Quest to Remouve the Broken Spark Plug

I have never had to address that problem, but here's my best suggestion anyway. I have used this method in other circumstances with success.
1 Soak it with Kroil or the like for days and days.
2 Use a drill bit of a diameter a little bigger than the threaded portion of the spark plug to remove all of the plug metal above the threads, that tightens flat against the head. That way there is no torque on the plug any more. Soak it in Kroil for another day or two.
3 Then drill the hole through the plug to a size suitable for a left hand thread tap, no bigger than necessary, coarse thread.
4 Tap it.
5 Put a little spacer with minimal OD on the bolt to keep it from bottoming against the head and only against the plug remainder.
6 Thread it in, CCW, and keep turning. With a little luck, OK, a lot of luck, it will turn out.

 

I would suggest taking the head off and removing the arcing hook from the plug. I had the same problem a while back I managed to get the plug out but the arcing hook bent out from the removing tool and dug into my head. I ended up having to buy a new head on ebay and got it for 18 bucks.

 

if you can tap the spark plugs use left handed taps and bolts when you tighten them they will turn the correct way to remove the spark plug