ORIGINAL: Rob6
ORIGINAL: Checkpointracer
Check if you engine has compression by trying to turn the flywheel with you hand, if it gets very difficult at some point then the engine's good, but if it turns over very easy then you going to need to replace your piston/sleeve.
Or do the Traxxas exchange.
You'd save quite a bit of money changing it yourself, A new piston/sleeve for the 3.3 is $60-$70. The traxxas exchange is about $120 to $130 I beleive.