What was found
AD2020-16-11 PREVIOUSLY COMPLIED WITH ON 11/12/24 AT 2158.7 FLIGHT TIME (536.5 SFRM) TO PREVENT CYLINDER CRACKS. SEVEN MONTHS AND 64.5 HOURS LATER, CYLINDER #5 CRACKED AND BROKE FREE WHILE AIRBORNE AT 12,000 FEET APPROXIMATELY 18.5 MILES WEST-NORTHWEST OF MGW (MORGANTOWN, WV) LEADING TO A ROUGH RUNNING ENGINE, LOSS OF SOME ENGINE POWER, AND THAT CYLINDER GOING OFFLINE. AN EMERGENCY WAS DECLARED AND A SAFE DIVERSION TO MGW WAS MADE WITH THE ENGINE STILL RUNNING AND NO INDICATION OF A LOSS OF OIL PRESSURE. UPON LANDING, AN OIL LEAK FROM THE BOTTOM RIGHT COWLING WAS EVIDENT, ALONG WITH THE CYLINDER CRACKED BETWEEN THE ROCKER BOX COVER. I AM UNSURE OF THE PART NUMBER OF THE CYLINDER (IT WAS INSTALLED WITH THE FACTORY REMANUFACTURED ENGINE BY THE PRIOR OWNER IN JANUARY 2022 AND THE SERIAL NUMBER IS LISTED AS AC21IB170) BUT WILL UPDATE THE REPORT IF I FIND OUT THE INFORMATION FROM THE MECHANIC CURRENTLY WORKING ON THE PLANE.