Date: 201211
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Yankee AA1
Operator: Personal
Operating under: Part 91
Mission: Personal
Flight phase: Parked
Aircraft component: Cylinder Head
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Situational Awareness; Confusion; Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Routine Inspection
Result: General Maintenance Action
Contributing factors: Aircraft; Procedure; Manuals; Human Factors
Primary problem: Human Factors

Narrative: Customer brought aircraft to me with a complaint of high oil consumption. I performed a Differential Cylinder Compression Test with all cylinders reading in the 70's. The only problem I could find was oil on the bottom plugs in the Number 1 and Number 2 cylinders. At the owner's request; I removed the Number 1 and Number 2 cylinders and delivered them to Engine Shop X; an [FAR] 145 Engine Repair Station in ZZZ1. Shop X repaired the cylinders in question knowing the model of the engine and the model cylinders they where repairing. They delivered them to me with yellow [Serviceability] tags and I re-installed them in the original Number 1 and Number 2 position. This was in October 2012. After (4) to (8) hours of operation; the cylinders were still using oil so the owner of the airplane; who is also an Airframe/Powerplant (A/P) Mechanic; removed them to verify I had the rings installed correctly. The engine was near Time Between Overhaul (TBO) so the owner had been looking at options of a complete overhaul or just a top overhaul so he had the cylinder part numbers fresh in his mind. While we where discussing the situation over the phone in November 2012; he noticed the part numbers on the yellow tags supplied by Engine Shop X; did not match the part numbers for the engine in the Parts Manual. In researching the logbooks; we learned another A/P had installed LW-11633 cylinders on the engine almost 24-years ago. This cylinder is used on the later series engines but not approved for the 0-235-C2C. I had no reason to suspect the cylinders I removed from the engine were the wrong cylinders for the engine. The Engine Shop did not catch the problem when they repaired the cylinders and I again had no reason to suspect a problem. I re-installed the cylinders on the engine and signed the engine off as eligible for return to service. The solution to this would be to suspect part numbers of anything removed from an airplane.

Callback: Reporter stated the cylinders that were installed 24-years earlier were chrome cylinders (hardened inner cylinder walls) that were not approved for the engine he worked. Difficulties with chrome cylinders not 'Wearing in' on engines using steel piston rings was also a problem.Reporter stated that the Lycoming Manual uses a series of Parts Numbers (P/N) that were superseded by newer P/Ns that changed over time; creating difficulty tracking the correct part numbers. He had contacted a local Federal Agency about what he found; only to find out that now he is under investigation for apparently improper maintenance.



Synopsis: A Repair Shop Mechanic describes the events that led to the discovery that unapproved chrome cylinders had been installed on a Grumman AA1 aircraft's Lycoming 0-235-C2C engine; approximately 24 years earlier.