I have since discovered what went wrong - the injector(s) can drip after the engine is turned off which fills the crown of the piston with petrol which seeps down the sides of the piston dissolving the oil around the piston rings. When the car starts up for a moment there is no oil around the piston rings meaning more friction. Over time this damages the rings and as in this case eventually cracked a piston.
Apparently this is not uncommon and BMW have had to repair quite a few of these engines under warranty
I gleaned this information from a former BMW Mastertech who also told me that these engines do not like being remapped - as this can lead to unexpected engine damage. Worth knowing.
**Update. Another possible reason for the failure is the engine was 'chipped' or remaped. This information comes from another former BMW Mastertech - apparently these engines are highly strung and do not react well to being remaped. Furthermore BMW themselves will not touch an engine that has been remapped and even worst they will not unremap a car as the software update can fail and right off the ECU.
#b38
#bmwmechanic
#minicooper
#theminispecialist
#mechanic
#timingchainreplacement
#timingchainreplacement
