The Carlisle independent., 1920-05-27

' essential part of the internal com bustion engine.
 Different Type of Valves
 The type of valve generally used for traction engines and automobile work is what is known as the poppet valve. There are, however, a few different types of sliding valves used such as are used in the Knight mo- tor, but this type of valve is not gen eral and the construction of a motor of this kind is more expensive than one using the poppet valves. The poppet valve gets it's name from the way it works. Some poppet valves are ground directly into the cylinder head and some are ground into cages which are in turn ground directly into the cylinder head. In cases where the cage is used, it is fitted into the cylin- der head and is held in perfectly tight by means of bolts so that gas cannot leak past it.
 The type of motor in general use on farm tractors is one of the two or four cylinders four stroke cycle type and have one admission valve and one exhause valve for each cylin- der. It must be operated and timed in such manner that it will permit the fuel to enter only at the exact time that it is needed. It must never permit fuel or gas to escape from the cylinder. The exhaust valve controls the letting out of the burnt gases af- ter the charge has exploded. Importance of Keeping Motor Prop
 erly Timed
 It is very important that the oper- ation of these two valves on the en- zine should be absolutely controlled by the engine itself. There must be l no guess work about the operation. | No chances should be taken. The l successful and economical working of | the engine itself depends to so great | an extent upon the proper timing and working of these valves that great | care and precaution must be taken | in keeping them properly adjusted.
 
 Operation of Valves
 The admission and exhaust valves on tractor motors are generally me- chemically operated. In other words | they are positively operated and are under proper control. The motor with l mechanically operated valves can be timed to open and close at any time 1 the manufacturer may designate. In | the timing of these valves the me chanical operation of the valves is generally done either by means of a 1 lever or rocker arm or directly by the 1 cam itself. acting on the end of the l valve stem. In the case of most farm tractors, the valves are mechanically operated by rocker arms which are actuated by push rods connected with the cam rollers and the cam rollers 1 are operated directly by the cam shaft l In this way we have followed the tim ing of the valves back to the cams and cam shaft where the valve tim ing adjustments are made.
 Functions of the Admission Valve |
 On the suction or admission stroke | thisis when the piston is-on it's for ward movement or towards the open | end of the cylinder, it tends to form a vacuum in the cylinder. The pres sure of air outside the cylinder forces | a volume of air through the carbure tor into the cylinder just as soon as the admission valve is open, thus the | admission valve should begin to open l just after the piston starts on it's out ward or admission stroke. At the | outer dead center, this is when the piston has reached the farrnest for ward position in the cylinder or just | after the crank has gone over the center and the piston begins to trav- el in the opposite direction or on the | compression stroke there is still a l slight vacuum in the cylinder which | is not completely filled. In order to | fill this slight vacuum it is necessary l to hold the admission valve open for short space of time while the piston l is moving on the backward or com P1 CoolOh SS1OhCt SO tii0t titC bltCl Ia | of the inrushing air will fill up this | space. This is the reason that the timing on the admission valve is so that it does not close until consider able distance after the piston has started on the compression stroke. | In this way the cylinder is complete ly filled with the new charge before the admission valve is closed. Wei time the movement of the admission valve so that it will close just in time to prevent any part of. the in- coming charge from being forced back out through the open admission valve. During the other three valves of the cycle the admission valve must remain closed. Functions of the Exhaust Valve
 The exhaust valve is provided for letting out the burnt gas after the charge has been exploded, so this valve is called the exhaust valve. The Exhaust valve should open sufficient ( L e &l- .-&< ..l>