5i° 



ENGINEERING ON THE FARM 



J '/h/er ya/ 

 370' 



four-cycle or four-stroke cycle engine. The cycle strokes are 

 by name and order: intake, compression, work, and exhaust. 

 The cycle strokes do not coincide with the strokes of the 



piston. A piston stroke is 

 180 of crank movement. 

 Each cycle stroke differs from 

 the piston stroke and also from 

 each of the other cycle strokes. 

 The four-cycle strokes are: 

 first, power stroke of 140 

 (from o to 140), second, ex- 

 haust stroke of 225 (from 140 

 to 365) ; third, intake stroke of 

 200 (from 370 to 570) ; fourth, 

 compression stroke of 150 

 (from 570 to 720) (Fig. 404). 

 An interval of 5 exists between 

 365 and 370 when all valves 

 are closed. 



At first glance the length in degrees of the cycle strokes 

 would seem somewhat distorted. If, however, the pressures 

 inside the piston could be examined, they would be found 

 about as follows: • 



Fig. 404. Showing the path of the 



crank and the relative positions 



of the valve timings 



Lb. 



o 250-300 



UO 35-37 



!8o 5- 7 



360 ^ + 



365 . o 



37° Slightly negative 



54° 3 negative 



570 Normal or o 



710 40-70 



The aim is to get a long power stroke and still let the pressure 

 within the combustion space come down as near as possible 

 to normal at 180 and give but a small back pressure for the 

 next 180. The interval of 5 is left because it would be 

 useless to open the intake valve while there was still a positive 



