Originally Posted by
1967brutus
In "real" aviation, I have no idea how it is nowadays, but in the past, sparkplugs would have threads, and the HV leads would have some sort of screw on plug, a bit like that gland. At least, I have seen that on the big radials. EDIT, I see John allready posted that, and better than me, with a linky...
Serviced thousands of spark plugs in my day... we had a fleet of PA-31's and every 100 hours we pulled all the plugs and cleaned/gapped and tested them. The lead is fully shielded (although they are rubber or silicone covered) and the cap is a gland nut that completed the sheild and holds the HT lead and seal into the plug. We could clean then and use them again until they wore the centre electrode to an oval and when they went into the "no-go" gauge they were done. The centres would end up looking like a football - (started round) . After cleaning they would be tested in a pressurized tester to insure they sparked well - we never rejected very many. They are a very sturdy plug.
