The drop lever B is keyed to the valve stem V, and is connected with the dash pot by a rod as indicated by the dotted line.
The upper end of the valve stem passes through a plug V, through which is a vent hole W.
The amount of clearance allowed depends entirely upon the design of the engine and length of valve stem.
The upper side of the shell has an opening to receive the bonnet C, through which the valve stem D passes.
If the motor is turned but very little beyond this point, a lifting should be felt at the proper push rod or valve stem.
This is primarily intended for taking up any wear that may occur at the ends of the push rod or valve stem.
If the valve stem has worked loose from the valve, trouble will be caused.
valve stem guides and valve stems must be machined very accurately to insure correct action.
The easiest way is to clamp the valve stem to hold valve in mid position; this should cover all ports.
See if rocker arm tappets have a .020′′ clearance from valve stem when valve is seated.