I remember reading that when assembling a rear exh. engine, when possable, the blind end of the pin should be facing the E. opening and the open end toward the F. intake port(s ) so theoretically the pin can be cooled by the incomming mixture.


One thing I noticed is the orientation of the clip...
If you look at the clip in the new one, it is orientated properly...so vibration will have less effect. Look at the position of the failed one for comparison.
I'm not sure how to word this...but if the clip (e clip, snap ring, whatever ) is positioned so that the tabs or tang is horizontal, the up and down (rapid and abrupt ) changes in direction can cause the tang/tabs to wiggle/twang, resonate until metal fatigue causes failure. That and the heat perhaps???