Spark plug gap closing up in motor

[Woodchukka]

Also when changing plugs the first time we had the intake pipe off the turbo and the blades looked ok to me. Might be worth another closer look.

Check both sides. Intake and exhaust with snails removed. I have seen turbos with fins broken off hidden more inside the housings that look ok at a glance from just the intake or outlet of the snail.

[swingtan]

Two popular reasons are...

1. Mechanical Contact: Anything that touches the electrode will move it to some degree. I've heard of many motors that had this issue and once fixed, the motor blew... Whether it was stretched rod bolts, broken piston skirts or bad bearings, something was allowing the piston to just touch the plug and close the gap. I've also heard of motors that had no issues once the plug was replaced and the belief was that some carbon had come loose and caught between the plug and the piston. This leaves no sign of the "touch" but is sufficient to close the gap. I've heard of some "tolerance" issues as well, where the plug length on some plugs was just enough to touch the piston, but only at max RPM. Finally on this one, there was one report that the ceramic centre of the plug can come loose and slip down onto the electrode.
   
2. Detonation: The theory here is that the shock wave and heat from detonation can close the gap. I find it a bit hard to believe, but given what I've heard some Toyota's do, I guess it could happen.

What I'd do is to look at the plugs and confirm the ceramic has not moved. Then I'd check the thread to see how much was exposed to the combustion chamber. There should be some soot one the start of the thread, but no further into the threads. If the threads have soot on them, then the plug may be protruding too far into the cylinder.

If the plugs turn out fine, then check the turbo as already suggested. It may never happen again and maybe nothing will happen, if so, go buy a lottery ticket....

[Woodchukka]

Good call on the center electrode. Detonation might cause that to happen as well I suppose? A bit off topic but now you mention it I had a Honda Odyssey and it completely lost the center electrode on 2 plugs. Completely gone with no apparent damage to the piston or head.

[***VX*R8***]

This is the plug that was in for about 3 weeks.

[Bling Bling]

Try a double washer see if it still does it, have you had the tune checked.

[Woodchukka]

Did the flash go off when you took that picture? It is just that the center electrode has a lighter patch on it. It is not a uniform colour like something has hit it. Plus in that picture the centre electrode look off centre.

[***VX*R8***]

Try a double washer see if it still does it, have you had the tune checked.

It's standard tune still.

Did the flash go off when you took that picture? It is just that the center electrode has a lighter patch on it. It is not a uniform colour like something has hit it. Plus in that picture the centre electrode look off centre.

That's not from the flash, the electrode is just very clean at that part, I'm guessing once the plug closed it got washed with unburnt fuel (??)...
The centre electrode has been hit by the ground strap which probably did push it off centre as it did damage it.

[lmoengnr]

The centre electrode has been hit by the ground strap which probably did push it off centre as it did damage it.

Detonation wont cause that, definitely impact damage.

[seldo]

Detonation wont cause that, definitely impact damage.

If it was my engine I'd be pulling it out for a close look pronto, before you had a lot of smaller pieces to sweep-up...
It has either ingested something, (although to do it twice suggests that the foreign body is still there) or else there is something loose and about to part company with whatever it is supposed to be attached to (Piston crown, con-rod...)
Once upon a time back in the dark-ages I had a bit of miss with an oily plug and thought I'd give it a bit of a rev to clear its throat........Never found the rod or the side of the block.....

[IJ.]

From my earlier post questions I'm thinking it's missing a piston Skirt....

[seldo]

From my earlier post questions I'm thinking it's missing a piston Skirt....

Could be. It's sure as hell not as simple as boost or detonation.

[XUV]

This is the plug that was in for about 3 weeks.

I think ford's "Cylinder deactivation system" needs re-evaluating ......

[Ausmartin1]

God I miss owning a Ford not!
so many weird issues I had - pre ignition, detonation - carbon golf balling the valves & seats, very selective on heat range of plugs and type & on & on...
Funny haven't done any major work on the GM product, may be I'm lucky\
- but I still reckon Ford can't build these 6's with any decent quality or durability with the ancient engine factory in Geelong.
So another story like this just doesn't raise an eyebrow any more.... lucky it got to 100K with out the head off for work.

[Micks]

Very true our Ls's will go for a coupla hundred thousand K's without a spannering!