What was found
AIRCRAFT WAS IN SHOP FOR ANNUAL INSPECTION, CHECKING COMPRESSIONS. FOUND 3 CYLINDERS WITH BELOW ACCEPTABLE COMPRESSION READINGS. PULLED CYLINDERS TO EXAMINE. FOUND BROKEN RINGS IN 2 CYLINDERS AND CRACKED PISTONS. DECISION WAS MADE TO REMOVE THE 3 OTHER ACCEPTABLE CYLINDERS. OUT OF 6 CYLINDERS, 5 PISTONS WERE CRACKED STARTING FROM AN OIL RETURN HOLE AT THE 4 RING GROOVE UP. OUT OF 5 PISTONS WITH CRACKS, 2 OUT OF 5 HAD BROKEN RINGS ALSO WHICH RENDERED THE BARRELS OF CYLINDERS UNSERVICEABLE AND SCRAP.