It's my understanding that the failure is caused from the ring pin and the piston being made from different metals and of different size....they expand and contract at different rates..Thus they slowly work there way out.
+1 FNF. you hit the nail on the head. They are made from two different alloys,thus heating up at 2 different rates. You can find alot of people that have lots of hours at WOT with side pins, but I wouldn't chance it myself.In fact I didn't.When I bought my 280, I took it out for about 2 hrs,pulled the powerhead,took it to Paul Nichols & had the pistons top-pinned.Paul called me & told me that one of the pins would just fall out when the piston was taken out.Would it have eventually come out & wreck my powerhead,who knows?It's not a matter of if,it's a matter of when they come out.
