Valve Stem Installed Height
The valve stem installed height is the measurement from the tip of the valve stem to the spring seat. All of the valve stems heights must be within specification, if one is higher than the others it is likely the valve face or seat is worn or over ground. A valve stem height gauge is usually required to measure valve stem height.
When the valve closes it must provide a tight seal and seat properly "squarely" into the valve seat. When closed, the valve face sits against the valve seat to provide a tight compression seal and good heat dissipation. The valve and seat are cut at different angles that create an interference angle. The interference angle guides the valve into the seat and seals the cylinder with the appropriate pressure.
Check the condition of the valves tip and make sure all appears normal. The valve stem installed height must be checked any time the valves have been replaced or if the seats have been replaced or machined. Valves become stretched at the neck just above the fillet. This is known as stem necking. Stem necking is usually caused by hot exhaust gases swirling around the neck. When a valve has stretched at its neck it must be replaced.
This measurement is important because it effects the geometry and naturally the volume of the combustion chamber. It also effects lifter preload, spring height, valve lift, and the life span of the valve train in general. Many manufacturers recommend that you grind the valve tips if necessary.
There is a definite limit to how far a valve tip can be ground. If the distance gets too close to the retainer or rotator then it will be out of specifications and the valve will need to be replaced. It may also be necessary to remove the old seat and install a new seat into the cylinder head.
