Sounds like you have the RTR mp9.
If you're looking to replace the engine, lose the pull starter. Buy a starter box.
The blue Ofna Truggy start is fine; as is about any name brand starter box on the market.
Now pick an engine... anything by a major name brand around the $200 mark will do well.
Given the nature of your question, do not lose any sleep over bearing choice.
But to answer your question they are referring to the engine's rear crankshaft bearing. Some use ceramic balls vs steel balls. Ceramic balls are slightly superior as they require less lubrication, tolerate higher operating temp & less rust.
However in offroad there is only a nominal performance increase.