Those engines are disposable, you'd be better off buying a new one. Always replace your engine's bearings if you plan on a rebuild.
You need to install a new piston and sleeve at the same time, it is not recommended to put a new piston in an old cylinder. It won't last long. That's why rebuild kits always package pistons and sleeves together.
Shop E-bay for a new mill. You can buy those engines for under 100 bucks. http://cgi.ebay.com/Nitro-Pull-Star...66:2|39:1|72:1205|240:1318|301:1|293:1|294:50