Heres some pictures of the pistons in sierra cosworth that I stripped last week. Piston number 2 was melted and had no compression. Piston 4 has a lot of little marks on the top. Was it starting to melt too??
I think piston 2 melted because of a lean mixture but im not too sure about the marks on number 4....could this be detonation...what do ye think?




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think marks are valve touching

 

nope..dont think the valves were touching. @Its not clear in the pics but the best way to describe it is that it looks like an aero chocolate bar with lots of little holes

 

Detonation fella........

And you might find the electrode is missing off the spark plug too...

 

Valve contacted the pistons at that point, creating a hot spot that probably caused det at that specific point.

 

My melted piston

 

elctrode came off plug number 4 in my old saph

was just lucky ot went out the exhaust and never feked the engine

all down to a faulty injector

 

all electrodes are fine.. i think the melted piston was caused by a faulty fuel pump.

Do the pistons normally protrude higher than the block at TDC..cause they are by 1mm on this engine.

 

Yes they do, but I think that it could be too much. That all depends what kind of headgasket (how thick) you have?

 

did it damage your turbo then?

 

dont think so

sold the car soon after though

 

mine as just done exactly the same thing but its feked my engine

 

noddys old engine- it got hot at the last bedford track day so
we let it cool down then topped up the coolant then went back out and was running fine, decided to change the gasket to be on the safe side when we got back

took the head off to find this


the old (cometic) gasket must have moved over as the head was dropped on causing a hotspot which resulted in 2 melted pistons, 1 melted head and a cracked block, i have a cosworth shaped door stop now