Incident
During the flight over Lake Michigan, while cruising at 13,000 feet, the pilot became aware of binding in the controls for one engine. Specifically, the throttle lever, mixture control, and propeller pitch control for that engine were becoming difficult to move. The corresponding controls for the other engine functioned without issue. The pilot elected to descend to 9,000 feet and operated the engines at reduced power for the remainder of the flight.
Investigation
Following landing, a thorough inspection was conducted. The examination revealed that the exhaust stack was loose at a slip joint located where it passed through the firewall. The hot exhaust gases escaping from this leak had damaged several components: the engine control cables, an engine mount, and the firewall itself. It was noted that the aircraft had just come out of maintenance prior to this flight.
Additional Context
The aircraft had recently been released from maintenance before the flight. No further details regarding the nature of the maintenance or the aircraft type were provided by the investigation.