Note on traxxas topfuel(the name is very misleading) main issue I had with it is it was over loaded with oil to the point it would be an oily mess. When I would run the RC you would see an oil trail coming out of the exhaust. I also had issues getting the vehicles to start swapped to odonell's and never had the issues again.
As for the engine problem could be a few things stuck at BDC, broken con rod, bushing in the conrod shatter where it would block the piston (I've had that happen once when the engine didn't get up to 270ish in breakin)