After an oil & filter change the engine developed a tappet noise from the rear cylinder. Suspected the JIMs valve lifters, removed and cleaned the lifters, didn't find much wrong with them but as a precaution the OEM lifters were installed. This made no difference as the noise was still there. Further investigation found that the exhaust valve rocker arm was sitting deeper on the valve cap than it should. Will be removing the head to investigate further.
Anyone had this on their engine or seen this before?

That doesn’t look like the standard collar...

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08 Specialized Langster

That's the standard collar that's been gouged out by the rocker arm. Haven't taken the head off yet, maybe the valve has pocketed causing the rocker arm to contact the collar.

check height against other valve?
also rocker shaft bearing for lift.
although i would be inclined down the pocketed valve route as well.