SH 



ENGINEERING ON THE FARM 



In a twelve-cylinder engine (Fig. 411) there is an impulse 

 for each twelfth of 720 , or each one-sixth revolution. The 

 twelve-cylinder crank shaft is a duplicate of the six. It 



uses a similar type of con- 

 necting rod, and the angle 

 between the two sets of 

 cylinders is 6o°. 



Order of firing. In order 

 to issue instructions regard- 

 ing the multiple-cylinder 

 engine, it is necessary to 

 number the cylinders. It is 

 conventional to begin at the 

 radiator end of the engine. 

 The cylinder nearest the 

 radiator will be No. 1 for 

 the four- and the six-cylinder 

 engines. In the 8's and 12's No. 1 is at the right next the 

 radiator. The cylinders are numbered back in order and 

 continue in sequence from front to rear on the left side. 

 There are two orders of firing for a four-cylinder engine: 

 1-3-4-2 and 1-2-4-3. There are two orders of firing found 

 in left-hand crank shaft six-cylinder engines: 1-2-3-6-5-4 and 

 1-5-4-6-2-3; and for the right-hand crank shaft: 1-3-2-6-4-5 

 and 1-4-5-6-3-2. An eight-cylinder engine may fire: 1-8-2- 

 6-4-5-3-7; 1-8-2-7-4-5-3-6; 1-8-3-6-4-5-2-7, or 1-8-3-7-4-5-2-6. 

 Dead center. An engine is on dead center when the 

 center of the piston, the center of the crank shaft, and the 

 center of the crank pin are in a straight line. There are two 

 such positions. Incenter is the dead center when the crank 

 pin is nearest the cylinder. Outcenter is the dead center 

 when the crank pin is farthest from the cylinder. 



Fig. 411. Showing relation of cylin- 

 der blocks as used in the "V"- 

 type twelve-cylinder engine 



VALVES 



Types and adjustment. The most common type of gas- 

 engine valve is the poppet or mushroom valve. A poppet 



