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Several weeks ago, on a 30min Encore flight, My #6 CHT went to over 600° as recorded by my JPI 711. Unfortunately, this went unnoticed in flight until engine roughness was detected on the next takeoff which was aborted. On inspection, all cylinders had compression in the 70s except #6 which was 15. Borescope inspection showed piston damage. The cylinder and piston were returned to the engine overhaul since the engine had only 200hrs since overhaul. The #6 spark plugs all had broken center electrode insulators. The overhaul shop is contributing toward the new cylinder and piston and says the classic detonation damage is caused by pre-ignition from “cross fire”, either inside the magneto or in the spark plug wire bundles. They recommend not tie-wrapping spark plug wires together. 1. Has anyone heard of this? 2. If the magneto only fires every 120°. then the only possible pre-ignition crossfire would be 120° BTDC, which if it occurred during the initial compression stroke would do it? 3. Firing order is 1-6-3-2-5-4 so the crossfire pre-ignition would have to come from #1, during #6 compression stroke. Right? thanks for any comments. Dave Ketcham, Mooney 252/Encore
