Aviation Training

Each valve is closed by two or three helical springs. If a single  spring were used, it would vibrate or surge at certain speeds. To eliminate this difficulty, two or more springs (one inside the other) are installed on each valve. Each spring vibrates  at a different engine speed and rapid damping out of all  spring-surge vibrations during engine operation results. Two or more springs also reduce danger of weakness and possible  failure by breakage due to heat and metal fatigue. The springs  are held in place by split locks installed in the recess of the  valve spring upper retainer or washer, and engage a groove  machined into the valve stem. The functions of the valve  springs are to close the valve and to hold the valve securely  on the valve seat.

The push rod, tubular in form, transmits the lifting force from  the valve tappet to the rocker arm. A hardened-steel ball is  pressed over or into each end of the tube. One ball end fits into  the socket of the rocker arm. In some instances, the balls are  on the tappet and rocker arm, and the sockets are on the push  rod. The tubular form is employed because of its lightness and  strength. It permits the engine lubricating oil under pressure  to pass through the hollow rod and the drilled ball ends to  lubricate the ball ends, rocker-arm bearing, and valve-stem  guide. The push rod is enclosed in a tubular housing that  extends from the crankcase to the cylinder head, referred to  as push rod tubes