We have an old '87 Maxima. 3L V-6. A head bolt on one of the end cylinders was completely loose and was rattling against the valve cover when the engine was running. We retorqued the bolt. About an hour's worth of driving and the head bolt was loose again and knocking against the valve cover. This time it actually punched a small hole straight up through the valve cover.
We have one theory that the head gasked broke through in the the location of the head bolt and the combustion is loosening the bolt and forcing its way out through to the valve cover. Does anyone else have any other valid theories as to what would cause this phenomenon?