Bad Luck Mathew,Yamaha test these engines to destruction and for 660cc it is in a low state of tune so something is definitely amiss for this to happen.My XT is on 47k and is regularly bounced of the limiter with no problems.Item number: 120771488540 ebay is an engine for �200.Good Luck
PS I would want to know what caused the damage in case you have to repair your motor so that it does not happen again.