5i6 



ENGINEERING ON THE FARM 



EXC-/-4 



'-fiead 'center 



/.C.2-3 



ex. 0-2-3 



the gears one or more teeth will change the time of open- 

 ing, but will also change the time of closing. 



Flywheel markings. The purpose of flywheel markings 



is to aid the operator of a 

 gas engine in checking up 

 the manufacturer's intended 

 valve timing. These mark- 

 ings are rather confusing to 

 the beginner, especially in 

 the case of a flywheel which 

 bears the marks for the time 

 of opening and closing for 

 both intake and exhaust 

 valves on a multi-cylinder 

 engine. The markings for 

 engines using automatically 

 operated intake valves are 

 comparatively simple, as 

 only the exhausts are 

 marked. In a mechanically operated four-cylinder engine 

 the markings will be: 



EX.0-/- 



AC. 1-4 



\-/.0.-E-3 



EX. C- 2-3 



Fig. 413. The flywheel markings as they 



would be found on a four-cylinder 



four-cycle automobile or tractor 



engine on dead center 



C. or D. C. 

 E. 0. or Ex. Op. 

 E. C. or Ex. CI. 

 I. 0. or In. Op. 

 I. C. or In. CI. 



1 — 4 (dead center) 



1 — 4 (exhaust opens) 



1 — 4 (exhaust closes) 



1 — 4 (intake opens) 



1 — 4 (intake closes) 



Similar markings are used for cylinders 2 and 3 at 180 

 respectively from these for 1 and 4. (See Fig. 413.) Since 

 the four-cylinder crank shaft is made with cranks 1 and 4 

 at 360 , and with cranks 2 and 3 at 360 , the flywheel mark- 

 ings will be exactly the same for each pair of cylinders. 

 Many flywheels have no valve operation markings. Some 

 have no dead-center markings. (See Fig. 414.) 



Governors. All stationary and tractor gas engines and 

 most truck engines are supplied with a governor which 

 automatically controls the speed. There are two types of 



