That looks like someone in the past has overtorqued the locknut and stretched the thread. Mr. Bad Pliers probably used a long box end wrench or a breaker bar on the locknuts to be sure the next guy would have a rough time adjusting the valve lash!

Here's a novel idea- - - -a spring loaded ball bearing in the adjuster screw that keeps a little pressure on the rocker arm tip all the time- - - - -The "Q-T" adjusting screw! I've got a couple of sets of them stashed away.

www.ebay.com/itm/397868790926?

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!