SBI Valve Guides are manufactured using the highest quality cast iron. Each Valve Guide is manufactured to the specified tolerances to ensure they can be installed directly into the cylinder head guide bore with minimal additional work. During installation, the Valve Guide inner diameter can encounter crush and become distorted due to interference, this is why SBI recommends checking all valve guides after installation for the correct OEM recommended specification for clearance. By doing so, this can prevent wear and potential valve stem seizure.