Cant get my current set free - probably due to rust or something in the block head.

So far have tried -

1. Brute force

2. WD40 on the threads (when cold)

3. Running engine for a bit then trying to free them

None of this has worked. Have been advised to spray WD40 or "penetrating oil" onto the threads when the engine is HOT but not tried that yet.

Any other clues?

try applying WD40 then turning them the other way, effectivly trying to tighten them up. That should help break any corrosion on the thread, then you can loosen them as normal

if all else fails try to loosen them with a impact driver you may need a extension bar to reach down to the offending plug then give it a whack with a lump hammer:thumbsup:

If they break off you can get a special tool that you can remove the stuck part with.

Essentially it's a socket with a special screw where the thread is the other way round. You screw it into the hollow spark plug stub using an unscrewing motion (I know, it's weird, but it works), and then continue to unscrew and it'll grip the spark plug stub firmly and hopefully free it.

Stuck spark plugs in aluminium engine blocks are not uncommon - they will seize unless you use an anti-seizing compound. This actually happened many years ago to me, which is why I know about the tool. Can't remember what it's called though.

Thanks - hopefully my Fiesta's iron block will release them without snapping off!