i have hear about motorcraft plugs breaking up and go into the engine which causes internal damage to the engine normally piston and block

also have seen this on my m8's supercharged mondy

normally due to the car running lean and heating the plugs up which breaks the tip of the plugs

on all zetecs/rs it seems the number three piston and bore always pop
when headgasket go or other failures like yours


dont know who told that is cant be rebuilt is bs m8
they can be rebuilt but will need to be over bored with over size pistons and upgrade con rods have to go this way as ford dont do pistons only rings the other route is new block or engine from ford

but like the others said speak to ian howell or power engineering or jamie going of jamsport plays with a lot of zetec's
as the rs focus is a black top zetec engine with a turbo attached to it with a few other mods