The hammering action of the rocker arm on the valve stem tends to beat the keepers up, particularly on a solid-lifter engine with slightly wide valve clearances. A radical cam with lots of valve spring pressure and/or high RPM makes it worse. It's something we were particularly careful to check when doing a rehab on the race engines during a mid-season freshen-up.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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