Kibblewhite Precision Fat Stem Black Diamond Intake Valve 20-20772Some late model Twin Cam heads with 7. 0mm valves have a tendency to crack in the port of the valve guide boss The Fat Stem valves have +. 005in. oversize stems for engine builders who need to re establish the correct valve stem to guide clearance but do not want to create a crack or worsen an existing crack in the head by changing the valve guides Valve guides MUST be reamed to set correct clearance, and a valve job should be performed to ensure