ran for 10mins in between, just to make sure everything was flushed out
What exactly do you mean by this....?
Hopefully not that you drained the oil and ran the car 10 mins. before you filled it with new oil......... (no offence just checking)
perhaps it's vales hitting the pistons because the valve timing is out? Is that possible??
In theory yes. But when this happens it is very likely that the engine won't run properly anymore.