5 o8 



ENGINEERING ON THE FARM 



i --Porce/a/n 



electric current may be conducted through the cylinder wall 

 and the circuit made and broken there at the desired instant. 



Jump-spark system. 

 When engines using high 

 speeds were developed, the 

 make-and-break system of 

 ignition began to show its 

 limitations. The moving 

 parts were heavy and noisy, 

 and the precision necessary 

 to exact timing was difficult 

 to secure. The outcome 

 was the development of the 

 jump-spark system (Figs. 

 400-402). This requires : a 

 source or current (battery 



Gaskef 



'Pef/icoa/- 

 Fig. 402. Two types of jump-spark plugs 



or magneto), an induction coil, a circuit-breaking device, 

 and a spark gap. The induction coil is the heart of the 

 jump-spark system. A circuit-breaking device, which may 

 be mechanical or automatic, is a part of the primary circuit. 

 The induced current possesses a sufficiently high voltage 

 to jump the small gap provided in the system. The spark 

 gap, as usually provided, is in the form of a spark plug 

 which has one stationary insulated terminal. The current 

 is conducted to this terminal and allowed to jump a gap of 

 from ito^ inch. In the jump-spark system it is not 

 desirable to have a spark occur at the points of the breaker 

 in the primary circuit. To prevent this, a condenser is 

 connected across the breaker points. The function of the 

 condenser is to absorb the electrical energy which would 

 otherwise produce a spark at the breaker points. 



CYLINDERS 



Types. The three standard commercial types of cylinders 

 are: dome head ("1" head), ell head ("L" head), and tee 

 head ("T" head) (Fig. 403). The designation is indicative 



