be cheaper just to buy new engine.what kind is it?what engine is in it now?might as well take it off the rc and tear it apart and see what happened.but yes i agree ran it too lean and got the rod if it's not making any noise.can you spin the flywheel with your fingers?thats how it goes when you buy used rc's.but if you like the rc you have it would be cheaper just to drop a new engine in it.if you don't like it then next time i sugg. to buy a new 1 and break it in right and do your maintence and it will give you plenty of fun.breaking stuff,working on stuff,trying differant tunes and set-ups,maintence is half of the hobby.what gets me is some folks go out and buy a rc run it till it do no maintence just run it till it breaks then they put it in the closet or see it on ebay.if you enjoy the hobby don't be scared to take it apart check things out so when it breaks you can fix it yourself.good luck with it and welcome to nitro.
