. The faster the motor turns over the more advanced must be the spark. The volume of the spark is not changed by advancing or retarding, but simply the time of the spark in relation to position posi-tion of the crank pin. When a motor is turning over very fast the spark may be advanced as much as 40 degrees de-grees ; that is to say, the charge will begin to ignite 40 degrees before the' crank pin reaches top center. As the speed of the motor is reduced the advance ad-vance must be reduced, otherwise the force of the explosion will be exerted on the piston too soon and the tendency ten-dency will be to reverse the direction of the crank shaft. When the spark Is too far advanced a knock Is noticeable. notice-able. This is caused by the piston acting act-ing against the explosive force. The momentum of the flywheel carries the piston through the cycle; otherwise !t would reverse. Four Segments. The Ignition distributor has four segments, one for each cylinder. The secondary finger "rotating clockwise" touches the segments In the order of L, 2, 4, 3, which may be the firing order. or-der. Pistons No. 1 and No. 4 will be at top center and pistons No. 2 and NTo. 3 at bottom center. If piston No. I Is up on compression and ready for Ignition then piston No. 4 has just completed the exhaust and ready for the intake. Likewise piston No. 3 has lust completed firing and piston No. 2 :he intake. |