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[JayMV6]

Opened up the engine while it was on the stand to discover this.


And the head


looks like something had been in there and got munched up 

This was supposed to be a replacement engine for mine

[JayMV6]

So basicly i told this could be down to detonation? just wanted other peoples opinions on this?

[noel]

possibly the electrode off the plug

[omega3000]

Had similar on my 2.0 vectra , never did find out what caused it 

[JayMV6]

all its done to the bore is a slight score down the length.You can feel it with your fingernail. Will that mess around with the compression as its only slight

[albitz]

Imo,probably. It might also possibly let oil up to the combustion chamber and burn it out the exhaust. If the score has sharp edges it could cause the piston to seize.You really need to get someone who is experienced in these things to take a look at it for you imo.
Im not sure a plug electrode would do that much damage,but I may be wrong. Have you looked at the valves to see if one of them has a piece chipped out of it ? Could be a piece of valve has been bouncing around in there.You may well never find out what caused it but it needs  some expert attention.

[JayMV6]

Cheers for the replys. If the bore works out to be ok then ill stick a piston in from another engine i got and im using a diffrent head anyway.

[SJKOO01]

Not sure if it's connected.  But looking at the piston, near the centre is a small circle patch, then if you look just under where the plug is, it looks as if there's a chunk of metal (like a smile) missing / doesn't look to be any reason for it to be cast that way?  Not sure if it's connected or if it indicates what might have caused the problem?

[VXL V6]

possibly the electrode off the plug

Agree with the above 

[noel]

possibly the electrode off the plug

Agree with the above 

i only suggested plug electrode because if you look @ picture 2 one of the electrodes appears to be missing off the plug

[albitz]

You may be right actually.I find it hard to tell from the pic,but then my eyesight aint what it used to be.

[noel]

You may be right actually.I find it hard to tell from the pic,but then my eyesight aint what it used to be.

i can see the moon when its not out with my bins on 

[feeutfo]

possibly the electrode off the plug

Agree with the above 

That was my first thought too. And closer inspection shows the dents at the bottom of the second pic are almost exactly electrode shaped when viewed from the side.
 

[Andy B]

You may be right actually.I find it hard to tell from the pic,but then my eyesight aint what it used to be.

i can see the moon when its not out with my bins on 

You need to change your bins for differenter bins ..................... even I can see that there are two electrodes on the plug 

[Entwood]

Bit of image manipulation and zooming in .. the left hand electrode is certainly missing about 1/3 to 1/2 of its tip. Whether that is sufficient to have caused that amount of damage is debatable though.