Am I right in thinking that you are running with 618 high lift cams at the moment on this engine? Hopefully this sort of failure is not common on a "standard" 121 cu in engine, or with 569 cams and standard valve springs? I have heard of valve springs breaking but not the retainers, that is new. It looks like you have damage to the rocker and inlet valve, are the piston and cylinder head OK?
