Usually the wrist pin and crank can be cleaned up and saved but the bearings tend to get pitted and flakes of rust can get between them and the race. You can clean them out well enough to start and run but they tend not to last very long. You can usually feel and hear bearings that are pitted. For under $15.00 you can get a new set from rcbearings.com. Why bother putting the engine back together when you can just replace the bearings now.