American Champion 8GCBC Scout
Failed Electrode/Engine Damage
After a scheduled spark plugs change, pilot reported a rough engine with loss of power. Found lower plug in the #4 cylinder was missing the ground lug portion of the electrode. Inspection included cylinder borescoping, oil filter and screens. No contamination was noted. Champion REB37E plug replaced. About eight engine hours later, another rough engine event occurred, with no compression in the #3 cylinder and loss of oil. That spark plug was missing the same ground lug on the electrode. It appears the lug became lodged between the piston and ring, holing the piston and cylinder wall.
Part total time: 105.0 hours
Cessna 172N Skyhawk
Out Of Tolerance Plugs
Engine was running on only three cylinders. Found one of the eight Champion REM38E spark plugs was not firing. Resistance of five of the eight plugs exceeded the two-megaohm limit. Current in the plugs that were still working probably arced across small air gaps within the resistors. An open current path in the failed spark plug was the probable reason for its failure. An open current path causes extremely high voltages in the ignition system
Part total time: 300.0 hours
Cirrus SR20
Preignition Engine Damage
Aircraft returned to airport shortly after takeoff with smoke and fumes in cockpit. Pilot observed high CHT/EGT indications from the #1 cylinder. Examination revealed paint burned off #1 cylinder barrel caused smoke fumes. Further investigation revealed preignition damage to cylinder, piston and connecting rod bearing. Plug ceramics were broken with chunks missing. Damage to piston contaminated the engine and led to its replacement. One spark plug had only 105 hours since new.
Part total time: 105.0 hours
Piper PA-46-350P Malibu Mirage
No-Resistance Spark Plugs
Pilot performed an in-flight mag check, noting the engine was very rough on the left magneto. Inspection of magnetos and harnesses was satisfactory. Each spark plug was tested using an ohmmeter, and several were found to have an excessive amount of resistance with a couple having no resistance. There are no published values for this parameter, but various suppliers and groups have confirmed resistance has an effect on the plug’s operation. Spark plugs should be checked closely upon reaching 700 hours.
Part total time: 895.0 hours
