I have had nothing but bad luck with ceramics in aero and ducted fan engines. They are fast...for a while. Contact RC Bearings and get stainless if they come with non metallic retainers. If not, get steel bearings with non metallic retainers. In either case, remove the glow plug,cover the hole with a rag and spin the engine with starter while squirting ATF in the carb to flush out the nitro. Yes it's messy, but the bearings last a long long time. On planes I run them a few moments on FAI fuel, not as messy.