Some Twin Cam heads using 7.0mm valves may crack in the port end of the valve guide bossThese valves have .005'' oversize stems to re-establish the correct valve stem to valve guide clearance if the head has crackedValve guides must be reamed/honed to set correct clearance, the a valve job performed to ensure proper sealingOversize portion of the valve stem does not extend into the keeper groove area OEM valve keepers can be used