worst day ive had in a long while......

[quattro84]

You tell me how exactly it happened...
There were certain grave mistakes made during the last time the head was taken off as well, as I found out.

But the point is that it is molten close to the water jacket, right in the middle and the plug looks just fine.
Also no leaning of air fuel mixture showed up on WBO2 and no knock was registered by my ears or by the control unit. And even if my ears can be deceiving - the ECU always heard knock very well on this car.

The car was constantly driven around during mapping, and this happened after it was left to idle a bit, and then 1->2->3 from start... Before that it did lots of pulls without problems. Engine noise went from OK to "ok, this is bad" in 0.5 seconds or less.

There were no signs of damage on any of the other pistons. There was even no damage in the same cylinder on the other side and no damage to the spark plug.
This car has also done more than 20k miles on my map before, standing mile races etc.

When taking off the head there was lots of coolant in the cylinder.

Looks like an uncontrolled flame outside main flame front melting the piston. Not directly knock originated because piston ring looks "fine", but it can lead to glow ignition.

How is/was the valve clearance? Could be due to glowing exhaust valve not fully closing & not tranferring heat.
Being on the edge of the quench area, makes it the ideal lower flow area for glow ignition. Gas speeds will push it even further down so piston can be melted even below the ringlands.
Checked the spark plug rating? Could be a too "cold" plug causing auto ignition.
By reading your post mortem it is nearly impossible to stop the proces once it starts...

This is common on newer DI diesels with worn valve guide seals. Oil comes in combustion chamber, burns very poorly, forms carbon above top rings, starts glowing and hey presto! Melted piston. If this doesn't happen very rapidly the carbon polishes the bore and makes the blowby gasses pushing oil consumption trough the roof and in some cases makes the engine go stampede.

[prj]

Not checked the head yet.
But there are signs of the head lifting.

When the head was removed the cylinder was full of coolant.
I don't remember what plugs were used - but this engine has done 20000+ km on a very similar tune with the same type of plugs.
The plug in said cylinder is not molten at all.

Lately bigger injectors were fitted and the head was taken off, and put back on.
In this process the head bolts were not replaced (!) and from what I have been told now, the gasket was not replaced either (!!!).

And the bolts used were stretch to fasten, OEM.

As I said - there was absolutely no leaning of the air-fuel mixture, and there was no audible knock present or timing pulled by the ECM.
At 6000 rpm during 3rd gear pull engine sound suddenly changed and by 7000 rpm there was smoke due to all the oil pushed out of the catch tank (it was vented to atmosphere) and onto everything under the bonnet, including the turbo hotside.
After this the car was stopped and the run was made for the fire extinguishers in the boot, but luckily we did not need them.

So you can see how quickly this happened.
The head temperature remained 95C during the entire time. I have a full 40hz log of everything, but all parameters are exactly as in the prior pulls.

[Sleeper_Avant]

bolts and gasket not replaced............. shocking!

[prj]

bolts and gasket not replaced............. shocking!

Tell me about it...
I have to work with what I am given - I don't build engines, so I can only hope that the work was done to good standard.

Had I been told this before, I would have flat out refused to map it...

So you see how it relates to your situation. Not really at fault, but feel really bad.

[Rikki Kitto]

Cheers SA....alwways look 4 the upside....there usually is one....BTW the motorbike guy's why not take the test when he gets to India ? Must be easiier and cheaper if do-able ?

Would be much easier but not valid when he gets back here