Noisy valve gear, why?

Started as noisy tappet on No4 cylinder after adjustment seemed ok for a mile or two then all hell let loose, rocker shaft broken in two places and rocker carrier also shattered between 3 and 4 cylinders, fortunately all pieces found and after a call to LZ member Brian S, back on the road within 24 hours. ? Why did it happen?

they do just snap sometimes from age , or securing stud giving way , or if after adjustment it could be poor adjustment,worth checking brass followers for damage to edge of seat