It is odd that 2 broke on the same cylinder.Iīve seen that happen on V8 cars that ran into the rev limiter on their burnout,it happened to my Mustang back in 1992.I broke 3 rocker arms due to valve float when I ran into the limiter (set it lower after that
),but they were all on different cylinders.Other than that,I would say that they just wore out and broke,stress cracking and fatigue. But very lucky indeed that it didnīt take a bunch of other parts with it!