A friend left her Fiesta for MOT and service. Garage says on way back from MOT the centre electrode of a spark plug fell into the cylinder and damaged piston and valves.

His story sounds reasonable to me but has anyone ever heard of a spark plug falling apart like this ?

When were they last replaced?? Overtightened?

That a new one on me, but I'm no expert. I would have thought it more likely it dropped a valve that damaged the piston and the spark plug

yes they can break up. if the engine wasn't runnin right or the plugs were very old or overtightened they will have a hard time and eventually give up.

Removing the offending plug and if necessary the cylinder head will soon confirm what's happened.

Yup. They can...... But you'ld expect to notice the difference when it happened.....

if the car is running lean ( hot ) then it is Very possible for the electrode to melt, and drop onto the cylinder...

.. although you normally hear about things like that happening on a poorly tuned turbo'd car that is suffering from Pre-Detonation

Not impossible especially if the engine has run very hot or lean but usually they go the other way -- I have seen a Hitachi plug where the complete insulator was blown out cleanly and was found hanging on the end of the plug lead.



[Edited on 12/6/08 by britishtrident]

Oh well - apparently garage is charging about £300 to replace valves and piston so reasonable result.

I'm still puzzled how centre electrode could break up and drop past the side elecrtode unless the latter had completely burned away. But thanks for comments anyway.