Valves hitting piston X2

[superd]

Hey guys hope you can help me out . I just recently bought a stock 2002 TRX 400 EX that had just had recent motor work done at the local dealer. I was told by the mechanic, the cam tensioner broke allowing the cam to spin, kicking the exhaust valves into the piston. The piston was also reringed at the time.
I picked it up when finished, and took out for a ride. Wouldn't idle very well, but seemed to run well otherwise. Rode for 1 hour and parked it in garage.
Week later tried to start it and it would only backfire. Changed plug and checked carb, but no change.
So I took it back to the dealer again, told them the motor had 1 hour on it and wouldn't start. Mechanic works on it, and tells me the intake valves hit the piston this time. They are blameing it on over revs allowing the valves to float and hit the piston. I know it was not over reved, and also thought 99 and up had rev limiters. They are not warranting their engine work and are still blameing the over revs and want me to pay for repairs again.
What could be the real cause of this and can the cam spin the the valves into the piston when the tensioner breaks?
Feel like I'm not getting the whole story from the dealer and any help appreciated. Thanks, Superd.

[Colby@C&DRacing]

Their claim as to the cause of the first problem can happen. As for you causing the second problem by over revving a stock 400ex is probably not the case. The 400ex has a real conservative rev limiter. I would say they missed something and are trying to cover their butts. ?? Did they also install a new timing chain the atv the first time?? It may be stretched and causing the timing to be off.