There are just some tools in the automotive world that nobody ever wants to see. Like the scent of a steak to Pavlov’s dog, the mere sight of a bolt extractor — aka "EZ Out" — elicits a visceral reaction from anyone who’s had to use one. That goes double when you end up contemplating the use of an extractor after something that should have been as simple as a spark plug change. But, that’s wrenching.
Getting the Plug Out
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Usually, when a plug snaps off in the head, it will do so just below the hex head, where the thick head material meets the thin shell of the plug threads. That leaves you with the center electrode hanging in the middle, and the thread body shell. You can probably pull the center electrode out with a pair of pliers, but the threads will still be stuck. The problem is that once you drill into the shell, you end up dropping metal shavings into the cylinder. The default solution is to use wheel bearing grease on the drill bit and tap, which will catch the majority of the shavings. Silicone is an option, and could work — but it’s unnecessary, expensive, and far more sticky and messy than need be. It also won’t provide adequate lubrication for the machining of the new threads with the tap, which increases the odds of failure with the bolt extractor. Better to stick with time-tested wheel bearing grease and hope for the best; silicone offers no real advantages, and you’ll have enough to deal with as it is.