Recently bought 2006 TRX250ex, cleaned the carb, changed the oil, new plug and air filter. Son's bike, has been running great until the other day. He was running in 3rd gear when he heard what he described as a small bang or crack, bike died and won't restart. The starter is new and spins fine, bike does not turn over at all, it almost sounds like the starter gear is spinning but nothing else. Could this be a timing chain or tensioner?