Are you getting plenty of oil to the rockers ? I still think your rocker shafts and oiling may be the link . I have some old 216 rockers if you need them.You pay for shipping and you can have them.I think one may be missing to the set.I hate for you to keep buying rockers and have them break.Seems like if the valve was hitting the piston,it would bend the valve and break the piston top.

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