As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON RUN-UP, PILOT AND INSTRUCTOR FELT ENGINE VIBRATION. MAG DROPS WERE GOOD. AIRPLANE WAS TAXIED TO MAINTENANCE. MECHANIC FOUND NR 3 CYLINDER WITH 4 BROKEN MOUNT STUDS AND OIL COMING FROM EXHAUST. CYLINDER REMOVED AND REPAIRED BY ENGINE SHOP. ENGINE INSPECTION REVEALED NO FURTHER DAMAGE. SUSPECT DETONATION AS CAUSE.