IA (INSPECTION AUTHORIZED MECH) RPTED AN SMA SEL ENG OVERHAUL PROB WHICH RESULTED IN THE GNDING OF THE ACFT.

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ACFT ENG (CONT. T510-360-F) HAS ONLY 267 HRS FROM MAJOR OVERHAUL WITH A HISTORY OF #4 CYLINDER EATING EXHAUST VALVES. THIS INSPECTION; #4 CYLINDER COMPRESSION TEST WAS 16/80 COLD -- 20/80 HOT. A LIST OF UNAIRWORTHY ITEMS ON ENG WAS GIVEN TO OWNER. I FEEL THAT THE CURE IS MORE THAN JUST REPLACING THE VALVE. THE ENG IS BEING RETURNED AGAIN TO THE OVERHAULER (COLUMBIA). I SUSPECT CAM LOBE; BUT COULDN'T DETERMINE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAD SINCE LEARNED THAT THE VALVE PUSH RODS WERE FOUND TO BE TOO LONG CAUSING THE VALVES NOT TO SEAT PROPERLY. THIS WOULD EXPLAIN THE LACK OF COMPRESSION WHEN THE ENG WAS COLD AND EVEN AFTER WARMING UP. THIS WAS NOT A MANUFACTURING DEFECT SINCE THE ENG HAD BEEN OVERHAULED. DURING OVERHAUL; THE PUSH RODS NEED TO BE EITHER REPLACED WITH SHORTER ONES OR GND DOWN TO ALLOW FULL SEATING SINCE THE VALVE SEATS HAVE BEEN GND DOWN ALSO FOR PERFECT SEATING WHICH THEN REQUIRES A SLIGHTLY SHORTER VALVE PUSH ROD. SUBSEQUENT INSPECTION OF THE ENG DISCLOSED THAT THE PUSH RODS WERE STANDARD AND NOT SHORTER THAN STANDARD. HOWEVER; THE RPTR DOES NOT NECESSARILY AGREE WITH THIS FINDING SINCE THE VALVES ARE HYDRAULICALLY OPERATED WHICH WOULD ALLOW FOR SMALL DIFFERENCE IN THE VALVE PUSH ROD LENGTH. OF COURSE; KEEP IN MIND THAT THE MANUFACTURER OF THE ENG SPECIFIES THAT THE ROD LENGTH HAS TO BE ADJUSTED WHEN THE VALVES ARE GND!