What was found
BOTH PISTON PIN PLUGS WERE OMITTED FROM A CYLINDER DURING ENGINE ASSEMBLY AT THE FACTORY. DURING AN ANNUAL INSPECTION, THE COMPRESSION TEST INDICATED NO PRESSURE BEING HELD IN NR 4 CYLINDER. WHEN THE CYLINDER WAS REMOVED FOR REPAIR, THE PISTON PIN PLUGS WERE DISCOVERED TO BE MISSING. THE ENDS OF THE PISTON PIN WERE WORN TO THE CONTOUR OF THE CYLINDER AND CYLINDER WALLS HAD 2 DEEP SCORE LINES ON EACH SIDE, WHERE THE PIN HAD BEEN RIDING. ENGINE LOG BOOK RESEARCH INDICATED THAT THE CYLINDER HAD NOT BEEN REMOVED SINCE THE AIRPLANE AND ENGINE WERE NEW. THE REMAINING CYLINDERS WERE REMOVED TO VERIFY THE INSTALLATION OF THE PLUGS. ALL OTHER PLUGS WERE FOUND INSTALLED. ENGINE OPERATION APPEARED TO BE NORMAL.