Failed spark plug or piston?

[Ian H]

My daughters boyfriend has a Megane RS250 that's just blown up.

A spark plug came out looking like this:

And the piston on the same cylinder looked like it had a chunk out of it.

What could have been the cause?

 

[Burnerman]

Oh dear - Iridium plug failure
In the good old days I would have expected the ignition timing to be too advanced but that's fixed now. I'd suggest incorrect plug for the car or maybe grossly overheated for some reason. Maybe the engine is designed to use high octane petrol?
The tip of the plug has gone, hence the mark on the piston crown.
John

 

[DaveHerns]

Never heard of a Megane RS250. Has it been chipped or otherwise modified? Does he give it some stick?
Have you got the head off? Any hope of a compression test proving if the piston is holed and if not fishing the bit of plug out? Wishful thinking?

 

[Ian H]

It's the same as this:

It's been very modified, it has 320bhp and he did track days in it.

He actually sold it yesterday, the cost of a used engine is around £2000 so he thought it best to sell it on.

There was zero compression in that cylinder.

 

[Burnerman]

I've had the odd bit of debris bouncing round on the top of the piston.....it was the valves that finally copped it.
With that sort of BHP available, anything can happen!
John

 

[Keithmac]

Was the hole in the middle of the piston?.

 

[Burnerman]

Was the hole in the middle of the piston?.

Reminds me of the RD / LC Yamaha's Keith......fiddle with the air cleaners at your peril (without rejetting.)
John

 

[DaveHerns]

Maybe the people who tuned it didn't consider upgrading the spec of the spark plugs.
.

 

[Ian H]

I think the piston was more a big chip rather than a hole. He fitted those plugs as an upgrade after he had the ECU remapped.

When he bought it it was running very rich due to a poor map so he had it done again. That was about a year ago and it's been fine since.

 

[DaveHerns]

You want him to get a nice sensible car if he's got your daughter as a passenger.

 

[Burnerman]

I'd guess the compression has gone courtesy of the plug electrode getting familiar with a valve.....seen that before.
John

 

[Ian H]

You want him to get a nice sensible car if he's got your daughter as a passenger.

I told him to get a Golf GTI Edition 30 but he is looking at a Civic Type R

I'd guess the compression has gone courtesy of the plug electrode getting familiar with a valve.....seen that before.
John

So you think a spark plug failure was the cause?

 

[Burnerman]

For sure, yes.....the plug electrode has melted because it couldn't handle the heat that it was subjected to.
Personally I think it was the wrong plug for the job but that's difficult to prove. Over advanced ignition could also cause this, depending on how the engine was mapped.
John

 

[DaveHerns]

Looks like he drives his cars to the max. Hope he's a good driver.

 

[durhamplumber]

It's been very modified, it has 320bhp and he did track days in it.

Floggin the tits off it...then wonderin why the engine is Feked!....???