You'll have to pull the head to really get an idea if what's up in there. If there's nothing obvious, then you'll have to get into the bottom end. At this point, there are a number of things you can speculate. This might be a good opportunity to rebuild the motor. Metric Mechanic sells some pretty nifty stuff you could install in the motor to really beef it up for track duty (360 deg thrust bearing, enhanced oiling grooves on main bearings, lightened pistons/conn rods, etc).
Good luck!