Valve Stem Installed Height
Valve stem installed height is the measurement from the tip of the valve stem to the valve spring seat or cup. This is different from valve spring installed height that is measured from underside of the valve spring retainer/rotator to the valve spring seat. All valve stem heights must be within specification. If one valve stem is higher than the others, suspect that the valve face or seat is worn. A valve stem height gauge may be required to measure this height.
The seal between a valve and its seat must be very tight. When closed, the valve must provide a tight seal for good heat dissipation. The valve and seat are cut at different angles. This creates an interference angle. An interference angle guides the valve into the seat and seals the cylinder with the appropriate pressure.
Valve stem installed height is important because it affects the geometry and volume of the combustion chamber. It also affects lifter preload, spring height, valve lift, and the life span of the valve train in general. Many manufacturer’s recommend that valve tips be ground if necessary.
There’s a limit to how far a valve tip can be ground though. If the distance gets too close to the retainer or rotator, it will be out of specifications and will need to be replaced. It may be necessary to remove the old seat and install a new one into the cylinder head to bring measurements back to specifications.
Check the condition of the valve's 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 caused by hot exhaust gases swirling around the neck. When a valve has stretched at its neck it must be replaced.