A CESSNA 421B WAS DISPATCHED AND OPERATED AFTER AN ENG CHANGE AND AN ANNUAL INSPECTION WITH SOME LACK OF CONFIDENCE THAT ALL AIRWORTHINESS DIRECTIVES WERE ACCOMPLISHED.

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DURING AN ENG REPLACEMENT ON THE R ENG THE OWNER OF SAID ACFT DID NOT WANT THE EXHAUST SYS REPLACED ONLY THE ENG; GASKETS; AND TURBO SYS. OUR SHOP RECOMMENDATION WAS TO REMOVE AND REPLACE THE EXHAUST SYS TO PRECLUDE PROBS. THE ENG REPLACEMENT WAS COMPLETED BY MYSELF AND ANOTHER TECHNICIAN; INSPECTED BY MYSELF; A 3RD PARTY AND THEN THE ENG BUILDER WITH THE MINOR NOTED DEFECTS CORRECTED. APPROX 2 MONTHS LATER AN ANNUAL INSPECTION WAS COMPLETED ON THE SAME ACFT BY MY SHOP AND AGAIN THIS ENG WAS INSPECTED BY ANOTHER TECHNICIAN WITH THE MINOR DEFECTS NOTED AND CORRECTED. AFTER THE ACFT WAS RETURNED TO SVC AND A REVIEW OF ALL ASSOCIATED PAPERWORK WAS COMPLETED I WAS NOT CONFIDENT THAT ALL AIRWORTHINESS DIRECTIVES WERE PROPERLY COMPLETED BY THE OTHER TECHNICIANS INVOLVED OR THAT THE INSTALLATION WAS CORRECT. MY RELUCTANCE IS DUE TO THE NUMEROUS DISTRACTIONS AS WAS SUBJECTED TO DURING THIS ONGOING MAINT EFFORT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE HAD EXTREME LACK OF CONFIDENCE THAT ALL OF THE AIRWORTHINESS DIRECTIVES WERE ACCOMPLISHED. THE RPTR SAID THAT FOR THIS AIRPLANE THE PRESSURE TO RETURN IT TO SVC WAS EXTREMELY HIGH. THE RPTR SAID CONSTANT INTERRUPTIONS FROM VENDORS AND PHONE CALLS DID NOT PERMIT CLOSE OVERALL OBSERVATION OF THE WORK IN PROGRESS. THE RPTR STATED THE ACFT WAS OPERATED FOR ALMOST 5 MONTHS AND ONLY MINOR RPTS HAVE SURFACED.