Inspect the tips of the rocker arms where they contact the valve stem. They have an annoying habit of wearing a depression in the rocker that makes it impossible to get an accurate lash adjustment. A really bad wear pattern will actually destroy a feeler gauge blade if an adjustment is attempted on a running engine.
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
Love your enemies and drive 'em nuts!