The aforementioned and alarming noise is almost definitely a loose valve bucket guide, a common problem on later XK engines, more especially on the exhaust side, but also on earlier engines as they age. Inside the valve assembly on the XK engine, is the valve itself, valve seat, valve insert and springs. Between the valve stem and bucket is a shim, used to determine valve clearance size. The camshaft turns on a bucket, which fits neatly over the valve/spring/collet assembly, where
