During cylinder head rebuilding, ground valves may require shims under the valve springs. Why are these shims installed?

• A. To decrease the installed height
• B. To increase the installed height
• C. To increase spring tension
• D. To decrease spring tension

Answer: (C)

Shims are used to restore the correct valve spring preload after the valves have been ground. Grinding changes the spring’s seating height, which can alter how tightly the spring is loaded when the valves are closed. By installing shims under the springs, you adjust the effective length and seating of the spring so that the preload (the tension in the valve spring when the valve is seated) is brought back up to specification. This helps keep the valve train stable and prevents valve float at higher RPMs.