As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) NR 2 ENGINE RAN ROUGH AFTER TAKEOFF, AIRCRAFT RETURNED TO BASE. POST FLIGHT INSPECTION FOUND NO COMPRESSION ON THE NR 1 CYLINDER. THE NR 1 CYLINDER PISTON WAS FOUND BURNT ON THE SIDE. INSPECTION OF THE LT MAGNETO FOUND THE DISTRIBUTOR BLOCK TO HAVE CARBON TRACK, PLUG FIRING CAUSING DETONATION AND BURNING THE SIDE OF THE PISTON.