3126B popping noise

Good morning folks, On our 3126B we hear a loud popping in intake at idle. Found excessive rocker to valve stem clearance on #3 exhaust valve. Re-adjusted clearance and popping stopped. Popping returned later and more stem to rocker clearance was observed and readjusted clearance having checked pushrod and then made sea trial. wDT port 2700 stud 2650, individually wot port 2300 stud 22200. gives the impression of badly damaged cam lobe or cam follower on #3 exhaust.

Can anyone suggest otherwise as to what we can check before removing we move on to dismantle the engine?