Most hobby shops will tell you that you need this and that, just so they can make money.. chances are the engines are fine.. if not, take them apart, clean them, then rebuild it and try again.. otherwise buy a new piston and sleeve... my local hobby shops always try and sell me something i dont need, but i just laugh cause i know that i know more than they do about certain stuff...lol...

anyways, i hope you get the engines running..most of my engines have quite a bit of compression, but my friend has a traxxas nitro sport, and you can practically start it with one finger.. no compression,and it runs amazing...