The intake valve probably stuck just enough to let the pushrod jump out of place, and the piston slapped it shut again. Get the piston about halfway down the cylinder and work the rocker arm up and down with a pry bar- - - - -you might discover a sticky spot near the full open point of the valve.
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!