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Maintenance procedures to reduce possibility of sticking valves
In recent months, two Civil Air Patrol Cessna 172S aircraft (2023 and newer) equipped with Lycoming IO-360-L2A engines have experienced stuck exhaust valves, both on the #2 cylinder. These events resulted in inflight engine power loss emergencies. Similar incidents have also been reported to the FAA and Lycoming involving other newer Cessna 172S aircraft with the same engine model.
To mitigate the risk of valves sticking and ensure continued safe operation, CAP LG is implementing a preventive maintenance requirement for these aircraft based on advice from Lycoming and Lycoming Service Instruction 1425A.
This CAP preventive maintenance requirement applies to all 35 of our 2023 and newer CAP Cessna 172S aircraft equipped with Lycoming IO-360-L2A engines (see attached spreadsheet). These aircraft will need to have SI 1425A conducted at the next oil change at a CMF or other FAA-certified repair station qualified to perform valve guide reaming and exhaust valve cleaning in accordance with Lycoming SI 1425A. The shops will be required to measure the valve guides prior to reaming and provide the measurement in their logbook signoff and the signoff will need to be uploaded to the discrepancy prior to closing it in AMRAD.
After this procedure is completed initially these engines will need to have this process repeated anytime the engine starts experiencing any of the conditions listed below. We will track all occurrences in AMRAD.
- “Morning sickness” (roughness during cold start)
- Momentary power reduction accompanied by a single-cylinder EGT drop and recovery
A discrepancy for this requirement is being loaded in AMRAD for all aircraft affected by this requirement.
Affected aircraft: click here
Service instruction: click here
Lycoming specs: click here
For More Information:
Rodger Kirkpatrick
334-953-9096
