I spent last night searching the forum for possible answers to this conundrum.   The background is is as follows.   Engine completely rebuilt, machining all by a company with decades of TR experience. New Cam/ cam bearings and followers fitted with Cam lube and run as advised on here and by the machine shop.   Engine has now done 750 miles. the last 350 of which have been accompanied by a fairly loud tappet (individual) noise at tick over "when hot". Clearances have been checked and reche