The FAA is adopting a new airworthiness directive (AD) for certain Lycoming Engines (formerly Textron Lycoming) 360 and 540 series reciprocating engines with ECi connecting rods, part number (P/N) AEL11750, installed. The Airmotive Engineering Corp, Division of Engine Components Incorporated (ECi), holds the Parts Manufacturer Approval (PMA) for the affected parts, and markets the parts as ECi parts. This AD requires replacing certain lot and serial numbered connecting rods, P/N AEL11750, having forging part number AEL11488. This AD would also prohibit installing certain ECi connecting rods, P/N AEL11750, into any Lycoming 360 or 540 series reciprocating engines. This AD results from reports of connecting rods with excessive variation in circularity of the journal bores. We are issuing this AD to prevent fatigue failure of the connecting rod and a possible uncommanded shutdown of the engine.