Many Valve Keeper groove failures are due to the use of worn Valve Keepers. When an engine has to run for many miles, the components in the valve train "wear in" together and form wear patterns on mating parts. Often when a cylinder head is rebuilt, these parts are all cleaned together. When the head is reassembled, the mating parts are not assembled in the same order, and the wear patterns are now different. This will cause stress fractures especially when new valves are installed with mismatched worn keepers. It is recommended that new keepers are always installed during cylinder head reconditioning procedures.