excessive cylinder pressures?
Not sure, we were having trouble tuning it for a while, and found that the carb gasket had an air leak, and the head bolts started to get loose, so the piston got hot a couple of time after break in. We burned up about 3 glow plugs in 1 tank, then went back to see what the deal was, and that's what we found. Tightened the head, sealed the carb, and it ran fine after that. I've ran almost 3 gallons of Nitro through it in total.
The funny thing was, it was running the best it has ever ran right up until the piston blew...