Originally Posted by maviczap

I know one of my mates had a mobile Helicoil guy come round and insert a Helicoil when he'd stripped a plug thread in his car. Guy retapped the thread in situ, without removing the head, and stuck a helicoil in. Although access to the plug in question was easy.

You case is a bit different, with the remains of the plug in place, but might save you a job removing the head.

I guess its the front cylinder and the previous owner hadn't changed the plugs or didn't put any copaslip on the plug thread if he did.