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This afternoon I finished off the annual inspection. I did the annual compass swing, then checked the cylinder compressions while the oil was hot. I also drained the oil and replaced the filter. I had meant to take an oil sample to have analyzed, but I forgot. Drat.

The lower spark plug on cylinder #2 has always been a bit stiff to thread in and out. I bought a thread chaser from Aircraft Spruce, and used it to clean some carbon out of the #1 & #3 lower plug holes - it seemed to do a good job. Then I tried it on #2 cylinder, but it didn't feel right when I screwed it in, so I removed it. I was horrified to see that a piece of the cylinder head thread is coming off, exposing the helicoil thread insert. I need to get an experienced engine guy to look at this and recommend what the proper repair is. I've got a copy of Lycoming Service Instruction 1043A, which covers the replacement of helicoil thread inserts. That job can be done with the cylinder on the engine.

I had hoped to get the aircraft flying tomorrow, and take Terry on a fall leaves photo flight. That won't happen. I'm guessing it will be at least a week before the aircraft flies again, and that assumes I can find a local maintenance guy who has all the parts in stock to fix this. Worst case is the cylinder will need to come off and be sent out for repair - in that case it could be many weeks before the next flight.