On April 8, 2000, approximately 0830 mountain daylight time, a Beech A60, N928PT, received minor damage following an engine failure during initial climb after takeoff from Centennial Airport, Englewood, Colorado. The flight instructor, the private pilot receiving instruction, and a passenger were not injured. The airplane was being operated by the private pilot under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country instructional flight that originated approximately 15 minutes before the incident. An instrument flight plan had been filed. The flight instructor said that while on departure from Centennial Airport, the left engine failed. He said that they returned to the airport and landed without incident. Postincident examination of the left engine revealed a six-inch hole in the case, and that two rod bolts on the number one cylinder connecting rod had separated. Examination by a National Transportation Safety Board's (NTSB) Materials Laboratory engineer indicated that one of the rod bolts separated due to a fatigue failure. An SEM examination of the outside surface adjacent to the fracture face revealed no indication of a manufacturing anomaly. Fretting damage was found on the arm of the connecting rod that was associated with this bolt. Maintenance records indicate that the left engine received a major overhaul 2.5 hours before the incident. A representative of the engine manufacturer said that the rod bolts on this engine are properly installed when the tightening of the nut stretches the bolt to a specified dimension.