Yo, engine geeks...

The other pistons where fine. I'll get my dad to send me the piston so I can get pictures. Just so odd on an engine thats not really stressed.....i'd expect this from a boy-chaser's pimped out fiat that he regularly redlines and generally treats like a lump of poop

it;d be intersting if the car came back again with a similar problem

Originally Posted by Sid Squid

Seeing as over 21 million were sold, it would appear that yours is a minority view.

Not to mention utterly wrong.

With a global population of over 6 billion I would have said his opinion was a hugely majority view.

Oh and right ;]

Originally Posted by Jamiebridges123

it's a EVERY DAY, EVERY PERSONS car...what other car has done that?

Mark II Rover 200 (with the honda engine) I still see aload of them. Shame theyre right ugly things now

[embee]

Piston failures -
once you go into conditions where a failure will occur, the inevitable failure can take a number of forms.
Very often preignition is behind a piston failure like you describe, the reason for the preignition can be various.
As said previously, a reasoably well developed engine will withstand quite a lot of knock (detonation/pinking), though eventually it can lead to fatigue failure of the second land (the piece of piston between the top and second ring). Due to its very nature, the knock often occurs right at the edge of the chamber away from the plug, often near the exhaust valve but not necessarily. I have seen piston top lands "eaten" away with fatigue pits when I was involved in piston development, we were evaluating protective treatments for the top land, nickel plating/hard anodising etc.
Eventually the top ring can become trapped if the ring land material deforms or breaks, and this will often lead to torching through past the ring, then very quickly the material overheats locally and starts to weld to the bore and it's all over bar the shouting.
Alternatively the piston crown can just get too hot and expand to the point where it becomes an interference fit in the bore, then the friction generates heat, the material melts/welds, the rings trap, the flame torches through etc etc. Top land clearance is minimised these days in the interests of HC emissions, so the scope for tolerating overheating is marginal. Often simple crown overheating will lead to failures directly above the pin bosses since that's the direction the piston tends to expand more (heat paths away from the crown etc), and in a 2-valve engine like a wedge chamber or bathtub, the valves will be on this axis so knock will often be occurring directly above the pin boss.
Wrong plug grade or over advanced ignition or even loose spark plugs can be causes of pre-ignition. Combinations of conditions are often the cause, if for some reason the cylinder is running slightly lean (injector plugging is a common feature especially on earlier designs of FI engines, or if throttle body injection is used you can get lean cylinders (just like with single carbs), then if you run at full load the components get a bit hotter than normal, then you back off the load and the ignition advances and the plug overheats and hey presto.
Also with pressed gudgeon pin designs (pin is pressed into the rod and rotates only in the piston bosses) it's possible to get pick-up in the pin bores, or ovalising of the pin, and increased friction can cause excessive skirt loading, which can lead to failure.
I remember seeing an old Escort 1300 belonging to a friend which was rattling well but still running. When we pushed the pistons out of the block, on two of them the skirts fell completely off, it was only the fact that the breaks were like a jigsaw piece that the parts stayed together.