OC mp62: 18s head studs do have the breakaway groove. But since the head was punctured by a fragment of the piston right in the center where a relief was for the piston rod nut(one in a million shot)was the head gave up first. Normally water or the whole piston tires to blow the head off, that is when the grooved studs come into play.
As stated before she will be repaired. A quote for a new head has already been placed with the same machine shop that made the head that broke. We replaced the warped steel plate the SP had.
Jeff Taylor
CRRM curator of equipment and rolling stock.