RE: Lost air filter! Dust in the engine!
Like the others have already eluded to; any time sand gets inside of a nitro engine,....u can pretty much kiss the piston, sleeve, and conrod goodbye; because the grittiness from the sand will just tear the heck outta those 3 components, at which point u are much better off rather than rebuilding, it to do the trade in program(if its a traxxas engine 2.5 or 3.3)...u could try cleaning up the inside and see if it will run ok after that; but chances are is that it will probably do more harm than good trying to run it even further at that point....